Concomitant Traumatic Peroneal Tendon Dislocation and Medial Malleolus Fracture: A Case Report

Peroneal tendon dislocation in association with medial malleolus fracture is a very rare traumatic injury to the ankle. A 19-year old male patient was referred after injury sustained in a motorcycle accident with car, with concomitant traumatic peroneal tendon dislocation and medial malleolus fracture. The possible mechanism of this unusual injury could have been sudden external rotation force to the pronated foot in full dorsiflexed position of the ankle. Diagnosis of peroneal tendon subluxation or dislocation should be carefully evaluated in patients with single medial malleolus fracture.


INTRODUCTION
Peroneal tendon subluxation or dislocation is a rare traumatic injury to the ankle. Although, it was first described in a ballet dancer, other sport activities like skiing, soccer and basketball could result in traumatic dislocation of the peroneal tendon. Usually peroneal tendon subluxation or dislocation is mistaken or undiagnosed because of similarity of the mechanism of injury to that of lateral ankle sprain and lack of apparent findings in plain radiographs 1 .
Medial malleolus fracture usually occurs in association with fractures of lateral malleolus, posterior malleolus, proximal fibula, or with ligamentous injuries around the ankle joint. Concomitant traumatic peroneal tendon dislocation and medial malleolus fracture have been rarely reported in the literature 2,3 . We describe a case of minimally-displaced medial malleolus fracture in association with avulsion fracture of superior peroneal retinaculum to show the importance of small flake fractures around the ankle joint.

CASE REPORT
A 19-year old man was referred with pain in left ankle after motor-vehicle accident. On physical examination, swelling and ecchymosis around the ankle joint especially on medial side was obvious. Significant tenderness on medial malleolus and little tenderness on lateral malleolus were noted on palpation of the ankle joint. Neurovascular function of the foot and ankle was normal. Radiographs disclosed minimally-displaced fracture of the medial malleolus and a barely visible small avulsion fracture on the posterodistal part of the lateral malleolus ( Fig. 1). Computed tomography (CT) scan to determine the exact position of the avulsion fracture of lateral malleolus revealed a flake avulsion of superior peroneal retinaculum (SPR) from the posterior aspect of the lateral malleolus (Fig. 2).
After obtaining consent from the patient and under general anaesthesia in the operating room, open reduction and internal fixation of the medial malleolus fracture was carried out using a malleolar screw and a Kirschner wire was shortened and buried beneath the skin. Examination during surgery revealed dislocation of peroneal tendons to the anterior aspect of the lateral malleolus with passive full dorsiflexion of the ankle joint, following which, through an incision on the posterior aspect of the distal lateral malleolus, the avulsed superior peroneal retinaculum (SPR) was exposed. The flake of bone and SPR were anchored to the lateral malleolus with two sutures. Stability of the peroneal tendons was fully achieved.
Postoperatively, non-weight bearing short leg cast was applied for six weeks followed by a short leg walking slab to initiate range of motion of ankle for four more weeks. At follow-up one year after surgery, the patient was completely satisfied with the healed fracture and tendon injury (Fig. 3) and had a full range of motion of the joint despite retained devices.     (Grade I or II). This theory could explain the mechanism of injury of concomitant traumatic peroneal tendons dislocation and medial malleolus fracture. This is only a theory and it should be tested in research on cadavers.
In conclusion, more attention should be paid to the lateral part of the ankle joint in patients with a solitary medial malleolus fracture of Type B or Type C by the Herscovici classification. When any small avulsed bone fragment from the posterior aspect of the lateral malleolus is revealed on radiography, instability of peroneal tendons must be looked for. After fixation of medial malleolus fracture under general anaesthesia, it is important to exclude any possible peroneal tendon subluxation even in the absence of evidence of bone fragment avulsion.