# Patent

## Title
Modular prosthesis and use thereof for replacing a radial head

## 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.

## Background
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 Ser. No. 09/828,745, filed Apr. 9, 2001 now issued as U.S. Pat. No. 6,656,225 B2 on Dec. 2, 2003, which claims the benefit of U.S. Provisional Application No. 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 of FIG. 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 of FIG. 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 of FIG. 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 of FIG. 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 to FIG. 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 to FIG. 19A but shows a mechanical fastener securing the outer shell body to the inner core;
FIG. 19C is similar to FIG. 19A but shows the head components as a single piece;
FIG. 20 is similar to FIG. 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 to FIG. 21A but shows an alternative configuration between the head component, the stem component and the collar component;
FIG. 22 is similar to FIG. 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 to FIG. 21A but shows an angled collar component;
FIG. 25 is similar to FIG. 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, a stem component 10 is shown in FIG. 1. Generally, the stem component 10 comprises an anchoring portion 12 and a mounting portion 14. The anchoring portion 12 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 anchoring portion 12 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 mounting portion 14 is configured as a dovetail shaped mount when viewed from the front perspective shown in FIG. 1. On each side of the mounting portion 14 are the stem protuberances 16a, 16b. Though not required, the entire stem component 10 (i.e., the anchoring portion 12, the mounting portion 14, and the stem protuberances 16a, 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 to FIG. 2, a side view of the stem component 10 shown. As can be seen, the stem protuberances 16a are configured to span a distance of approximately one half of the depth of the mounting portion. The stem protuberance 16b (not shown) is configured similarly. In FIG. 3, a top view of the stem component 10 is shown. As the mounting portion 14 is configured in a dovetail-type shape, the stem protuberances 16a, 16b are not visible from this perspective, and thus, are shown as dashed lines.
The stem component shown in FIGS. 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 in FIGS. 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, and FIGS. 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 to FIG. 4, an inner core 20 of a head component is shown. An inner core body 22 defines the shape of the inner core 20 and can be constructed of a polymeric resin, such as, for example, a high molecular weight polyethylene. Additionally, the outer dimension of the inner core body 22 can be cylindrical in shape. Attached to the inner core body are a pair of inner core protuberances 24a, 24b. The inner core body 22 and the inner core protuberances 24a, 24b define an inner core open channel or groove 26 that can be slidably connected to the mounting portion (not shown) of the stem component (not shown). The inner core protuberances 24a, 24b can be constructed of the same material as the inner core body 22, though this is not required. Thus, the inner core body 22 and the inner core protuberances 24a, 24b can be a single polymeric or copolymeric unit. Whatever the structure, in this embodiment, the inner core protuberances 24a, 24b are constructed of a compressible material so that the inner core protuberances 24a, 24b can pass by the stem protuberances (not shown) as part of a locking mechanism.
As can be seen more clearly in FIGS. 5 and 6, the inner core protuberances 24a, 24b are configured such that they span only a portion of the depth of the open channel 26. Thus, the inner core protuberances 24a, 24b are 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 core open channel 26 does not traverse completely through the inner core body 22. Thus, the inner core groove 26 is just long enough such that when the mounting portion of the stem component (not shown) is tracked within the inner core open channel 26, the mounting portion and the inner core 20 will be coaxial.
In FIGS. 7 and 8, a radial head component 30 is shown. An outer shell body 32 is fashioned to approximate the dimensions of a damaged or removed radial head. Thus, the outer dimension is roughly cylindrical, having a slightly concaved top portion 37 for natural articulation with the capitellum (not shown). Because outer shell body 32 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. The outer shell body 32 also defines an inner hollow 34 that accepts the inner core (not shown) when the head component is fully constructed. Additionally, an outer shell open channel or groove 36 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, the outer shell body 32 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 the inner core 20 and the outer shell body 32 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 groove 36 can be present at only one edge of the outer shell body 32 and its edges can be tapered to avoid damage to the articular cartilage of the proximal radio-ulnar joint. As mentioned, the outer shell body 32 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 the outer shell groove 36 can be tapered to avoid damage to the proximal radio-ulnar joint.
Turning to FIG. 9, an exploded view of an embodiment of the present invention is shown. Specifically, the radial head component 30 is shown having an outer shell body 32, which defines an outer shell hollow 34. The outer shell hollow 34 fits over an outer dimension of the inner core body 22 of the inner core 20. Once the outer shell body 32 and the inner core 20 are fitted together such that the outer shell open channel 36 aligns with the inner core open channel 26, the entire head component (which comprises these two components) can be fitted on the mounting portion 14 of the stem component 10. Though not required, the locking mechanism can be at an interface between the mounting portion 14 and the inner core 20. As shown in this figure, a pair of the stem protuberances 16a, 16b can pass over a pair of the inner core protuberances 24a, 24b, as the inner core protuberances 24a, 24b are configured to compress. Once the stem protuberances 16a, 16b completely pass over the inner core protuberances 24a, 24b, the stem protuberances can lock into a pair of inner core concavities 25a, 25b, respectively. The inner core concavities 25a, 25b are configured in dimension to inversely match the stem protuberances 16a, 16b such 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, the inner core 20 and the outer shell body 32 in a completed assembly configuration. As can be seen, the cylindrical inner core 20 component fits centrally within the outer shell body 32. Thus, when the mounting portion 14 of the stem component 10 is inserted fully within the core and shell, all three components will be configured coaxially. Though the outer shell body 32 and the inner core 20 are shown as two separate components, in practice, the outer shell body 32 and the inner core 20 can be assembled and sterilized prior to attachment to the mounting portion 14 of the stem component 10. Thus, the surgeon would only be required to slide the assembled head component onto the stem component 10 by lining up the open channels 26, 36 with the mounting portion 14, and sliding the radial head component 30 into place. In FIGS. 11-13, additional views of an assembled prosthesis are shown.
When assembling the head component onto the mounting portion 14, due to elastic deformation of the inner core protuberances 24a, 24b, all of the protuberances 16a, 16b, 24a, 24b can 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 the proximal radius bone 38 and articulating with the capitellum 39 of the distal humerus. As can be seen, the anchoring portion 12 is within the medullary canal of the proximal radius 38, and the radial head 30 is articulating with the capitellum 39 of the distal humerus.
In FIGS. 15 and 16, a tool 40 is shown that can be used with the prostheses of the present invention is shown. In FIG. 15, the tool 40 is positioned in a first orientation with respect to proximal radius 38 for inserting the radial head component 30 onto the mounting portion 14. In FIG. 15, the tool 40 is positioned in a second orientation with respect to the proximal radius 38 for removing the radial head component 30 from the mounting portion.
Specifically, with respect to FIG. 15, a first arm 42 and a second arm 44 are shown that enable or surgeon to create translational force 45 to be placed on the radial head component 30. The first arm 42 and the second arm 44 are tracked parallel to one another by a track 46 and a slider 48. The second arm 44 is connected to a handle 52 by a hinge 50. The handle 52 is designed such that by applying a squeezing force 51, translational force 45 is applied to the head component 30. Thus, in this embodiment, the translational force mechanism is a lever. At the end of the first arm 42 is a pulling member 54 that acts to stabilize the proximal radius 38 (or alternatively, the mounting portion 14). At the end of the second arm 44 is a pushing member 56 for pushing the radial head component 30 onto the mounting portion 14.
In FIG. 16, the same tool 40 as described in FIG. 15 can be used by flipping it upside down. Thus, the first arm 42 now acts to provide the translational force 45 and the second arm 44 stabilizes the proximal radius 38 (or alternatively, the mounting portion 14). Thus, the arms are characterized as the first arm 42 and the second arm 44 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 in FIGS. 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 in FIGS. 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 in FIGS. 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 in FIGS. 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 to FIGS. 17 through 20, the inner core 20 and the outer shell body 32 of the radial head component 30 are shown. In the various embodiments, the outer shell body 32 can be comprised of ultra high molecular weight polyethylene. The outer shell body 32 can also be comprised of a suitable metal material such as cobalt chrome, titanium, or other biocompatible material. The inner core 20 can also be made of a material that is identical to the radial head component 30 (FIG. 19B) or as above described made of a softer material (FIG. 19A) that can otherwise be compressed when inserted over the stem protuberances 16a, 16b or any other biocompatible material, as above detailed and as shown in FIG. 1.
In other embodiments, the inner core 20 and the outer shell body 32 are comprised of the same material (FIG. 19B), for example, a metal such as cobalt chrome or titanium. By way of example, a mechanical fastener 60 can be used to secure the outer shell body 32 to the inner core 20 in lieu of the compressible inner core protuberances 24a, 24b (FIG. 4). In addition, the head component 30 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 the fasteners 60 can be used to secure the outer shell body 32 to the inner core 20. Moreover, other types of exemplary connections may be used such as chemical bonding, shrink fit and taper junctions. Furthermore, the outer shell body 32 can be configured to snap fit onto the inner core 20, while another method can include mechanical threading on the inner core 20 with complementary mechanical threading on the outer shell body 32. The outer body shell 32 of the radial head component 30 can also be configured to completely envelope the inner core 20, as shown in FIGS. 17 and 18, or otherwise be positioned over the inner core 20 as to not cover the open channel 26 thus exposing varying lengths of the inner core 20, as shown in FIGS. 19A, 19B and 20.
With reference to FIGS. 21A through 24, a collar component 62 can be used to connect the radial head component 30 to the stem component 10. The collar component 62 can have a collar open channel 64 and a collar mounting location 66, which are complementary to the head open channel 36 and the stem mounting location 14, respectively. The collar component 62 can be configured to vertically align the radial head component 30 and the stem component 10, as shown in FIG. 22. An angled collar component 68 can also be configured to provide a pre-determined angle between the radial head component 30 and the stem component 10, as shown in FIG. 25. As such, the angled collar component 68 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 in FIG. 14. It can be appreciated that the radial head component 30 and the stem component 10 can attach to the collar component 62 or the angled collar component 68 regardless of its length or angle.
In the various embodiments, the radial head component 30 can have a unitary construction (i.e., one-piece), thus omitting the inner core 20 and outer shell body 32. In this arrangement, the radial head component 30 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, the radial head component 30 can be secured to either the stem mounting portion 14 or the collar mounting portion 66 of the collar component 62 with a suitable mechanical fastener 60.
With reference to FIGS. 21A and 21B, the head component 30 includes a first connection portion 70 that connects to a second connection portion 72 on the collar component 62. The collar component 62 also includes a third connection portion 74 that connects to a fourth connection portion 76 on the stem component 10. It can be appreciated that the second connection portion 72 can be distal from the third connection portion 74 and can be on opposite ends of the collar component 62. As shown in FIG. 21A, the first connection portion 70 can be the open channel 26 on the head component 30. The second connection portion can be the collar mounting portion 66. The third connection portion 76 can be the collar open channel 64. The fourth connection portion 78 can be the mounting portion of 14 on the stem component 10. As shown in FIG. 21B, the first connection portion 70 can be a head component mounting portion 78. The second connection portion can be the collar open channel 64. The third connection portion 74 can be the collar mounting portion 66. The fourth connection portion 76 can be a stem component open channel 80.
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 by reference numeral 82. A complementary open channel 84 is similarly configured in a T-shape to accept the T-shaped protrusion 82. With reference to FIG. 23, it can be appreciated that other configurations are suitable such as, but not limited to, a cylindrical configuration 86, a dove-tail configuration 88, and a star shaped configuration 90. 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 a mechanical fastener 60. It can further be appreciated that the mechanical fastener 60 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 the fastener 60 can be inserted through a fastener aperture 92 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 length 94 (FIG. 22) and a collar angle 96 (FIG. 24) can be variable among multiple collar components 62, 68, while the collar mounting location 66 and the collar open channel 64 can have a fixed dimension to facilitate interchangeability among other stem components 10 and head components 30. With reference to FIG. 20, it can also be appreciated that an inner core length 98 can vary such that the inner core body 22 can be completely contained within the head component inner hollow 34 or extend beyond an outer body shell aperture 100. 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 in FIG. 14.
With reference to FIGS. 26A-26D, a threaded post 102 and a complementary threaded aperture 104 can be used to connect the collar component 62 to the head component 30 and the stem component 10. With reference to FIG. 26A, the first connection portion 70 of the head component 30 can include the threaded aperture 104. The second connection portion 72 of the collar component 62 can include the threaded post 102 that can engage with and connect to the complimentary threaded aperture 104 on the head component 30. The third connection portion 74 of the collar component 62 can include the above described T-shaped protrusion 82. The fourth connection portion 76 of the stem component 10 can include the above described T-shaped channel 84, which can connect with the T-shaped protrusion 82 included on the third connection portion 74 of the collar component 62. It can be appreciated that the angled collar component 68 (FIG. 26D) can be similarly configured to the collar component 62 (FIGS. 26A-26C) and, thus, can be used interchangeably.
With reference to FIG. 26B, the first connection portion 70 on the head component 30 can include the T-shaped protrusion 82. The second connection portion 72 of the collar component 62 can include the complimentary T-shaped channel 84 that can connect with and engage the T-shaped protrusion 82 included on the first connection portion 70 of the head component 30. The third connection portion 74 of the collar component 62 can include the threaded post 102. The fourth connection portion 76 of the stem component 10 can include the complementary threaded aperture 104 that can engage to and connect with the threaded post 102 included on the third connection portion 74 of the collar component 62.
With reference to FIG. 26C, the first connection portion 70 of the head component 30 can include the threaded aperture 104. The second connection portion 72 of the collar component 62 can include the threaded post 102 which can engage with and connect to the threaded aperture 104 included on the first connection portion of the head component 30. The third connection portion 74 of the collar component 62 can also include the threaded post 102. The first connection portion 76 on the stem component 10 can include the threaded aperture 104 that can engage with and connect to the threaded post 102 on the third connection portion 74 of the collar component 62.
With reference to FIG. 26D, the first connection portion 70 of the head component 30 can include the threaded aperture 104. The second connection portion 72 of the angle collar 68 can include the threaded post 102, which can engage with and connect to the threaded aperture 104. The third connection portion of the angle collar 68 can also include the threaded post 102. The fourth connection portion 76 of the stem component 10 can include the threaded aperture 104, which can engage with and connect to the threaded post 102. It can be appreciated that height 94 (FIG. 26C) and/or angle 96 of either the collar component 62 or angled collar component 68 can be varied to accommodate the native bone structure, as shown in FIG. 14. Moreover, the height 106 (FIG. 26C) of the threaded post 106 can be varied to further accommodate the modularity of the prosthesis. It can also be appreciated that the first connection portion 70, the second connection portion 72, the third connection portion 74 and the fourth connection portion 76 can be configured in various ways including, but not limited to, the respective threaded posts 102 and threaded apertures 104 and various combinations thereof.
With reference to FIG. 27, a kit 108 is shown including exemplary stem components 10, collar components 62, angled collar components 68 and head components 30. The kit 108 can include a collection of various sizes and shapes of the above-mentioned components. For example, the kit 108 can include a plurality of angled collar component 68 having varying collar angles 94. By way of further example, the kit 108 can include a plurality of head components 30 having varying shaped concave top portions 37 that complement the native bone to which they will contact. The kit 108 can also include a plurality of stem components 10 such that each of the stem components 10 has varying size anchor portions 12 in thickness, taper design and/or length. Moreover, the kit 108 can include a plurality of collar components 62 having varying collar lengths 92 to further accommodate the native bone structure. It can be appreciated that the kit 108 can include numerous head components 30, angled collar components 68, collar components 62, and stem components 10 of various sizes, shapes and configurations so that the modular prosthesis system can be assembled to closely match the native bone structure.
The kit 108 provides the plurality of head components 30, angled collar components 68, collar components 62, and stem components 10 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 the kit 108 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

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 stem longitudinal axis and configured to couple to the proximal radius, and a dovetail-shaped first mounting portion extending along a mounting longitudinal axis transverse to the stem longitudinal axis;
a head component having a dovetail-shaped second mounting portion slidably engaged with the first mounting portion along the mounting longitudinal axis; and
a locking mechanism formed by the stem component and the head component at an interface between the stem component and the head component and movable from a disengaged state to an engaged state, wherein one of the first and second mounting portions intersects the stem longitudinal axis and the locking mechanism is engaged through relative translational movement between the stem component and the head component along the mounting longitudinal axis, the locking mechanism preventing relative movement between the stem component and the head component in either direction along the mounting longitudinal axis when moved from the disengaged state to the engaged state.

2. The prosthesis system of claim 1 wherein the locking mechanism includes at least one elastically deformable protrusion movable from a compressed state permitting translational movement of the head component relative to the stem component along the mounting longitudinal axis to an expanded state restricting relative movement between the stem component and the head component.

3. The prosthesis system of claim 1 wherein the locking mechanism is formed by a protrusion and a complementary recess that define a pair of complementary faces that engage in a direction perpendicular to the mounting longitudinal axis when the stem component and the head component are connected.

4. The prosthesis system of claim 3 wherein the protrusion is deformable.

5. The prosthesis system of claim 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 of claim 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 of claim 1 wherein the locking mechanism 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 direction perpendicular to the mounting longitudinal axis when the stem component and the head component are connected.

8. The prosthesis system of claim 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 of claim 7 wherein the flange of the head component is deformable.

10. The prosthesis system of claim 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 stem longitudinal axis.

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

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

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

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

15. The prosthesis system of claim 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 stem longitudinal axis to a resected portion of the proximal radius; and
coupling a dovetail-shaped first mounting portion of a head component that extends along a mounting longitudinal axis transverse to the stem longitudinal axis to a dovetail-shaped second mounting portion of the stem component that extends along the mounting longitudinal axis, wherein coupling a dovetail-shaped first mounting portion includes:
slidably engaging the first mounting portion with the second mounting portion;
moving the head component along the mounting longitudinal axis relative to the stem component;
moving a locking mechanism from a disengaged state to an engaged state; and
preventing relative movement between the stem component and the head component in either direction along the mounting longitudinal axis when the locking mechanism is in the engaged state.

17. The method of claim 16 wherein moving the locking mechanism from the disengaged state to the engaged state includes moving a projection of the locking mechanism in a direction perpendicular to the mounting longitudinal axis.

18. The method of claim 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.