Effects of ligamentous injury on ankle and subtalar joints: a kinematic study

Using 10 normal fresh cadaveric legs, kinematic effects of ligamentous injuries around the ankle joint were studied while the ankle joint moved from maximum plantar flexion to maximum dorsiflexion in saggittal plane. A series of anteroposterior and lateral sequential roentgenograms was taken both in the normal and subsequently created injured condition, to evaluate instant center of rotation and horizontal rotation pattern in the hindfoot complex. Although the pattern of instant center of rotation of the ankle joint varied among normal condition, the majority fell in a prescribed area. The deviation of instant centers from those in uninjured condition was most evident in lateral ligament injury. The average horizontal rotation between the tibia and calcaneus was 8 degrees in the uninjured condition; 6 degrees in the subtalar joint and 2 degrees in the ankle joint. In both medial and lateral injuries, more rotation in the subtalar joint was noted in plantar flexion phase. In the ankle joint, the degree of excessive rotation in plantar flexion range was greater in lateral injury than medial injury, but that in dorsiflexion range was greater in medial injury. It appeared that while every component of collateral ligaments around the ankle was important in controlling rotation in plantar flexion range, the posterior portion of the deltoid ligament is most important in the forsiflexion range.