Causes / typical injury mechanism: The tendons of the peroneus brevis and longus muscles (ie, the peroneal tendons) have multiple injury mechanisms. For some patients, injury to the peroneal tendons may be acute, with an obvious inciting event, typically an ankle inversion injury. However, in most patients, injury to the peroneal tendons is a chronic issue caused by overuse, tendon degeneration, or tendon insufficiency. In these cases, a specific inciting injury may be remote or nonexistent.

Injury to the peroneus brevis tendon is significantly more common due to its more prominent role in ankle eversion.

Classic history and presentation: A patient typically presents with insidious-onset, long-standing lateral ankle pain. The patient may have impaired ankle eversion strength against resistance, pain upon resisted eversion, and pain upon palpation of the lateral ankle posterior to the lateral malleolus.

Prevalence: Prevalence among the general population has not been well described; however, peroneal tendon tears are found in 22%-77% of all cases of lateral ankle instability and comprise 4% of all ankle injuries. They can occur in people of all ages but are associated most with younger, more athletic populations.

Risk factors: Risk factors include previous inversion injury to the ankle and chronic ankle instability. Injury to the peroneal tendons is frequently associated with concurrent injury to lateral ankle ligaments (33%), injury to the superior peroneal retinaculum (13%), ankle fracture (13%), and fibular groove insufficiency (10%). A low-lying peroneus brevis muscle and the presence of a peroneus quartus muscle are both found to be risk factors for peroneal tendon tear, occurring in 33% and 7%-22% of cadaveric specimens, respectively. Cavovarus feet were found to be a risk factor for concurrent tears of both peroneal tendons.

Pathophysiology: Injury to the peroneal tendons is broadly defined as splitting or tearing of the tendon, for which there are multiple proposed mechanisms. First, injury to the superior peroneal retinaculum or chronic ankle instability may lead to subluxation of the peroneus brevis tendon, eventually resulting in attrition of the tendon by the posterolateral fibula. Second, an inversion injury may compress the peroneus brevis tendon between the fibula and the peroneus longus tendon, resulting in a tear or split. A fracture to the base of the fifth metatarsal may also tear the peroneus brevis in an inversion injury. Tears of the peroneus brevis typically occur in the retromalleolar groove.

Peroneus longus injuries occur most commonly between the inferior retinaculum and the cuboid notch, and, like peroneus brevis injuries, occur most commonly with inversion injuries and chronic stress to the tendon.

Grade / classification system: The Redfern and Myerson Peroneal Tendon Tear Classification

• Type I: Both tendons intact but with partial tearing
• Type II: One tendon is intact but the other is majority torn
• Type IIIa: Both tendons are majority torn (unusable) and muscle belly has no excursion
• Type IIIb: Both tendons are majority torn (unusable) but muscle belly has excursion