A method for hemiarthroplasty of a carpo-metacarpal (CMC) thumb joint that replaces a distal articular surface of a target trapezium with a trapezium implant, the comprising:
- a. exposing the target trapezium through an incision made in the volar radial aspect of the CMC joint, said target trapezium having a dorsal/volar length and a radial/ulnar length;
- b. inserting a cutting guide into the CMC joint of the thumb, said cutting guide comprising:
- i. a joint guide paddle perpendicularly connected to a cutting guide plate, said joint guide paddle configured to fit in the CMC thumb joint;
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- ii. a cutting slot within said cutting guide plate, said cutting guide plate configured to abut at least a radial border of the target trapezium with said cutting slot positioned a distance below the distal articular surface of the target trapezium along the radial border when the cutting guide is inserted;
- c. removing the distal articular surface of the target trapezium by inserting a surface cutting device into the cutting slot of said cutting guide, cutting through the target trapezium creating a cut bone wafer, and removing the cutting guide from the CMC thumb joint along with the cut bone wafer, wherein removing the distal articular surface leaves a receiving surface on the target trapezium;
- d. ensuring the receiving surface is sufficiently flat;
- e. securely positioning a slot guide on the receiving surface of the target trapezium, said slot guide being substantially L-shaped and comprising:
- i. a first arm having a first end and a second end and configured to run parallel to and engage the receiving surface of the target trapezium;
- ii. a second arm having a first end and a second end, said second arm extending downward perpendicularly from said second end of the first arm and abutting the radial surface of the target trapezium;
- iii. a stem slot passing through said second arm at a distance below the first arm and extending continuously upward through the first end of the second arm and across said first arm to define a slot extending through the first arm and running substantially parallel to said flat receiving surface from said second end of the first arm to a point near said first end of the first arm;
- iv. an anchor slot passing through said second arm below said stem slot, said stem slot merging into said anchor slot;
- v. a stop feature positioned within the first arm of the slot guide, said stop feature configured to protect the target trapezium by limiting ingress of the at least one cutting device;
- f. forming a stem channel in the target trapezium using a stem channel cutting device inserted into the stem slot of said slot guide, said stem channel extending from the radial border of the target trapezium to a distance at least half the radial/ulnar length of the target trapezium;
- g. forming an anchor channel in the target trapezium using an anchor channel cutting device inserted into the anchor slot of said slot guide, said anchor channel extending from the radial border of the target trapezium to a distance at least half the radial/ulnar length of the target trapezium;
- h. verifying dimensions of the receiving surface stem channel and anchor channel;
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- i. inserting the trapezium implant into the target trapezium by press fitting the implant into the stem channel and anchor channel to a position recessed about 1.0-2.0 mm from the radial border of the target trapezium, said trapezium implant comprising:
- i. a resurfacing body having:
- A. a periphery;
- B. a body center substantially equidistant from said periphery;
- C. a dorsal/volar length corresponding to a dorsal/volar orientation of a target trapezium;
- D. a radial/ulnar length corresponding to a radial/ulnar orientation of the target trapezium;
- E. a saddle-shaped articular surface defining a distal articular surface of the target trapezium configured to articulate with a natural existing base of a first metacarpal;
- F. articular surface features mimicking natural trapezium bone anatomy, said articular surface features preserving two centers of rotation of the CMC thumb joint;
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- G. a mounting surface engaging the receiving surface of said target trapezium, said mounting surface having a central portion spanning said dorsal/volar length through the body center;
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- ii. a single keel extending substantially from said central portion of said mounting surface along the radial/ulnar length and configured to embed said implant the target trapezium, said single keel having:
- A. a leading edge positioned approximately at the body center of the mounting surface of said resurfacing body;
- B. a trailing edge positioned proximate the periphery of said resurfacing body;
- C. a width between said leading edge and said trailing edge being substantially half the radial/ulnar length of the resurfacing body;
- D. a stem segment having a first end proximal said mounting surface, a second end distal said mounting surface, a length between said first end and said second end, and a thickness, said stem segment configured to fit snugly within the stem channel;
- E. an anchor segment extending from said second end of said stem segment, said anchor segment configured to fit snugly within the anchor channel;
- wherein, said resurfacing body has a height at the body center configured to minimize overstuffing of the CMC joint;
- wherein said single keel has a length of about 3.85 mm, said length including the stem segment and the anchor segment;
- wherein, said length of said stem segment is less than 2.54 mm (0.1 in.);
- wherein, said single keel is configured to minimally damage the trapezium and improve surgical implantation procedure;
- wherein, said single keel is positioned with said mounting surface to allow said stem segment and said anchor segment to reside in a thickest volar area of the target trapezium;
- and
- wherein, the resurfacing body is configured to substantially cover the prepared trapezium surface.