What is pes planus and what causes it?

Pes planus is the medical term for flat foot. The arch of the foot sags and sometimes touches the floor.

All children under 3 years of age have a flat foot which is entirely normal. The arch of the foot then develops through to adolescence, although many people continue to have a flat foot into adulthood. In the majority of cases, the problem is related to loose ligaments and joints, and tends to run in families. Upto 30% of the population have a flat foot, and in most cases it does not cause a problem.

The most common cause of a painful flat foot is damage to the tibialis posterior tendon. This important structure runs on the inside of the ankle and is the principal stabiliser of the arch. This problem is also known as Adult Acquired Flat Foot deformity and usually occurs in middle-aged females, most of whom have had a slightly flat foot all their lives. The tendon stretches out over time and becomes less able to carry out its important function. Occasionally an injury results in the tendon rupturing.

Another common cause is an accessory (extra) navicular bone. You may be able to feel this bone, as it is usually prominent on the inside of your foot. The tendon rather than attaching to the main body of the navicular bone, inserts onto this extra bone and so its pull is less effective and the arch of the foot collapses. The main symptom is pain from the repetitive stresses placed upon this extra bone.

Rarely a congenital (from birth) problem results in two bones in rear aspect of the foot being joined together. This is called a tarsal coalition. It results in a painful and stiff flat foot in children and tends to present between the ages of 8-15.

What symptoms may I experience?

Pain is the most common problem. It is usually located on the inside of your ankle, where the posterior tibial tendon lies, and many times the problem is wrongly attributed to your ankle joint. Symptoms are typically worse first thing in the morning and following walking long distances. You may experience cramping or fatigue in your calf muscle, which tries to compensate for your weak posterior tibial tendon. In some patients the flat foot results in pinching of the tissues on the outside of your ankle, with swelling and pain. The abnormal structure of your foot can cause pressure areas and hard skin to develop typically under your big toe, or on the inside of your heel.

What should I do if I have a painful flat foot?

You should ask your GP to refer you to a Consultant Orthopaedic Foot and Ankle surgeon. The diagnosis can often be made by asking you specific questions about your problem.

A full examination of your entire lower limb is required, as not infrequently a problem with your alignment (hip or knee) can cause a flat foot. A tight calf muscle can aggravate the problem and will be specifically examined. You will be asked to walk and to stand up on tip toes. If you are unable to tip toe on your affected side, this is a good sign that your tendon is not working. Your ankle and foot joints will be assessed for flexibility.

Weight-bearing X-rays will be organised to look specifically at your foot and ankle alignment and whether you have any ‘wear and tear’ or arthritis (fig 2). An accessory navicular bone, if present, can also be detected. A MRI scan is often ordered to assess the tibialis posterior tendon, and is used to confirm rather than make the diagnosis.

What are my options?

The initial treatment does not involve surgery. You will be referred to the physiotherapy department, to undergo a formal calf stretching program. Your foot joints will be manipulated and gait training will also be undertaken.

You will be referred to an Orthotist, who will examine you and if indicated he/she will make an impression of your foot with foam or plaster and a custom-made insole manufactured. If you have a flexible foot, the insole will be built up on the inner aspect both along the arch and under the heel. This will help tilt your foot back into a more normal position and also provide support. If you have a stiff foot – the insole will simply support the foot in its current position.

In some cases, the pain can be quite severe, and this usually indicates that the tendon is acutely inflamed. A period of rest in an Aircast boot often resolves this problem in the short-term.

These simple measures should be tried for 3-6 months before consideration of surgical intervention.

What does surgery entail?

The surgery will depend on the following factors:

• The exact cause of you flat foot
• Whether you have a fixed or flexible deformity
• Whether you have any arthritis

Will I have a normal arch following surgery?

n most cases there will be an improvement in the arch, and it will be better supported. However giving you back a normal arch is rarely possible, and the principal reason for undergoing surgery is pain relief.