The Peroneal Tendons: Function and Vulnerability

The peroneus longus and peroneus brevis tendons — together called the peroneal tendons — run behind the lateral malleolus in a shared fibro-osseous tunnel, restrained by the superior peroneal retinaculum, before diverging to their respective insertions: peroneus brevis to the fifth metatarsal styloid process, peroneus longus through the plantar foot to the first metatarsal base and medial cuneiform. Together they are the primary ankle evertors and lateral ankle stabilizers, firing powerfully during the push-off phase of gait and eccentrically resisting ankle inversion during cutting and landing movements.

Their shared curved course around the posterior lateral malleolus creates a shear stress concentration — particularly where the peroneus brevis lies against the fibula within the groove — that predisposes these tendons to longitudinal split tears under repetitive stress. These tears are among the most under-recognized causes of chronic lateral ankle pain, frequently attributed to ‘chronic ankle sprain’ until appropriate imaging reveals the tendon pathology.

Types of Peroneal Tendon Injury

Peroneus Brevis Longitudinal Split Tear

The most common peroneal tendon injury is a longitudinal split tear of the peroneus brevis — the tendon splits lengthwise along its flat surface where it contacts the posterior fibular groove. These tears occur through chronic attritional degeneration from the peroneus longus wedging against the brevis against the fibula during repeated ankle inversion stress events. An acute sprain mechanism often ‘uncovers’ a pre-existing attritional tear that has been developing asymptomatically. Clinically significant brevis split tears present as persistent lateral ankle pain posterior and inferior to the lateral malleolus, tenderness directly over the peroneal tendons, and pain with resisted eversion.

Peroneus Longus Tear

Peroneus longus tears are less common and occur at three anatomically vulnerable locations: the fibular groove (similar to brevis tears), the peroneal tubercle of the calcaneus where the longus exits the shared tunnel, and at the cuboid groove on the plantar foot surface where the tendon makes a sharp 90-degree turn around the cuboid. The os peroneum — a sesamoid bone within the peroneus longus tendon at the cuboid — may fracture as part of an acute longus tear mechanism. Cuboid tunnel syndrome presents specifically as lateral-to-plantar midfoot pain worst with push-off.

Fifth Metatarsal Avulsion Fracture

Rather than tearing within the tendon substance, the peroneus brevis can avulse its bony insertion — pulling off a fragment of the fifth metatarsal styloid process — during an acute inversion injury. This avulsion fracture is among the most common fractures in the foot, often presenting alongside a lateral ankle sprain that diverts clinical attention. Standard foot X-rays confirm the diagnosis; the fragment is typically small and non-displaced, treated conservatively with a walking boot for 4–6 weeks in most cases.

Peroneal Tendon Subluxation and Dislocation

The superior peroneal retinaculum — the fibrous band that holds the peroneal tendons within the fibular groove — can tear in an acute ankle sprain with a characteristic mechanism: sudden forceful dorsiflexion with peroneal muscle contraction (as occurs during a fall on a plantarflexed foot). When this restraint tears, the peroneal tendons subluxate (partially displace) or dislocate anteriorly over the lateral malleolus. The characteristic complaint is a snapping or popping sensation at the lateral ankle with activity. Peroneal subluxation is often misdiagnosed as an ankle sprain and requires specific examination maneuvers and imaging (ultrasound dynamic testing) for diagnosis.

Diagnosis

MRI

MRI is the imaging gold standard for peroneal tendon tears. It demonstrates longitudinal split tears as intratendinous signal on T2 sequences, characterizes the extent of tearing, identifies associated tenosynovitis (fluid within the tendon sheath), and assesses retinacular integrity. MRI findings guide surgical planning — the proportion of the tendon cross-section that remains intact determines whether primary repair, tubularization, or tenodesis is most appropriate.

Ultrasound

Dynamic ultrasound is particularly valuable for assessing peroneal subluxation — the tendons can be visualized in real time as they subluxate with provocative plantarflexion-eversion movements. Ultrasound also demonstrates tendon tears with good sensitivity in experienced hands and allows simultaneous diagnostic and therapeutic injection guidance.

Conservative Treatment

Incomplete longitudinal split tears involving less than 50% of the tendon cross-section, and those without associated instability or subluxation, may be managed conservatively with relative rest in a walking boot, NSAIDs, physical therapy for peroneal strengthening, and custom orthotics to control hindfoot valgus that increases peroneal groove shear stress. Ultrasound-guided tenosynovial injection may reduce acute inflammation. Conservative management succeeds in approximately 50–60% of patients with incomplete tears; failure of conservative management after 3–6 months indicates surgical evaluation.

Surgical Treatment

Peroneal Groove Deepening and Retinacular Repair

Surgical treatment for peroneal pathology typically combines assessment and treatment of the tendon tears with attention to the underlying anatomical factors that caused them: a shallow fibular groove, loose retinaculum, or low-lying peroneus brevis muscle belly occupying groove space. Groove deepening deepens the fibular groove with a burr, increasing tendon containment; retinacular repair or imbrication tightens the restraint against subluxation. Both procedures are performed through a limited incision posterior to the lateral malleolus.

Tubularization of Split Tears

Peroneus brevis split tears with less than 50% cross-sectional involvement are repaired by debriding the torn edges of the split and suturing the remaining normal tendon into a tubular round cross-section. This ‘tubularization’ restores the mechanical continuity of the tendon while removing the degenerative split tissue. Results are generally good — 80–90% of patients achieve satisfactory outcomes.

Tenodesis for Extensive Tears

When peroneus brevis tears involve more than 50% of the cross-section — particularly when segmental tears produce irreparable tendon sections — tenodesis is performed: the damaged brevis segment is excised and the proximal and distal stumps are sutured to the adjacent peroneus longus tendon. The longus then carries the mechanical function of both tendons. Peroneal function is maintained at the expense of reduced individual tendon mechanical independence.

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Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.