Flexor Forces and Rheumatoid Metacarpophalangeal Deformity

Abstract
A new theory concerning dynamics of deformity formation in the rheumatoid metacarpophalangeal (MCP) joint has been advanced which is pertinent to the management of the rheumatoid hand. The theory implicates the large forces normally present in the flexor tendons during pinch or grasp. Because of the bends at the MCP joints in these tendons, there is a strong tendency for them to "bowstring" volarly in all fingers, and also ulnad in digits 2, 3, and 4. If diseased joint structures can no longer restrain this tendency, the deformity of volar subluxation and ulnar deviation may follow. In the fifth digit, however, ulnar deviation appears to be the result of the incompletely opposed pull of the hypothenar muscles. The implications of the theory are significant for the prevention, conservative management, and surgical treatment of rheumatoid MCP-joint deformity.

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