Flat out with ankle pain

Case scenario

A 50-year-old woman presents with pain and swelling behind and distal to the medial malleolus with no history of trauma. The pain is often worse first thing in the morning, and over some months she has noticed her foot flattening. What is the most likely cause?

Tibialis posterior tendon deficiency 

Also known as adult acquired flat foot. This is mainly a condition of middle-aged females. The risk factors include: obesity, hypertension, diabetes, female sex and age 40–60 years. However, this painful condition can occur at any age.

Unfortunately, with 20% of Australians now being overweight or obese, the condition is becoming far more common.

The tibialis posterior is a strong tendon with a short excursion. It is opposed by peroneus brevis. 

Weakness results in flattening of the medial longitudinal arch. The medial restraints become