Health & Care Guide

The arch of the foot is also partly maintained by a strong ligament under the foot called the spring ligament, connecting the navicular with the calcaneus. It holds the arch together by resisting the tendency for the bones to separate under vertical stresses, becoming tighter the more weight is placed upon it. Due to its great strength the spring ligament is particularly useful when we are doing very vigorous movements such as running or jumping which might otherwise be too much for the muscle to resist the splaying of the arch. The muscles work more continuously at a lower level but between them and the spring ligament the talus is maintained at the top of the arch of the foot.

Accessory movements, small and almost unnoticeable internal joint movements, occur in the ankle as they do in the other synovial joints of the body. They occur naturally as the joint goes through its range of movement but we can’t perform them separately in isolation. If the joint loses a proportion or the entirety of its accessory movements some of the joint’s function will also be lost. An accessory movement of the talus in the ankle mortise occurs when the foot hits the ground and the forefoot and toes are flat, with the weight pressing down and inwards.

This tensions the foot by twisting it slightly and along with the stretching of the longitudinal ligaments by the arch being flattened this gives the foot some elastic recoil when the weight begins to be removed from the foot. This gives a little kick of propulsion as we step forwards, perhaps being what we refer to as a spring in the step. As the foot encounters the unstable surface of rough ground it must accommodate to the differing levels and the joint between the talus and the calcaneum, the subtalar joint, is important in this adjustment.

The ankle mortise holds the talus firmly in its grasp as the heel bone is enabled to make lateral movements under it via the subtalar joint and there is significantly more movement towards the inside than the outside. Our typical walking patterns can alter the foot postures we adopt in gait and this can compromise foot function and cause foot pain and disability. If we walk with our legs turned outwards this means the outer foot border contacts the ground first and requires the rest of the foot to roll inwards in order the get flat onto the ground.

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.

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