Fibular insufficiency fracture: an under-reported complication of advanced tibialis posterior dysfunction.

We present a case of fibular insufficiency (stress) fracture in a patient with pre-existing asymptomatic advanced tibialis posterior dysfunction. The patient had severe planovalgus (flat foot) deformity but no pain before the injury; hence had never sought any treatment. She was first treated conservatively for the fracture which failed to control the deformity and had ongoing symptoms. She eventually required tibio-talo-calcaneal fusion. To the best of our knowledge, this is the first case report of this condition in the English literature. In patients with severe tibialis posterior dysfunction, weight-bearing axis passes directly from calcaneum to fibula making it vulnerable to fracture. Patients should be made aware of this risk even if they are asymptomatic and encouraged to use orthotic support for protection against insufficiency fractures.