Ligament function and joint stability elucidated by a new technique

For analysing the ligaments of the ankle joint, their function, and the traumatic mechanisms which cause them to rupture, an apparatus was developed which enables graphic registration of rotatory movements in the ankle joint in two planes simultaneously, when a given torque is applied to the talus. In a modified form, this apparatus is applicable also for other joints. A lever with strain gauges and potentiometers is fixed in the talus of an osteoligamentous preparation. The lever is moved manually, and signals from the strain gauges and potentiometers are collected by a microcomputer for later transfer to a computer service centre where the mobility at the chosen torque is calculated and plotted as mobility patterns. The appearance of these patterns depends upon which ligaments are intact. The patterns plotted in any situation are reproducible, provided that the state of the ligaments is unchanged. In cutting experiments it was possible to demonstrate that rupture of the anterior talofibular ligament may occur simultaneously with partial rupture of the posterior talofibular ligament, although the calcaneofibular ligament remains intact. This occurs if the distortion trauma causing the rupture consists of an internal rotation of the talus, not if it consists mainly of a tilting of the talus in the ankle mortise