The Ankle Joint ” Part Two
Connecting across the two major bones of the navicular and the calcaneus and running under the talus is the spring ligament, a strong band-like structure which braces the foot arch. The weight of the body presses down to flatten the arch and the spring ligament holds between the two bones, becoming tauter as more weight is applied. Due to its great strength the spring ligament is adapted to manage the high forces generated by activities such as running, hopping or jumping, which are too vigorous for the musculature to able to hold the arch in place. The muscles contribute to arch maintenance but at a longer term lower level.
The ankle has accessory movements like all our other synovial joints. These are small internal gliding and sliding movements which naturally occur within a joint during normal movement but cannot be independently performed. Accessory movements are vital to the normal functioning of joints and if they are limited or lost then the joint loses some of its functional ability also. As the weight passes onto the foot the forefoot and toes are flat on the ground the talus is forced inwards to a small degree by the downwards forces.
The foot twists during this manoeuvre, storing up tension energy which allows the recoil to occur in an elastic manner as the foot begins to lift off, a recoil which is supported by the longitudinal ligament stretch as the arch is flattened. From this we feel a little push of energy each step, very appropriately often referred to as the spring in the step. Rough ground presents challenges to the foot in terms of differing angles of surface and differing levels and the foot adapts to this with the subtalar joint, the joint between the calcaneum and the talus.
Whilst the talus is solidly maintained within the ankle mortise the heel can move outwards and inwards underneath it by lateral movements of the subtalar joint, there being much less outward movement than inward. Our foot posture can vary depending on our walking patterns and this can interfere with normal foot function and precipitate painful conditions in the feet. For example lateral (outward) rotation of the feet makes us hit the ground initially with the outer border of the feet and forces the foot to roll significantly inwards to reach the ground each step.
As the foot rolls in this amount the arch tends to flatten, stretching the sling of supporting muscle tendons from the tibialis posterior and tibialis anterior muscles of the calf. This allows the talus to slip from its top position in the foot arch to some degree. As the forces involved in this medial rolling of the arch are very great this gradually over time makes the foot become abnormal when it performs like a static platform rather than a springy, dynamic part.
The foot has greater ranges of movement in an inwards direction than outwards, the outwards seemingly blocked by the more anteriorly placed fibula if you try and turn your foot that way. This makes it more likely, if subjected to lateral instability, that the foot will turn rapidly inwards and cause an ankle strain. Although flat feet may not be painful in many cases, they can affect a whole series of joints above them from the ankle and knee to the hips and back. The sideways arch of the forefoot, a minor arch compared to the longitudinal arch of the foot, can also flatten and allow excessive weight to be borne by the second metatarsal head.
The sprained ankle which can occur due to the tendency for the ankle to go over with the foot pointing inwards sprains the ligaments on the outside of the foot. A significant sprain of this area always involves the subtalar joint as well and the ankle commonly has a weakness from then on which means that repeated strains can become a problem. The sprain causes swelling in the local area and this can thicken into scar with time, becoming particularly problematic if the ankle has been held immobilised for some time as this way movement and stability is lost.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Windsor, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.