Ulnar-shortening effect on distal radioulnar joint pressure: a biomechanical study

The ulnar-shortening procedure has been successfully used to relieve ulnar impaction syndrome and may help in stabilizing the distal radioulnar joint (DRUJ) by increasing the tension within the triangular fibrocartilage complex. This procedure, however, may increase pressure at the DRUJ and possibly induce degenerative changes in the joint. This study aimed to examine the changes in pressure at the DRUJ by simulating the ulnar-shortening procedure in intact and torn states of the triangular fibrocartilage complex.

Seven fresh-frozen cadaver arms amputated at the midportion of the humerus were used. The ulna and humerus were affixed firmly to a custom mount that allowed 60 degrees forearm rotation. An external fixator was attached to the distal ulna, leaving a 10-mm space to allow progressive shortening. Pressure sensors were inserted in the DRUJ, and pressure distribution in the joint was recorded after every 1-mm shortening that was performed up to a maximum of 6 mm with or without the application of muscle load. These data were then compared with those obtained with the original length of the ulna in 3 joint positions: neutral, 60 degrees pronation, and 60 degrees supination. The tests were repeated after sectioning either the dorsal or the palmar portion of the radioulnar ligament (RUL) and finally after complete sectioning of the RUL.

The peak pressure at the DRUJ increased notably in the intact specimens during progressive ulnar shortening. Compared with the intact specimens, those with partial RUL sectioning exhibited a smaller increase in the peak pressure with ulnar shortening. Complete sectioning of the RUL at its attachment to the ulnar fovea resulted in even smaller increases.

The greater the amount of ulnar shortening, the higher is the peak pressure at the DRUJ. The amount of ulnar shortening should be carefully planned to avoid excessive pressure at the DRUJ.