The Ankle ” Part Two

The arch of the foot is also partly maintained by a strong ligament under the foot called the spring ligament, connecting the navicular with the calcaneus. It holds the arch together by resisting the tendency for the bones to separate under vertical stresses, becoming tighter the more weight is placed upon it. Due to its great strength the spring ligament is particularly useful when we are doing very vigorous movements such as running or jumping which might otherwise be too much for the muscle to resist the splaying of the arch. The muscles work more continuously at a lower level but between them and the spring ligament the talus is maintained at the top of the arch of the foot.

All the synovial joints in the body have accessory movements and the ankle is no exception. Accessory movements are little sliding or gliding motions which occur inside the joint normally during activity but which cannot be performed on their own. Joints need the accessory movements to function normally and a joint will lose some of its ability if these tiny movements are restricted or lost. An example is the inward slide of the talus in response to the vertical forces of the body as the toes and the forefoot are placed flat on the ground during stepping.

This slight twisting of the foot tensions it slightly and contributes to the elastic recoil as the weight begins to be lifted off the foot, added to by the stretch energy built up in the ligaments placed along the foot. As we step through this contributes a little pulse of energy to make things easier, often referred to perhaps as a spring in our step. To manage the challenges of rough surfaces the foot must adapt to different levels and angles, with much of this adaptation occurring at the subtalar joint below the talus and between it and the calcaneum.

The sideways movements of the subtalar joint allow the heel to move inwards and outwards whilst the talus is still held securely in the ankle mortise, with much more inward movement of the heel bone than outward. There are various ways in which we can walk, in our foot posture, which can compromise the function of the foot and lead to painful foot problems. If the hips and feet are turned out as we walk this tends to make the outer border of the foot hit the ground first, meaning the foot has to roll inwards to hit the ground itself.

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.

There is a greater range of movement in a medial (inwards) direction in the foot than in the lateral (outwards) direction which is limited by the fibula which gets in the way. This increases the likelihood of any sideways stresses resulting in a rapid inwards movement of the foot, causing an ankle sprain. Flat feet are often not painful in themselves but their abnormal position has knock on effects for all the joints above them including the ankle, knee, hips and low back. The forefoot also has a sideways arch even though this is small compared to the main foot arch, but if it flattens it places abnormal stresses on the head of the second metatarsal.

The inwards turning movement is much greater in range of motion than in the outwardly direction which the lower end of the fibula restricts. So it is much more likely that the foot will move rapidly inwards in response to a sudden inwards stress, resulting in a sprain to the ankle ligaments. Flat foot may not be a painful condition but it alters the alignment of the entire lower limb, with knock on effects as far up as the lumbar spine. The side to side arch in the forefoot is much less obvious than the primary foot arch, but when it loses its strength this places the second metatarsal head under greater stress.

Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Newcastle. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.