Metacarpophlangeal (MP) Joint Replacement

The metacarpophalangeal (MP) joint is the large joint where the finger attaches to the hand. Arthritis of the MP joint can lead to pain, swelling and stiffness. Nonoperative management includes a steroid injection or two, activity limitation and buddy taping the finger to its neighbor. In patients with rheumatoid arthritis, all of the MP joints can be involved, and the fingers can deviate away from the thumb, making it difficult to use the hand to pick up and pinch objects. Rheumatoid arthritis causes the fingers to angulate, sublux and/or dislocate because it is a systemic disease that destroys not only the joint, but also the ligaments that hold the joint in position.

Once rheumatoid arthritis causes the MP joint to dislocate, joint replacement should be strongly considered. The reason is because following the dislocation, the finger starts to drift up into the palm of the hand. This causes the soft tissues to shorten. Then, when MP joint replacement is finally performed, the finger cannot be brought out to length. At this point, in order place the new joint, a significant amount of bone needs to be removed from the metacarpal bone of the hand. So now the MP joint replacement can no longer be placed in the wide area at the end of the bone. It now must be placed in the narrow shaft of the bone (think of how a dog bone in wider on either end than in the middle). Placing an MP joint replacement in the narrow shaft doesn’t provide as much stability as the wider bone ends do, predisposing to complications.

If non-operative management fails, MP joint replacement is an effective surgical option. Patients without rheumatoid arthritis usually have good tendons and ligaments, and can therefore benefit from the newer total joint replacements now available. These newer MP joint replacements are made of metal and polyethylene (a very tough plastic-like material). Each side of the joint is resurfaced by a separate piece, for a total of two pieces. These replacements are made of the same materials that hip, knee and shoulder replacements are made out of, and are believed to last longer and provide better function than the older single-piece hinged silastic (a rubbery material) joint replacements.

If the ligaments have been compromised, which is almost always the case with rheumatoid arthritis, than the newer type of total joint replacement cannot be used, because there are no ligaments to stabilize the two separate pieces. The older hinged silastic replacement must be used, as these single-piece joint replacements provide their own stability to the joint. These silastic implansts work well, but will eventually break after a number of years. Having said that, good function often remains even after they break; broken silastic joints don’t necessarily have to be replaced.

Both types of replacement provide an average of about 50% of normal motion. However, that amount of MP joint motion is still very functional. Even though it’s not full motion, having 50% of pain-free motion is almost always better than having motion that causes pain, as when a joint hurts its function is usually significantly compromised.