The Influence of the Forearm Muscles on Distal Radioulnar Joint Stability

The distal radioulnar joint (DRUJ) is crucial for the rotational movement of the forearm, as well as for power and load transfer. Torque movements and other activities that put stress on the wrist lead to a physiological anteroposterior shift in the DRUJ. Little was known about the importance and relative contribution of musculoskeletal units to the stabilization of this joint. We quantified the influence of the flexor carpi ulnaris (FCU) and the extensor carpi ulnaris (ECU) muscles on DRUJ stability. The anteroposterior ulnar head translation in relation to the radius was measured sonographically when the forearm was in a neutral resting position and when the hand was actively pressed onto a surface. This was done with and without intentional FCU and ECU activation, with monitoring by an electromyogram. Data on 40 healthy participants indicated a mean anteroposterior translation in the distal radioulnar joint of 4.1 mm (SD 1.08) without and 1.2 mm (SD 0.54) with muscle activation. Our results indicate that intentional ulnar forearm muscle activation results in 70 % less anteroposterior ulnar head translation and greater DRUJ stability. Therefore, the FCU and ECU muscles serve as dynamic stabilizers of the DRUJ. 

The findings of this study have several clinical implications: Targeting this specific synergistic muscle group for strength training may be appropriate in postoperative rehabilitation programs for patients with DRUJ instability or in other similar clinical scenarios. It may also serve as a conservative therapy option. A corresponding training program has been designed and will be evaluated in further studies.