US20090312839A1

Movatterモバイル変換

Info

Publication number: US20090312839A1
Application number: US12/140,372
Authority: US
Inventors: Luis Roman Scheker; Bryan Babb
Original assignee: Aptis Medical LLC
Current assignee: Aptis Medical LLC
Priority date: 2005-12-22
Filing date: 2008-06-17
Publication date: 2009-12-17
Also published as: US8048162B2; US20110166663A9

Abstract

A proximal radioulnar joint (lateral elbow) prosthesis includes an ulnar brace member to be secured to the outer surface of the ulna bone. The ulnar brace member defines a bearing surface for supporting the radius. The prosthesis may also include a radial brace member which cooperates with the ulnar brace member.

Description

This application claims priority from U.S. patent application Ser. No. 11/306,312. filed Dec. 22, 2005, and from PCT/US2006/062463, filed Dec. 21, 2006, both of which are hereby incorporated herein by reference.

BACKGROUND

The present invention relates to an elbow or proximal radioulnar joint prosthesis. The elbow joint includes three bones—the humerus, which extends from the shoulder to the elbow, and the radius and ulna, which lie parallel to each other and form the forearm, which extends from the elbow to the wrist. Currently, when the proximal head (the upper end as seen inFIG. 1) of the radius bone is damaged or destroyed, the standard procedure is to excise the damaged portion of the radius and, if deemed necessary to insert a prosthesis into the radius bone to replace the radial head. This radial head replacement relies on the annular ligament to hold the radius in position as it did prior to the procedure. If this ligament is damaged as part of the incident which caused the damage to the radial head (such as a dislocation or a fracture of the radial head), which is typical, then the prosthesis may become dislocated from the proximal ulna and or humerus and unable to transmit any axial loads from the hand, via the forearm and the elbow to the humerus. As a result, the patient is not able to transmit axial loads from the radius to the humerus.

SUMMARY

The present invention provides a proximal radioulnar joint prosthesis that gives the patient a wide range of motion and the ability to bear weight with the affected hand.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of one embodiment of a proximal radioulnar joint prosthesis made in accordance with the present invention, installed on a human skeleton:

FIG. 2 is an enlarged, broken-away view of the installed proximal radioulnar joint prosthesis ofFIG. 1;

FIG. 3 is an exploded perspective view of the proximal radioulnar joint prosthesis ofFIG. 2;

FIG. 3A is a front view of an alternative radial stem that may be used in the proximal radioulnar joint prosthesis ofFIG. 1;

FIG. 3B a front view of still another alternative radial stem that may be used in the proximal radioulnar joint prosthesis ofFIG. 1;

FIG. 3C is a front view of still another alternative radial stem that may be used in the proximal radioulnar joint prosthesis ofFIG. 1:

FIG. 4 is a view taken along the line4-4 ofFIG. 2;

FIG. 5 is a front view of a second embodiment of a proximal radioulnar joint prosthesis made in accordance with the present invention, installed on a human skeleton;

FIG. 6 is a view taken along the line6-6 ofFIG. 5 with the bone removed for clarity;

FIG. 7 is a front view of a third embodiment of a proximal radioulnar joint prosthesis made in accordance with the present invention, installed on a human skeleton; and

FIG. 8 is a view taken along the line8-8 ofFIG. 7, with the bone removed for clarity.

DESCRIPTION

FIGS. 1-4 show one embodiment of a proximal radioulnarjoint prosthesis10 made in accordance with the present invention. The proximalradioulnar joint prosthesis10 includes anulnar brace member12, which is secured to theulna bone24 with a plurality ofscrews14. Also included is aradial brace member16, which includes astem rod46, which secures theradial brace member16 to the radius bone by being press fit into themedullary cavity48 of theradius bone22. In addition to or instead of the press fit, theradial brace member16 may be cemented, adhered, or secured by other means to theradius bone22. Theradial brace member16 is essentially a shaft, symmetrical about a central axis. Ahemispherical ball18 is mounted onto the upper or proximal end of theradial brace member16, and thestem rod46 extends downwardly from theball18. Further details of theradial brace member16 will be described later.

Referring toFIGS. 2,3 and4 theulnar brace member12 includes anelongated portion30, which lies adjacent to theulna24 and which is secured to theulna24 by means ofscrews14 that extend throughopenings32 in theelongated portion30. Theelongated portion30 is substantially flat, and its face33 that lies adjacent to theulna24 is generally shaped to conform to the surface of theulna24 in an area of theulna24 which is relatively flat and substantially free of important ligaments and tendons.

As shown inFIGS. 1 and 2, theelongated portion30 of theulnar brace member12 is secured to the outer surface of the side of theulna24. Securing theulnar brace member12 to the side of theulna24 means that theulna24 does not have to be excised in order to install theulnar brace member12. Thus if theulna24 has not been damaged, theulnar brace member12 can be installed without significantly modifying the length or structure of theulna24. With this design, if the radial head of theradius22 has been damaged and needs to be replaced, the ulnar brace member can be installed to retain the replacement radial head without altering or disturbing the natural interaction between the ulna and the humerus.

Securing the ulnar brace member to the side of the ulna also means that the ulnar brace member is secured to dense or compact bone tissue, providing a strong base against which to attach the prosthesis. Ideally, thescrews14 that secure theulnar brace member12 to theulna24 extend completely through theulna24, thereby providing a very secure attachment.

The upper orproximal end36 of theulnar brace member12 includes a projection39 (SeeFIG. 4), which is made up of abase20, which is integral with theelongated portion30, and aseparate base cover40, which is secured to thebase20 by means of self-locking bolts44. Thebase20 andbase cover40 together define a downwardly openingcurved recess41 which conforms to the shape of theball18 and receives theball18 with a close fit.

Thecurved surface38 in thebase20 defines half of thecurved recess41, and thecurved surface42 in thebase cover40 defines the other half of thecurved recess41. Thecover40 andbase20 terminate in vertical planar surfaces35,37, which abut each other when thecover40 is secured to thebase20 by means of the self-locking bolts44, which extend throughopenings43 in thecover40 and are anchored in threadedopenings45 in thebase20. Thebase20 also includesrounded projections55 which mate withrounded openings56 in thecover40. Theprojections55 andopenings56 help align thecover40 with thebase20 prior to threading in thebolts44. When thecover40 andbase20 are secured together, they form a cap, including a ring, which is part of a downwardly openingcurved recess41, which receives and surrounds theball18 at the upper end of theradial brace16. Therecess41 provides a bearing surface, and theball18 is free to swivel and slide within thatbearing surface41, in order to support theradius22 for rotation relative to theulna24. Since the ring portion of therecess41 surrounds theball18, it also serves to retain theball18 in position relative to theulnar brace12.

Once assembled, cap formed by thebase20 andcover40 also defines a shallow, upwardly openingcurved recess28 at the upper or proximal end of theulnar brace member12. This upwardlyopening recess28 is axially aligned with the downwardlyopening recess41, and it has a rounded or curved shape which conforms to the shape of and receives thecapitellum34. Thecapitellum34 is the rounded protuberance at the distal (or lower) end of thehumerus26 that articulates with theradius22. Therecess28 acts not only to receive thecapitellum34, but also to mechanically guide and cradle thecapitellum34 to keep it (and the humerus) in alignment with theprosthesis10.

Looking in more detail at theradial brace16, at the proximal end of theradial stem rod46 are aflange49 and a tear-shaped projection50 axially aligned with the longitudinal axis of theradial stem rod46. The tear-shaped projection50 is received in a corresponding tear-shaped cavity52 in thehemispherical ball18 with a snap-fit, and the flat bottom surface53 of theball18 abuts the top surface of theflange49. In this embodiment, theradial stem rod46 extends from the center of theflange49, and the central axis of theradial stem rod46 is aligned with the central axis of thehemispherical ball18 and the central axis of the tear-shaped projection50.

FIG. 3A is a view of another example of aradial brace16A, including aradial stem rod46A. Thisradial brace16A can be used as an alternative to theradial brace16 shown inFIG. 3. Thisstem rod46A includes a lower,constant diameter section46A, a middletapered section46A″, and a toptapered section46A′″. The taper angle of the toptapered section46A′″ is greater than the taper angle of the middletapered section46A″. Thus, there is anuntapered section46A′, a firsttapered section46A″, and a secondtapered section46A′″. Like the other radial stem, thisstem46A is designed for insertion into the medullary cavity of the radius bone (similar toFIGS. 1 and 2).

FIG. 3B is a view of still another example of aradial brace16B, including astem rod46B, and again thisradial brace16B can be used as an alternative to theradial brace16. Like the previous example, thisradial stem46B also has a lower,constant diameter section46B′, a middletapered section46B″, and a toptapered section46B′″. However, thisradial stem rod46A has an axis that is slightly offset from the central axis of the tear-shapedprojection50B and from the central axis of theball18B. Offsetting the stem may be desired in order to more closely approximate the natural relative positions of the radial head and the shaft of the radius bone.

FIG. 3C is a view of still another example of aradial brace16C, including astem rod46C and aball18C. In this case, theball18C is more than a hemisphere. However, it has the same radius of curvature as thehemispherical ball18 and thus is received in thesame recess41 as thehemispherical ball18.

As indicated above, theball18 is able to pivotably rotate and slide within the downwardly openingrecess41 formed by thebase20 and thebase cover40. Since theball18 of theradial brace16 is received in the downwardly openingrecess41 of theulnar brace12, which is secured to theulna24, and thecapitellum34 of thehumerus26 is received in the upwardly openingrecess28 of theulnar brace12, theradius22 is thereby stabilized relative to theulna24 and thehumerus26.

In thisparticular embodiment10, the metal components of theprosthesis10 are made from cobalt chromium. Of course, other materials may alternatively be used. The metal components include the

brace members

12 and16, including thebase20 andbase cover40, the securing screws14 andbolts44, and theflange49 and tear-shapedprojection50 on thebrace member16. The non-metal components are made from an ultra-high molecular weight polymer, such as UHMW polyethylene. These non-metal components include theball18.

To assemble and install the proximal radioulnarjoint prosthesis10, first the damaged portion of the proximal head of theradius bone22, if present, is excised and readied for receipt of theradial brace member16. Theradial stem rod46 of theradial brace member16 is pressed into the medullary cavity of theradius22. Theradial stem rod46 may be cemented or adhered in place, if desired. Then theball18 is snapped onto the tear-shapedprojection50 to assemble theball18 onto theradial brace16. Alternatively, theball18 could be snapped onto theradial brace16 before theradial brace16 is inserted into the medullary cavity of theradius22. However, if theradial brace16 is inserted into the bone before theball18 is mounted to the stem, a tool (not shown) may be used, acting against theflange49 or against theprojection50, to “hammer” thestem rod46 into themedullary cavity48 of theradius22 prior to snapping theball18 onto theprojection50. Then, holes are drilled into theulna bone24, and theulnar brace member12 is mounted, via self-lockingscrews14, onto the upper portion of theulna24, as shown, with theelongated portion30 of theulnar brace member12 in contact with theulna24. Alternatively, compression screws, pegs or other means of fixation may be used in place of the self-lockingscrews14. In addition, a template may be used to determine where the holes are to be drilled.

As is best appreciated inFIGS. 3 and 4, theelongated portion30 of theulnar brace member12 extends downwardly from thebase20 and is substantially tangent to thebase20. This orientation allows the mounting of theelongated portion30 onto a relatively flat area of theproximal ulna24, where no important ligaments or muscle connections are located, while the downwardly openingrecess41 is axially aligned with theradial head18 of theradius22, and the upwardly openingrecess28 is axially aligned with thecapitellum34 of thehumerus26.

With thecover40 removed, theradius22 is moved toward theulna24 until the ball18 (which serves as a prosthesis for the radial head) of theradial brace member16 is inserted into thepartial cavity38 of thebase20. Thebase cover40 is then installed onto the base20 with thebolts44 so as to “capture” theball18 within the downwardly openingrecess41. Theball18 is able to rotate and slide within thecavity42, which is fixed relative to theulna24. This stabilizes theradius22 relative to theulna24. The overall length of theradius22, together with theradial brace member16, is such that theball18 is trapped within therecess41, and it is unlikely to “pop” out or otherwise become dislocated as theradius22 rotates relative to theulna24 and as the elbow joint is flexed. The upwardly openingcurved recess28 receives thecapitellum34 of thedistal humerus26, as explained earlier. There generally is a slight space or gap between the capitellum34 and therecess28, so they do not come into contact until the person bears weight, at which point thecapitellum34 comes into contact with therecess28, thereby providing support for the weight.

While the embodiment described above shows a simple means for rotationally securing theball18 of theradial brace member16 to theulnar brace member12, various other mounting mechanisms could be used to achieve this result. For instance, theentire projection39 containing the downwardly openingrecess41 could hinge up or out of the way far enough for theball18 to clear the edge of the recess and then could hinge downwardly and be fixed in the downward position to retain theball18 in therecess41. Alternatively, the body that forms the downwardly opening recess and upwardly opening recess could be a separate piece from theulnar brace member12, designed to be placed over theball18 and then to be fixed relative to theulnar brace member12 by means such as snapping or bolting. Similarly, theulnar brace member12 could be secured to the outer surface of theulna24 by other means, such as by being adhered to theulna24.

FIGS. 5 and 6 show another embodiment of a proximal radioulnarjoint prosthesis100 made in accordance with the present invention. As in the previous embodiment, this embodiment includes anulnar brace member112 having anelongated portion130, which conforms to the outer surface of theulna bone124 and is secured to theulna bone124 viascrews114. Theulnar brace member112 again includes abase portion120 and acover140. Thebase120 includes rounded projections155 (shown inFIG. 6) to aid in aligning thecover140 and thebase120, and thecover140 is secured to the base120 withbolts144. In this embodiment, thebase120 and cover140 collectively form aring139 that defines anopening159. As in the first embodiment, thering139 has an inside diameter that is slightly larger than the outside diameter of theradial head123 of theradius bone122, and thering139 encircles theradial head123, as shown inFIG. 5. Thering139 retains theradial head123 of theradius bone122 and provides a bearing surface that rotationally supports theradius bone122. Theopening159 allows contact between theradial head123 and thecapitellum134, thereby preserving the natural interaction between theradial head123 and thecapitellum134. Thering139 of this embodiment is similar to theprojection39 of the previous embodiment, except it is open instead of being closed, where the cap of the previous embodiment defines the closedupper surface28, which receives thecapitellum134 and the downwardly openingrecess41, which receives theradial head18 of theradius bone22.

In this embodiment, thering139 is lined with apolymeric liner159A, such as UHMW polyethylene, which is the material that comes into contact with and provides the bearing surface for theradius bone122. Of course, in other embodiments, the liner may be made of another suitable material or may be omitted altogether. As with the first embodiment, thering139 holds theradius122 in position relative to theulna124, thereby performing a function similar to that of the natural annular ligament, which may have been damaged. In this embodiment, there is no radial brace member.

However, in addition to being used with a healthy,undamaged radius bone122 as shown inFIG. 5, this embodiment of the proximal radioulnarjoint prosthesis100 could also be used with a variety of artificial radial head replacements, such as the

radial brace members

16,16A,16B described earlier, or others. When replacing the radial head, the proximal radioulnarjoint prosthesis100 can be used by securing theulnar brace member112 to theulna124, and then securing thecover140 to the base120 to encircle the particular radial head replacement being used. Thus theprosthesis100 provides the ability to retain and rotationally support theradius bone122 for a variety of radial heads, both natural and prosthetic.

In addition, the ring of the proximal radioulnar joint prosthesis could be positioned in a slightly more distal direction. That is, the ring could encircle the radius bone below the radial head, instead of encircling the radial head.

FIGS. 7 and 8 show another embodiment of a proximal radioulnarjoint prosthesis200 made in accordance with the present invention. Like the previous embodiments, thisulnar brace member212 includes anelongated portion230, which conforms to the outer surface of theulna bone224. In this embodiment, thebase220 of theprosthesis200 defines a partial-ring259, which provides the bearing surface for theradial head223, but it has no cover or other means for completely encircling the proximal end of theradius bone222. In this case thepartial ring259 is a half-ring, so it is very similar to the embodiment ofFIG. 6 with thecover140 removed. Thisprosthesis200 is not designed to replicate the retaining function of the annular ligament, but it is designed to provide a bearing surface for supporting theradial head223 of a radius bone as it articulates relative to theulna224. Similar to the previous embodiment, thepartial ring259 is lined with apolymeric liner259A, which provides the actual bearing surface against which theradial head223 slides. Thisprosthesis200 may be used with the naturalradial head223 of the radius bone as shown inFIG. 7 or with an artificial replacement for the radial head. Thisprosthesis200 is secured to the outer surface of theulna bone224 withscrews214 in the same manner as described for the previous embodiments.

While some embodiments of the present invention have been described above, it will be obvious to those skilled in the art that various modifications may be made to these embodiments without departing from the scope of the present invention as claimed.

Claims

1. A proximal radioulnar joint prosthesis, comprising:

an ulnar brace member having an upper end and a lower end, and including a substantially flat, downwardly-extending elongated portion defining an elongated abutment surface having a shape which conforms to the outer surface of the ulna bone near its proximal end;

said ulnar brace member defining a curved radius-bone guide surface fixed relative to said elongated portion and positioned to be aligned with and to receive and support the proximal end of the radius bone for rotation relative to the ulnar brace member when the elongated portion is abutting and mounted on the proximal end of the ulna bone; and said ulnar brace member further including means for transmitting axial loads from the radius to the humerus.

2. A proximal radioulnar joint prosthesis as recited inclaim 1, wherein the curved radius bone guide surface is part of at least a partial ring which is positioned to at least partially encircle the proximal end of the radius when the ulnar brace member is mounted on the proximal end of the ulna bone.

3. A proximal radioulnar joint prosthesis as recited inclaim 2, wherein the means for transmitting axial loads from the radius to the humerus includes said curved radius bone guide surface defining an opening through which the radial head may extend to contact the capitellum.

4. A proximal radioulnar joint prosthesis as recited inclaim 2, wherein the means for transmitting axial loads from the radius to the humerus includes a cap, having an upwardly opening concave surface for receiving and supporting the capitellum and a downwardly opening concave surface for receiving and supporting the proximal radial head.

5. A proximal radioulnar joint prosthesis as recited inclaim 3, wherein the at least partial ring is a complete ring and includes a base, which is integral with the elongated portion and forms part of the ring; and a cover, which mates with the base to complete the ring.

6. A proximal radioulnar joint prosthesis as recited inclaim 4, wherein the at least partial ring is a complete ring and includes a base, which is integral with the elongated portion and forms part of the ring and part of the cap; and a cover, which mates with the base to complete the ring and the cap.

7. A proximal radioulnar joint prosthesis as recited inclaim 6, wherein said elongated portion defines lateral through holes for use in securing the ulnar brace member to the ulna bone.

8. A proximal radioulnar joint prosthesis as recited inclaim 1, and further comprising a radial brace member including a rod defining a longitudinal axis and distal and proximal ends; and a ball at the proximal end of said rod which serves as the radial head of the radius bone, wherein said radius bone guide surface conforms to the shape of said ball.

9. A proximal radioulnar joint prosthesis as recited inclaim 4, and further comprising a radial brace member including a rod defining a longitudinal axis and distal and proximal ends, and a ball at the proximal end of said rod which serves as the radial head of the radius bone, wherein said downwardly opening concave surface conforms to the shape of said ball.

10. A proximal radioulnar joint prosthesis as recited inclaim 9, wherein said ball defines a central axis, and the longitudinal axis of the rod of said radial brace member is offset from the central axis of said ball.

11. A proximal radioulnar joint prosthesis as recited inclaim 10, wherein the at least partial ring is a complete ring and includes a base, which is integral with the elongated portion and forms part of the ring and part of the cap; and a cover, which mates with the base to complete the ring and the cap; and wherein said elongated portion defines lateral through holes for use in securing the ulnar brace member to the ulna bone.

12. A method of installing a proximal radioulnar joint prosthesis, comprising the steps of:

fixing an ulnar brace to the outer surface of the ulna bone of a patient near the proximal end of the ulna bone; and

aligning said ulnar brace with the patient's radius bone so that the ulnar brace provides a bearing surface that supports the patient's radius bone.

13. A method of installing a proximal radioulnar joint prosthesis as recited inclaim 12, wherein said ulnar brace includes a base member and a cover, and including the step of assembling said cover and base member together to form a ring which encircles the radius bone adjacent its proximal end.

14. A method of installing a proximal radioulnar joint prosthesis as recited inclaim 12, and further comprising the step of:

inserting a radial brace member into the medullary cavity of the radius bone, said radial brace member including:

a rod, defining a longitudinal axis and distal and proximal ends: and

a radial head prosthesis at the proximal end of said rod;

wherein said bearing surface supports said radial head prosthesis.

15. A method of installing a proximal radioulnar joint prosthesis as recited inclaim 13, and further comprising the step of:

a rod, defining a longitudinal axis and distal and proximal ends; and

a radial head prosthesis at the proximal end of said rod;

wherein said bearing surface supports said radial head prosthesis.

16. A method of installing a proximal radioulnar joint prosthesis as recited inclaim 15, wherein said ulnar brace member includes a cap which defines said ring, said cap also defining an upwardly opening concave surface surface which cradles the capitellum and a downwardly opening recess, said recess receiving said radial head prosthesis.