Peroneal Tendon Tears

Peroneal tendon tears are a commonly missed cause of lateral ankle pain, often misdiagnosed as a chronic ankle sprain. The tendons are critical for hindfoot eversion and lateral ankle stability, and an untreated tear leads to progressive weakness, recurrent instability and functional limitation. Early recognition and the right operation, debridement for minor tears and reconstruction for major ones, achieve 80-90% good outcomes and prevent chronic disability.

Who. Active adults aged 30-40, with an equal sex distribution, in contrast to tibialis posterior tendon dysfunction, which is female-predominant. Peroneal tears account for 11-37% of chronic lateral ankle pain, and 10-15% of patients have contralateral involvement.

The association that shapes management. 80% of patients with a peroneal tear have lateral ankle instability, meaning ATFL/CFL insufficiency, and it has to be looked for and treated alongside the tear.

Risk factors. Chronic lateral ankle instability is the most significant.

• Extrinsic - chronic lateral ankle instability, recurrent inversion ankle sprains, high-level sport (basketball, soccer, tennis), and steroid injections, which have a degenerative effect on tendon
• Intrinsic - a low-lying peroneus brevis muscle belly, a shallow retromalleolar groove with less fibular containment, and cavovarus hindfoot alignment, which increases peroneal load

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Two tendons in one groove. Both tendons pass behind the lateral malleolus in the retromalleolar groove, held there by the superior peroneal retinaculum (SPR). In the groove the peroneus brevis runs anterior to the peroneus longus, so the brevis is compressed between the fibula in front and the longus behind. That compression, with the tendon's excursion during hindfoot inversion and eversion, creates a high-friction zone, and it is why PB tears are far more common than PL tears.

What the tendons do. The peroneus brevis is the primary everter of the hindfoot, the longus secondary, and both resist inversion in stance to stabilise the lateral ankle. The longus also contributes to plantarflexion through its plantar first metatarsal insertion, and depresses the first ray, which locks the transverse tarsal joint. Both muscles are supplied by the superficial peroneal nerve, which exits the leg's anterior compartment.

In gait. In stance the peroneals contract eccentrically to resist inversion; in swing they evert the foot in preparation for heel strike. When the lateral ligaments are insufficient the peroneals compensate for them, so chronic ankle instability increases peroneal load.

How the brevis splits. The tear is a degenerative lesion of chronic friction and compression, and it develops in sequence:

1. PB is compressed between the fibula and PL
2. Excursion during inversion-eversion creates friction
3. Chronic microtrauma degenerates the tendon
4. A longitudinal split develops, parallel to the fibres
5. The split propagates with continued stress

Friction damages the tendon within its substance and the split follows the fibre direction, so the tear runs lengthways. The Achilles, by contrast, usually ruptures transversely.

The low-lying brevis belly. Normally only tendon occupies the groove. In 20-30% of the population the brevis muscle belly extends into it, increasing compression and the risk of a tear.

The peroneus quartus. An accessory muscle present in roughly 10-22% of the population. It usually arises from the peroneus brevis (or the distal fibula) and most often inserts onto the retrotrochlear eminence of the calcaneus, when it is termed the peroneocalcaneus externus. As an extra structure in the groove it increases the volume the SPR must contain; the crowding raises compression on the brevis and can stretch the SPR or render it incompetent, predisposing to PB splits and to subluxation.

On MRI the quartus appears as an additional muscle and tendon posteromedial to the peroneal tendons. Recognising it before surgery explains the crowding.

Longitudinal split tears. Sobel et al (Foot & Ankle, 1992) first described the mechanism and longitudinal-split pattern of peroneus brevis tears, the eponymous "Sobel" lesion. Krause and Brodsky (Foot Ankle Int, 1998) then defined the surgical grade in clinical use, based on the percentage of cross-sectional area involved. It is the most commonly used surgical grading, and the grade decides between debridement and reconstruction (see Management Algorithm).

Tear patterns. The split is one of several patterns, and each has its own typical site and treatment.

Painful os peroneum syndrome (POPS). The os peroneum is a sesamoid in the peroneus longus tendon, and POPS is the spectrum of PL pathology around it. It is the peroneus longus counterpart to the peroneus brevis split tear, and explains why a normal-looking brevis does not exclude peroneal pathology.

• Acute os peroneum fracture, or diastasis of a multipartite os peroneum, with sudden plantar-lateral midfoot pain
• PL tendinosis or a partial or complete tear at or distal to the os peroneum, often from attrition against the cuboid or a hypertrophied peroneal tubercle
• Chronic plantar-lateral foot pain along the PL course, with tenderness over the os peroneum

History. The pain is lateral, posterior to the lateral malleolus, and usually chronic, lasting months to years. The mechanism is recurrent inversion ankle sprains, often treated conservatively and misdiagnosed as sprains. Patients describe weakness of eversion and difficulty on uneven ground, and popping or snapping suggests a torn SPR with the tendons subluxing over the fibula.

Examination. Look for swelling posterior to the lateral malleolus, with ecchymosis if the injury is acute, and feel for tenderness along the tendons and thickening at the retromalleolar groove. Resisted eversion is weak and painful compared with the other side. A Grade I tear gives lateral ankle pain, mild weakness and a palpable, tender brevis; a Grade II tear significant weakness, a feeling of instability and a thickened brevis; and a complete Grade III rupture severe weakness, with no eversion against resistance.

Differential diagnosis. The retromalleolar pain of a peroneal tear shares its territory with instability, subluxation and several bony and neural causes.

Plain radiographs. They are not diagnostic for tendon tears, but they rule out bony pathology. Take ankle AP, lateral and mortise views and foot AP, lateral and oblique views, and look for:

• 5th MT base avulsion fracture (PB insertion tear)
• Os peroneum fracture or displacement
• Calcaneofibular distance (SPR avulsion may show a fleck sign)
• Cavovarus alignment, which predisposes to peroneal overload

MRI. The imaging investigation of choice, and its performance must be known: it is highly specific but only moderately sensitive for peroneus brevis tears. Park 2010 reported sensitivity 83.9% and specificity 74.5% for peroneal tendinopathy overall; Park 2012, with surgery as the reference standard, found only 44% sensitivity (99% specificity) for PB interstitial tears. A positive scan is reliable, but a normal scan does not exclude a tear, and in a clinically suspicious ankle with a negative MRI, dynamic ultrasound or surgical exploration may still be warranted.

What MRI is for. It characterises tear morphology, shows associated pathology (lateral ligaments, SPR, bone oedema), and guides preoperative planning. Obtain axial, sagittal and coronal sequences; the axial images at the retromalleolar groove are critical.

• Longitudinal split - linear high T2 signal within the tendon substance, parallel to its long axis; the tendon may appear thickened
• Partial tear - high signal at the tendon surface, not extending through the substance
• Complete rupture - tendon discontinuity, a gap and retracted ends
• Tenosynovitis - fluid surrounding an intact tendon without intrasubstance signal; the tendon may be thickened
• SPR tear - discontinuity of the retinaculum, fluid in the peroneal sheath
• Associated findings - lateral ligament (ATFL/CFL) tears, bone marrow oedema

Dynamic ultrasound. It can show subluxation in real time during eversion, it is less expensive than MRI, and it has none of MRI's contraindications, such as implant compatibility. It is, however, operator-dependent, less sensitive than MRI for intrasubstance tears, and cannot assess bone marrow oedema or deep structures. Consider it if MRI is unavailable or contraindicated, or to assess dynamic subluxation.

Treatment follows the grade of the tear, on the principle of treating the tear and its cause: instability, subluxation and hindfoot varus.

Conservative management. Indicated for mild tears (Grade I under 25% width), tenosynovitis without a structural tear, or a patient unfit for surgery.

• Weeks 0-6 - CAM boot or short leg cast, weight-bearing as tolerated in the boot; ice 15-20 minutes QID for the first 2 weeks, NSAIDs if there is no contraindication, elevation
• Weeks 6-12 - lateral support ankle brace; physiotherapy for range of motion (dorsi/plantarflexion, inversion/eversion); resistance-band eversion strengthening from week 8-10; balance-board proprioception
• Weeks 12-16 - progressive strengthening, gradual sport-specific return, brace for sport, avoid repetitive eversion stress
• Long term - brace for high-risk activities, maintenance strengthening and proprioception, lateral heel wedge if cavovarus, review if symptoms recur

Results. Conservative success for peroneal tears is poor compared with other tendinopathies: 60-70% for tenosynovitis without a structural tear, 30-40% for Grade I tears and under 20% for Grade II-III. Peroneal tears are degenerative splits within a high-friction zone, and continued use perpetuates them, so most Grade I-III tears ultimately need debridement or reconstruction.

Grade I. Debridement alone is usually sufficient under 25%; between 25% and 50%, tubularisation (side-to-side repair of the split) gives a more robust repair.

Grade II. Debride the diseased tissue first, then judge how much healthy tendon remains. If a tube of adequate diameter (over 50% of normal) can be made, tubularise; if the tissue is inadequate, reconstruct with allograft. Tenodesis to PL is an option for low-demand patients.

Grade III. An allograft interpositional graft is preferred for active patients, and tenodesis of PB to PL is acceptable for the low-demand or elderly. FHL transfer is an option in a young active patient if allograft is unavailable. The choice rests on age, activity level, graft availability and the surgeon's preference and experience.

The lateral ligaments. Assess the ATFL with the anterior drawer and the CFL with the talar tilt test. Stress radiographs help if the diagnosis is uncertain (talar tilt over 10° = CFL tear), and MRI confirms the ligament tears, the ATFL most commonly, with the CFL often involved. If instability is present, the ligaments are reconstructed at the same operation as the tendon.

• Brostrom repair - direct anatomical repair, the primary choice if tissue quality is good
• Brostrom-Gould augmentation - Brostrom reinforced with the inferior extensor retinaculum
• Allograft reconstruction - poor tissue quality or a revision case

Preventing recurrence. Uncorrected lateral ankle instability is the most common cause of recurrent peroneal tears (see Management Algorithm). The other preventable causes are dealt with at and after the index operation:

• Repair the SPR if torn, to prevent subluxation
• Debride all diseased tissue; incomplete debridement leaves recurrent pathology
• Immobilise appropriately after surgery to protect the repairs (see Rehabilitation)
• Address cavovarus alignment if present, with a lateral heel wedge or calcaneal osteotomy

After debridement or tubularisation.

• Weeks 0-2 - short leg splint kept dry, NWB with crutches or a walker, elevation, ice and DVT prophylaxis; at the week-2 review remove the splint, check the wound and change to a CAM boot (removable for hygiene)
• Weeks 2-6 - NWB in the boot for the full 6 weeks
• Weeks 6-8 - partial weight-bearing in the boot (25-50% body weight); gentle ankle range of motion (dorsi/plantarflexion); no forced eversion until week 10
• Weeks 8-12 - full weight-bearing in the boot; resistance-band eversion strengthening and proprioception; wean from the boot to a supportive shoe and ankle brace
• Week 12 onwards - shoe and brace for activities, progressive and sport-specific strengthening, return to full activity at 4-6 months, and a brace long term for high-risk sports

Why six weeks. Tubularisation sutures achieve biological strength at 6-8 weeks, and early weight-bearing risks re-tearing at the repair site; an SPR repair, if performed, also needs 6 weeks to heal. Patients who bear weight early have higher recurrent tear rates, 20-30% against under 10% with compliant NWB.

After allograft reconstruction.

• Weeks 0-6 - strictly NWB in a cast or boot; elevation, ice, DVT prophylaxis
• Weeks 6-10 - partial weight-bearing (25-50% body weight) in the boot; gentle range of motion, avoiding forced eversion
• Weeks 10-12 - full weight-bearing in the boot; range of motion and light strengthening
• Weeks 12-16 - wean from boot to shoe and brace; progressive strengthening and proprioception
• 4-6 months - gradual return to sport, with a brace for high-risk activities; full strength typically returns by 6 months

After SPR repair. Immobilise in slight plantarflexion and inversion, which reduces tension on the repair. The patient is NWB for 4-6 weeks and avoids forced eversion until 12 weeks.

After combined lateral ligament repair. 4-6 weeks NWB protects both the peroneal and the ligament repairs, followed by progressive weight-bearing in the boot over weeks 6-10 and physiotherapy for range of motion and strengthening from week 10-12. Return to sport is at 4-6 months, when both have healed.

Predictors of poor outcome. These are the risk factors for a poor result after peroneal tendon surgery:

• Lateral ankle instability not addressed - 50% recurrence if instability is not repaired
• SPR not repaired - recurrent subluxation, progression of pathology
• Workers' compensation - lower satisfaction, prolonged recovery
• Smoking - impaired wound and tendon healing
• Advanced degenerative tears - Grade III complete ruptures have lower success than Grade I-II
• Delayed diagnosis - chronic tears (over 6 months) are more degenerate, with worse tissue quality

Patients with several risk factors may benefit from earlier surgical intervention and from counselling towards realistic expectations.

Long-term results. After debridement or tubularisation, 75-80% maintain a good outcome at 5 years; 10-15% develop recurrent tears or progression, and 5-10% need revision. After allograft reconstruction, 70-80% maintain a good outcome at 5 years; 15-20% have graft-related problems (failure, persistent weakness), and 10-15% need revision.

Return to sport. Among recreational athletes, 70-80% return to the same level, 15-20% to a lower level, and 5-10% are unable to return. Among high-level athletes, 60-70% return to elite competition, recovery is longer (6-8 months minimum), and returning too early raises the risk of recurrence. Long-term brace use is recommended for pivoting sports such as basketball, soccer and tennis.

Global Epidemiology (PubMed-backed)

Guidance and Consensus Across Regions

Global Practice Variation