How are thumb deformities in rheumatoid arthritis (RA) classified?

Updated: Jun 11, 2021
  • Author: Michael Neumeister, MD, FRCSC, FACS; Chief Editor: Joseph A Molnar, MD, PhD, FACS  more...
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Nalebuff described 5 types of deformities of the thumb associated with RA, and Ratliff described a sixth type.

Type 1 thumb disorder is a boutonniere deformity. The pathology originates at the MP joint with significant synovitis, dorsal hood disruption, and subluxation of the EPL tendon ulnarly. The distal phalanx is drawn into extension as the proximal phalanx subluxes dorsally. The type 1 deformity is the most common in persons with RA.

Type 2 thumb deformity maintains the hyperextension at the MP joint, but it is also associated with hyperextension at the IP joint. Also, the CMC joint is often subluxed.

The type 3 thumb deformity is a swan-neck deformity and is the second most common type of thumb disfigurement in persons with RA. CMC joint synovitis initiates the subluxation of the first metacarpal radially and dorsally. The first metacarpal is adducted. This adduction combined with volar plate laxity results in hyperextension of the MP joint. A relative shortening of the lateral bands and the pull of the flexor pollicis longus draw the distal phalanx into flexion.

The type 4 deformity is analogous to skier thumb or gamekeeper thumb. The MP joint synovitis initiates the pathology, with resultant laxity of the ulnar collateral ligament with or without subsequent adduction of the first metacarpal.

The type 5 deformity is identical to the type 3 deformity but does not involve adduction of the first metacarpal. The disease in type 5 is initiated at the MP joint, fostering volar plate laxity, subsequent MP hyperextension, and IP joint flexion.

The type 6 deformity involves isolated IP joint and/or MP joint destruction with subluxation, as a result of bone resorption and destruction.

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