Peroneal tendon dislocation: a missed cause of ankle pain and instability

Two tendons, peroneus longus and peroneus brevis, run behind the outer ankle bone (the lateral malleolus) in a shared groove held in place by a band of tissue called the superior peroneal retinaculum. A published case report describes how the shape of the groove and the integrity of this retinaculum matter most for stability.

In dislocation or subluxation the tendons are displaced out of the groove, usually after the retinaculum is torn or pulled away from the fibula. Patient.info's clinical reference lists peroneal tendon subluxation among the tendon injuries to consider when someone has acute ankle pain, alongside Achilles injury and other tendon problems.

This should not be confused with peroneal tendinopathy, a gradual overuse problem. NHS Borders' toolkit describes peroneal tendinopathy as chronic lateral ankle pain, and notes that ankle sprains are common and 40% go on to develop chronic ankle pain including peroneal tendinopathy.

Reports describe lateral ankle pain, swelling behind the outer ankle bone, a sensation of popping or snapping, and a feeling that the ankle gives way, especially on turning the foot up and out. One reported patient had ongoing lateral ankle instability on dorsiflexion or eversion of the foot and ankle popping three months after an injury initially treated as a sprain.

In chronic cases people can present with pain, stiffness, instability and snapping. Many have a history of an injury during sport such as skiing or football, or a fall or twisting injury.

• Pain and swelling behind the outer ankle bone after a twist or fall.

• A snapping or popping sensation as the foot turns.

• Feeling that the ankle is unstable, especially on uneven ground.

• An ankle sprain that is not settling as expected.

A case report says a proper history and clinical assessment are mandatory, and that conventional radiography, ultrasound, MRI and CT are all described as helping to show the integrity of the peroneal tendons. Radiography helps detect bone injury, while MRI is better at assessing the tendons and the retinaculum, although in both of that report's cases the MRI was inconclusive. A second report notes that dynamic MRI images, taken as the ankle moves, are more helpful than static ones because the problem depends on foot position.

Because of the similarity to a sprain, it is worth asking for review if an apparent sprain brings repeated giving way, snapping or persistent pain. A foot and ankle specialist, often within orthopaedics or sports medicine, will usually make the diagnosis.

The reports describe conservative treatment as the usual first choice after the acute phase, and suggest it may be offered to non-athletes with an acute dislocation. They caution that the recurrence rate is high: one cites recurrent dislocation in 55% of cases, another up to 60%.

Surgery is described as the choice for recurrent dislocation and sometimes for athletes in the acute phase. The reported options include repairing or reattaching the superior peroneal retinaculum, deepening the groove, bone block procedures and tendon rerouting. A case report notes that only case reports and small series exist and no randomised trials have established the best method, so surgeons choose according to the patient and the injury.

When the outer ankle ligament (the anterior talofibular ligament) is also torn, one report describes repairing both in the same operation. Rehabilitation after surgery is led by physiotherapists, and the time to return to sport varies with the procedure.

Case reports describe good outcomes after retinaculum repair, with improved function scores and return to activity, though they are small studies and not a guarantee for any individual. Early diagnosis helps because delay can lead to chronic instability and extra ligament damage. If you have had a sprain that has not recovered after several weeks, ask your GP or physiotherapist about further assessment.

On the NHS, a GP, emergency department or musculoskeletal service can refer on to orthopaedic foot and ankle surgery. Private foot and ankle consultants may provide quicker MRI and surgery, but the same assessment and decision-making apply. The sources read for this guide are largely non-UK case reports, so UK surgical practice may vary in detail.