Review of literature on the axis of rotation at the sub talar joint

Abstract

The motion between the talus and the calcaneus takes place around the sub talar joint axis. This axis runs from posterior, inferior and lateral to anterior, superior and medial through the rearfoot. However, the specific orientation of the axis, and consequently the ratio of frontal to transverse plane sub talar joint motion, varies considerably among individuals. Thus, in theory, individual variations in axis orientation and position should be considered in relation to a patient's pathology if sub talar motion is believed to be an aetiological factor. Individual variations should also be considered in relation to any planned orthotic therapy. However, since any effect of variation in the orientation of the axis has not been investigated, it remains difficult for the clinician to take into account what is likely to be an important factor when making clinical decisions. In addition, the sub talar joint axis is not fixed in position or orientation during the range of joint motion. The nature of the talar and calcaneal articular facets means that the joint axis moves from a low pitch and medial orientation in pronation, to a high pitch and forward orientation in supination. It is suggested that the current model of sub talar joint function be updated. The currently accepted model of sub talar joint function is based on an axis that does not vary between individuals, is fixed during the range of sub talar joint motion and displays hinge motion. In contrast to this, detailed kinematic studies have illustrated that the sub talar joint axis has a variable orientation between individuals, changes orientation during the range of motion, and is a screw axis since rotation around the axis is accompanied by translation of the talus relative to the calcaneus along the axis. An updated sub talar joint is particularly necessary if the role of the sub talar joint within the rearfoot complex is to be correctly understood.