Influence of the pronator quadratus and supinator muscle load on DRUJ stability

Purpose: To determine the effects of altering load contributions of the pronator quadratus and supinator muscles on in vitro distal radioulnar joint (DRU) stability during pronation and supination and before and after ulnar head excision. Methods: Multiple pronation trials were conducted with incremental loading of the pronator quadratus relative to the pronator teres muscle; suprination trials were similarly conducted with incremental loading of the suprinator relative to the biceps muscle. All trials were conducted using the upper limb apparatus capable of stimulating muscle/tendon loading and displacement. Stability measurements included dorsal-volar translations of the radius relative to the ulna and DRUJ diastasis and convergence. Results: Increased pronator quadratus loading did not affect intact DRUJ stability but effects were noted after ulnar head excision when the forearm was positioned between neutral and full pronation. Incremental loading of the suprinator muscle did not modify DRUJ stability in the intact or ulnar head excised state. Conclusions: Pronator qaudratus muscle activity aggravates forearm instability after ulnar, head excision. Immobilization of the forearm in mid- to full supination should minimize pronator quadratus activity and optimize soft-tissue healing. This information may be useful to develop in vitro muscle loading scenarios and analytical forearm models. Copyright (C) 2003 by the American Society for Surgery of the Hand.