Peroneal spasm. View of a peroneal spasm on a patients foot. A swelling is visible on the inside of the ankle at right. This is caused by the peroneal tendons, that connect the bone of the lower leg (the fibula) to the foot, going into spasm. This may be caused by injury to the foot or may be a congenital condition known as metatarsal coalition, when the bones of the foot do not separate properly at birth.