Flat foot, or pes planus, is a common foot condition. It may occur in up to 20 per cent of adults. Patients who are obese, elderly, have rheumatoid arthritis or foot trauma are at an increased risk of developing this condition.
It may be painful or painless, correctible (flexible) or non-correctible (rigid). There are two arches in the foot, the inner one, or medial arch, and the outer or lateral arch. The arches are made up of a number of foot bones held together in an arch by ligaments, capsules, tendons and plantar fascia.
If any of these gives way, the patient will develop flat foot, most dominantly the inner arch. The arches of the foot do not develop until the around the age of six, so the condition is not diagnosed until this age.
Some patients have normal or constitutional weakness in the ligaments, predisposing them to develop collapsed arches. In these patients the ligaments normally have an excess of stretchy elastic tissue.
Moreover, certain racial attributes and conditions such as Ehlers Danlos Syndrome increase the risk of developing pes planus. If the condition is not painful then treatment is not indicated. However, patients may develop foot deformity with the foot being pronate, or pointing outwards. This may be associated with pain and swelling on the top of the foot or on the outside. There may be heaviness, fatigue and ache of the foot as a result.
Due to poor mechanics, there may also be associated leg, knee and back pain. The condition is often obvious clinically, but an X-ray or MRI scan may sometimes be required to evaluate the condition in detail.
In the majority of cases where pes planus is symptomatic, then it may be corrected by using tailor-made insoles and supportive shoe wear which correct the anatomy of the foot. Weight loss and anti-inflammatories may also be beneficial. Stretching and exercises may also help, particularly if the tendon at the back of the heel, called Achilles’s tendon, is tight.
The second most common cause of a symptomatic flat foot is related to degenerative disease of the foot joints. This may be accompanied by incompetence of a large tendon called the tibialis posterior tendon, vital in maintaining the medial arch. This may result in the joints of the foot maintaining the arch to collapse causing the foot to pronate. Sometimes this condition may not be correctable. Collapsed arches are not reversed with the use of insoles.
Another cause of a stiff pes planus is tarsal coalition, which is a rare condition in young patients where the bones of the foot fail to segment and remain united, ultimately causing this condition to develop.
Flat foot is very rarely treated with an operation. Surgical procedures, however, may involve fusing the bones of the foot or repairing the torn tibialis posterior tendon to recreate the arch.
Alistair Melvyn Pace, Consultant orthopaedic surgeon