Radioulnar convergence after distal ulnar resection: mechanical performance of two commonly used soft tissue stabilizing procedures.

Resection of the distal ulna (Darrach operation) is a common method for salvaging the arthrotic distal radioulnar joint (DRUJ). However, problems have been reported with this procedure due to residual instability and radioulnar convergence. As a result, several methods of soft tissue stabilization for the unstable distal ulna have been developed. Although their clinical efficacy has been reported, biomechanical investigations of these procedures have not been reported. The purpose of our study was to evaluate the dynamic effects on radioulnar convergence and dorsal-palmar displacement of three procedures: the Darrach procedure, a pronator quadratus interposition flap and an extensor and flexor carpi ulnaris tenodesis. We tested 7 fresh-frozen cadaver upper extremities using a dynamic computer-controlled device that generated forearm rotation with physiologic loading of relevant muscles. Displacement data concerning the ulna relative to the radius through the range of forearm rotation was collected for 4 experimental conditions: intact, distal ulna resection alone, distal ulna resection with pronator quadratus interposition and distal ulna resection with extensor and flexor carpi ulnaris tenodesis. Distal ulna resection altered the kinematics, most predictably creating a convergence of the radius towards the ulna. Anteroposterior translations in each loading condition could be detected as well. The interposition of the pronator quadratus muscle or tenodesis with the extensor and flexor carpi ulnaris tendons did not reduce the radioulnar convergence created by resection of the distal ulna.