Ulnar deviation after volar subluxation of the proximal interphalangeal joint.

A rare case of irreducible and progressive ulnar deviation after volar subluxation of the proximal interphalangeal joint is presented. An immobilized proximal interphalangeal joint with remaining volar subluxation after improper reduction showed ulnar deviation at 3 weeks after injury. During surgery, the radial collateral ligament was found to be ruptured at its origin, with formation of concomitant scar tissues. There were no apparent lesions at the central slip, lateral band, and volar plate. Interposition of the ruptured ligament and infiltration of the surrounding scar tissues into the proximal interphalangeal joint were identified. Surgical incision of the capsule along the dorsal margin of the radial collateral ligament readily produced successful reduction. The irreducible and progressive ulnar deviation of the proximal interphalangeal joint seemed to result from gradual infiltration of the scar tissues, subsequent to remaining volar subluxation because of interposition of the ruptured collateral ligament.