The Ankle Joint

Published: 09th October 2009
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The ankle is a very particular joint, commonly referred to as a mortise joint. It hinges backwards and forwards whilst we are walking and also gives the sideways support to allow us to hold our balance in moving and unstable conditions. The ankle hinge connects the foot to the lower leg and allows transmission of the forces of the bodyweight across it and onto the mobile and propulsive platform of the foot. In the lower leg the tibia makes up most of the upper part of the ankle with the fibula contributing a small amount towards the outside.

The mortise of the upper part of the ankle encloses the ankle bone or talus, which is set on top of a group of mid foot or tarsal bones which make up the foot arch. The upper dome of the talus articulates with the tibia surface and the talus makes two other important joints. One is with the navicular bone in front of it so it can transfer weight forward onto the forefoot. The other is the joint below the talus, the talo-calcaneal joint, a very complex and important foot joint.

The tibia takes the weight of the body and carries it down to be borne by the talus which passes it on vertically and rearwards to the calcaneum and forwards through the navicular to the forefoot metatarsals. Spreading out forwards with an almost parallel radiation , the metatarsals are slender bones which give significant mobility and stability to the foot. The foot arches are important structures and mean that the forefoot weight bearing areas are mainly under the first and fifth metatarsal heads, with the others bearing weight if the arch gives way to some degree.

The ankle upward and downward movements are known as dorsiflexion (up) and plantarflexion (down) and the inwards and outwards movements of the foot do not occur at the ankle. The inwards movement is known as inversion, the outwards as eversion, and both of these movements occur at the talo-navicular, forefoot and talo-calcaneal joints. Together these complex joints allow the body weight to be held stable over the feet as the body moves and to allow the feet to cope with irregular surfaces. The foots design allows it to satisfy these competing demands.

The foot is amazingly engineered to cope with the strong requirements which it is asked to. When bearing weight the direct downward forces are of a very high level and these are routed through the foot and transmitted further. The tarsal bones make up the foot arch and the forces are taken by their arched structure and by the ligaments which connect the individual foot joints. The muscles of the foot also have a strong role in managing to keep the foot structurally stable against the weight of the body and the forces generated by large body movements.

On the outside of the shin lies the prominence of the tibialis anterior muscle, with its tendon obvious and prominent as it runs across the front of the ankle towards the inside to insert into the foot. Three bones which make up the top of the arch of the foot are the insertion points for the tibialis anterior tendon and it helps lift the arch as the muscle contracts. From the posterior calf the tibialis posterior muscle's tendon runs around the inner ankle bone and finally inserts near the tendon of the tibialis anterior, drawing the bone posteriorly and increasing the arch.

These two muscles together pull the arch up from above and clench it from the side, stopping the weight of the body from flattening the arch. This maintains the springiness of the foot which is so important in walking and running. They are helped by the peroneus longus muscle which comes from the rear calf again and round the outside of the ankle and acts as a sling as it travels under the foot from the outside towards the big toe. This way the foot can be kept stable by strong muscles able to pull from every direction to maintain the posture of the foot under the pressure of the body weight.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in Haywards Heath, 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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