Osteochondromas in the lower fibula can result in valgus ankle deformity. The lower end of the fibula is called the lateral malleolus and is important for the stability of the ankle. An osteochondroma in this region will cause the fibula to grow less than the tibia; the lateral malleolus is underdeveloped. The tibia will then tilt towards the fibula leading to a shift of the ankle bone. This shifting is compensated by the subtalar joint (the foot joint under the ankle) by turning the foot inward (a process called inversion). What results is a propensity by the patient to walk on the outer border of their foot. Since this is a longstanding process, the subtalar joint becomes fixed in this position of compensation for the ankle joint.
This deformity is fairly well tolerated but can lead to arthritis of the ankle later in life. To correct the deformity, we will perform an osteotomy of the lower tibia and fibula, excise the osteochondroma, and apply a specialized external fixator, the Taylor spatial frame (TSF). The TSF corrects the varus deformity by gradually distracting (pulling apart) the subtalar joint.