Wrist involvement in rheumatoid swan-neck deformity.

Two observations have led to the consideration of another possible factor in the etiology of rheumatoid swan-neck deformity. Distraction of the rheumatoid wrist with correctable carpal collapse and reversible swan-neck deformities resulted in easier initiation of proximal interphalangeal joint flexion, not found in hands with boutonniere deformity or lack of deformity. Review of x-rays of rheumatoid patients with swan-neck deformity indicates that most have evidence of carpal collapse. With carpal collapse and proximal migration of the carpal-hand unit, long or extrinsic motor systems are no longer working at physiological length or optimal efficiency. An imbalance is created, resulting, in effect, in an "extrinsic-minus" phenomena and swan-neck finger deformity.