Which deformities of the metacarpophalangeal (MP) joint are associated with rheumatoid arthritis (RA)?

Updated: Jan 11, 2019
  • Author: Michael Neumeister, MD, FRCSC, FACS; Chief Editor: Joseph A Molnar, MD, PhD, FACS  more...
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Answer

Answer

The condylar structure of the MP joint, which permits motion in 2 planes, makes the MP joint inherently more unstable than the IP joints; therefore, the distorting effects of RA are more pronounced. The classic deformities associated with RA of the MP joints are ulnar drift, which is made up of ulnar shift and ulnar deviation, and volar dislocation. The cumulative effects of various factors contribute to these deformities. Initially, the MP capsule and ligamentous structures are stretched by the proliferation of the synovium, which loosens the collateral ligaments and decreases joint stability. Normally, in the flexed position, minimal lateral movement occurs at the MP joint, but, with increased laxity of the collateral ligaments, up to 45° of lateral deviation occurs in this position. [2]


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