Peroneal Tendinopathy

A lateral view of the foot, peroneus longus, brevis and tertius, the superior and inferior extensor retinaculum, and the superior and inferior fibular retinaculum.

Peroneal Tendinopathy is an uncommon condition of the lower leg that involves pain in the tendons of two of the peroneal muscles, namely peroneus longus and/or peroneus brevis. It can be both acute (less than 6 weeks) or chronic (longer than 6 weeks). Some sources also call this “peroneal tendinitis”, although in many cases there is no inflammation, making this term inaccurate. The “-opathy” in tendinopathy means “pain”, with or without inflammation, and could be considered a better term.

The peroneus longus and peroneus brevis muscles are found in the lateral compartment of the lower leg. The peroneus longus muscle originates (arises) from the head and proximal two-thirds of the lateral aspect (outside) of the shaft of the fibula and the peroneus brevis orginates from the distal two-thirds of the shaft of the fibula just medial to the peroneus longus muscles (just to the inside of it). Both muscles transition into tendons just proximal to the ankle (just above it), and pass posterior to (behind) the lateral malleolus through the “retromalleolar groove”, which is a groove or tunnel formed by the fibula, the posterior talofibular ligament, the calcaneofibular ligament, and the superior fibular retinaculum. See the image below:

Both tendons share a synovial sheath until they are distal to the fibula (past it), at which point they divide and have their own sheaths. The tendon of the peroneus longus passes under the cuboid bone and the plantar aspect of the foot (underneath it) and inserts (attaches) to the plantar aspect of the medial cuneiform and base of the 1st metatarsal. The peroneus brevis tendon inserts on the styloid process of the 5th metatarsal.

There are three avascular zones in the tendons of these two muscles (areas with no blood supply). The first avascular area is where the tendons both pass behind the lateral malleolus through the retromalleolar groove; the second is where the peroneus longus tendon curves under cuboid. This is important as will be shown later.

If the tendons are subjected to accumulative loads that are greater than they can accommodate and repair during the period of rest before being stressed again (called a “training load error” or “overuse injury”), or damaged due to traumatic injury, then this can lead to pain, and sometimes inflammation, swelling or instability of the posterior-lateral aspect of the ankle and rearfoot.

The peroneus longus and brevis muscles are everters of the foot (they pull the foot outward), and also plantarflex the foot (pull the foot downward). They are the key muscles that stabilise the lateral ankle (the outside of the ankle). As such, they are easily injured in sports and activities that involve side-to-side movements and high torsion forces acting on the lower part of the leg, usually from changing direction frequently, as in football, dancing, basketball or ice skating.

Tendinitis and tendinopathy are caused by the mechanical stresses acting on the tendons as they pass behind the lateral malleolus through the retromalleolar groove. It can also occur at the site where the peroneus longus tendon curves around the cuboid. These areas of bone act like a pulley system for the tendons, improving the amount of power they can deliver when they are working. However, if the loads on the tissues are higher than they can accommodate, and if the person does not rest sufficiently, then the tendon can become inflammed and begin to degenerate, especially at the aforementioned avascular regions.

The person with peroneal tendinitis or tendinopathy may experience pain when walking or running, when raising themselves up onto the balls of the their feet, or from walking on uneven surfaces. It may also be painful to stand after a period of rest, especially in the morning. The pain usually worsens gradually over a period of weeks or months if the person continues those activities or maintains the levels of activity that are aggravating these tissues, or if they continue not getting enough rest.

A diagnosis is usually made by taking a detailed history, by observing the area, palpating the area, and by preforming particular diagnostic tests such as a prevocative test where slight pressure is applied to the peroneal tendons within the retromalleolar groove while the patient leg is hanging with the knee flexed to 90 degrees and the foot in a relaxed position. The patient is then asked to forcefully (quickly) evert and dorsiflex the foot. A positive results means there is pain or subluxation of the tendons when this is done. Imaging, such as MRI and ultrasound, may be helpful for spotting any lesions or oedema, but are necessary to make a diagnosis. X-Rays can be used to determine if the calcaneal tuberacle has become enlarged, as this may be pressing on the tendons if present.

Alternative diagnoses can include: a lateral ankle sprain; there can also be a tear in the superior fibular retinaculum which may lead to the tendon dislocating in an anterior direction (toward the toes); the tendons can also rupture, resulting in complete loss of function in that muscle.

Treatment usually includes reducing activity for a period of time, taking non-steroidal anti-inflammatory drugs (NSAIDs), and using rest-ice-compression-elevation (RICE), all of which are especially important in the acute phase. Strengthening and stretching exercises can be given to address muscle imbalances that may be contributing to this condition, particularly the peroneals themselves (the peroneals are often weak). Proprioception exercises may also be indicated, as is the use of foot and ankle mobilising and manipulation therapy (e.g. FMT). A clinical biomechanics assessment may be helpful to determine if poor foot, ankle and lower limb mechanics are the cause of this condition or contributing to it, in which case bespoke orthoses can be provided to reduce the forces acting upon the tissues, allowing them to heal more easily and reducing the risk of reinjury. In severe cases, the foot may need to be immobilised using a cast or boot.

If conservative treatments fail to resolve this condition after 3-6 months, surgery may be indicated, as it is in the case of subluxation and rupture.

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