US20110144759A1 - Modular prosthesis and use thereof for replacing a radial head - Google Patents

Abstract

A modular prosthesis system for replacement of a head portion of a proximal radius includes a monolithic stem component, a head component, and a locking mechanism formed by the stem and head components. The stem component defines a stem anchoring portion having a longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion on a first end face that extends in a first direction transverse to the longitudinal axis. The head component has a dovetail-shaped second mounting portion on a second end face opposite the first end face slidably engaged with the first mounting portion along the first direction. One of the first and second mounting portions intersects the longitudinal axis. The locking mechanism is formed at an interface between the stem and head components and is engaged through relative translational movement between the stem and head components. A related method is provided.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 10/999,297, filed on Nov. 29, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10/464,043, filed Jun. 18, 2003 (now abandoned), which is a continuation of U.S. patent application Ser. No. 09/828,745, filed Apr. 9, 2001 now issued as U.S. Pat. No. 6,656,225 on Dec. 2, 2003, which claims the benefit of U.S.Provisional Application 60/195,444, filed on Apr. 10, 2000. The disclosures of the above applications and patents are hereby incorporated by reference as fully set forth herein.
FIELD
• The present invention relates to prostheses for the elbow joint, and more specifically to prostheses for replacing a proximal head of the radius.
BACKGROUND
• Trauma to the elbow joint frequently involves damage to the ligamentous support of the elbow and fractures of the osseous structures responsible for the skeletal integrity of the elbow joint. The proximal aspect of the radius, or radial head, is frequently injured either in isolation or in combination with injury to other bony or ligamentous structures of the elbow joint. The radial head may also be fractured in association with injuries to the forearm axis, including disruptions of the interosseous membrane between the radius and the ulna. Whether in isolation or in combination with other injuries, fractures of the radial head can be difficult to treat.
• Fractures of the radial head are either reconstructable or unreconstructable. Despite various technical advances in the reconstruction of radial head fractures, a certain percentage of fractures are not amenable to reconstruction due to the degree comminution or severity of the fracture. In general, unreconstructable radial head fractures result from high energy trauma and are therefore frequently associated with significant injuries to other osseous or ligamentous structures of the elbow joint or forearm. In these cases, restoration of the stabilizing function of the radial head is critical to allow the ligaments of the elbow or forearm to heal in appropriate relationships, thereby restoring stability to the elbow or forearm. This stabilizing function depends, in part, upon re-establishing the appropriate distance between the capitellum and the proximal shaft of the radius.
• Prosthetic replacement of the radial head has evolved rather slowly. The first widely used prosthetic radial head was introduced in the 1970's and was composed of silicone. Silicone implants placed in various joints throughout the body led to “silicone synovitis,” in which the silicone induced an inflammatory response within the joint. Further, silicone radial head prostheses were found to be incapable of resisting the stresses to which the radial head is subjected, rendering it less useful in stabilizing the injured elbow or forearm.
• The difficulties apparent with silicone led to experimentation with metal radial head implants. These prostheses are fashioned from a single piece of metal (often titanium) and include a stem and a head portion. The head portion is shaped to approximate the anatomy of the radial head. These metallic prostheses are capable of resisting the compressive stresses to which the radial head is subjected, as has been demonstrated in several biomechanical studies. However, significant problems remain with these prostheses.
• Anatomic and radiographic studies of the dimensions of the radial head reveal a disparity with currently available metallic prostheses. Therefore it has been difficult to restore appropriate anatomic alignments within the elbow. Therefore restoration of the appropriate relationship between the capitellum and proximal shaft of the radius has been very difficult to achieve with these prostheses. Additionally, the fact that these prostheses are fashioned from a single piece of metal has led to technical difficulties with insertion and removal. Surgeons have had difficulty with matching both the size of the stem to the canal of the proximal radius and the size of the head portion to the patient's native radial head. Removal of these non-modular components frequently requires release of the lateral ligaments of the elbow and the annular ligament, which binds the neck of the proximal radius to the proximal ulna. Thus the elbow is frequently destabilized during removal of these prostheses.
• Designers of prosthetic joint replacements in the hip, shoulder, knee and fingers have circumvented the above mentioned difficulties by employing the use of modular components. Modularity allows for each aspect of a prosthesis to be sized appropriately to its recipient anatomic site. The concept of modularity has only recently been applied to commercially available radial head prostheses. Currently available modular radial head prostheses employ a mechanism by which the head component is impacted over and onto the stem component. The surgical exposure must therefore allow sufficient room for the head to be maneuvered over the stem prior to being impacted. With impaction, the height of the prostheses may be decreased, resulting in an increased distance between the capitellum and the proximal end of the radius. Increasing this distance alters the bony anatomy such that the ligaments of the elbow joint are not held in their appropriate lengths and tensions. Instability of the elbow or inappropriate healing of the ligaments may result. Furthermore, removal of these prostheses is accomplished in the same manner as the above mentioned metallic implants, often requiring destabilization of the lateral aspect of the elbow joint.
• In order to reap the benefits of modularity in radial head prosthetic replacement, a reliable and surgically appropriate method to secure the stem of the prostheses to the head of the prostheses and which allows for accurate restoration of the appropriate spatial relationships between the bones of the elbow is required.
SUMMARY
• A modular prosthesis system for replacement of a head portion of a proximal radius includes a monolithic stem component, a head component, and a locking mechanism formed by the stem component and the head component. The stem component defines a stem anchoring portion having a longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion on a first end face that extends in a first direction transverse to the longitudinal axis. The head component has a dovetail-shaped second mounting portion on a second end face opposite the first end face slidably engaged with the first mounting portion along the first direction. One of the first and second mounting portions intersects the longitudinal axis. The locking mechanism is formed at an interface between the stem component and the head component and is engaged through relative translational movement between the stem component and the head component along the first direction.
• A method of use for a modular prosthesis for replacement of a head portion of a proximal radius includes coupling a stem anchoring portion of a monolithic stem component having a longitudinal axis to a resected portion of the proximal radius, and coupling a dovetail-shaped first mounting portion on a first end face of a head component that extends in a first direction transverse to the longitudinal axis to a dovetail-shaped second mounting portion on a second end face of the stem component that extends in the first direction. The coupling the first mounting portion includes slidably engaging the first mounting portion with the second mounting portion by moving the head component in the first direction, and connecting the head component and the stem component by moving the head component in the first direction after the slidably engaging until a locking mechanism formed by the stem component and the head component at an interface is engaged, wherein one of the first and second mounting portions intersects the longitudinal axis.
• Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
• FIG. 1 is a front view of a stem component;
• FIG. 2 is a side view of the stem component from a perspective perpendicular to that ofFIG. 1;
• FIG. 3 is a top view of the stem component;
• FIG. 4 is a front view of an inner core of a head component;
• FIG. 5 is a side view of the inner core of the head component from a perspective perpendicular to that ofFIG. 4;
• FIG. 6 is a top view of the inner core of the head component;
• FIG. 7 is a front view of an outer shell of the head component;
• FIG. 8 is a side view of an outer shell of a head component from a perspective perpendicular to that ofFIG. 7;
• FIG. 9 is an exploded perspective view of an assembly of a stem component, a inner core, and an outer shell;
• FIG. 10 is a perspective view of an assembled prostheses;
• FIG. 11 is a front view of an assembled prostheses;
• FIG. 12 is a side view of an assembled prostheses from a perspective perpendicular to that ofFIG. 11;
• FIG. 13 is a top view of an assembled prostheses;
• FIG. 14 is a posterior oblique view of a human elbow depicting a radial head prostheses in position within a proximal radius bone and articulating with a capitellum of a distal humerus;
• FIGS. 15 and 16 are perspective views of a tool that can be used to insert or remove a head component from a stem component via a translational force;
• FIG. 17 is a perspective view of the head component showing the outer shell body completely enveloping the inner core
• FIG. 18 is similar toFIG. 17 but shows the head component disassembled;
• FIG. 19A is a perspective view of the head component showing the inner core extending beneath the outer shell body;
• FIG. 19B is similar toFIG. 19A but shows a mechanical fastener securing the outer shell body to the inner core;
• FIG. 19C is similar toFIG. 19A but shows the head components as a single piece;
• FIG. 20 is similar toFIG. 19 but shows the head component disassembled;
• FIG. 21A is a perspective view of the head component, the stem component and a collar component;
• FIG. 21B is similar toFIG. 21A but shows an alternative configuration between the head component, the stem component and the collar component;
• FIG. 22 is similar toFIG. 21A but the components are assembled;
• FIG. 23 are perspective views of exemplary alternative connections between components of the modular prosthesis;
• FIG. 24 is similar toFIG. 21A but shows an angled collar component;
• FIG. 25 is similar toFIG. 24 but the components are assembled;
• FIGS. 26A-26D are perspective views of exemplary alternative connections between the head component, the stem component and the collar component; and
• FIG. 27 is perspective view of a kit including a plurality of head components, stem components and collar components having various sizes, shapes and configurations.
DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS
• The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application or uses.
• Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular configurations, process steps and materials disclosed herein as these may vary to some degree. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to be limiting as the scope of the present invention. The invention will be limited only by the appended claims and equivalents thereof.
• It must be noted that, as used in this specification and the appended claims, singular forms of “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise.
• “Radial head” is defined as the essentially cylindrical protrusion found at the proximal end of a radius bone. The term “radial head” can also be used to modify or describe the prostheses of the present invention.
• “Longitudinal axis” is an imaginary line that is defined by the center of the stem component in the direction of intramedullary canal insertion. Thus, the “longitudinal axis” is also roughly defined as running parallel to a centerline running between the proximal and distal end of the radius bone.
• “Transverse axis” or “assembly axis” is an axis that intersects the longitudinal axis. The transverse axis can be linear or non-linear. For example, if non-linear, the axis can be arcuate, provided the assembly axis intersects the longitudinal axis. Thus, angles >0° and <180° qualify as “transverse.” However, for practical purposes, the transverse axis can be from 45° to 135° with respect to the longitudinal axis in order to significantly benefit from the modular assembly benefits described herein. In many instances, an essentially perpendicular transverse axis with respect to the longitudinal axis will be present.
• “Protuberance” can include any protuberance functional with the present invention, particularly with respect to certain locking mechanisms. For example, such protuberances can be convexities.
• “Concavity” is intended to describe an open space defined by a mounting portion of a stem component, or an inner core. With respect to a locking mechanism, the concavity can be configured to inversely match and accept a protuberance, though this is not required.
• “Intramedullary” shall mean the within the marrow cavity of a bone.
• “Native” is used to describe the condition of the bone or the head of a bone prior to damage or removal.
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
• In order to remedy the shortcomings of prosthetic radial head replacement, a radial head prosthesis is disclosed that enables the assembly without having to significantly remove or manipulate bone and tissue as part of an overhead assembly. By implementing a sliding mechanism for the assembly of the modular radial head prostheses as described herein, improvement over the commercially available prosthetics can be achieved. Specifically, a sliding mechanism in conjunction with a locking mechanism enables the secure attachment and reasonable removal of a head component from an intact stem component, without the disadvantages associated with head component insertion along the longitudinal axis.
• With the above descriptions and definitions in mind, astem component10 is shown inFIG. 1. Generally, thestem component10 comprises an anchoringportion12 and a mountingportion14. The anchoringportion12 is the portion that is anchored within a canal of the proximal radius, providing support to the radial head prosthetic as a whole. In this embodiment, the anchoringportion12 is tapered and can be coated or textured to allow bone ingrowth after insertion into the radius bone of a patient. The anchoring portion can be cemented, press fit, and/or impacted into the intramedullary canal as is known by those skilled in the art. If a cement is used, then a cement such as, for example, methyl methacrylate, can be used. If desired, various sized broaches (not shown) can be provided such that the surgeon can sound the diameter of the proximal radial shaft, thereby selecting an appropriate sized stem component. In this embodiment, the mountingportion14 is configured as a dovetail shaped mount when viewed from the front perspective shown inFIG. 1. On each side of the mountingportion14 are thestem protuberances16a,16b. Though not required, the entire stem component10 (i.e., the anchoringportion12, the mountingportion14, and thestem protuberances16a,16b) can be constructed of a rigid material such as metal, alloy, or ceramic. If the rigid material is metal or alloy, appropriate materials can include, for example, titanium, stainless steel, and cobalt chrome.
• Turning toFIG. 2, a side view of thestem component10 shown. As can be seen, thestem protuberances16aare configured to span a distance of approximately one half of the depth of the mounting portion. Thestem protuberance16b(not shown) is configured similarly. InFIG. 3, a top view of thestem component10 is shown. As the mountingportion14 is configured in a dovetail-type shape, thestem protuberances16a,16bare not visible from this perspective, and thus, are shown as dashed lines.
• The stem component shown inFIGS. 1-3 has the dual purpose of attaching the prostheses to the radius bone, as well as to provide a mechanism to mount a head component (not shown) to the stem component. Though the head component can be a single unit, in the embodiment shown in the subsequent figures, the head component comprises an outer shell and an inner core. The practical reason for this is that it is often desirable to have a rigid outer shell, while having a less rigid inner core when utilizing the locking mechanism described inFIGS. 1-13. However, if the locking mechanism does not utilize compressible protuberances as part of the locking mechanism, the inner core can be a rigid material as well.FIGS. 3-6 show an embodiment of the inner core, andFIGS. 7-8 show an embodiment of the outer shell. However, the inner core and the outer shell will generally be pre-assembled prior to surgery.
• Turning specifically toFIG. 4, aninner core20 of a head component is shown. Aninner core body22 defines the shape of theinner core20 and can be constructed of a polymeric resin, such as, for example, a high molecular weight polyethylene. Additionally, the outer dimension of theinner core body22 can be cylindrical in shape. Attached to the inner core body are a pair ofinner core protuberances24a,24b. Theinner core body22 and theinner core protuberances24a,24bdefine an inner core open channel or groove26 that can be slidably connected to the mounting portion (not shown) of the stem component (not shown). Theinner core protuberances24a,24bcan be constructed of the same material as theinner core body22, though this is not required. Thus, theinner core body22 and theinner core protuberances24a,24bcan be a single polymeric or copolymeric unit. Whatever the structure, in this embodiment, theinner core protuberances24a,24bare constructed of a compressible material so that theinner core protuberances24a,24bcan pass by the stem protuberances (not shown) as part of a locking mechanism.
• As can be seen more clearly inFIGS. 5 and 6, theinner core protuberances24a,24bare configured such that they span only a portion of the depth of theopen channel26. Thus, theinner core protuberances24a,24bare positioned opposite the stem protuberances (not shown) such that when the head component is in place on the stem component, all of the protuberances act together to form a locking mechanism.
• As shown in this embodiment, the inner coreopen channel26 does not traverse completely through theinner core body22. Thus, theinner core groove26 is just long enough such that when the mounting portion of the stem component (not shown) is tracked within the inner coreopen channel26, the mounting portion and theinner core20 will be coaxial.
• InFIGS. 7 and 8, aradial head component30 is shown. Anouter shell body32 is fashioned to approximate the dimensions of a damaged or removed radial head. Thus, the outer dimension is roughly cylindrical, having a slightly concavedtop portion37 for natural articulation with the capitellum (not shown). Becauseouter shell body32 is the portion of the prostheses that will articulate with the capitellum upon joint movement, this structure can be constructed of a biologically acceptable rigid material. Such a material can include, for example, metal, alloy, or ceramic. If the rigid material is metal or alloy, appropriate materials can include, for example, titanium, stainless steel, and cobalt chrome. Theouter shell body32 also defines an inner hollow34 that accepts the inner core (not shown) when the head component is fully constructed. Additionally, an outer shell open channel orgroove36 is present that essentially matches the inner core open channel or groove (not shown) such that the mounting portion (not shown) can be inserted into the aligned grooves. For example, theouter shell body32 and the inner core (not shown) can both be cylindrical components that define dovetail shaped grooves, which substantially fits the dovetail shaped mount of the stem component. If theinner core20 and theouter shell body32 are two different materials (as in the present embodiment), then the two components can be fitted together with a bonding cement, friction fit, and/or other known techniques. The outer shell open channel or groove36 can be present at only one edge of theouter shell body32 and its edges can be tapered to avoid damage to the articular cartilage of the proximal radio-ulnar joint. As mentioned, theouter shell body32 should be composed of metal suitable for biologic implantation, and be shaped to approximate the dimensions of the radial head. If the surgeon requires assistance in selecting an appropriately sized head component, then an estimate of the patient's anatomy can be ascertained using plastic trials (not shown) provided for this purpose. Though not required, the edges of theouter shell groove36 can be tapered to avoid damage to the proximal radio-ulnar joint.
• Turning toFIG. 9, an exploded view of an embodiment of the present invention is shown. Specifically, theradial head component30 is shown having anouter shell body32, which defines an outer shell hollow34. The outer shell hollow34 fits over an outer dimension of theinner core body22 of theinner core20. Once theouter shell body32 and theinner core20 are fitted together such that the outer shellopen channel36 aligns with the inner coreopen channel26, the entire head component (which comprises these two components) can be fitted on the mountingportion14 of thestem component10. Though not required, the locking mechanism can be at an interface between the mountingportion14 and theinner core20. As shown in this figure, a pair of thestem protuberances16a,16bcan pass over a pair of theinner core protuberances24a,24b, as theinner core protuberances24a,24bare configured to compress. Once thestem protuberances16a,16bcompletely pass over theinner core protuberances24a,24b, the stem protuberances can lock into a pair ofinner core concavities25a,25b, respectively. Theinner core concavities25a,25bare configured in dimension to inversely match thestem protuberances16a,16bsuch that a locking action occurs. Thus, an abutment of the protuberances occurs and can prevent unwanted motion between the head component and the stem component after the prostheses is inserted. The protuberances also serve to prevent the head component from slipping off the stem component without intentional force, e.g., during removal by a surgeon. With this and other similar designs, the stem component can be placed in a canal of the radius bone, followed by the fitting of the head component.
• FIG. 10 shows the stem component, theinner core20 and theouter shell body32 in a completed assembly configuration. As can be seen, the cylindricalinner core20 component fits centrally within theouter shell body32. Thus, when the mountingportion14 of thestem component10 is inserted fully within the core and shell, all three components will be configured coaxially. Though theouter shell body32 and theinner core20 are shown as two separate components, in practice, theouter shell body32 and theinner core20 can be assembled and sterilized prior to attachment to the mountingportion14 of thestem component10. Thus, the surgeon would only be required to slide the assembled head component onto thestem component10 by lining up theopen channels26,36 with the mountingportion14, and sliding theradial head component30 into place. InFIGS. 11 -13, additional views of an assembled prosthesis are shown.
• When assembling the head component onto the mountingportion14, due to elastic deformation of theinner core protuberances24a,24b, all of theprotuberances16a,16b,24a,24bcan be slid past opposing protuberances under sufficient translational force. In this embodiment, the protuberances are shaped such that the force required to press the protuberances past their opposing protuberances is intentional and reasonable, but not excessive.
• FIG. 14 is a posterior oblique view of the human elbow depicting the radial head prostheses in position within theproximal radius bone38 and articulating with thecapitellum39 of the distal humerus. As can be seen, the anchoringportion12 is within the medullary canal of theproximal radius38, and theradial head30 is articulating with thecapitellum39 of the distal humerus.
• InFIGS. 15 and 16, atool40 is shown that can be used with the prostheses of the present invention is shown. InFIG. 15, thetool40 is positioned in a first orientation with respect toproximal radius38 for inserting theradial head component30 onto the mountingportion14. InFIG. 15, thetool40 is positioned in a second orientation with respect to theproximal radius38 for removing theradial head component30 from the mounting portion.
• Specifically, with respect toFIG. 15, afirst arm42 and asecond arm44 are shown that enable or surgeon to createtranslational force45 to be placed on theradial head component30. Thefirst arm42 and thesecond arm44 are tracked parallel to one another by atrack46 and aslider48. Thesecond arm44 is connected to ahandle52 by ahinge50. Thehandle52 is designed such that by applying a squeezingforce51,translational force45 is applied to thehead component30. Thus, in this embodiment, the translational force mechanism is a lever. At the end of thefirst arm42 is a pullingmember54 that acts to stabilize the proximal radius38 (or alternatively, the mounting portion14). At the end of thesecond arm44 is a pushingmember56 for pushing theradial head component30 onto the mountingportion14.
• InFIG. 16, thesame tool40 as described inFIG. 15 can be used by flipping it upside down. Thus, thefirst arm42 now acts to provide thetranslational force45 and thesecond arm44 stabilizes the proximal radius38 (or alternatively, the mounting portion14). Thus, the arms are characterized as thefirst arm42 and thesecond arm44 for convenience only. It would be apparent to one skilled in the art that the first arm or the second arm can function as the stabilizer. Likewise, the first arm or the second arm can act to provide desired translational force.
• The use of such a tool is particularly helpful when a locking mechanism such as that described inFIGS. 1 -13 is in place. Locking and unlocking can be carried out as previously described. Specifically, in the present embodiment, the tool can press the components onto one another while maintaining alignment of the dovetail shaped mount and groove. In the absence of intentional and sufficient pressure to translate the head component off of the stem component, the rigidity provided by the polyethylene is sufficient to secure the modular components to each other. Removal is accomplished by generating sufficient translational pressure on the head component with the use of a specially designed handle. This tool binds the far end of the head component while stabilizing the proximal radius bone, and thereby the stem component. Translational force is generated which presses the protuberances of the inner core past the protuberances of the mounting portion, thereby releasing the head component from the stem component.
• A procedure that can be followed for the insertion of the modular radial head prostheses is as follows. If necessary, after resection of a substantially unreconstructable radial head bone, a proximal edge of the radius bone can be removed by transverse sawing or some other removal technique. After the damaged radial head has been removed, the medullary canal of the bone can then be broached with one or more of a series of broaches, the shapes of which approximate the various stem sizes available. Once an appropriate size stem component size has been selected, the anchoring portion can be inserted into the proximal radius bone such that the mounting portion protrudes from the proximal radius bone. The head component can then selected based upon parameters such as proper ligament tensioning, circumference, and height. If desired, this assessment can be assisted with the use of plastic trials made available for this purpose. After an appropriately sized head component is selected, the forearm can be rotated so that the mounting portion is positioned to receive the head portion, i.e., an assembled outer shell/inner core combination or a single piece head component. If the head component comprises an outer shell and an inner core, the head component can either be assembled at the time of manufacture or by the surgeon. In any event, the outer shell groove and the inner core groove should be position such that the grooves line up for accepting the mounting portion. Once the stem component is in place and the proper head component is assembled and selected, the head component is then translated onto the stem component fully. If a locking mechanism is used such as that described inFIGS. 1 -13, a click will be palpable as the stem protuberances and the inner core protuberances slip fully past each other. The prostheses will then be secure within the canal of the proximal radius bone and is positioned to articulate with the capitellum of the distal humerus.
• With the above figures and surgical procedures in mind, a modular prostheses system for replacement of the radial head portion of the radius bone is disclosed comprising a stem component and a head component. The stem component comprises an anchoring portion and a mounting portion, and the head component can have an open channel configured to connect to the mounting portion along an assembly axis that is transverse to a longitudinal axis of the stem component. The connection can be by a sliding motion. Though the system requires only that the assembly axis be transverse to the longitudinal axis of the stem component, for practical purposes, the transverse angle will generally be from about 45° to 135° with respect to the longitudinal axis. This is due to the fact that as you approach angles closer to parallel with the longitudinal axis, the head component becomes more difficult to put in place. In many incidences, the assembly axis will intersect the longitudinal axis at essentially a perpendicular angle.
• The system can further comprise a locking mechanism to prevent the open channel of the head component from indeliberately sliding on the mounting portion once connected to the mounting portion. This is desirable because once the prosthesis has become part of the functioning elbow joint, any slippage could require surgery for repair. Thus, the only circumstance wherein sliding should be allowed should occur at the hand of the surgeon, with deliberate action. The locking mechanism can be configures such as that shown inFIGS. 1-13, or by any other locking mechanism known by those skilled in the mechanical arts. For example, after sliding the head component onto the mounting portion, the head component can be locked in place with a pin or screw.
• In a one embodiment, the mounting portion can be configured for allowing the head component to slide along a single axis via the open channel. Such an embodiment is shown inFIGS. 1-13 where the dovetail-shaped mounting portion is inversely matched with a dovetailed-shaped groove. Thus, head component can be slid onto the mounting portion along a single axis only.
• Though not required, the head component can be inserted and removed from the mounting portion with a specially designed tool. Thus, the system of the present invention can further comprise a tool for inserting and removing the head component while the stem component is in place within a radial canal. Such a tool can comprise a first arm for inserting the head component onto the mounting portion or removing the head component from the mounting portion; a second arm for stabilizing the radius bone; and a translational force mechanism for moving the first arm while the second arm stabilizes the radius bone. The terms “translation” and “stabilizing” are used loosely depending on whether the tool is being used for insertion or removal of the head component, the arm acting to provide the translational force and the arm act to provide stabilization can be changed. Thus, the terms are relative as to the action, rather than to the specific structure. For example, when insertion of the head component is being carried out, the first arm carrying out the translational insertion does so by a pushing force, and the second arm stabilizes the radius bone by a pulling force. Conversely, when removal of the head component is being carried out, the first arm removes the head component by a pulling force (i.e., the tool is flipped over, and the second arm stabilizes the radius bone by a pushing force).
• As part of the system, a method for fitting a damaged radius bone with a modular radial head prostheses is disclosed comprising the steps of securing a stem component partially within a proximal intramedullary canal of the damaged radius bone such that a mounting portion of stem component is exposed above the damaged radius bone; selecting a head component that will provide a desired result; and sliding the head component onto the mounting portion in a direction along an assembly axis that is transverse to a longitudinal axis of the stem component. Typically, a preliminary step of removing a radial head of the damaged radius bone is carried out prior to fitting the radius bone with the prostheses of the present invention, though there can be circumstances where this preliminary step is not necessary. Additionally, before securing the stem component within the intramedullary canal, it may be desirable to carry out the preliminary step of sizing the stem component to securely fit within the proximal canal. This can be done using a set of broaches designed for this purpose. The stem component can be secured within the intramedullary canal by one of a number of techniques including the use of cement, firm pressure into the canal, or impacting the stem component into the canal, for example.
• Once the stem component is in place, the next step of selecting an appropriate head component is carried out. Considerations can include assessing a desired tensioning of one or more ligaments attached to the radius bone and/or assessing the height and shape of the head component to be used. Aid in this area can be provided by the use of trials designed for this purpose. Such trials can be plastic structures configured to approximate the size and shape of the head component to be ultimately placed on the mounting portion. It is appreciated that the trials can be made of other suitable materials.
• Referring toFIGS. 17 through 20, theinner core20 and theouter shell body32 of theradial head component30 are shown. In the various embodiments, theouter shell body32 can be comprised of ultra high molecular weight polyethylene. Theouter shell body32 can also be comprised of a suitable metal material such as cobalt chrome, titanium, or other biocompatible material. Theinner core20 can also be made of a material that is identical to the radial head component30 (FIG. 19B) or as above described made of a softer material (FIG. 19A) that can otherwise be compressed when inserted over thestem protuberances16a,16bor any other biocompatible material, as above detailed and as shown inFIG. 1.
• In other embodiments, theinner core20 and theouter shell body32 are comprised of the same material (FIG. 19B), for example, a metal such as cobalt chrome or titanium. By way of example, amechanical fastener60 can be used to secure theouter shell body32 to theinner core20 in lieu of the compressibleinner core protuberances24a,24b(FIG. 4). In addition, thehead component30 can be made of single piece of biocompatible material (FIG. 19C), such that the head component is a unitary construction. It is appreciated that a plurality of thefasteners60 can be used to secure theouter shell body32 to theinner core20. Moreover, other types of exemplary connections may be used such as chemical bonding, shrink fit and taper junctions. Furthermore, theouter shell body32 can be configured to snap fit onto theinner core20, while another method can include mechanical threading on theinner core20 with complementary mechanical threading on theouter shell body32. Theouter body shell32 of theradial head component30 can also be configured to completely envelope theinner core20, as shown inFIGS. 17 and 18, or otherwise be positioned over theinner core20 as to not cover theopen channel26 thus exposing varying lengths of theinner core20, as shown inFIGS. 19A,19B and20.
• With reference toFIGS. 21A through 24, acollar component62 can be used to connect theradial head component30 to thestem component10. Thecollar component62 can have a collaropen channel64 and acollar mounting location66, which are complementary to the headopen channel36 and thestem mounting location14, respectively. Thecollar component62 can be configured to vertically align theradial head component30 and thestem component10, as shown inFIG. 22. Anangled collar component68 can also be configured to provide a pre-determined angle between theradial head component30 and thestem component10, as shown inFIG. 25. As such, theangled collar component68 can be configured at various angles, for example, between vertical (i.e., 180°) and narrower angles to match the native geometry of the bones, as shown inFIG. 14. It can be appreciated that theradial head component30 and thestem component10 can attach to thecollar component62 or theangled collar component68 regardless of its length or angle.
• In the various embodiments, theradial head component30 can have a unitary construction (i.e., one-piece), thus omitting theinner core20 andouter shell body32. In this arrangement, theradial head component30 can be constructed of metal such as cobalt chrome, titanium or any other suitable biocompatible material for implementation into the human body. By way of example, theradial head component30 can be secured to either thestem mounting portion14 or thecollar mounting portion66 of thecollar component62 with a suitablemechanical fastener60.
• With reference toFIGS. 21A and 21B, thehead component30 includes afirst connection portion70 that connects to asecond connection portion72 on thecollar component62. Thecollar component62 also includes athird connection portion74 that connects to afourth connection portion76 on thestem component10. It can be appreciated that thesecond connection portion72 can be distal from thethird connection portion74 and can be on opposite ends of thecollar component62. As shown inFIG. 21A, thefirst connection portion70 can be theopen channel26 on thehead component30. The second connection portion can be thecollar mounting portion66. Thethird connection portion76 can be the collaropen channel64. Thefourth connection portion78 can be the mounting portion of14 on thestem component10. As shown inFIG. 21B, thefirst connection portion70 can be a headcomponent mounting portion78. The second connection portion can be the collaropen channel64. Thethird connection portion74 can be thecollar mounting portion66. Thefourth connection portion76 can be a stem componentopen channel80.
• It can be appreciated that the various components of the modular prosthesis system can use various connection portions with myriad configurations. By way of example, the mounting portion on the various components is configured in a T-shaped protrusion generally indicated byreference numeral82. A complementaryopen channel84 is similarly configured in a T-shape to accept the T-shapedprotrusion82. With reference toFIG. 23, it can be appreciated that other configurations are suitable such as, but not limited to, acylindrical configuration86, a dove-tail configuration88, and a star shapedconfiguration90. It can also be appreciated that, regardless of the configuration, various fits can be used such as, but not limited to, an interference fit, a taper lock fit and a sliding fit secured by amechanical fastener60. It can further be appreciated that themechanical fastener60 can be inserted through an aperture and contact the T-shaped protrusion. The mechanical fastener can also connect to the T-shaped protrusion such that thefastener60 can be inserted through afastener aperture92 in the open channel and/or in the mounting location. It can be additionally appreciated that the fastener can be placed at various angles and position to further secure the components of the prosthesis.
• It can be appreciated that the various components of the modular prosthesis can be scaled to fit the patients native bone structure. A collar length94 (FIG. 22) and a collar angle96 (FIG. 24) can be variable amongmultiple collar components62,68, while thecollar mounting location66 and the collaropen channel64 can have a fixed dimension to facilitate interchangeability amongother stem components10 andhead components30. With reference toFIG. 20, it can also be appreciated that aninner core length98 can vary such that theinner core body22 can be completely contained within the head component inner hollow34 or extend beyond an outerbody shell aperture100. It is further appreciated, that various dimensions such as length, diameter, thickness etc. can be varied to more closely match the native bone structure of the patient, as shown inFIG. 14.
• With reference toFIGS. 26A-26D, a threadedpost102 and a complementary threadedaperture104 can be used to connect thecollar component62 to thehead component30 and thestem component10. With reference toFIG. 26A, thefirst connection portion70 of thehead component30 can include the threadedaperture104. Thesecond connection portion72 of thecollar component62 can include the threadedpost102 that can engage with and connect to the complimentary threadedaperture104 on thehead component30. Thethird connection portion74 of thecollar component62 can include the above described T-shapedprotrusion82. Thefourth connection portion76 of thestem component10 can include the above described T-shapedchannel84, which can connect with the T-shapedprotrusion82 included on thethird connection portion74 of thecollar component62. It can be appreciated that the angled collar component68 (FIG. 26D) can be similarly configured to the collar component62 (FIGS. 26A-26C) and, thus, can be used interchangeably.
• With reference toFIG. 26B, thefirst connection portion70 on thehead component30 can include the T-shapedprotrusion82. Thesecond connection portion72 of thecollar component62 can include the complimentary T-shapedchannel84 that can connect with and engage the T-shapedprotrusion82 included on thefirst connection portion70 of thehead component30. Thethird connection portion74 of thecollar component62 can include the threadedpost102. Thefourth connection portion76 of thestem component10 can include the complementary threadedaperture104 that can engage to and connect with the threadedpost102 included on thethird connection portion74 of thecollar component62.
• With reference toFIG. 26C, thefirst connection portion70 of thehead component30 can include the threadedaperture104. Thesecond connection portion72 of thecollar component62 can include the threadedpost102 which can engage with and connect to the threadedaperture104 included on the first connection portion of thehead component30. Thethird connection portion74 of thecollar component62 can also include the threadedpost102. Thefirst connection portion76 on thestem component10 can include the threadedaperture104 that can engage with and connect to the threadedpost102 on thethird connection portion74 of thecollar component62.
• With reference toFIG. 26D, thefirst connection portion70 of thehead component30 can include the threadedaperture104. Thesecond connection portion72 of theangle collar68 can include the threadedpost102, which can engage with and connect to the threadedaperture104. The third connection portion of theangle collar68 can also include the threadedpost102. Thefourth connection portion76 of thestem component10 can include the threadedaperture104, which can engage with and connect to the threadedpost102. It can be appreciated that height94 (FIG. 26C) and/orangle96 of either thecollar component62 orangled collar component68 can be varied to accommodate the native bone structure, as shown inFIG. 14. Moreover, the height106 (FIG. 26C) of the threadedpost106 can be varied to further accommodate the modularity of the prosthesis. It can also be appreciated that thefirst connection portion70, thesecond connection portion72, thethird connection portion74 and thefourth connection portion76 can be configured in various ways including, but not limited to, the respective threadedposts102 and threadedapertures104 and various combinations thereof.
• With reference toFIG. 27, akit108 is shown includingexemplary stem components10,collar components62, angledcollar components68 andhead components30. Thekit108 can include a collection of various sizes and shapes of the above-mentioned components. For example, thekit108 can include a plurality ofangled collar component68 having varying collar angles94. By way of further example, thekit108 can include a plurality ofhead components30 having varying shaped concavetop portions37 that complement the native bone to which they will contact. Thekit108 can also include a plurality ofstem components10 such that each of thestem components10 has varyingsize anchor portions12 in thickness, taper design and/or length. Moreover, thekit108 can include a plurality ofcollar components62 having varyingcollar lengths92 to further accommodate the native bone structure. It can be appreciated that thekit108 can includenumerous head components30, angledcollar components68,collar components62, and stemcomponents10 of various sizes, shapes and configurations so that the modular prosthesis system can be assembled to closely match the native bone structure.
• Thekit108 provides the plurality ofhead components30, angledcollar components68,collar components62, and stemcomponents10 that can be assembled and adjusted during a medical procedure to provide a fit that can be in-situ determined and adjusted. It can be appreciated that a medical professional can determine a proper length and angle and select among the components of thekit108 to achieve the proper length and angle. Nevertheless, the medical professional can select and substitute components in-situ to adjust to achieve the proper length and angle.
• The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements. Thus, while the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiment(s) of the invention, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made, without departing from the principles and concepts of the invention as set forth in the claims.

Claims (18)

1. A prosthesis system for replacement of a head portion of a proximal radius, comprising:

a monolithic stem component defining a stem anchoring portion having a longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion on a first end face that extends in a first direction transverse to the longitudinal axis;

a head component having a dovetail-shaped second mounting portion on a second end face opposite the first end face slidably engaged with the first mounting portion along the first direction; and

a locking element formed by the monolithic stem component and the head component at an interface between the stem component and the head component, wherein one of the first and second mounting portions intersects the longitudinal axis and the locking element is engaged through relative translational movement between the stem component and the head component along the first direction.

2. The prosthesis system ofclaim 1 wherein the locking element is engaged through relative translational movement between the monolithic stem component and the head component along a single axis.

3. The prosthesis system ofclaim 1 wherein the locking element is formed by a protrusion and a complementary recess that define a pair of complementary faces that engage along a second direction perpendicular to the first direction when the stem component and the head component are connected.

4. The prosthesis system ofclaim 3 wherein the protrusion is deformable.

5. The prosthesis system ofclaim 3 wherein the protrusion is formed on a mounting surface defined by one of the first mounting portion and the second mounting portion.

6. The prosthesis system ofclaim 3 wherein the recess is formed on a mounting surface defined by one of the first mounting portion and the second mounting portion.

7. The prosthesis system ofclaim 1 wherein the locking element is formed by a female connection portion of the stem component and a male connection portion of a flange of the head component that engage along a second direction perpendicular to the first direction when the stem component and the head component are connected.

8. The prosthesis system ofclaim 7 wherein the female connection portion and the male connection portion are brought into engagement through relative translational movement between the stem component and the head component along a single axis.

9. The prosthesis system ofclaim 7 wherein the flange of the head component is deformable.

10. The prosthesis system ofclaim 1 wherein the first and second mounting portions define a pair of complementary bearing surfaces and one of the pair of complementary bearing surfaces intersects the longitudinal axis.

11. The prosthesis system ofclaim 10 wherein the one of the pair of complementary bearing surfaces intersects the longitudinal axis at an angle of 90 degrees.

12. The prosthesis system ofclaim 10 wherein the pair of complementary bearing surfaces has an area of contact that intersects the longitudinal axis.

13. The prosthesis system ofclaim 1 wherein the first and second mounting portions form an assembly plane that is normal to the longitudinal axis.

14. The prosthesis system ofclaim 1 wherein the head component is a monolithic component.

15. The prosthesis system ofclaim 1 wherein the head component includes an articulating surface that is formed to slidably engage a native capitellum.

16. A method of use for a modular prosthesis for replacement of a head portion of a proximal radius, comprising:

coupling a stem anchoring portion of a monolithic stem component having a longitudinal axis to a resected portion of the proximal radius; and

coupling a dovetail-shaped first mounting portion on a first end face of a head component that extends in a first direction transverse to the longitudinal axis to a dovetail-shaped second mounting portion on a second end face of the monolithic stem component that extends in the first direction, wherein coupling a dovetail-shaped first mounting portion includes:

slidably engaging the first mounting portion with the second mounting portion by moving the head component in the first direction, and

coupling the head component and the stem component by moving the head component in the first direction after the slidably engaging until a locking mechanism formed by the stem component and the head component at an interface is engaged, wherein the first and second mounting portions intersect the longitudinal axis.

17. The method ofclaim 16 wherein the locking mechanism is formed by a protrusion and a complementary recess that define a pair of complementary faces, and the connecting the head component and the stem component further includes engaging the pair of complementary faces along a second direction perpendicular to the first direction.

18. The method ofclaim 16 further comprising determining in-situ a prosthetic length and selecting in-situ one of a plurality of head components, and one of a plurality of stem components to achieve a prosthetic length.

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