The foot ankle bone is known as the talus and is contained within the mortise of the upper ankle, sitting at the apex of a group of foot bones which construct the arch of the foot. The lower surface of the tibia articulates with the dome of the talus but the talus makes two further joints in the foot. To the front is the talar joint with the navicular bone, taking weight towards the front of the foot. Below is the talar joint with the calcaneum, a complicated joint taking vertical stresses.
As the weight comes down through the tibia it is distributed forwards through the navicular on to the metatarsals in the forefoot, down and backwards to the calcaneal joint and the heel. The metatarsals spread out in the front of the foot, lying in parallel and with mobile joints between them, allowing a great degree of mobility in the foot to cope with unstable surfaces. With the foot arches the weight is borne on the heads of the first and fifth metatarsals primarily, although if the foot develops problems the remaining metatarsals can also bear weight and become problematic.
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.
Severe demands in terms of force, weight and movement are asked of the foot and its engineering design is elegant and effective. The downward forces generated in bearing weight are very large and the foot’s role is to accept them and pass them on effectively to the ground or up through the body. The arch of the foot is made up of the tarsal bones and this suffers high levels of body weight through its joints, reinforced by the connecting joint ligaments. The structural stability of the foot is also partly maintained by the muscles of the calf and foot against the high movement forces.
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.
