Prosthetic wrist implant
A wrist implant requires minimal resection of the distal radius and preserves the sigmoid notch and articulation with the head of the distal ulna. The wrist implant generally includes a radius portion, a carpal portion and a carpal ball. The wrist implant includes a primary articulation and a secondary rotational articulation. The primary articulation occurs between the radius portion and the carpal ball. The secondary articulation occurs between the carpal ball and the carpal portion.
1. A wrist prosthesis for implantation in a patient comprising:
a carpal ball having a concave back surface with a first radius of curvature and a convex articular surface opposite the concave back surface having a second radius of curvature, the first radius of curvature being larger than the second radius of curvature;
a carpal plate having a convex surface with a radius of curvature matching the first radius of curvature and configured to articulate with the concave back surface of the carpal ball; and
an articular cup having a concave articular surface configured to articulate with the convex articular surface of the carpal ball.
2. The wrist prosthesis of claim 1 , wherein the carpal ball is configured to articulate with the articular cup about a first axis of rotation in flexion-extension and about a second axis of rotation in radial-ulnar deviation when the wrist prosthesis is implanted in the patient.
3. The wrist prosthesis of claim 2 , wherein the carpal ball is configured to articulate with the articular cup about a third axis of rotation generally along a long axis of a radius bone of the patient when the wrist prosthesis is implanted in the patient.
4. The wrist prosthesis of claim 1 , wherein the wrist prosthesis includes a degree of incorporated laxity in a rotational degree of freedom between the carpal ball and the articular cup.
5. The wrist prosthesis of claim 1 , wherein the concave articular surface of the articular cup is configured to demonstrate line to line contact with the convex articular surface of the carpal ball.
6. The wrist prosthesis of claim 1 , wherein the articular cup includes a convex exterior surface configured to conform to a curvature of an unresected distal end of a radius bone of the patient.
7. The wrist prosthesis of claim 1 , wherein the convex surface of the carpal plate is configured to articulate with the concave back surface of the carpal ball about a rotational axis generally parallel to a long axis of a third metacarpal of the patient when the wrist prosthesis is implanted in the patient.
8. The wrist prosthesis of claim 7 , wherein the convex surface of the carpal plate is configured to articulate with the concave surface of the carpal ball no more than about ten degrees.
9. The wrist prosthesis of claim 1 , wherein the convex surface of the carpal plate and the concave back surface of the carpal ball are curved along a spherical radius of curvature.
10. The wrist prosthesis of claim 1 , wherein the concave articular surface of the articular cup includes a major radius and a minor radius.
11. The wrist prosthesis of claim 10 , wherein the convex articular surface of the carpal ball comprises a major radius and a minor radius generally matching the major radius and minor radius of the concave articular surface of the articular cup.
12. The wrist prosthesis of claim 1 , further comprising a protrusion secured to the convex surface of the carpal plate, and wherein the carpal ball includes a socket for receiving the protrusion therein.
13. The wrist prosthesis of claim 12 , wherein the socket is configured to form an interference fit with the protrusion when the protrusion is received in the socket.
14. The wrist prosthesis of claim 12 , wherein the protrusion is configured to align with a long axis of a third metacarpal of the patient when the wrist prosthesis is implanted in the patient.
15. The wrist prosthesis of claim 1 , wherein the carpal plate includes a buttress surface opposite the convex surface and a carpal stem extending from the buttress surface.
16. The wrist prosthesis of claim 15 , wherein the carpal stem has a length proportioned so as to be implantable into a carpus of the patient without the carpal stem intruding into a carpal-metacarpal joint.
17. The wrist prosthesis of claim 15 , wherein the carpal stem defines two holes for receiving carpal screws therethrough, and wherein the carpal stem is offset from a line connecting the two holes.
18. The wrist prosthesis of claim 15 , wherein the buttress surface is substantially flat.
19. The wrist prosthesis of claim 1 , further comprising a carpal screw having a head and a shaft, wherein the carpal plate defines a hole for receiving a carpal screw therethrough, and wherein the carpal screw is configured to conically rotate with respect to the carpal plate.
20. The wrist prosthesis of claim 19 , wherein the concave back surface of the carpal ball includes an excavation configured to receive the head of the carpal screw.