Workings Of The Human Ankle-Part 2

                                                                                         

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.

The sideways movements of the subtalar joint allow the heel to move inwards and outwards whilst the talus is still held securely in the ankle mortise, with much more inward movement of the heel bone than outward. There are various ways in which we can walk, in our foot posture, which can compromise the function of the foot and lead to painful foot problems. If the hips and feet are turned out as we walk this tends to make the outer border of the foot hit the ground first, meaning the foot has to roll inwards to hit the ground itself.

The foot arches are subjected to flattening forces as the feet roll inwards in this way and this leads to stretch of the supportive tendon sling for the arch made up of the tibialis anterior and tibialis posterior muscles. As this happens the talus can slide inwards from its apical position at the top of the foot arch. When we walk in this manner the forces involved are very large in pushing the foot inwards, converting it from a dynamic structure to a static platform.

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 inwards turning movement is much greater in range of motion than in the outwardly direction which the lower end of the fibula restricts. So it is much more likely that the foot will move rapidly inwards in response to a sudden inwards stress, resulting in a sprain to the ankle ligaments. Flat foot may not be a painful condition but it alters the alignment of the entire lower limb, with knock on effects as far up as the lumbar spine. The side to side arch in the forefoot is much less obvious than the primary foot arch, but when it loses its strength this places the second metatarsal head under greater stress.

About the author:
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, Physiotherapists in Exeter, 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.

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