[Transmission of pronation-supination movements in the wrist]

The wrist plays an essential in role the transmission of pronosupination movements. The four main muscles responsible for these movements are situated above the radiocarpal joint. This anatomic configuration allows a passive movement: Radio Metacarpal Rotation or RMR which is analysed here. Radio Metacarpal Rotation varies according to grip and the couple which is applied distally. An apparatus has been designed to simultaneously measure the angle, the force of grip and the couple. Radio Metacarpal Rotation is firstly measured with the wrist relaxed (grip strength < 5 N) and a distally applied rotation couple of 0.2 N.m in the supination direction and 0.5 N.m in the pronation direction. Secondly, the patient is asked to maintain a grip strength between 80 N and 100 N, and a couple of 1 N.m is applied distally in each direction. One hundred wrists were evaluated. We have looked for the rotation centers of active pronosupination and Radio Metacarpal Rotation. A three dimensional motion analysis device was used (ELITE system). Thirty normal wrists were evaluated. An anatomic study of the radiocarpal ligaments stretched by Radio Metacarpal Rotation was carried out on ten cadaver wrists. When the wrist is relaxed: there is an average Radio Metacarpal Rotation of 42 degrees. This Radio Metacarpal Rotation is reduced when grip is tightened. We have defined a locking test based on these two parameters. This clinical test is represented by two curves on a graph. The active pronosupination center and the radio metacarpal center do not coincide. The center of active pronosupination is situated near the center of the ulnar head and the center of radio-metacarpal rotation is always more lateral. On the anatomical preparations, we found a helicoidal configuration of the radiocarpal ligaments: a ligamentous double helix pronosupination. Radio Metacarpal Rotation interferes with transmission of pronosupination movements. When the wrist is not well locked there is a large lateral sweeping between radius and scaphoid. This sliding at the level of the cartilage can head to development of osteoarthritis of the wrist with a horizontal scaphoid and the good cartilage results after proximal row carpectomy. Radio Metacarpal Rotation must be taken into account when a prothesis designing. We propose a wrist locking test. The results of this test are directly related to the capacity of the joint surfaces to transmit pronosupination movements. Radio Metacarpal Rotation shows the importance of the horizontal plane in the wrist and its essential role in the transmission of pronosupination movements.