Flat foot is common in the population and classed either as congenital flat foot which is not a pathology as such and may not give symptoms, and acquired flat foot which develops in adult life from a foot problem. There are many potential causes of flat foot acquired in adulthood which include arthritic diseases, neurological conditions, foot abnormalities and dislocations or foot fractures. In the acquired form of flat foot the most frequent type is secondary to a dysfunction of one of the foot tendons, the tendon of the tibialis posterior muscle. Tendon changes can occur from inflammatory, degenerative or traumatic conditions.

Studies of this condition have revealed that it is more common in groups who are obese, diabetic, hypertensive, on steroid medication or had previous trauma or operations to the mid part of the foot. Patients with arthritic conditions, often called spondyloarthropathies, have typically a family history of psoriasis or inflammatory conditions and have a higher incidence of this condition. Older people without specific medical problems are also seen, pointing to a mechanical cause secondary to age related degenerative changes. This tendon problem is moderately commonly seen in patients with rheumatoid arthritis.

Just underneath the inside bones of the ankle and for a short distance forward there is an area of reduced blood supply which affects the tendon which runs through this area, perhaps helping to explain why degenerative changes might be more important in this area. This tendon forms part of the support for the medial arch of the foot which has both active and passive components. The passive or static supports for the stability of the arch are the plantar fascia, the short and the long plantar ligaments and the spring ligament, also called to calcaneonavicular ligament. The spring ligament supports the ankle bone or talus and prevents it from sliding downwards or inwards.

The tendon of the posterior tibialis muscle is the most powerful support for the medial arch of the foot. Muscle contraction through the tendon raises the inside of the medial arch of the foot and turns the foot inwards if it is not planted. Loss of this muscle function from a rupture or damage to the tendon deprives the foot arch of its most powerful supporting influence which allows the muscles which turn out the foot to act without restraint. The foot can then undergo three main postural alterations: flattening of the medial foot arch; turning out of the forefoot and turning out of the hindfoot area.

All these changes lead to a loss of the ability of the rearfoot and the forefoot to be a rigid and stable platform which changes the patient’s pattern of gait, making it less efficient. The tibialis posterior muscle has a powerful function and once this is reduced or lost the gastrocnemius and soleus, the main calf muscles, perform their action further back in the foot than normal. The talus or ankle bone is then moved inwards and down, stretching the spring ligament and gradually allowing the medial foot arch to lower as the joints move into different relationships with each other.

When developing symptoms from acquired flat foot patients will complain of swelling and pain on the inside of the ankle and foot when they are standing on the foot. The arch may gradually reduce and the patient realise they are walking on the inner part of the foot instead of normally. There is a loss of strength as the patient pushes off in walking and they may limp, the changes in gait often reflected in abnormal patterns of wear underneath the shoes. Physiotherapy assessment of the foot initially involves comparing both feet in standing to see if the arch is different on either foot.

Observation by the physiotherapist of the heel from behind will allow the visualisation of the two outer toes, if more show then the forefoot is laterally deviated. The physio will assess the angle between the lower leg and the heel to determine the valgus angle of the hindfoot, an important determining factor in foot health. To rise on tiptoe the calf muscle power must be engaged, in a normal foot causing an inversion of the heel.

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