How does rheumatoid arthritis (RA) affect the wrist?

Updated: Feb 07, 2020
  • Author: Howard R Smith, MD; Chief Editor: Herbert S Diamond, MD  more...
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Answer

Multiple deformities may occur in the wrist. Disruption of the radioulnar joint with dorsal subluxation of the ulna (caput ulnae) as well as rotation of the carpus on the distal radius with an ulnarly translocated lunate are common. The combination of an ulnar drift of the fingers and carpal rotation is known as a zigzag deformity. Shortening of the carpal height (noted on radiographs), due in part to cartilage loss, is seen with rotational deformities.

Dorsal subluxation of the ulna often allows the ulnar styloid to be depressed volarly on examination, much as a piano key is depressed when played. It may lead to rupture of the extensor tendons of the little, ring, and long fingers because the end of the distal ulna is roughened secondary to erosion of bone and may abrade the tendons as they move during normal hand function, much as a rope is frayed when rubbed over a sharp rock (see the image below). This process is especially likely to lead to tendon rupture if tenosynovitis is present.

Coronal, T1-weighted magnetic resonance imaging sc Coronal, T1-weighted magnetic resonance imaging scan shows characteristic pannus and erosive changes in the wrist in a patient with active rheumatoid arthritis. Courtesy of J. Tehranzadeh, MD, University of California at Irvine.

Entrapment neuropathy may result from synovitis about the flexor tendons. Entrapment of the median nerve as it passes through the carpal tunnel leads to decreased sensation on the palmar aspect of the thumb, index finger, and long finger and on the radial aspect of the ring finger; weakness and atrophy of the muscles in the thenar eminence also occurs. Entrapment of the ulnar nerve at the wrist, a less frequent event, causes decreased sensation over the little finger and the ulnar aspect of the ring finger and decreased interosseous muscle strength and mass.


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