The Ankle Joint-Part 2

Published: 09th October 2009
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The spring ligament, a strong fibrous band, stretches from the calcaneus to the navicular, running under the talus on the way, keeping the foot arch in place. The arch of the foot is maintained by the spring ligament holding the bones together against the forces pushing down from above, with the arch becoming stronger as more weight is placed on it. A very strong ligament, the spring ligament is well suited to resisting the high levels of force involved in jumping, hopping or running which might otherwise cause the arch to spread. Maintenance of the arch by muscular control is more continuous and postural, holding the talus in place along with the ligament.

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.

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 lateral ligaments of the foot are the ones typically sprained due to the tendency of the ankle to go over as the foot moves forcibly inwards. The subtalar joint is always involved and damaged when there is a significant sprain of the ankle joint and this can cause instability of this area and lead to repetitive ankle sprains. Multiple sprains make the local tissues swell and this with time thickens up, turning into scar and giving problems if the ankle has been held still for some weeks in a cast, reducing both the stability and mobility of the area.

Jonathan Blood Smyth is the Superintendent of Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapists in Bolton visit his website.

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