The pathogenesis of the rheumatoid swan neck deformity.

Disappointment with the late results of intrinsic release for the rheumatoid "intrinsic-plus" hand has led to a re-appraisal of the role of intrinsic muscle contracture in the pathogenesis of the rheumatoid swan neck deformity. In cadaveric fingers, a properly placed suture typing the lateral band to the middle slip insertion causes a swan neck deformity. It is suggested that the usual "intrinsic-plus" hand and the fixed swan neck deformity of rheumatoid arthritis is caused by adhesions between the extensor tendons on the dorsum of the proximal interphalangeal joint, rather than by intrinsic muscle contracture and/or metacarpo-phalangeal dislocation.