What is it?
The peroneal tendons are two tendons on the outside of the ankle, just behind the fibula. Their respective muscles lie in the outer compartment of the lower leg and they are known as the peroneus longus and peroneus brevis. Both tendons have a role in stabilizing the ankle and midfoot and propelling the body forward during normal walking.
What is it caused by?
The peroneal tendons are no different to any other tendon in the body, in that they can suffer from overuse, become inflamed and start giving pain. The tendons can become swollen and start abnormally moving over one another and even dislocate from their usual position behind the fibula. This instability and “tendonopathy” can occur in association with a tear of either tendon.
Lateral ankle pain and swelling can be the initial symptoms. As the tendons swell and become unstable there may be palpable instability as well as clicking and snapping arising from behind the fibula. Sometimes it is possible to dislocate and relocate the tendons.
The peroneal tendons can become over-worked in trying to stabilize an ankle that has deficient lateral ligaments. A history of repeated ankle sprains is not uncommon, particularly with a structural deformity of the foot and ankle, called “pes cavus” where the arch of the foot is noticeably high and the heel turns inward.
It may be possible to reproduce peroneal instability at-will by the patient in clinic but most often a dynamic imaging study is needed to demonstrate tendonopathy and instability. Ultrasound evaluation is therefore the most useful initial investigation. It enables assessment of possible tendon tears with analysis of higher-than-normal blood-flow indicating inflammation, as well as identifying the rare chance of a small accessory muscle being present.
In order to assess some of the structural problems around the ankle that may give rise to instability, cross-sectional imaging with CT or MRI is likely to be needed. CT scanning in particular can be conducted under load-bearing conditions and the groove behind the fibula in which the tendons glide can be evaluated for shallowness.
Tendonopathy can improve if enough rest is prescribed and one of the most straight-forward ways to accomplish this is by immobilizing the ankle in a walker boot or ankle brace for at least 2-3 weeks. Physio-taping can hamper ankle movements that may provoke tendon dislocation and can also be of benefit. Anti-inflammatory tablets and simple pain-killers such as paracetamol may be beneficial in the early stages.
If there is a supple and correctable hindfoot/forefoot deformity such as pes cavus, which is driving the peroneal tendon inflammation and instability, a corrective insole may be all that is required after the initial 2-3 week rest period. If this is successful then a short period of dedicated physiotherapy to strengthen the peroneal tendons may be all that is required.
If a peroneal tendon tear is identified on ultrasound, the tear will most likely heal if it is identified early (within two to three months of symptom onset) and treated as previously stated. Tendons will not however heal if they are injected with steroids which do little more than arrest the healing response, although they may offer temporary pain relief.
Biological healing with injections of platelet rich plasma (PRP) may offer some additional benefit to rest, immobilization and physiotherapy but their use is confined to patients presenting early in the course of their disease.
Peroneal tendon surgery often involves combining several small operations into one. For example, structural deformity such as pes cavus may require bony surgery, often through minimally-invasive techniques and if there is ankle instability it is straight-forward to reconstruct the lateral ankle ligaments. This is of course in addition to carrying out the surgery to repair the tear or stabilize dislocating tendons.
It is most common for tendons to split longitudinally when it is therefore necessary to suture and “tubularise” the torn tendon. When extensive sections of tendon are involved or if the whole tendon is torn, it might not be appropriate or even possible to primarily repair the tendon. In these situations, if one of the tendons is intact and healthy it is common practice to suture the further (distal) end of the torn tendon to the intact tendon (if there is one)- a procedure called “tenodesis”. This causes one healthy muscle belly to pull on both tendons and is adequate for normal function. If both tendons are severely diseased it may be necessary to undertake a tendon transfer procedure where a healthy, donor tendon in the same foot or even near the knee is harvested and implanted to take over the function of the diseased tendon.
Dislocating tendons are treated by deepening the fibular groove in which they glide and repair of the overlying stabilizing retinaculum which is often baggy after repeated episodes of tendon dislocation. With almost all surgery, a short period of immobilization in plaster after the operation is needed to allow healing.