Peroneal Tendon Injury

The peroneus longus and brevis run behind the lateral malleolus within the retromalleolar groove, held by the superior peroneal retinaculum. They evert and plantarflex the ankle and protect against inversion injury. Injuries are tendinopathy, split tears (the brevis most often, in about 88% of tears) and subluxation or dislocation from retinacular failure.

Subluxation follows sudden forced dorsiflexion with reflex peroneal contraction, seen in skiing, football and basketball. Grades: I retinaculum stripped from the fibula with the tendon displaced beneath the periosteum, II fibrocartilaginous rim elevated, III cortical avulsion fragment (the fleck sign). Predisposing factors are a shallow or convex groove, a low lying brevis muscle belly, a peroneus quartus, cavovarus foot and chronic lateral ankle instability. Missed injuries cause chronic pain, recurrent snapping and tendon attrition.

• Lateral ankle pain behind and below the fibula, swelling and tenderness along the tendons
• A snap or pop and visible tendon displacement over the fibula on resisted eversion with circumduction
• Weakness of resisted eversion, a sense of instability
• Associated lateral ankle ligament laxity
• Red flags: a history of one acute event with persistent swelling, and failure of an ankle sprain to recover in 6 weeks

• Examination: palpation, resisted eversion, provocative circumduction.
• Radiographs (mortise and lateral): the fleck sign, an avulsion at the lateral distal fibula pathognomonic of retinacular injury, and a cavovarus alignment.
• Dynamic ultrasound: tendon displacement during active dorsiflexion and eversion, split tears, effusion.
• MRI (avoid the magic angle artifact): tendon splits, retinacular injury, fibular groove shape, peroneus quartus.

Differentials: lateral ankle sprain, sural neuritis, fibular fracture, os peroneum syndrome, anterolateral impingement, lateral process of the talus fracture.

Acute subluxation: a non-weight-bearing short leg cast with the foot in neutral or slight plantarflexion for 4 to 6 weeks, then a boot and physiotherapy. About half redislocate.

Tendinopathy: a lace up brace or walking boot for 3 to 6 weeks, a lateral heel wedge, eccentric peroneal strengthening for 12 weeks, and ibuprofen 400 mg orally every 8 hours with food for up to 7 days. Avoid injecting corticosteroid into the tendon sheath.

Surgery (failed conservative care for 3 to 6 months, recurrent subluxation, athlete):

• Tear involving under 50% of the tendon: debridement and tubularization with 3-0 absorbable suture.
• Tear involving over 50%, or both tendons with viable muscle: tenodesis of the torn segment to the intact tendon.
• Irreparable tears: allograft or flexor digitorum longus transfer in a staged procedure.
• Instability: superior peroneal retinaculum repair with transosseous sutures or anchors, groove deepening in a shallow groove, and excision of the peroneus quartus.
• Correct cavovarus with a dorsiflexion first metatarsal osteotomy or lateralizing calcaneal osteotomy.
• Cefazolin 2 g IV before incision (3 g if over 120 kg).

Rehabilitation: non-weight-bearing for 2 weeks, protected weight bearing in a boot for 4 weeks, resisted eversion from week 6, and return to sport at 4 to 6 months. Complications: sural nerve injury, wound problems, re-rupture and stiffness.

Follow up at 2, 6 and 12 weeks. Counsel on footwear and ankle stability training.