Joint classification puts the ankle joint into the category of a mortise joint and it is specialised for its function. A front and rear movement action is performed by the ankle hinge for walking and it stabilises the lower leg on rough ground and when moving. The ankle forms the connection between the lower leg and the foot to facilitation the transfer of the weight of the body to the mobile and stable foot. The upper joint structures are mostly made up of the tibial surface with the fibula making up a small part of the lateral side of the joint.
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.
The tibialis anterior muscle is the prominent long muscle on the outside of the shin and you can see the tendon as it rolls down towards the ankle and crosses over to the inside to some degree. The tendon attaches to three bones which are placed at the top of the arch of the foot, so when the muscle contracts it lifts and supports the arch to some degree. The tibialis posterior muscle comes from the rear calf and round the inner side of the ankle bone to end up inserting close to the tibialis anterior tendon. It pulls the bone to the rear and accentuates the arch again.
The arch is pulled up to some degree by these two muscles working in concert to pull it up and stabilise it from the side against the weight of the body. The spring of the foot, vital in running and walking, is maintained by this. Another important muscle is the peroneus longus which runs down the leg and its tendon runs under the outside of the foot to insert over towards the first toe. This arrangement stabilises the foot from any direction as there are muscles which pull from each direction to maintain the foot posture against the forces generated by movement and body mass.
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 Nottingham visit his website.
