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  5. The Ankle Joint in Control of the Dancer's Foot

The Ankle Joint in Control of the Dancer's Foot

By Dr Kenneth Backhouse OBE

In a previous anatomy article, Hazel Fish focused her attention on the foot. We now move back to the ankle and its relationship with the foot. The important point to be aware of is that the ankle joint itself is a pure hinge joint, designed to give firm support to the foot when standing and as the base joint through which power is transmitted to the foot in activity.

The ankle joint is made up of three bones. The tibia (the shin bone) sits on the upper surface of the talus and a small projection from the tibia, the medial malleolus, runs down on the medial (inner) side of the talus. A similar, rather longer slip of bone, the lower end of the fibula, the lateral malleolus, runs down the lateral (outer) side of the talus. These are the bony knobs readily seen on the two sides of the ankle and sometimes colloquially called anklebones. The upper surface of the talus in the joint is somewhat barrel shaped and, with reciprocal curving on the lower end of the tibia, there is free movement at the ankle joint allowing the foot to be raised or lowered but only in the single plane. However, the ankle joint has to take the full load of the body when standing as well as transmitting the controlled power to the foot in action. The double role is seen in the surface of the talus where the more anterior part of the barrel is broad and fits closely between the two malleoli. It is said to be in a close compact state for stability in stance and allows no lateral movement. The more posterior surface of the talus that becomes related to the tibia on raising the heel is narrower, so allowing a degree of freedom between the two malleoli. (Figure 1) When rising onto pointe, jumping or landing, the bones of the ankle joint are much looser, requiring good lateral muscle control, largely unnecessary in stance. Obviously if one landed badly in the close compact position of stance, there would be great danger of damage to the malleoli whereas with their separation from the sides of the talus in activity that danger is much reduced, the stress being taken by the ligaments and lateral controlling muscles. Fitting with the actions of the joint, the main firm ligaments run down from the two malleoli giving lateral support but really the joint, as any in activity, should be totally dependent upon the supporting muscles.

The Ankle and the Foot

The talus acts rather as a central link bone between the leg and foot. In stance it sits on top of the calcaneum that acts as the bone of the heel and so transmits the load of the standing body to the ground. Anteriorly the talus has a short neck and rounded head that links it with the bones of the inner side of the foot; those involved in the medial arch of the dynamic foot. Following the bones into the foot from the talus it is possible to divide them into two parts: (Figure 2)

The weight bearing calcaneum joins the cuboid and that in turn links with the outer two metatarsals and toes.

The head of the talus links to the navicular, then the three cuneiform bones and on to the inner three metatarsals to the great toe and the adjoining two.
Although ligaments and muscle link the two components, nevertheless they represent different functional entities in the foot; the first weight bearing, the other mobility. Examining a pedogram, i.e. a picture taken of the load bearing area of a reasonably arched foot, it will consist of the heavily padded portions of the sole, namely the heel, the outer portion and the metatarsal heads. The first group of bones and their underlying soft tissues represents it, together with the inner metatarsal heads. Although it is common to describe a lateral longitudinal arch, this is rather misleading in that the arch is mainly bony and small, related to the cuboid bone and acting essentially as a space through which tendons can pass. It is not evident in the weight-bearing surface of the foot.

The second (inner) portion is that part of the foot designed for dynamic activity and involving the sprung medial arch which, in a really effective foot should have strong muscular control. It is also the component that allows rotation (inversion or rolling out and eversion, rolling in), movements occurring primarily between the head of the talus and the navicular and between the navicular and the cuneiforms. The lateral bones follow round keeping the load bearing outer surface of the foot in contact with the ground. Under normal circumstances these movements are to link the foot with variations in slope of the ground but should play no real part in dance on a flat surface, where a strong central balance should be maintained. When raising onto the toes the load becomes concentrated onto the metatarsal heads and, as the outer two metatarsals are shorter, particularly the fifth, the load becomes limited to the inner three. Although the great toe is the most important from a weight bearing point of view all three inner bones should share the load. When on full pointe the inner three toes (the ideal would be of the same length) transmit the load through the metatarsals to the same inner dynamic part of the foot. There should be virtually a straight axial line taking the load back through the talus to the tibia.

Muscle Control

The only muscle group working purely on the ankle joint is gastocnemius and soleus whose combined tendon the Achilles tendon (tendo calcanei) is attached to the back of the calcaneum (Fig 2). On this first class lever it gives power to lift the foot onto the toes as when walking, running or rising onto pointe, giving the power to a jump and to take the load on landing. When standing in the close packed position at the ankle joint little lateral support is need but when rising onto the toes the two malleoli become separated from the talus and then lateral support is needed for the ankle; a problem for so many people with “weak ankles”. However two muscles run down on each side of the ankle joint into the foot where they are also responsible for the rotational movements within the foot. On the inner side two tibialis muscles (anterior and posterior) produce inversion but from the dancer’s point of view they are also prevent rolling in. On the outer side two peroneal muscles (longus and brevis) produce eversion (rolling in). The lateral stability of the ankle joint depends on muscles also controlling the balance of the dynamic medial component of the foot. To allow the foot to roll in as so often occurs in attempting to force turn-out the inner supporting muscles of the ankle must relax. What is required is a strong balancing muscle system giving stability to the ankle when rising onto the toes and also controlling the rotation of the hind-foot to maintain equal pressure on the three important metatarsal heads. Rolling in must be prevented as not only does this reduce control on the inner side of the ankle but also throws the load onto the great toe, reducing the dynamic effect of the whole medial unit of the foot and the risk of injury, particularly on landing. Also by throwing the load more to the inner side of the great toe it increases the risk (particularly prevalent in females) of developing hallux valgus and bunion.

The ankle could be said to have support also from the long digital muscles running through to the toes but in practice these can only work with full efficiency on a well-controlled ankle and hind-foot. From the point of view of dance the long muscles to the toes produce their extension or flexion but also, if working alone, producing clawing of the toes. What is needed is the ability to use the toes straight (vital for full pointe) with powerful flexion at the metatarso-phalangeal joints to help elevation and control of stability on demi and particularly half pointe. The muscles controlling this are the intrinsic muscles of the foot ( mainly the interosseous muscles) that act in support of the long flexors on the toes to concentrate activity on the metatarso-phalangeal joints, where they act as the prime flexors while also supporting the long extensors to keep the toes straight. In a high arched foot these muscles tend to be more at a disadvantage and therefore there is a greater need to develop intrinsic control, focussing exercises onto flexion at the base joint of the inner toes while keeping the toes straight. (In a fixed high arched foot the interosseous muscles can actually move out of line and then change their function and actively induce clawing; a disastrous situation for dance but sadly quite commonly seen.)

Training the Muscles

Although carefully controlled class work may well suffice for many people, from time to time some individual strengthening exercises might be needed. For the ankle supporting muscles a wobble board is useful. This amounts to a board mounted on a central ball and the exercise is to stand on and move the board under good muscle control. A simple equivalent can be constructed by laying a board on a rounded stone. Alternatively, even more simply, lay a short plank across a brick or thick wooden block.

The intrinsic muscles can be exercised by putting the foot on a transversely lain piece of wood just behind the metatarsal heads and practicing firm flexion at the metatarso-phalangeal joints (the equivalent of the knuckle joints in the hand) while ensuring that no active flexion takes place in the toes and eventually maintaining them straight. Dancers must never do the oft-suggested method of exercising the toes by picking up a pencil as it merely produces clawing; the last thing any dancer (or really anyone else) needs.