What causes ulnar drift in 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

With loss of MP stability, other forces on the MP produce the characteristic ulnar drift. For example, wrist collapse contributes to ulnar drift. Weakened radiocarpal ligaments cause radial rotation of the metacarpals and carpus on the radius, which results in ulnar deviation of the MP joint via the Z mechanism. This phenomenon describes the consequence of an imbalance of opposing forces at a joint; when a particular joint is continuously angulated in one direction, the joints on either side of it will adopt the opposite position if no physical impediments are present. [2] Moreover, the extensor tendons can be shifted or dislocated in the ulnar direction and contribute to the ulnar drift. The normal ulnar shift of the fourth and fifth extensor tendons during flexion of the MP joints is exaggerated when the radial side of the transverse lamina fibers stretches as a result of synovial proliferation.


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