THE ANKLE JOINT – AN INTRODUCTION TO ASSESSMENT AND DIAGNOSIS
The ankle is the most commonly injured joint in the lower limb, the anterior talo-fibular ligament (the classic sprained ankle) is a relatively simple ligamentous injury but as the severity of inversion injury increases, the sub-talar joint and the mortice of the true ankle joint can be disrupted which can be as severe as any knee injury. We will consider the ankle, sub-talar joint and foot in this article.
BY DR SIM BY DR SIMON KAY, GP
The function of the ankle and foot is to allow dissipation of force at heel strike and secondly to provide a rigid level to allow a stable and propulsive phase of gait during walking and running (see Box 1 for more information). As part of positioning the foot, the sub-talar joint allows for rough and uneven ground. Eccentric and concentric movements of the shin muscles are used to control the movements of the foot during pronation and supination. Excess pronation can put a strain on the invertors of the foot ie. tibialis anterior, when contracting eccentrically, to control the rate of pronation. This can cause trigger points to occur. The ankle consists of two main
joints: 1. the ankle joint (similar to a mortice and tenon joint in woodwork) - consists of the articular facet of the talus
LEARNING EXERCISE n (kinaesthetic): Try examining an articulated foot which can be prised apart slightly, to fully appreciate the 3-D aspects of the subtalar joint.
(tenon) which articulates with the two congruent surfaces on the tibia and fibula (which form the mortice) 2. the complicated sub-talar joint between the three inferior facets of the talus and the congruent facets on the calcaneum and cuboid bones.
MOVEMENTS OF THE ANKLE Movement of the true ankle joint occurs in one direction, plantar and dorsi-flexion (sagittal plane) (video 1). The three dimensions of the subtalar joint however allows for inversion and eversion (video 2) and pronation and supination (see Definitions box and figures 3-5 for a description of the movements). The movement of eversion and it’s counteracting movement of inversion allows the foot to take rough ground into account without putting excess strain on the true ankle joint. There are no intra-articular ligaments or cartilages of note within either joint capsule. The neutral and the anatomical positions of the ankle are one and the same and consist of the foot positioned at a right angle to the shin. The most stable position of the ankle is fully dorsi-flexed because the talus is slightly wider anteriorly thereby