There are three peroneal muscles: the long peroneal, the short peroneal and the third peroneal. The long peroneal is the most superficial muscle of the outer compartment of the tibia. It arises from the head of the fibula, is carried around the external malleolus on the peroneal groove and lodges in the medial sphenoid and the 1st metatarsal. The short fibula arises from the lower two thirds of the fibula, is carried under the outer hammer on the outer surface of the heel and is attached to the base of the 5th metatarsal. The tendons of the long and short fibulae shall be brought together in the fibular groove in a common sheath and shall be held in place by the upper forefoot vertical ligament. Both the long and short peroneum are innervated by the superficial peroneal nerve. Their action helps in pronation and dorsiflexion of the foot.
Under normal conditions the superior peroneal vertical ligament helps the tendons to contract with extremely high forces without dislocating. Without this ligament, the tendon cannot produce enough force during activity. If the peroneal tendons dislocate, they lose their mechanical advantage and become weak and painful and often rupture.
Causes of peroneal dislocation include rotator cuff injuries, hypertrophy of the peroneal muscles, increased laxity of the ligaments, which can allow the tendons to dislocate. The shallow peroneal groove in the membrane may not allow the tendons to sit properly.
Symptoms of the disease include swelling behind the fibula on the outside of the ankle, bouncing sensation with foot movement, appearance of tendons on the front of the ankle instead of in their normal position behind the fibula where they are not visible. Other symptoms are muscle weakness, frequent ankle sprains and chronic instability.
X-rays are usually taken to determine if a bone injury has occurred. MRIs are necessary to evaluate for ligamentous injury and dislocation and peroneal tendon rupture. CT scans may be necessary to evaluate the depth of the peroneal groove.
In the case of an acute injury, immediate splint application will probably allow the ligament to heal while maintaining the tendons in their correct position behind the fibula. If it fails, surgical repair of the ligament is required. If a shallow peroneal groove is observed, it can be surgically deepened to allow the peroneal tendons to sit in a better position without recurrent hyperextension. If one of the peroneal tendons is ruptured, it is repaired at the same time as the ligament holding it in place. If chronic instability of the ankle ligaments is observed at the same time, they are also repaired to restore normal ankle functionality. The prognosis of the disease is excellent in athletes, allowing for future participation at the pre-injury level.