US20090076518A1 - Method and system for stabilizing adjacent vertebrae - Google Patents

Abstract

A method of stabilizing adjacent vertebrae including the steps of forming at least one annulotomy in an annulus. At least a portion of the nucleus material is removed through the annulotomy to form a cavity in an intervertebral disc space between the adjacent vertebrae. A reservoir containing a flowable biomaterial is fluidly coupled to the intervertebral disc space. A flowable biomaterial is delivered to the cavity. The delivery of the flowable biomaterial into the intervertebral disc space is controlled in accordance with at least a first operating parameter. The biomaterial is at least partially cured to stabilize the adjacent vertebrae.

Description

• The present application is a divisional of U.S. patent application Ser. No. 10/984,493 entitled MULTI-STAGE BIOMATERIAL INJECTION SYSTEM FOR SPINAL IMPLANTS and U.S. patent application Ser. No. 10/984,566 entitled MULTI-STAGE BIOMATERIAL INJECTION SYSTEM FOR SPINAL IMPLANTS, both of which claim the benefit of U.S. Provisional Application Ser. No. 60/555,382 entitled MULTI-STAGE BIOMATERIAL INJECTION SYSTEM FOR SPINAL IMPLANTS filed on Mar. 22, 2004, the complete disclosures of which are hereby incorporated by reference.
FIELD OF THE INVENTION
• The present invention relates to a method and apparatus for stabilizing adjacent vertebrae with an in situ curable biomaterial using a biomaterial injection system to form an implant device and to a method for replacing, in whole or in part, an intervertebral disc using the present method and apparatus.
BACKGROUND OF THE INVENTION
• The intervertebral discs, which are located between adjacent vertebrae in the spine, provide structural support for the spine as well as the distribution of forces exerted on the spinal column. An intervertebral disc consists of three major components: cartilage endplates, nucleus pulpous, and annulus fibrosus. The central portion, the nucleus pulpous or nucleus, is relatively soft and gelatinous; being composed of about 70 to 90% water. The nucleus pulpous has a high proteoglycan content and contains a significant amount of Type II collagen and chondrocytes. Surrounding the nucleus is the annulus fibrosus, which has a more rigid consistency and contains an organized fibrous network of approximately 40% Type I collagen, 60% Type II collagen, and fibroblasts. The annular portion serves to provide peripheral mechanical support to the disc, afford torsional resistance, and contain the softer nucleus while resisting its hydrostatic pressure.
• Intervertebral discs, however, are susceptible to a number of injuries. Disc herniation occurs when the nucleus begins to extrude through an opening in the annulus, often to the extent that the herniated material impinges on nerve roots in the spine or spinal cord. The posterior and posterio-lateral portions of the annulus are most susceptible to attenuation or herniation, and therefore, are more vulnerable to hydrostatic pressures exerted by vertical compressive forces on the intervertebral disc. Various injuries and deterioration of the intervertebral disc and annulus fibrosus are discussed by Osti et al., Annular Tears and Disc Degeneration in the Lumbar Spine,J. Bone and Joint Surgery,74-B(5), (1982) pp. 678-682; Osti et al., Annulus Tears and Intervertebral Disc Degeneration,Spine,15(8) (1990) pp. 762-767; Kamblin et al., Development of Degenerative Spondylosis of the Lumbar Spine after Partial Discectomy,Spine,20(5) (1995) pp. 599-607.
• Many treatments for intervertebral disc injury have involved the use of nuclear prostheses or disc spacers. A variety of prosthetic nuclear implants are known in the art. For example, U.S. Pat. No. 5,047,055 (Bao et al.) teaches a swellable hydrogel prosthetic nucleus. Other devices known in the art, such as intervertebral spacers, use wedges between vertebrae to reduce the pressure exerted on the disc by the spine. Intervertebral disc implants for spinal fusion are known in the art as well, such as disclosed in U.S. Pat. Nos. 5,425,772 (Brantigan) and 4,834,757 (Brantigan).
• Further approaches are directed toward fusion of the adjacent vertebrate, e.g., using a cage in the manner provided by Sulzer. Sulzer's BAK® Interbody Fusion System involves the use of hollow, threaded cylinders that are implanted between two or more vertebrae. The implants are packed with bone graft to facilitate the growth of vertebral bone. Fusion is achieved when adjoining vertebrae grow together through and around the implants, resulting in stabilization.
• Apparatuses and/or methods intended for use in disc repair have also been described but none appear to have been further developed, and certainly not to the point of commercialization. See, for instance, French Patent Appl. No.FR 2 639 823 (Garcia) and U.S. Pat. No. 6,187,048 (Milner et al.). Both references differ in several significant respects from each other and from the apparatus and method described below. For instance, neither reference teaches switching the flow of biomaterial between discrete operating parameters or methods of detecting ruptures in the mold. Further, neither reference teaches shunting an initial portion of a curing biomaterial in the course of delivering the biomaterial to the disc space.
• Prosthetic implants formed of biomaterials that can be delivered and cured in situ, using minimally invasive techniques to form a prosthetic nucleus within an intervertebral disc have been described in U.S. Pat. Nos. 5,556,429 (Felt) and 5,888,220 (Felt et al.), and U.S. Patent Publication No. US 2003/0195628 (Felt et al.), the disclosures of which are incorporated herein by reference. The disclosed method includes, for instance, the steps of inserting a collapsed mold apparatus (which in a preferred embodiment is described as a “mold”) through an opening within the annulus, and filling the mold to the point that the mold material expands with a flowable biomaterial that is adapted to cure in situ and provide a permanent disc replacement. Related methods are disclosed in U.S. Pat. No. 6,224,630 (Bao et al.), entitled “Implantable Tissue Repair Device” and U.S. Pat. No. 6,079,868 (Rydell), entitled “Static Mixer”.
BRIEF SUMMARY OF THE INVENTION
• The present invention relates to a method and apparatus for stabilizing adjacent vertebrae with an in situ curable biomaterial. The biomaterial injection system can be used, for example, to implant a prosthetic total disc, or a prosthetic disc nucleus, in a manner that leaves the surrounding disc tissue substantially intact. The phrase intervertebral disc prosthesis is used generically to refer to both of these variations. Optionally, the device and system of the invention are adapted for minimally invasive use. Various implant procedures, implant molds, and biomaterials related to intervertebral disc replacement suitable for use with the present invention are disclosed in U.S. Pat. Nos. 5,556,429 (Felt); 6,306,177 (Felt, et al.); 6,248,131 (Felt, et al.); 5,795,353 (Felt); 6,079,868 (Rydell); 6,443,988 (Felt, et al.); 6,140,452 (Felt, et al.); 5,888,220 (Felt, et al.); 6,224,630 (Bao, et al.), and U.S. patent application Ser. Nos. 10/365,868 and 10/365,842, all of which are hereby incorporated by reference.
• In one embodiment the method of stabilizing adjacent vertebrae includes the steps of forming at least one annulotomy in an annulus. At least a portion of the nucleus material is removed through the annulotomy to form a nuclear cavity in an intervertebral disc space between the adjacent vertebrae. A reservoir containing a flowable biomaterial is fluidly coupled to the intervertebral disc space. A flowable biomaterial is delivered to the nuclear cavity. The delivery of the flowable biomaterial into the intervertebral disc space is controlled in accordance with at least a first operating parameter. The biomaterial is at least partially cured to stabilize the adjacent vertebrae.
• In one embodiment, the biomaterial is adhered to at least a portion of an inner surface of the cavity to stabilize the adjacent vertebrae. In another embodiment, the inner surface of the nuclear cavity is coated with a reinforcing material before delivery the flowable biomaterial to the nuclear cavity.
• In another embodiment, the flowable biomaterial is delivered to a mold located in the intervertebral disc space. An outer surface of the mold preferably bonds to at least a portion of the inner surface of the nuclear cavity. In one embodiment, the annulus is substantially removed before delivering the flowable biomaterial. Natural tissues is optionally relied on for at least a portion of the mold.
• The biomaterial optionally facilitates growth of vertebral bone or fusion of the adjacent vertebrae. The biomaterial is preferably configured to stabilize the adjacent vertebrae.
• The present method of stabilizing adjacent vertebrae includes the step of fluidly coupling a reservoir containing the flowable biomaterial to the intervertebral disc space. The delivery of the flowable biomaterial into the intervertebral disc space is controlled in accordance with a first operating parameter. At least one injection condition is monitored. The delivery of the flowable biomaterial is controlled in accordance to a second operating parameter in response to one or more of the injection conditions reaching a threshold level. The second operating parameter is maintained during at least a portion of the curing of the flowable biomaterial.
• In one embodiment, the method includes fluidly coupling the reservoir containing the flowable biomaterial to a mold located in the intervertebral disc space. The delivery of the flowable biomaterial is controlled in accordance to a first operating parameter so that the mold substantially fills the intervertebral disc space.
• In another embodiment, a predetermined period of time is permitted to lapse after the at least one injection condition reaches the threshold level before initiating the second operating parameter. This dwell time comprises a third operating parameter. The length of this dwell time can be fixed or can vary from patient-to-patient.
• The first operating parameter preferably applies sufficient pressure to rapidly fill the mold and to expand the mold to fill the disc space. A first injection condition triggers a second operating parameter, which maintains adequate pressure for a certain dwell time to completely fill the disc space and to distract the intervertebral disc space. Following the dwell time, a third operating parameter optionally permits a portion of the flowable biomaterial to be expelled from the intervertebral disc space, followed by a second dwell time that continues until the biomaterial adequately cures.
• The present method optionally includes pretreating the flowable biomaterial. The biomaterial can also be exposed to ultraviolet light, heating and/or mixed prior to delivery to the intervertebral disc space.
• In one embodiment, the flow of biomaterial is directed away from the intervertebral disc space until a predetermined quantity of biomaterial is delivered to a chamber in a purge device. In one embodiment, the first operating parameter includes the step of applying a first operating pressure to the flowable biomaterial in the reservoir and applying a second operating pressure, lower than the first operating pressure, to the flowable biomaterial in the reservoir. In another embodiment the intervertebral disc space exerts a pressure on the flowable biomaterial in the intervertebral disc space greater than the second operating pressure.
• The step of monitoring at least one injection condition typically includes monitoring the pressure of the flowable biomaterial between the reservoir and the intervertebral disc space and/or the pressure of the flowable biomaterial in the intervertebral disc space. The step of monitoring at least one injection condition can be monitoring at least one of the pressure, the flow rate, elapsed time, or the total volume of the flowable biomaterial flowing between the reservoir and the intervertebral disc space.
• The present method also includes the step of recording data corresponding to at least one of the injection conditions during the flow of flowable biomaterial. The injection condition data is optionally uploaded to a computer. The present method also includes determining whether any of the injection conditions is in an out of specification condition and indicating an out of specification condition. Alternatively, the flow of biomaterial is altered and/or the biomaterial is withdrawn from the intervertebral disc space in response to an out of specification condition.
• The flow of flowable biomaterial can be manually switched to the second operating parameter in response to one or more of the injection conditions reaching a threshold level or automatically switched by a controller. The present method optionally includes adjusting the threshold level as a function of patient parameters. The first and second operating parameter typically comprises a plurality of variables, such as for example, injection pressure, biomaterial temperature, and the like.
• The present method also includes positioning an evaluation mold in the intervertebral disc space prior to the delivery of the biomaterial. A liquid is delivered to the evaluation mold so that the mold substantially fills the intervertebral disc space and measurements, such as for example disc height, pressure, and the like, are taken. The liquid is removed from the evaluation mold and the volume of liquid injected and/or removed is measured. The evaluation mold is then removed from the intervertebral disc space. The liquid is preferably delivered under pressure sufficient to distract the intervertebral disc space. The liquid and/or the evaluation mold optionally have radiopaque properties. The present invention also includes use of the present biomaterial injection system to control delivery and/or removal of the liquid to the evaluation mold.
• In the preferred embodiment, imaging can be used to measure the distraction of the intervertebral disc space, to evaluate whether the mold substantially fills the intervertebral disc space, to evaluate the geometry of the intervertebral disc space, and/or to supply information to the surgeon regarding adequacy of the nucleus removal. The evaluation mold can either be positioned in the implant mold, directly in the annulus, or within the disc space in the case of complete disc removal. In another embodiment, the intervertebral disc space containing the evaluation mold and the liquid is imaged and at least one of the first operating parameter and/or the second operating parameter are established based on the imaging of the intervertebral disc space. In one embodiment, the intervertebral disc space is imaged to estimate the volume of biomaterial required. That estimate can then be compared to the amount of liquid removed from the evaluation mold.
• In another embodiment, a liquid is delivered under pressure to the evaluation mold sufficient to distract the intervertebral disc space. The volume of liquid in the evaluation mold may be held constant for a period of time. Additional liquid is added to the evaluation mold when the pressure in the mold drops to a predetermined level. The steps of delivering, holding and adding additional liquid is preferably repeated a plurality of cycles.
• In another embodiment, a liquid is continuously delivered to the evaluation mold at a constant pressure. The rate at which the liquid is delivered to the evaluation mold is measured. The compliance of the intervertebral disc space is measured as a function of the rate of change of the delivery of liquid.
• The present method also includes positioning a guide wire in the mold and imaging the intervertebral disc space containing the guide wire. The guide wire optionally includes an imaging target.
• The present method also includes positioning a radiopaque sheath over the mold before the delivery of the biomaterial. The intervertebral disc space containing the radiopaque sheath is imaged and the radiopaque sheath is removed before delivering the biomaterial.
• The present invention is also directed to an apparatus adapted to deliver a flowable biomaterial to an intervertebral disc space. The apparatus includes a reservoir containing the flowable biomaterial fluidly coupled to the intervertebral disc space, at least one sensor adapted to monitor at least one injection condition of the flowable biomaterial, and a controller. The controller is programmed to monitor the at least one sensor and to control the flow of the flowable biomaterial into the mold in accordance with a first operating parameter. In response to one or more of the injection conditions reaching a threshold level, the controller controls the flow of the flowable biomaterial in accordance with a second operating parameter and maintains the second operating parameter during a certain time period or dwell time before switching to the third operating parameter and maintaining the third operating parameter during at least a portion of the curing of the flowable biomaterial.
• In one embodiment, the apparatus includes a mold located in the intervertebral disc space fluidly coupled to the reservoir containing the flowable biomaterial. The controller is programmed so that the first operating parameter delivers the flowable biomaterial to the mold so that the mold substantially fills the intervertebral disc space.
• In one embodiment, the controller is programmed to initiate a second operating parameter during which the system waits a predetermined period of time after the first operating parameter (i.e., the at least one injection condition reaches the threshold level at a second operating parameter) before initiating the third operating parameter. In another embodiment, the controller is programmed to deliver the flowable biomaterial in accordance with a third operating parameter that maintains the flowable biomaterial at a predetermined pressure in the intervertebral disc space for a predetermined period of time after the at least one injection condition reaches the threshold level and before the second operating parameter. Operating parameters can be linear, non-linear, continuous, discontinuous, or any other configuration necessary to achieve the desired injection profile. The operating parameter can also be modified real-time based on feedback from the sensors monitoring the injection conditions.
• The controller is preferably programmed so that the first operating parameter comprises a pressure sufficient to distract the intervertebral disc space. In another embodiment, the controller is programmed so that the second operating parameter permits a portion of the flowable biomaterial to be expelled from the intervertebral disc space. The controller is also optionally programmed to control pretreatment of the flowable biomaterial.
• The apparatus optionally includes a source of ultraviolet light and/or heating directed at the flowable biomaterial prior to delivery to the intervertebral disc space. The present apparatus also optionally includes a mixing device located between the reservoir of flowable biomaterial and the intervertebral disc space. The present apparatus also optionally includes a purging device adapted to direct a predetermined quantity of the flow of biomaterial away from the intervertebral disc space.
• In one embodiment, the controller is programmed so that the second operating parameter applies a second operating pressure to the biomaterial in the reservoir that is lower than the first operating pressure applied under the first operating parameter. The controller can monitor the pressure of the flowable biomaterial between the reservoir and the intervertebral disc space and or in the intervertebral disc space. The controller is preferably programmed to monitor at least one injection condition comprises monitoring at least one of the pressure, the flow rate, elapsed time, or the total volume of the flowable biomaterial flowing between the reservoir and the intervertebral disc space.
• The controller is preferably programmed to record data corresponding to at least one of the injection conditions during the flow of flowable biomaterial. In one embodiment, the controller is programmed to upload to a computer data corresponding to at least one of the injection conditions recorded during the flow of flowable biomaterial.
• The controller may also be programmed to determine whether the at least one injection condition comprises an out of specification condition and to indicate an out of specification condition. Alternatively, the controller is programmed to alter the flow of flowable biomaterial or to withdraw at least a portion of the biomaterial from the intervertebral disc space in response to an out of specification condition.
• The controller preferably adjusts the threshold level as a function of patient parameters. The first, second and third operating parameters typically comprises a plurality of variable.
• The present invention may also include an evaluation mold adapted to be positioned in the intervertebral disc space prior to the delivery of the biomaterial and a liquid adapted to be delivered to the evaluation mold so that the mold substantially fills the intervertebral disc space. The controller is preferably programmed to remove the liquid from the evaluation mold and to measure the amount of liquid removed from the evaluation mold. The liquid and/or the evaluation mold optionally have radiopaque properties.
• In one embodiment, the controller is programmed to estimate the volume of biomaterial required to fill the intervertebral disc space and to compare the amount of liquid removed from the evaluation mold with an estimated volume of the intervertebral disc space measured using imaging techniques.
• In another embodiment, the controller is programmed to deliver a liquid under pressure to the evaluation mold sufficient to distract the intervertebral disc space, to hold the volume of liquid in the evaluation mold constant for a period of time, and to add additional liquid to the evaluation mold when the pressure in the mold drops to a predetermined level. The controller is preferably programmed to repeat the steps a plurality of cycles and estimate the compliance of the intervertebral disc space or spinal unit. In one embodiment, the operating parameters are modified in response to the estimate of compliance.
• In another embodiment, the controller is programmed to continuously deliver a liquid to the evaluation mold at a constant pressure, to measure the rate at which the liquid is delivered to the evaluation mold, and to estimate the compliance of the intervertebral disc space as a function of the changing rate at which the liquid is delivered.
• In one embodiment, the present invention includes a guide wire positioned in the mold. In another embodiment, a radiopaque sheath is positioned over the mold.
• The present invention is also directed to a controller programmed to determine whether at least one injection condition comprises an out of specification condition and to generate a signal of the out of specification condition.
• The present invention is also directed to an apparatus adapted to deliver a flowable biomaterial to a mold located in an intervertebral disc space. The apparatus includes a reservoir containing the flowable biomaterial fluidly coupled to the mold, an actuator providing a flow of the flowable biomaterial into the mold in accordance with a first operating parameter and at least one sensor monitoring at least one operating parameter of the flowable biomaterial. The apparatus also includes a display adapted to indicate that the at least one injection condition has reached a threshold level and a switch that controls the flow the flowable biomaterial in accordance with a second operating parameter.
• As used herein the following words and terms shall have the meanings ascribed below:
• “biomaterial” will generally refer to a material that is capable of being introduced to the site of a joint and cured to provide desired physical-chemical properties in vivo. In one embodiment the term will refer to a material that is capable of being introduced to a site within the body using minimally invasive mechanism, and cured or otherwise modified in order to cause it to be retained in a desired position and configuration. Generally such biomaterials are flowable in their uncured form, meaning they are of sufficient viscosity to allow their delivery through a delivery tube of on the order of about 1 mm to about 6 mm inner diameter, and preferably of about 2 mm to about 3 mm inner diameter. Such biomaterials are also curable, meaning that they can be cured or otherwise modified, in situ, at the tissue site, in order to undergo a phase or chemical change sufficient to retain a desired position and configuration;
• “cure” and inflections thereof, will generally refer to any chemical transformation (e.g., reacting or cross-linking), physical transformation (e.g., hardening or setting), and/or mechanical transformation (e.g., drying or evaporating) that allows the biomaterial to change or progress from a first physical state or form (generally liquid or flowable) that allows it to be delivered to the site, into a more permanent second physical state or form (generally solid) for final use in vivo. When used with regard to the method of the invention, for instance, “curable” can refer to uncured biomaterial, having the potential to be cured in vivo (as by catalysis or the application of a suitable energy source), as well as to the biomaterial in the process of curing. As further described herein, in selected embodiments the cure of a biomaterial can generally be considered to include three stages, including (a) the onset of gelation, (b) a period in which gelation occurs and the biomaterial becomes sufficiently tack-free to permit shaping, and (c) complete cure to the point where the biomaterial has been finally shaped for its intended use.
• “minimally invasive mechanism” refers to a surgical mechanism, such as microsurgical, percutaneous, or endoscopic or arthroscopic surgical mechanism, that can be accomplished with minimal disruption of the pertinent musculature, for instance, without the need for open access to the tissue injury site or through minimal incisions (e.g., incisions of less than about 4 cm and preferably less than about 2 cm). Such surgical mechanism are typically accomplished by the use of visualization such as fiberoptic or microscopic visualization, and provide a post-operative recovery time that is substantially less than the recovery time that accompanies the corresponding open surgical approach;
• “mold” will generally refer to the portion or portions of an apparatus of the invention used to receive, constrain, shape and/or retain a flowable biomaterial in the course of delivering and curing the biomaterial in situ. A mold may include or rely upon natural tissues (such as the annular shell of an intervertebral disc) for at least a portion of its structure, conformation or function. The mold, in turn, is responsible, at least in part, for determining the position and final dimensions of the cured prosthetic implant. As such, its dimensions and other physical characteristics can be predetermined to provide an optimal combination of such properties as the ability to be delivered to a site using minimally invasive mechanism, filled with biomaterial, prevent moisture contact, and optionally, then remain in place as or at the interface between cured biomaterial and natural tissue. In one embodiment the mold material can itself become integral to the body of the cured biomaterial. The mold can be elastic or inelastic, permanent or bio-reabsorbable.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
• FIG. 1 is a schematic illustration of the method and apparatus of the present invention.
• FIG. 2 is an exemplary delivery tube and mold in accordance with the present invention.
• FIG. 3 is a schematic illustration of one embodiment of a biomaterial reservoir in accordance with the present invention.
• FIG. 4 is a schematic illustration of a purge device in accordance with the present invention.
• FIG. 5 illustrates the purge device ofFIG. 4 in an open configuration.
• FIG. 6A is a schematic illustration of an alternate method and apparatus of the present invention.
• FIG. 6B is schematic illustration of a delivery tube that seals against the annulus in accordance with the present invention.
• FIG. 6C is schematic illustration of the delivery tube ofFIG. 6B sealed against the annulus.
• FIG. 7 is a schematic illustration of a communication system between a central computer and a plurality of controllers in accordance with the present invention.
• FIGS. 8A-8C illustrate an imaging and mold positioning technique in accordance with the present invention.
• FIG. 9 illustrates an alternate imaging technique in accordance with the present invention.
• FIG. 10A-10B illustrate an alternate imaging technique using a radiopaque sheath in accordance with the present invention.
• FIG. 11 is an exemplary injection profile in accordance with the present invention.
• FIGS. 12-14 are schematic illustrations of one method in accordance with the present invention.
• FIG. 15 illustrates an alternate embodiment of the present method and apparatus.
• FIGS. 16A-16B illustrate an alternate delivery tube for posterior access into the annulus in accordance with the present invention.
• FIGS. 17A-17B illustrate an alternate delivery tube for lateral access into the annulus in accordance with the present invention.
• FIG. 18 illustrates an alternate delivery tube in accordance with the present invention.
• FIG. 19 illustrates another alternate delivery tube in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 illustrates one embodiment of abiomaterial injection system1 in accordance with the present invention. Thebiomaterial injection system1 includes areservoir3 containing thebiomaterial23 fluidly coupled to animplant mold13 by adelivery tube11. The deflatedimplant mold13 is dimensioned to be positioned within theintervertebral disc space19. The mold is filled withuncured biomaterial23 in order to provide a replacement disc. As thebiomaterial23 is delivered to theimplant mold13, themold13 expands to substantially fill theintervertebral disc space19, and in particular, fill thecavity24 formed in theannulus25 as a result of removal of some or all of the nucleus.
• Intervertebral disc space refers generally to the space between adjacent vertebrae. The embodiments illustrated herein are equally applicable to both a complete disc replacement and to a full or partial nucleus replacement. A replacement disc refers to both a complete disc replacement and to a full or partial nucleus replacement.
• Thereservoir3 is adapted to hold thebiomaterial23, and in some embodiments, thereservoir3 heats and/or mixes thebiomaterial23. In some embodiments, thebiomaterial23 is pretreated before use. Thebiomaterial23 can either be pretreated before being placed in thereservoir3 or the pretreatment can be performed in thereservoir3. For example, thebiomaterial23 can be heated, mechanically agitated, or both, such as heating in a rotating oven before being placed in thereservoir3. For some polyurethane biomaterials, for example, sealed packages ofbiomaterial23 are heated while rotating in an oven at about 75° C. for about 3 hours, maintained at 75° C. degrees C. without rotating for an additional 3 hours, and then kept in the oven at about 37° C. until surgical implantation. During the second 3 hour period, the package ofbiomaterial23 is preferably retained in the oven without rotating and in an upright position during heating so that bubbles rise to the top. Theflowable biomaterial23 containing the bubbles is preferably purged before it reaches the mold, as will be discussed below.
• Achamber5 is optionally located in-line between thereservoir3 and themold13. Thechamber5 can be used to heat, mix and/or stage thebiomaterial23. In some embodiments, thechamber5 can be used to initiate curing of thebiomaterial23, such as for example by exposing thebiomaterial23 to an ultraviolet light source or aheat source5b.
• Anactuator21 is mechanically coupled to the reservoir to expel thebiomaterial23 from thereservoir3 and into thedelivery tube11. Theactuator21 can be a pneumatic or hydraulic cylinder, a mechanical drive such as an electric motor with a ball screw, a drive screw or belt, or a variety of other mechanisms well know to those of skill in the art. Control of theactuator21 is typically the primary operating parameter used to create the desired injection profile. Other possible operating parameters that can be controlled by thecontroller15 include releasingbiomaterial23 through one or more of thepurge devices7a,7b, biomaterial temperature, biomaterial viscosity, and the like.
• As used herein, “operating parameter” refers to one or more independent variables that can be controlled during the injection of biomaterial. The operating parameters can be linear, non-linear, continuous, discontinuous, or any other configuration necessary to achieve the desired injection profile. The operating parameter can also be modified real-time based on feedback from the sensors monitoring the injection conditions. For example, a control algorithm, such as Proportional Integral Derivative (PID) control, can be used to evaluate the injection condition data in light of the desired injection profile.
• For embodiments where theactuator21 is a pneumatic cylinder, it should be noted that many hospitals and clinics do not have sources of compressed air greater than 50 pounds per square inch (hereinafter “psi”). Thus, in some embodiments the pneumatic cylinder needs to magnify the available compressed air source by a factor of about 3. Thus, an initial pressure of about 50 psi becomes about 150 psi in thereservoir3.
• Thedelivery tube11 preferably includes at least onepurge device7a. In the illustrated embodiment, thepurge device7ais located downstream of thechamber5. In another embodiment, asecondary purge device7bis located closer to themold13. Thepurge devices7aand7bare referred to collectively as “7”. Suitable purge devices can include but are not limited to, reservoirs, three-way valve systems, and the like. The purge devices7 can divert or redirect the flow ofbiomaterial23 aside in order to purge a portion, which can include an initial portion that may be inadequately mixed or contain bubbles. The purge devices7 can also be employed if there is a system failure, such as rupture of amold13, to quickly divert biomaterial from the intervertebral disc space.
• Thepurge devices7a,7bcan be operated manually or automatically. In the preferred embodiment one or both are operated bycontroller15 and/or using the mechanism inFIGS. 4 and 5. In one embodiment, thepurge device7ais operated manually by the surgical staff and thepurge device7bis operated by thecontroller15.
• In the illustrated embodiment, thebiomaterial injection system1 preferably includes one ormore sensors9a,9b,9c,9d,9e,9f,9gand9h(referred to collectively as “9”) located at strategic locations in the presentbiomaterial injection system1. In the illustrated embodiment,sensor9ais located between thereservoir3 and thechamber5.Sensor9bis located between thechamber5 and thepurge device7a. Anothersensor9cis located downstream of thepurge device7a.Sensor9dis located close to themold13. In the preferred embodiment, thesensor9dis located as close to themold13 as possible. Thepressure sensor9gis located substantially in themold13. Thesensor9his optionally located in theintervertebral disc space19, but outside themold13. Thesensor9eis located in thereservoir3 and thesensor9fis located in theactuator21.
• Each of the individual sensors9 can measure any one of a plurality of injection conditions, such as for example biomaterial color, biomaterial viscosity, pressure, quantity and/or size of air bubbles in the biomaterial, flow rate, temperature, total volume, duration of the flow of thebiomaterial23, or any other injection condition that characterizes a proper injection profile. As used herein, “injection condition” refers to one or more dependent variables that are effected by one or more operating parameters. An “injection profile” refers to values of one or more injection conditions evaluated over time. An exemplary injection profile is illustrated inFIG. 11.
• Output from the sensors9 is preferably delivered tocontroller15. Thecontroller15 preferably attaches a time/date stamp to all injection condition data. Not all of the sensors9 necessarily perform the same function. For example, thesensors9aand9dmay monitor pressure, while thesensor9bmonitors temperature and thesensor9cmonitors flow.
• The sensors9 can be in-line with thedelivery tube11, fluidly coupled to thedelivery tube11, coupled to thedelivery tube11 by a diaphragm, or engaged with the delivery tube using a variety of other techniques. The sensors9 may be disposable or reusable. A suitable pressure sensor9 can include any device or system adapted to measure or indicate fluid pressure within a surgical fluid system and adapted for attachment to adelivery mechanism11. Examples of suitable pressure sensors include, but are not limited to, those involving a suitable combination of pressure gauge, electronic pressure transducer and/or force transducer components. Such components that can be adapted to permit the accurate and substantially real time measurement of pressure in a remote fluid, by shunting a sample of such fluid, can also be used particularly where the fluid is itself undergoing a change in properties in the course of its ongoing cure.
• The various components of thebiomaterial injection system1 are preferably fabricated from polymeric or other materials that provide an optimal combination of properties such as compatibility with thebiomaterial23 and the ability to be sterilized and/or to be disposable.
• Operation of theactuator21 is preferably monitored and/or directed by thecontroller15. Output from the sensors9 is preferably delivered to thecontroller15 to create a closed-loop feed back system. Thecontroller15 preferably includes a processor and a memory device. Thecontroller15 can be a special purpose computer, a general purpose computer such as a personal computer, independent signal conditioning circuits, threshold comparator circuits and switch circuits. In some embodiments, thecontroller15 is a user interface to effect manual control of thesystem1.
• Thecontroller15 preferably includes one ormore displays16 that communicate injection conditions to the surgical staff. Thecontroller15 can also provide audio indications of the injection condition data shown on thedisplays16. In another embodiment, the surgical staff manually overrides the operation of thecontroller15 so as to permit one or more operating parameters to be controlled manually based on data obtained from thedisplays16.
• As illustrated inFIG. 2, thebiomaterial injection system1 also preferably includes asecondary tube11′ that evacuates air from themold13 before the biomaterial is delivered. Thesecondary tube11′ can either be inside or outside thedelivery tube11. Removal of air from themold13 through thesecondary tube11′ is preferably controlled by thecontroller15. Connection to thesensor9gin themold13 can optionally be connected through thesecondary tube11′.
• FIG. 3 illustrates an embodiment where thereservoir3 includes two or morediscrete compartments37aand37b. Eachcompartment37a,37bis engaged with apiston35a,35bcoupled to anactuator21. As the actuator21 advances thepistons35a,35binto thecompartments37a,37b, respectively,components23a,23bof thebiomaterial23 flow into thechamber5 where they are mixed.
• The mixing of the two ormore components23a,23bof thebiomaterial23 can initiate a chemical curing reaction. Although the reservoir ofFIG. 3 is illustrated with twocompartments37a,37b, three or more compartments can be used for applications where the biomaterial has more than two components.
• Alternatively, the biomaterial may be a single component system that can be located in one or more of thecompartments37a,37b. Single component biomaterials can be cured using, for example, ultraviolet light, ultrasonic energy, or heat. In one embodiment, thechamber5 can optionally include an ultraviolet light source, a heater, or any other device or source of energy that initiates the curing process of thebiomaterial23.
• FIG. 4 is a schematic illustration of an exemplaryautomatic purge device70 in accordance with the present invention. Thepurge device70 can optionally be substituted for thepurge device7a.Delivery tube11 is fluidly coupled toinlet72 using connectingstructure74. In the illustrated embodiment, connectingstructure74 is a plurality of threads. In an alternate embodiment, the connectingstructure74 can be a quick-connect device, or variety of other structures. Theinlet72 on thepurge device70 is fluidly coupled tochamber76 bypassageway78.Piston80 is located in thechamber76. Thepurge device70 is in a closed configuration withvalve82 obstructing the flow ofbiomaterial23 tooutlet84.Outlet84 also includes a connectingstructure86, such as threads.
• As biomaterial is delivered to theinlet72 under pressure, it is advanced through thepassageway78 into thechamber76. The volume of thechamber76 is designed to accommodate the optimum amount ofbiomaterial23 that is typically purged prior to delivery to themold13. Once thechamber76 is filled withbiomaterial23,force88 is applied to thepiston80. As thepiston80 is driven towardsurface90 onhousing92 by the pressure of thebiomaterial23, connectingmember94 displaces thevalve82 along with thepiston80.Vent hole81 allows air to escape from behind thepiston80 as it advances in thehousing92.
• FIG. 5 illustrates thepurge device70 ofFIG. 4 in an open configuration. Thepiston80 has been advanced all the way to thesurface90, causing thevalve82 to create anopening96 through which thebiomaterial23 can be advanced to theoutlet84.Pressure transducer98 is optionally located on theinlet side72 of thevalve82 to measure the pressure of the bio-material23 both before, during and after thevalve82 is opened.
• FIG. 6A illustrates thebiomaterial injection system1 ofFIG. 1, except that theannulus25 acts as the mold to retain the biomaterial. As thebiomaterial23 is delivered to theannulus25 it substantially fills thecavity24. In one embodiment, the interior surface of thecavity24 in theannulus25 is coated with a reinforcingmaterial27, such as a curable polymer, prior to the delivery of the biomaterial. The reinforcingmaterial27 preferably adheres to the interior surface of thecavity24. The reinforcingmaterial27 can be flexible and can be either permanent or bio-absorbable. In one embodiment, the reinforcingmaterial27 also adheres to the biomaterial, securing the biomaterial forming the implant to the inner surface of thecavity24.
• In another embodiment, thedelivery tube11 is sized to fit theinlet26 formed in theannulus25 snuggly to allow thebiomaterial23 to be delivered under pressure without leaking. In the embodiment ofFIGS. 6B and 6C,flange250 is located neardistal end252 of thedelivery tube11 to reduce or eliminate leakage of thebiomaterial23 from thecavity24. Also illustrated inFIGS. 6B and 6C,distal end252 of thedelivery tube11 adjacent to theinlet26 includes a thin wall that expands when subjected to the pressure of the biomaterial23 (seeFIG. 6C). The expandeddistal end252 of thedelivery tube11 forms a seal with theinlet26. Theflange250 and the thin-walleddistal end252 can either be used alone or in combination with each other.
• As discussed above, thecontroller15 preferably monitors and records the injection condition data and attaches a time/date stamp.FIG. 7 illustrates an embodiment in which a plurality ofcontrollers15a,15b,15c, . . . (referred to collectively as “15”) communicate with aremote computer18 using a variety ofcommunications channel22, such as for example the Internet, phone lines, direct cable connection, wireless communication, and the like. The injection profiles20a,20b,20c,20d. . . (referred to collectively as “20”) for a plurality of patients are optionally uploaded to thecomputer18 for storage and processing. Pre-surgical and post-surgical data about each patient is also preferably uploaded to thecomputer18. Patient parameters typically includes weight, age, disc height after the procedure, disc degree index, disc compliance, and the like.
• By linking the historic injection profiles20 with the patient's pre-surgical and post-surgical patient parameters, a database is created that can be searched by surgeons for theinjection profile20 that most closely matches the current patient's parameters. Once the optimum profile is selected, it can optionally be downloaded to thecontroller15 prior to performing the present method.
Preliminary Analysis of the Patient
• The optimum injection profile and the corresponding injection conditions may vary as a function of patient parameters, such as for example, the patient's weight, age, gender, disc height, disc degeneration index, disc compliance, general clinical goals, patient-specific clinical goals, and the like. For example, a diseased disc may require a higher injection pressure and a higher termination pressure to restore more disc height and a longer dwell time at the threshold and/or termination pressure. Alternatively, if a bone scan indicates reduced bone density or that the vertebral bodies are otherwise compromised, a lower injection pressure may be indicated. The present invention includes creating an injection profile as a function of patient parameters and clinical goals. In some embodiments, a custom injection profile is created for each patient.
• One mechanism for selecting the appropriate injection profile for the patient is to conduct an analysis on theannulus25. Imaging or palpitation of the annulus, preferably after nuclectomy, is optionally performed before the delivery of the biomaterial to assess annular integrity. In one embodiment, an instrument is used that applies a known force to theannular wall25 and measures the amount of deflection. In one embodiment, anevaluation mold13′ (which may be the same mold or a different mold than the implant mold13), is inserted into the patient'sannulus25 after the nuclectomy is completed, such as illustrated inFIG. 1. Theevaluation mold13′ is inflated with a contrast medium that is easily imaged or other liquid, such as saline, to a target pressure (see e.g.,FIGS. 4-6). Inflation and deflation of theimaging mold13′ is preferably controlled by the presentbiomaterial injection system1, and annular deflection is measured either automatically or manually. Alternatively, operations related to theevaluation mold13′ can be handled manually.
• In some embodiments, theevaluation mold13′ and/or thedelivery tube11 have radiopaque properties. The radiopaque properties can be provided by constructing theevaluation mold13′ and/or thedelivery tube11 from a radiopaque material or including radiopaque markings, such as inks, particles, beads, and the like on theevaluation mold13′ and/or thedelivery tube11 to facilitate imaging. An image, such as an x-ray, MRI, CAT-scan, or ultrasound, is then taken of the patient'sintervertebral disc space19 to check if the nuclectomy (i.e., the cavity24) is symmetrical, of adequate size, of the desired geometry and/or if the required amount of distraction has been achieved. This information is used by the surgeon to decide when the proper amount of nucleus material has been removed from theannulus25.
• The volume of contrast medium necessary to fill thecavity24 and to achieve the desired amount of distraction, as verified by the image sequence, provides an indication of the volume ofbiomaterial23 necessary for the procedure. In another embodiment, imaging is used to estimate the amount of nucleus that needs to be removed. The volume of liquid necessary to fill theevaluation mold13′ is then compared to the estimated volume measured using imaging techniques and a determination is made whether additional nucleus material should be removed.
• In another embodiment illustrated inFIGS. 8A-8C, animaging device100 including anevaluation mold13′ is positioned in themold13. After themold13 is positioned in thecavity24 of thecavity24 of theannulus25 between thevertebrae17,delivery tube11′ containing anevaluation mold13′ is inserted into thedelivery tube11. Theevaluation mold13′ is preferably a small pliable, stretchable contrast balloon. A contrast medium102 (seeFIG. 10B) is delivered through thetube11′ into theevaluation mold13′ to fill the nominal volume of themold13. Themold13 and/or thedelivery tube11 may also have radiopaque properties.
• Thecontrast medium102 is preferably delivered at a pressure sufficient to fully expand themold13 into thecavity24. Theevaluation mold13′ also serves to position themold13 within theannulus25. As best illustrated inFIG. 8B, the fully expandedevaluation mold13′ corresponds generally to the shape of thecavity24 within theannulus25 that will be filled by the implant. Imaging, as discussed above, is then performed to confirm the shape of the cavity within theannulus25 and placement of themold13 within theannulus25. The quantity ofcontrast medium102 can be used to estimate the volume of thecavity24 within theannulus25.
• As illustrated inFIG. 8C, thecontrast medium102 is then removed from theevaluation mold13′. Thetube11′ andevaluation mold13′ are then removed from thedelivery tube11 in preparation for delivery ofbiomaterial23 into themold13. The procedure ofFIGS. 8A-8C can also be performed in connection with the embodiment ofFIG. 6A, where theevaluation mold13′ is positioned directly in thecavity24, rather than in themold13.
• FIG. 9 illustrates an alternate imaging method usingimaging device110 in accordance with the present invention. A guide wire orwire stylus112 with anoptional imaging target114 at a distal end116 is inserted into thedelivery tube11. Theimaging target114 can be a variety of shapes, preferably easily recognizable geometric shapes such as for example a sphere. Imaging techniques are then used to confirm the positioning of theevaluation mold13′ or themold13 in theannulus25. Theguide wire112 can also be used to evaluate the geometry of the intervertebral disc space created by removal of nucleus material and/or to press themold13 into position within theannulus25.
• FIGS. 10A and 10B illustrate an alternate imaging technique usingimaging device120 in accordance with the present invention. Thedelivery tube11 andmold13 are provided with aradiopaque sheath122. Thedelivery tube11 and/or themold13 may also have radiopaque properties. In the illustrated embodiment, theradiopaque sheath122 includesbend124 that directs the mold113 at a predetermined angle relative to the longitudinal axis of thedelivery tube11. Once positioned in thecavity24 formed in theannulus25, imaging techniques can be used to determine placement of the assembly in the cavity. Once positioning has been confirmed, theradiopaque sheath122 can be withdrawn along thedelivery tube11 in preparation for delivery of biomaterial to themold13.
Compliance Testing
• Theevaluation mold13′ can also be used to measure the compliance of theannulus25. For example, theevaluation mold13′ can be pressurized with a fixed volume of saline or a liquid contrast medium to the level anticipated during delivery of the biomaterial. Images of theintervertebral disc space19 are optionally taken at various pressures to measure the distraction of theadjacent vertebrate17. After a period of time, such as about three to about five minutes, the tissue surrounding theintervertebral disc space19 generally relaxes, causing the pressure measured in theevaluation mold13′ to drop. Additional saline or contrast medium is then introduced into theevaluation mold13′ to increase the pressure in theintervertebral disc space19 to the prior level. The tissue surrounding theintervertebral disc space19 again relaxes as measured by the reduction in pressure within theevaluation mold13′. By repeating this procedure several times, the surgeon can assess the compliance of theintervertebral disc space19 and/or theannulus25, and the likely volume ofbiomaterial23 necessary for the procedure.
• In another embodiment, compliance is measured by continuously adding a liquid to theevaluation mold13′ at a rate sufficient to maintain a generally constant pressure in thebiomaterial delivery system1 and/or in the intervertebral disc space. The change in the rate at which liquid needs to be added to maintain a constant pressure provides information that can be used to estimate compliance of theannulus25 and/or theintervertebral disc space19.
• A healthy, compliant annulus can typically handle several pressurization/relaxation cycles. Adiseased annulus25 may show less relaxation (e.g., less compliance) after being pressurized. Depending upon the status of theannulus25 and theintervertebral disc space19, a patient-appropriate injection profile can be selected.
• This compliance evaluation can be either controlled manually or by thecontroller15. The compliance data collected can be used to determine the operating parameters to produce the injection profile best suited to the patient.
Injection Conditions
• The presentbiomaterial delivery system1 permits one or more operating parameters to be controlled to achieve the desired injection conditions. The injection conditions are monitored, recorded and controlled real-time. The injection conditions may include, for example, biomaterial temperature and viscosity, biomaterial flow rate, biomaterial pressure, volume of biomaterial, distraction pressure, total distraction, and time, such as for example distraction time. These injection conditions can vary over the course of the medical procedure, so a plurality of injection conditions are preferably monitored and recorded as a function of time. The injection conditions can also be evaluated as a function of any of the other injection conditions, such as for example, pressure as a function of volume or flow. In the present invention, the pressure in themold13 is one possible injection condition for determining when to terminate the flow ofbiomaterial23. Alternatively, the volume ofbiomaterial23 delivered to themold13 can also be used for this purpose.
• Once an optimum injection profile for the patient is determined (see e.g.,FIG. 11), thecontroller15 preferably controls one or more operating parameters so that the injection conditions are maintained within a predetermined margin of error.
• The injection conditions can be used to signal that the procedure is out of specification. Alternatively, thecontroller15 can calculate trends or slopes of the injection conditions to predict whether a particular injection condition will likely be out of specification. As used herein, “out of specification” refers to one or more injection conditions that have deviated from the desired injection profile and/or are exhibiting a trend that indicates a future deviation from the injection profile.
• In those situations where the injection conditions can not be brought under control, such as for example if themold13 malfunctions, the procedure is aborted and thebiomaterial23 is preferably withdrawn from the patient before it cures. As used herein, malfunction refers to ruptures, fractures, punctures, deformities, kinks, bends, or any other defect that results in more or less biomaterial being injected into the patient than would otherwise occur if the mold was operating as intended. Alternatively, if the malfunction occurs in a location other than the mold, such as in thedelivery tube11 or if the mold kinks and can not be deployed and expanded to fill the intervertebral disc space, or if thevacuum tube11′ is obstructed an air in themold13 can not be evacuated, less biomaterial will be injected into the mold than is desired.
• Thecontroller15 monitors one or more sensors9 to determine if the injection conditions are under control. If any one or a combination of the injection conditions are out of specification, a number of corrective actions can be taken. If the deviation from the preferred injection profile is minor, thecontroller15 can attempt a correction. During a given medical procedure where the resistance to the flow ofbiomaterial23 is essentially fixed, the primary mechanisms for controlling the injection conditions are 1) decreasing, increasing or reversing the drive pressure exerted on thereservoir3 by theactuator21; 2) releasingbiomaterial23 through one or more of thepurge devices7a,7b; and 3) changing the temperature, and hence the viscosity, of thebiomaterial23.
• If the deviation is above a particular threshold, thecontroller15 may signal the surgical staff. Alternatively, the surgical staff can monitor thedisplays16 for any out of specification injection conditions. Thedisplays16 preferably highlight the injection condition(s) that have deviated from the preferred injection profile. In those instances where an injection condition is seriously out of specification, thecontroller15 will signal that the procedure should be aborted and/or automatically abort the procedure. Typically, theactuator21 will decrease or reverse the drive pressure on thereservoir3 in anticipation of aborting the procedure. If the procedure is aborted, anybiomaterial23 in themold13 and/or theintervertebral space19 is removed, either through thepurge device7bor manually by the surgeon. Themold13 is also removed.
• FIG. 11 illustrates asimulated injection profile70 that illustrates the benefits of the presentbiomaterial delivery system1. Theinjection profile70 includes three injection condition curves forflow rate72,injection pressure74 andtotal volume76 all as a function oftime78. In the illustrated example, theflow72 is calculated by thecontroller15, theinjection pressure74 is measured as thesensor9band/or9c, and thevolume76 is measured by thesensor9f. In another embodiment, the injection profile may include flow, pressure or volume curves measured at other locations along thebiomaterial injection system1.
• At the beginning oftime sequence81, thebiomaterial23 is immediately upstream of thepurge device7a. Duringtime sequence81, thebiomaterial23 begins to enter thepurge device7a. Duringtime sequence82, thebiomaterial23 is filling the purge device. Theflow rate72 is relatively constant and thetotal volume76 of biomaterial continues to increase. The sudden increase ofinjection pressure74 between the end oftime sequence81 and the beginning oftime sequence82 is the result of internal resistance to the flow ofbiomaterial23 at thepurge device7a.
• Attime sequence83, thepurge device7aswitches the flow ofbiomaterial23 to thedelivery tube11, resulting in a rapid spike ininjection pressure74. Attime sequence84, thebiomaterial23 fills thedelivery tube11.Injection pressure74 increases due to resistance to the flow ofbiomaterial23 through thedelivery tube11. Attime sequence91, thebiomaterial23 reaches the foldedmold13, resulting in a rapid increase ininjection pressure74 as the mold unfolds.
• Attime sequence85 thebiomaterial23 begins to fill themold13. The slight drop ininjection pressure74 is the result of thebiomaterial23 flowing freely into themold13. The expandingmold13 hits the inner wall of the annulus attime sequence86. Theflow rate72 continues to drop and thetotal volume76 ofbiomaterial23 continues to increase at a generally constant rate. Attime sequence87, theinjection pressure74 of thebiomaterial23 continues to increase at a different rate as it displaces thevertebrae17 and distracts theintervertebral disc space19. The muscles and tendons attached to the vertebrate17 are stretched elastically by theinjection pressure74 of thebiomaterial23 in themold13.
• Attime sequence88, thethreshold injection pressure74 is reached.Time sequence88 represents the maximum distraction of theintervertebral disc space19. In the illustrated example, the drive pressure exerted by theactuator21 on thereservoir3 duringtime sequences81 through88 is generally constant. Once theinjection pressure74 attime sequence88 is reached, a transition is triggered where the drive pressure at theactuator21 is reduced from a first operating parameter to a second operating parameter. As a result, theinjection pressure74 is reduced. Theflow rate72 is about zero and thetotal volume76 of biomaterial is at a maximum.
• In another embodiment, once theinjection pressure74 attime sequence88 is reached, a transition is triggered from a first operating parameter to a second operating parameter where the drive pressure at theactuator21 is held constant for some period of time, such as for example 3-120 seconds. At the end of the dwell time, the drive pressure is reduced from the second operating parameter to a third operating parameter. Again, theinjection pressure74 is reduced and theflow rate72 is about zero and thetotal volume76 of biomaterial is at its final volume.
• Attime sequence89 the drive pressure exerted on thebiomaterial23 in thereservoir3 by theactuator21 is reduced. This reduction can alternatively be achieved by releasing a portion of thebiomaterial23 through apurge device7a,7b. The pressure created in theintervertebral disc space19 acting on themold3 is now greater than theinjection pressure74 of thebiomaterial23 in thebiomaterial delivery system1. Consequently, tension of the muscles and tendons surrounding the vertebrate17 provides a compressive force that results in a flow ofbiomaterial23 out of themold13, as indicated by thenegative flow rate72 duringtime sequence89 and a decrease intotal volume93.
• Attime sequence90 theinjection pressure74 of thebiomaterial23 is generally constant. The pressure exerted by themold13 andbiomaterial23 is nearly in balance with the pressure exerted by the vertebrate17 on themold13. Theflow rate72 and the change intotal volume76 are both about zero. With thesystem1 now in stasis, thebiomaterial23 begins to cure. Once thebiomaterial23 is at least partially cured, thedelivery tube11 is removed.
• FIGS. 12-14 schematically illustrate one embodiment of the present invention. The embodiments ofFIGS. 12-14 are illustrated as a complete disc replacement. The embodiments of these Figures are equally applicable to a full or partial nucleus replacement.
• In these embodiment, thebiomaterial injection system1 initially operates at a first operating parameter. When one of the injection conditions reaches a threshold level, such as for example a threshold pressure as measured in themold13, thecontroller15 switches or transitions to second operating parameter. In an alternate embodiment, the threshold trigger could be flow rate, time, volume or temperature of the biomaterial. In the embodiment ofFIGS. 12-14, the trigger from the first to the second operating parameter causes the controller to reduce the pressure applied by theactuator21 on thebiomaterial23 in thereservoir3.
• In another embodiment, the second operating parameter is a dwell cycle where the pressure is maintained as some predetermined level for a predetermined period of time. At the end of the dwell cycle, the controller switches to a third operating parameter, which includes reducing the pressure applied by theactuator21 on thebiomaterial23 in thereservoir3.
• FIG. 12 illustrates a first operating parameter during which the deflatedmold13 is filled withbiomaterial23 until it conforms to the shape of theintervertebral disc space19. In one embodiment the first operating parameter includes a drive pressure created by theactuator21 which results in an injection parameter (i.e., injection pressure) measured at thesensor9eof about 150 psi. Alternatively, the first operating parameter includes a drive pressure created by the actuator that results in an injection pressure in the range of about 100 psi to about 270 psi.
• The relatively high injection pressure provides a number of benefits, including rapid filling of themold13 to reduce the chance of leaving voids or under-filled regions. Thebiomaterial injection system1 continues to operate at the first operating parameter until one of the injection conditions reaches a threshold level that triggers use of the second operating parameter.
• FIG. 13 depicts the time sequence in the procedure when the pressure of thebiomaterial23 measured at thesensors9b,9c, and preferably thesensor9d, triggers thecontroller15 to change to second operating parameter. Once the injection pressure measured at thesensors9b,9cor9drises to a particular level, the drive pressure exerted by theactuator21 is reduced to a predetermined level.
• The injection pressure used to determine a suitable threshold typically corresponds to the distraction pressure brought about by the delivery ofbiomaterial23 within thedisc space19. The injection condition in this instance is the injection pressure measured at thesensors9cor9d, such as for example about 80 psi to about 150 psi. In one embodiment, the injection pressure triggers thecontroller15 to transition to the second operation condition. In another embodiment, the second operating condition holds the injection pressure at a predetermined level for a predetermined dwell time.
• FIG. 14 illustrates the second operating parameter (or a third operating parameter where the second operating parameter is a dwell cycle). In the embodiment ofFIG. 14, the second operating parameter includes a reduction in drive pressure exerted by theactuator21. The tension built up in the tissues surrounding the vertebrate17 is permitted to act on themold13 to expel a portion of thebiomaterial23 out of theintervertebral disc space19 and back into thedelivery tube11. In one embodiment, the injection pressure measured atsensor9aduring the second operating parameter is about 0 psi to about 120 psi, and typically about 10 psi to about 50 psi.
• It is possible to measure the pressures discussed above using any of the sensors9a-9dand9g-9h. Doing so would require calibrating thebiomaterial injection system1 so that a measured pressure at one of the sensors9 is correlated to the actual pressure in theintervertebral disc space19, such as measured bysensor9gor9h. The factors required for such a calibration include the size of themold13, the resistance to fluid flow between thereservoir3 and themold13, the flow rate, the viscosity and temperature of thebiomaterial23, the cure time of the biomaterial, and a variety of other factors. For example, with regard to mold size, the transition from the first operating parameter to the second operating parameter occurs when the injection conditions measured at thesensor9bis about 100 psi to about 125 psi for amold13 with a volume of about 1.8 cubic centimeters; about 105 psi to about 130 psi for amold13 with a volume of about 2.7 cubic centimeters; and about 110 psi to about 135 psi for a mold with a volume of about 4.0 cubic centimeters.
• FIG. 15 illustrates an alternate method and apparatus for performing the present invention where theactuator21 is attached to an external source ofcompressed air57. Thecontroller15 includes adirectional control valve49 that extends or retracts thepneumatic actuator21 and apressure control switch51 to change between the first operating parameter and the second operating parameter. At least twopressure regulators53,55 are used to regulate the pressure reaching thepressure control switch51. Thefirst pressure regulator53 provides the first pressure injection and thesecond pressure regulator55 provides the second pressure injection. In an embodiment where the operating parameters comprise multiple variables, multiple pressure regulators will typically be required.
• Initially, thepneumatic actuator21 is supplied with compressed air through thefirst pressure regulator53. When one or more of the sensors9a-9ddetects a threshold pressure, thepressure control switch51 selects compressed air from thesecond pressure regulator55 to drive thepneumatic actuator21. In one embodiment, thedirectional control valve49 is a normally open, four-way valve such as those available under the trade name of Four-Way Valve (SV271) available from Omega Engineering, Inc. Stamford, Conn.
Mold Placement
• In a related embodiment, the mold, or a kit that contains or is adapted for use with such a mold, can include tools adapted to position themold13 in situ. In one embodiment, the tool is a guide wire, such as for example the guide wire shown inFIG. 9, that is placed through thedelivery conduit11 itself, or preferably through an air passageway that terminates at or near the point of contact with themold13. The guide wire can be designed to substantially assume the curved contour of the extended but unfilled mold, and to provide a plane of orientation, in order to both facilitate placement of the mold and provide an outline of the periphery of the mold in position and prior to filling. Thereafter, the guide wire can be removed from the site prior to delivery of the biomaterial and air evacuation. The use of a guide wire in this manner is particularly facilitated by the use of an air passageway that is unconnected to, and positioned outside of, the biomaterial delivery tube. In another embodiment, thedelivery tube11 includes one or more curves that facilitate placement of themold13.
• Optionally, and in order to facilitate the placement of the collapsedmold13 within a sheath, the invention further provides a rod, e.g., a plastic core material or a metal wire, dimensioned to be placed within themold13, preferably by extending the rod through the conduit. Once in place, a vacuum can be drawn on themold13 through the air passageway in order to collapse themold13 around the rod. Simultaneously, themold13 can also be twisted or otherwise positioned into a desired conformation to facilitate a particular desired unfolding pattern when later inflated or filled with biomaterial. Provided the user has, or is provided with, a suitable vacuum source, the step of collapsing themold13 in this manner can be accomplished at any suitable time, including just prior to use.
• In certain embodiments it will be desirable to collapse themold13 just prior to its use, e.g., when using mold materials that may tend to stick together or lose structural integrity over the course of extended storage in a collapsed form. Alternatively, such mold materials can be provided with a suitable surface coating, e.g., a covalently or noncovalently bound polymeric coating, in order to improve the lubricity of the surface and thereby minimize the chance that contacting mold surfaces will adhere to each other. In another embodiment, the outer surface of themold13 can be coated with a material that bonds to the inner surface of thecavity24 in theannulus25.
• FIG. 16A illustrates thedelivery tube200 andmold13 with abend202 at theconnection204 between themold13 and thedelivery tube11. In the illustrated embodiment, thebend202 extends along about 3-5 millimeters of thedelivery tube200 near theconnection204 and has a curvature of about 30°+/−15°. As illustrated inFIG. 16B, this configuration is particularly well suited for posterior entry into theannulus25. The embodiment ofFIG. 16A can also be achieved with a straight, flexible delivery tube and acurved guide wire206 in thedelivery tube200.
• FIG. 17A illustrates acurved delivery tube210. As illustrated inFIG. 17B, this configuration is particularly well suited for lateral entry of themold13 into theannulus25. The curve of thedelivery tube210 can also be achieved by using a flexible delivery tube containing a curved guide wire. In another embodiment, the guide wire may be malleable.
• FIG. 18 illustrates adelivery tube220 withmultiple bends222,224,226. Thebends222,224,226 can be co-planar or located in multiple planes. Thebend226 is located near theconnection228 with themold13, similar toFIG. 16A.FIG. 19 illustrates themold13 attached to analternate delivery tube230 withbends232,234. Similarly, thebends232,234 can be co-planar or located in multiple planes. Alternatively, the embodiments ofFIGS. 18 and 19 can be achieved by using a flexible delivery tube containing a curved guide wire.
Biomaterials
• The method of the present invention can be used with any suitable curable biomaterial such as a curable polyurethane composition having a plurality of parts capable of being aseptically processed or sterilized, stablely stored, and mixed at the time of use in order to provide a flowable composition and initiate cure, the parts including: (1) a quasi-prepolymer component comprising the reaction product of one or more polyols, and one or more diisocyanates, optionally, one or more hydrophobic additives, and (2) a curative component comprising one or more polyols, one or more chain extenders, one or more catalysts, and optionally, other ingredients such as an antioxidant, hydrophobic additive, dyes and radiopaque markers. Upon mixing, the biomaterial is sufficiently flowable to permit it to be delivered to the body and fully cured under physiological conditions. A suitable biomaterial also includes component parts that are themselves flowable at injection temperature, or can be rendered flowable, in order to facilitate their mixing and use. Additional discussion of suitable biomaterials can be found in U.S. patent application Ser. Nos. 10/365,868 and 10/365,842, previously incorporated by reference.
• The biomaterial used in this invention can also include polyurethane prepolymer components that react in situ to form a solid polyurethane (“PU”). The formed PU, in turn, includes both hard and soft segments. The hard segments are typically comprised of stiffer oligourethane units formed from diisocyanate and chain extender, while the soft segments are typically comprised of more flexible polyol units. These two types of segments will generally phase separate to form hard and soft segment domains because these segments tend to be thermodynamically incompatible with one another.
• Those skilled in the relevant art, given the present teaching, will appreciate the manner in which the relative amounts of the hard and soft segments in the formed polyurethane, as well as the degree of phase segregation, can have a significant impact on the final physical and mechanical properties of the polymer. Those skilled in the art will therefore further appreciate the manner in which such polymer compositions can be manipulated to produce cured and curing polymers with a desired combination of properties within the scope of this invention. In some embodiments of the present invention, for instance, the hard segment in the formed PU ranges from about 20% to about 50% by weight and more preferably from about 20% to about 30% by weight and the soft segment from about 50% to about 80% and more preferably from about 70% to about 80% by weight, based on the total composition of the formed PU. Other embodiments may be outside of these ranges.
• The biomaterial typically includes a plurality of component parts and employs one or more catalysts. The component parts, including catalyst, can be mixed to initiate cure, and then delivered, set and fully cured under conditions such as time and exotherm sufficient for its desired purpose. Upon the completion of cure, the resultant biomaterial provides an optimal combination of properties for use in repairing or replacing injured or damaged tissue. In a further embodiment, the biomaterial provides an optimal combination of properties such as compatibility and stability, in situ cure capability and characteristics (e.g., extractable levels, biocompatibility, thermal/mechanical properties), mechanical properties (e.g., tensile, tear and fatigue properties), and biostability.
• Many mixing devices and methods have been used for biomaterials having a plurality of parts such as bone cement and tissue sealant. Mechanical mixing devices, such as the ones disclosed in U.S. Pat. Nos. 5,797,679 (Grulke, et al.) and 6,042,262 (Hajianpour), have been used for bone cement mixing. These mechanical mixing devices, however, can take a long time to get thorough mixing and can be difficult to operate in sterile field, especially for biomaterials having a plurality of parts with short cure time. On the other hand, some prior art two-part polyurethanes have a gel time of about 30 minutes. Without a proper seal method to seal off the delivery tube, a cure time of 30 minutes can be too long for operating room use.
• It is important that mixing of the biomaterial occurs quickly and completely in the operating room in a sterile fashion. Biomaterial with induction times of less than 60 seconds and cure times of less than 5 minutes require a different mixing and delivery device than biomaterials of about 15 minutes of cure time. For biomaterial having two-part issocyanate-based polyurethane biomaterials, due to the sensitivity of NCO to OH ratio to the final properties of the cured biomaterial, there are several features that are important to the final properties of the in situ cured biomaterial. Several factors appear to have an impact on the in situ curable biomaterial mixing and delivery such as the number of mixing elements, purging of the initial volume from the static mixer and the effect of polymer flow during delivery using a static mixer.
• The compatibility of the biomaterial can also be achieved by having more than the traditional two parts, e.g., three or more parts, and mixing them all together prior to polymer application. By storing the incompatible components in different cartridges and/or preconditioning each component according to individual requirements, it often can minimize the concern of component incompatibility. One example of a three-part biomaterial is to separate the polyol and chain extender in a two-part biomaterial.
• In situ curability is largely dependent on the reaction rate, which can be measured by induction time and cure time. In general, fast cure (short induction time) will improve in situ curability by providing more complete polymerization, less leachable components, and better mechanical properties (e.g., less “cold layer” formed due to the cold surface of the implant). However, induction time should also be balanced with adequate working time needed for biomaterial injection, distraction, to provide enough time to access the injection conditions, identify if the injection conditions fall inside or outside an acceptable range, and if falling outside the acceptable range, halting or reversing the injection process.
• Particularly for use in the disc, it has been determined that shorter induction times tend to provide improved biomaterial properties. For such uses, the induction time can be between about 5 and about 60 seconds, for instance, between about 5 and about 30 seconds, and between about 5 and about 15 seconds. By comparison, the total cure time for such biomaterial can be on the order of 5 minutes or less, 3 minutes or less, and one minute or less. In one embodiment of the present invention, however, the cure time can be on the order of about 15 minutes. In either case the cure time can be greater than 15 minutes by adjusting the amount of catalyst used.
• The method of the present invention can be used for a variety of applications, including for instance, to provide a balloon-like mold for use preparing a solid or intact prosthesis, e.g., for use in articulating joint repair or replacement and intervertebral disc repair. Alternatively, the method can be used to provide a hollow mold, such as a sleeve-like tubular mold for use in preparing implanted passageways, e.g., in the form of catheters, such as stents, shunts, or grafts.
• The present invention also provides a method and system for the repair of natural tissue that involves the delivery of biomaterial using minimally invasive mechanism, the composition being curable in situ in order to provide a permanent replacement for natural tissue. Optionally, the biomaterial is delivered to a mold that is positioned by minimally invasive mechanism and filled with biomaterial composition, which is then cured in order to retain the mold and cured composition in situ.
• As can be seen, the annular shell can itself serve as a suitable mold for the delivery and curing of biomaterial. Optionally, the interior surface of the annular shell can be treated or covered with a suitable material in order to enhance its integrity and use as a mold. One or more inflatable devices, such as the molds described herein, can be used to provide molds for the delivery of biomaterial. The same inflatable devices used to distract the joint space can further function as molds for the delivery and curing of biomaterial.
• The method of the present invention can also be used to repair other joints, including diarthroidal and amphiarthroidal joints. Examples of suitable diarthroidal joints include the ginglymus (a hinge joint, as in the interphalangeal joints and the joint between the humerus and the ulna); throchoides (a pivot joint, as in superior radio-ulnar articulation and atlanto-axial joint); condyloid (ovoid head with elliptical cavity, as in the wrist joint); reciprocal reception (saddle joint formed of convex and concave surfaces, as in the carpo-metacarpal joint of the thumb); enarthrosis (ball and socket joint, as in the hip and shoulder joints) and arthrodia (gliding joint, as in the carpal and tarsal articulations).
Implant Procedure
• An illustration of the surgical use of one embodiment of the intervertebral prosthesis system of the invention is as follows:
• 1) A nuclectomy is performed by surgically accessing the nucleus through one or more annulotomies and removing at least a portion of the nucleus of the disc to form a cavity. The cavity is preferably symmetrical relative to the spine.
• 2) The distal (patient end) portion of a device of this invention is inserted into the surgical site and intervertebral space. In one embodiment, the distal tip contains a deflated mold. The mold is then inserted into the intervertebral disc space by pushing the distal end of the biomaterial delivery portion in a longitudinal direction through the annulotomy in the direction of the disc to the extent necessary to position the mold only into the nuclear cavity.
• 3) Optionally, if pre-distraction of the intervertebral disc is needed when the patient has pre-existing disc height loss, it can be accomplished using any suitable intervertebral distraction mechanism, including both external and internal mechanism. Internal distraction can be accomplished by using an apparatus similar to that of the invention, e.g., by first delivering a suitable solution (e.g., saline or contrast solution) into the mold in order to exert a force sufficient to “distract” the intervertebral joint to the desired extent. After the distraction, the solution can be removed from the mold by applying vacuum. It is optional either to use the same mold for hosting the injectable biomaterial or to replace the distraction mold with a new mold.
• 4) The components of a biomaterial delivery system are assembled as generally illustrated inFIG. 1a.
• 5) The controller applies a first pressure to the biomaterial in the reservoir. For embodiments that use multi-part biomaterials, the biomaterial components are forced by positive pressure out of the reservoir and through a static mixer. The initially inadequately mixed portion of the mixed biomaterial are preferably shunted through a purge device. Once the initial portion of the biomaterial has been shunted, the valve is redirected to permit the biomaterial to continue onward through the flow path and into the mold.
• 6) When the fluid pressure of the biomaterial in the biomaterial delivery system and/or the mold reaches a threshold operating parameter, such as the measured injection pressure, the controller reduces the pressure on the reservoir to a second pressure. The second pressure permits the tissues of the intervertebral disc space to expel a portion of the biomaterial out of the mold and back into the biomaterial injection system.
• 7) When the desired pressure has been reached, the parameters are maintained during the curing phase of the biomaterial.
• 8) The delivery tube is detached from the mold, thereby leaving the filled mold containing the cured biomaterial in situ to function as an intervertebral disc prosthesis.
• 9) The patient is sutured and closed and permitted to recover from the surgery.
• Patents and patent applications disclosed herein, including those cited in the Background of the Invention, are hereby incorporated by reference. Other embodiments of the invention are possible. It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims (23)

1. A method of stabilizing adjacent vertebrae, comprising the steps of:

forming at least one annulotomy in an annulus;

removing through the annulotomy at least a portion of a nucleus material to form a cavity in an intervertebral disc space between the adjacent vertebrae;

fluidly coupling a reservoir containing a flowable biomaterial to the intervertebral disc space;

delivering a flowable biomaterial to the cavity;

controlling the delivery of the flowable biomaterial into the intervertebral disc space in accordance with at least a first operating parameter; and

at least partially curing the biomaterial to stabilize the adjacent vertebrae.

2. The method ofclaim 1 comprising adhering the biomaterial to at least a portion of an inner surface of the cavity to stabilize the adjacent vertebrae.

3. The method ofclaim 1 comprising the steps of coating the inner surface of the cavity with a reinforcing material before delivering the flowable biomaterial to the cavity.

4. The method ofclaim 1 comprising the steps of:

fluidly coupling the reservoir containing the flowable biomaterial to a mold located in the intervertebral disc space;

delivering a flowable biomaterial to a mold located in the cavity; and

bonding an outer surface of the mold to at least a portion of an inner surface of the cavity.

5. The method ofclaim 4 comprising the step of substantially removing the annulus before delivering the flowable biomaterial.

6. The method ofclaim 4 comprising relying on natural tissues for at least a portion of the mold.

7. The method ofclaim 1 wherein the first operating parameter comprises delivering the flowable biomaterial at a pressure sufficient to distract the intervertebral disc space.

8. The method ofclaim 1 comprising selecting the biomaterial to facilitate growth of vertebral bone.

9. The method ofclaim 1 comprising selecting the biomaterial to facilitate fusion of the adjacent vertebrae.

10. The method ofclaim 1 comprising configuring the biomaterial to stabilize the adjacent vertebrae.

11. The method ofclaim 1 comprising the step of monitoring the pressure of the flowable biomaterial in the intervertebral disc space.

12. The method ofclaim 1 comprising the steps of monitoring at least one injection condition, wherein the at least one injection condition comprises pressure, the flow rate, elapsed time, or the total volume of the flowable biomaterial flowing between the reservoir and the intervertebral disc space.

13. The method ofclaim 1 comprising the steps of:

determining that at least one injection condition comprises an out of specification condition; and

indicating an out of specification condition.

14. The method ofclaim 1 comprising the steps of:

determining that at least one injection condition comprises an out of specification condition; and

altering the flow of flowable biomaterial to the intervertebral disc space.

15. The method ofclaim 1 comprising the step of removing at least a portion of the annulus before delivering the flowable biomaterial.

16. The method ofclaim 1 comprising the steps of:

monitoring at least one injection condition; and

controlling the delivery of the flowable biomaterial in accordance with a second operating parameter in response to one or more of the injection conditions reaching a threshold level.

17. The method ofclaim 16 comprising the step of waiting a predetermined period of time after at least one injection condition reaches a threshold level before initiating the second operating parameter.

18. The method ofclaim 16 wherein the step of controlling the delivery of the flowable biomaterial comprises a third operating parameter that occurs between the first and second operating parameters, the third operating parameter comprising maintaining the flowable biomaterial at a predetermined pressure in the intervertebral disc space for a predetermined period of time.

19. The method ofclaim 16 wherein the first operating parameter comprises the step of delivering the flowable biomaterial at a first operating pressure and the second operating parameter comprises the step of delivering the flowable biomaterial at a second operating pressure lower than the first operating pressure.

20. A method of stabilizing adjacent vertebrae, comprising the steps of:

forming a cavity in an intervertebral disc space between the adjacent vertebrae;

delivering a flowable biomaterial to the cavity;

controlling the delivery of the flowable biomaterial into the intervertebral disc space in accordance with a first operating parameter;

at least partially curing the biomaterial; and

adhering the biomaterial to at least a portion of an inner surface of the cavity to stabilize the adjacent vertebrae.

21. The method ofclaim 20 comprising the steps of:

delivering the flowable biomaterial to a mold located in the cavity; and

bonding an outer surface of the mold to at least a portion of an inner surface of the cavity.

22. A method of stabilizing adjacent vertebrae, comprising the steps of:

forming a cavity in an intervertebral disc space between the adjacent vertebrae;

delivering the flowable biomaterial to a mold located in the cavity;

controlling the delivery of the flowable biomaterial into the intervertebral disc space in accordance with a first operating parameter;

at least partially curing the biomaterial; and

bonding an outer surface of the mold to at least a portion of an inner surface of the cavity to stabilize the adjacent vertebrae.

23. The method ofclaim 22 comprising the step of substantially removing the annulus before delivering the flowable biomaterial.

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