DEMINERALIZED BONE IMPLANT IN SEGMENTS DESCRIPTION OF THE INVENTION This invention relates to a device made from segmentally demineralized bone and appropriately formed and machined for implantation such as a ligament, tendon, support or in any other application in which a unitary implant have a first rigid machined segment and a second flexible segment is required. There is a continuing need in the art for replacement of biologically acceptable ligament or tendon. Various efforts have been made in the art to solve this need. For example, U.S. Patent 5,053,049, a flexible prosthesis of "predetermined shape and a process for making the prosthesis are described." According to that description, a flexible and non-antigenic biocompatible prosthesis for replacement of a cartilaginous part was prepared by machining bone in a desired shape corresponding to the shape of a cartilaginous body part to be replaced, bone demineralization to impart flexibility and tanning to reduce antigenicity.There is no description or suggestion of the use of demineralized bone as a tendon or ligament replacement In US Patent No. 5, 092, 887, a method for replacing or augmenting a damaged fibrous connector tissue was described wherein a ligament made from a segment of bone that has been demineralized was joined between first and second. body parts There is no description or suggestion of bone machining before demineralization Ation to "produce the ends of fixation therein and demineralization only in a segment of the bone machined to produce a flexible segment, while leaving the joint ends machined in a fully mineralized and rigid state for attachment directly to the bone. adapted to receive such fastening ends. The disclosure in U.S. Patent 5,092,887 with respect to its discussion of the prior art and bone demineralization methods are incorporated herein by reference. . This invention provides a novel unitary bone implant having at least one segment of rigid mineralized bone, which can be machined to include: threads, slots, a handling head, a recess or a symmetric or asymmetric shape, and a Flexible demineralized segment which can also be machined to any desired shape before demineralization or after demineralization. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 provides a view of a first embodiment of the implant of this invention in which a rigid bone segment is machined to exhibit threads on each end (figure 1A) and which is then demineralized only in the section internal to provide a flexible segment between the machined ends (Figure 1C); Figure IB provides a view of an alternate embodiment in which one end of the implant has a rigid fixation bone block; Figure ID shows an extreme view of a cannula embodiment of the implant of this invention. Figure 2 provides a view of a second embodiment of the implant of this invention in which a rigid bone segment is machined to exhibit threads on one end and a junction hole on the other (Figure 2A), and on which it is demineralized then on the end of the attachment hole of the implant to provide a flexible segment, while retaining the threaded segment as a rigid member (Figure 2B). A partial cannulation of the implant is shown in the upper (FIG. 2C) top (FIG. 2D) and lateral views (FIG. 2E). Figure 3 provides a view of a third embodiment of the implant of this invention in which a rigid bone segment is machined to exhibit a fixation block at each end of the implant (Figure 3A) and which is then demineralized between two ends to provide a flexible segment between the ends of the machined fixing block (Figure 3B).
Figure 4 provides a view of a fourth embodiment of the implant of this invention in which a rigid bone segment is machined to exhibit a locking block at one end and a connecting hole _ (Figure 4A) or various holes or perforations (Figure 4B) in the other and which is then demineralized at the end that abuts the joining holes (Figures 4C and 4D), to provide a flexible segment while retaining the fixing block end as a rigid member. Figure 5 shows a method of implanting the implant of this invention in which fixation screws were used to retain the implant of this invention in place either by locking the implant in place through holes in the segment Rigid implant (Figure 5A) or by locking the implant in place at the rigid end of the implant via a tapered recess (Figure 5B and 5C). Figure 6 shows an embodiment of this invention in which the implant is a femoral ring in which the upper and lower ends of the ring are retained in a mineralized-rigid state and can be machined to exhibit a taper or groove. , and the inner segment of the implant is demineralized to exhibit a soft spongy layer to provide flexible support for the insertion of this embodiment of the invention between adjacent vertebral bodies. Figure 7 shows several cross sections for the demineralized segment of the implant of this invention. Figure 8 illustrates one embodiment of a prosthetic joint-in accordance with this invention. This invention provides a biologically acceptable tendon or ligament support or other implant for replacement of ligaments, tendons, damaged vertebral discs and the like, where there is a need for an implant having a machined rigid portion or segment as well as a flexible demineralized portion or segment. . According to one embodiment of this invention, a segment of cortical bone is preferably machined into a desired shape, with at least one end that is machined to provide a means for attaching that end directly to a bone machined in a complementary fashion. Referring to Figure 1A, a first embodiment of the implant of this invention 100 is shown in which the ends 101 and 102 of the implant are machined to exhibit a threading, and the bone to which the implant is to be fixed is tapered to exhibit A complementary taper to the thread of the implant end.
Alternatively, the threaded ends 101, 102 can be self-tapering, thereby eliminating the need for tapering the receiving bone. A simple bore of a diameter slightly smaller than the diameter of the threaded implant ends may be punctured or produced by similar means to receive the threaded implant end. An internal segment 103 of the implant is demineralized to provide a flexible segment of the implant, while the transition zones 104, 105 are provided where the bone mineralization level gradually changes from a fully mineralized state to one. demineralized. In a preferred embodiment of this embodiment of the invention, the two ends 101, 102 of the implant are machined to exhibit threads so that the left or right rotation of the entire implant results in the simultaneous insertion of both ends of the implant or removal of the implants. of the implant inside or outside the additionally machined bones to which the implant is to be fixed, without screwing in the flexible segment 103 of the implant. In Figure IB, an alternate embodiment is shown wherein one of the ends 101 'is not threaded, although it is machined to any desirable shape, such as a locking block, so that the threaded end 102 can be threaded into the bone receiver, while the locking block 101 'is fixed in place by interference screws or similar means known in the art. In still an additional modality, shown in Figure ID, the entire implant is machined to display a cannula 110 across its entire length or a portion thereof. In this way, the implant can be inserted on a guide wire or similar guiding means. Alternatively, the aspect 110 may be an internal thread capable of receiving a threaded retaining screw. It will be recognized that the features described for this embodiment or any of the other embodiments of the invention may be applied to other embodiments thereof, to produce embodiments exhibiting a variety of combinations of different characteristics described for each of the individually described embodiments. In a further embodiment of this invention 200 shown in Figure 2, only one end 202 of the implant 200 is machined to exhibit a thread or other machined feature, while the other end 201 can be machined to exhibit a fixation hole 210 or a similar feature, which allows to suture or otherwise attach to that end to a ligament or a tendon. A transition zone 204 from a mineralized to a demineralized state is provided, as it is a flexible segment of the implant 203. In FIGS. 2C-E, an end view, a side view and a top view respectively are shown. In this embodiment of the invention, an optimal cannulation 220 is shown, allowing the machined portion 202 of the implant to be threaded onto a guidewire, for example, as long as it does not interfere with the flat demineralized segment 203 of the implant. In a further embodiment 300 of this invention shown in Figure 3, the implant can be used to replace a ligament. In this embodiment two transition zones 304, 305 from the flexible segment 303 to the terminal mineralized fixing blocks 301, 302 are provided. The fixing blocks 301 and 302 each have a channel 306, 307 machined therein for receiving a fixing screw or pin. The mineralized sections 302, 303 can be machined into any desired shape of an anchoring device. The anchoring device may contain a screw thread, a hole for receiving an anchor pin or an anchor screw or a screw that rotates inside a sleeve. In the 400 mode shown in Figure 4A, the implant is used to repair or replace a tendon. In this embodiment, only one end 402 of the implant 400 is machined for fixation in a bone and the second end 401 of the implant is adapted to a variety of shapes terminating in means such as threaded hole 410, for attachment of that end to the bone, muscle, tendon, or ligament. In an alternative embodiment shown in Figures 4B and 4D, the end 401 'is machined to exhibit a plurality of holes or perforations 410', so that the end 401 'can be sutured to a biological receptor structure such as a muscle, ligament , tendon, bone or similar. In Figure 5, a method of implantation of the implant 500 of this invention is shown in that the fixation screws 553 are used to retain and the embodiment of the implant 500 of this invention in a machined groove 551 in a bone 550 either while in locking the implant in place (Figure 5A) through holes 552 in the rigid segment 501 of the implant (Figure 5A) or by locking the implant in place at the rigid end 503 of the implant via a tapered recess(figure 5B and 5C). The other end of the implant 504 is demineralized and therefore flexible and terminates in a hole 502 or other fixation means by which that end of the implant is fixed to the bone, tendon, ligament or muscle. As noted above, section 501 could be coiled, end 502 can be retained in a mineralized state and can be formed as a locking block for retention by an interference or threaded screw. In addition, implant 500 can be cannulated with recess 503 that continues through the entire length of the implant or some portion thereof. Figure 6 shows an embodiment of this invention in which the implant 600 is a femoral ring member in which the upper and lower ends 6Q1, 604 are held in a rigid mineralized state and can be machined to exhibit a thread or a slot by means known in the art (see WO 97/25945, incorporated herein by reference for this purpose.) The inner segment of the implant 603 is demineralized to exhibit a soft spongy region to provide flexible support to the insert. of this embodiment of the invention between, for example, adjacent vertebral bodies, an internal channel 601 is shown in the femoral ring, which "derives from the natural intramedullary canal of the bone from which the femoral ring is obtained by cuts. transverse, substantially planar, through the diaphysis of a femur or similar long bone. The implant of this invention comprising a unitarily machined segmentally demineralized bone comprising a first mineralized portion or segment and a second flexible demineralized segment or portion is produced by machining a preferably cortical bone piece in any desired condition. The bone is preferably selected to be a strong cortical bone, such as from the femur, tibia, fibula, radius, or ulna. The source of the donor bone can be autograph bone, allograph or xenograph, with the appropriate precautionary steps known in the art that are taken in each case to prevent the introduction into the container of pathogenic or antigenic agents. After properly forming the existence of an implant bone, a segment of the implant is preferably machined to exhibit a similar thread or fastening means whereby the implant can be fixed directly to the receiving bone machined in a complementary fashion. That segment of the implant is retained in a mineralized state, by appropriate protection of that implant-segment with any protective device, such as parafilm, rubber or latex coating, plastic wrap and the like. The remaining segment of the implant is then demineralized after according to methods known in the art. For example, in the embodiment 100- of this invention shown in Figure 1A, both ends 101, 102 can be inserted into rubber seals that expand the transition zones 104, 105 and the inner segment 103, is exposed to an acid solution. of sufficient resistance to filter the minerals * from that segment of the bone. A solution of 5% acetic acid "or a solution of 1 N hydrochloric acid can be used, and the implant periodically verified for the desired level of flexibility of the inner zone 103. It is important that an excessively high concentration of strong acid is not Use for this process, as this will result in cracking of the peptide bonds of the collagen matrix within which the minerals were deposited.Accordingly, HCl concentrations of between approximately 0. IN to 2N are acceptable, with the period of exposure to acid that increases for lower acid concentrations and decreases for higher acid concentrations, likewise depending on the strength of the acid used., 105 are formed by diffusion of the acid and diffusion of the minerals out of the bone in that segment of the implant covered by the protective cover. By varying the degree of demineralization, the properties of the implant of this invention can be altered to provide optimum strength and flexibility, as required for the particular application for which the implant is employed. The implant thus treated can be further treated by tanning or other means known in the art to reduce the antigenicity of the implant. For example, glutaraldehyde treatment (see U.S. Patent No. 5,053,049, hereby incorporated by reference for this purpose), may be used.
In Figure 7, various transverse shapes of the implant of this invention are shown. Therefore, in Figure 7A, a cylindrical cross section is shown. It will be recognized that various diameters, as small as 0.5 mm or smaller up to the largest of 10 mm or in certain even larger applications may be desirable. In Figure 7B, an oval cross section is provided. In. Figure 7C, a planar cross section is provided. In FIG. 7D a cross-section is provided in cross-shape. Those skilled in the art will recognize that the description of this invention allows essentially any desirable shape to be generated by the flexible or rigid segments of the implant of this invention and such variations come within the scope of this description in the appended claims. In the formation of the different transverse shapes suggested herein, it is desirable that a uniform transition be present between the rigid ends of the implant - and the flexible segment. This is achieved by properly machining the ends so that a taper in the flexible segment is presented and carefully controlling the demineralization process to ensure a graduated demineralization from the fully mineralized segment to the demineralized segment.
It will further be understood from the foregoing description that the implant of this invention can be appropriately formed by a wide variety of applications. For example, an implant of this invention can be applied to repair ligaments or tendons in the hand, elbow, knee, foot, ankle or any other anatomical location as necessary. In addition, the implant of this invention can be applied for replacement to any of a variety of joints. Methods and forms of implant known in the art for joint replacement (see, for example, U.S. Patent Nos. 4,871,367; Des 284,099; Des 277,784; Des 277,509; 3,886,600; 3,875,594; 3,772,709; 5,484,443; 5,092,896; 5,133,761; 5,405,400 and 4,759,768; all of which are incorporated herein by reference for their teachings of various considerations applicable to prosthetic joint implants), may be presented in accordance with and replaced by the implant of the present disclosure. Therefore, in one embodiment of this invention, a piece of cortical bone is molded to form a surgically implantable prosthetic joint having a flexible load distribution joint, analogous to that described in US Patent 3,875,549 (which was made from of molded silicone rubber). In accordance with this embodiment of the invention, a prosthesis is formed consisting of an elongated middle section, and a pair of proximal and distant rod portions projecting in opposite manner. The plantar aspect of the midsection is machined to exhibit an indentation or transverse channel extending across its width, to form the flexible joint to the demineralization of the midsection. The middle section, intended to act as the joint, is demineralized, and the mineralized limbs of the implant are retained in a mineralized state for the insertion of each end into the intramedullary space of the bones adjacent to the joint that the implant replaces. The mineralized limbs are machined to exhibit a threading or a gear tooth structure, so that at the insertion of each end into the intramedullary space of the adjacent bones, the end is -fixed in place. Since the ends are made from bone, the natural process of fusion between the implant and the bone between which it is inserted occurs over several weeks, permanently fixing the prosthesis in position and avoiding any movement of the ends. of the implant. The implants according to this embodiment of the invention can be used, for example, to replace mertacaplanar joints, proximal interphalangeal joints and the like. Accordingly, this invention represents a significant advance in the art in that it provides a natural alternative to the metal, hydroxyapatite, sillast, silicone or similar elastomeric materials used for joint artoplasty. ~~ In Figure 8, a diagrammatic representation of an implant of a prosthetic joint according to this invention and which can be prepared according to the central concepts of the present invention is provided. The implant 800 has an elongated midsection 810 that is demineralized to and includes a portion of the transition segment 820. On each side of the midsection 810 are the mineralized projections 830 adapted for insertion into the intramedullary channels of the bones adjacent to the bone. joint replacing the implant 800. Slot or channel 850 is provided to act as the joint and to allow the bending movement of the joint in accordance with the principles described in US Patent No. 3,875,594, incorporated herein by reference to this purpose Optionally, projections 830 may exhibit an external feature designed to improve implant retention in the intramedullary spaces. In the embodiment shown in Fig. 8, this feature is shown as a tooth-like acer which can be machined in an upper or lower aspect of each projection 830 or which can be projected around the circumference of the projections. Alternative external features that can assist in retention of the implant include holes through which retention pins may be inserted, slots, ribs and the like. The demineralized middle section 810 allows the implant 800 to be sufficiently flexible to allow that portion of the implant to act as a joint as the projections 830 fuse with the bone within which they are inserted to form a permanent fixation. Having now generally described various embodiments of this invention, the following examples are provided by way of further illustration of this invention. It should be recognized that the invention described and claimed herein is not limited to the specific details provided in those examples: Example 1 MACHINING THE IMPLANT OF THIS INVENTION The starting bone material was selected such that a piece of bone substantially consists of cortical bone. it was used to machine the implant of this invention. Implants from the rough line of the femur or an anterior aspect of the tibia were used for this purpose, although other cortical sources of bone would be acceptable. The desired bone segment was removed with a bone closure or diamond core cutter cooled with water and trimmed to fit on a lathe for machining of desired external characteristics. The bone was first machined to a known diameter and length. The ends were then machined to exhibit an internal threading, an external threading or to have a machined end while the other end of the implant was punctured to exhibit from one to several holes. The internal segment destined for demineralization was retained in a cylindrical form or machined in a grinding machine or a mill, to exhibit a flat internal segment, or other desired shape, between the threaded ends or the fastening ends. Example 2 SEGMENTAL DEMINERALIZATION OF MACHINED BONE GRAFT 1. Long Cylindrical Ligament Repair Grafts: The demineralization of a long cylindrical cylindrical ligament repair graft was completed in three days using approximately 40 mL of 0.75M-1.0M hydrochloric acid solution. The implant was exposed to fresh solution at least once per day. In order to produce a gradual transition from a fully mineralized end to a completely demineralized segment, the contact point of the HCl solution with the implant was varied during the duration of the demineralization process. - - 2. Short Cylindrical Ligament Repair Grafts: The demineralization of a short machined cylindrical ligament repair graft was completed in two days using approximately 40 mL of 0.75M-1.0M hydrochloric acid solution. The implant was exposed to fresh solution at least once a day. In order to produce a gradual transition from a fully mineralized end to a completely demineralized segment, the contact point of the HCl solution with the implant was varied during the duration of the demineralization process. 3. Flat Ligament Implantation or Tendon Repair: The demineralization of a ligament ligament or tendon repair where an internal segment of the graft was machined flat, was completed in twenty-four hours using approximately 40 mL of 0.75 hydrochloric acid solution. M-1.0M. The implant was exposed to fresh solution at least once a day. In order to produce a gradual transition from a fully mineralized end to a completely demineralized segment, the point of contact of the HCl solution with the implant was varied during the duration of the demineralization process. 4. Double Flat Ligament Repair Grafts Having Two Rigid Extremes:The demineralization of a machined flat ligament repair graft was completed in twenty-four hours "using approximately 40 mL of 0.75M-1.0M hydrochloric acid solution.The implant was exposed to fresh solution at least once a day. to produce a gradual transition from a fully mineralized end to a completely demineralized segment, the point of contact of the HCl solution with the implant was varied during the duration of the demineralization process In order to protect both rigid ends of the implant, a thread and the other having a fixation block, the implant was exposed to the acid solution only in the middle segment by keeping the threaded end of the implant on the meniscus of the acid, and the end of the implant fixation block "was inserted into a perforated retainer, which also acted as a plug in the bottom of the acid container, inside which a suitable hole To receive the implant bearing retainer had been punctured. In view of the description above, in which various embodiments of the invention of this invention were described including the best mode, the following claims are provided to define the scope of this invention. Those skilled in the art will recognize that various modifications to the specific details of the invention described herein fall within the scope of the appended claims.