The peroneus brevis tendon provides dynamic stability to the ankle, helping control foot position during movement. It is one of two peroneal tendons located along the outside of the ankle and leg, and its function is important in preventing the ankle from rolling inward. A longitudinal split tear of the peroneus brevis is an injury where the tear runs parallel to the tendon’s natural fibers, rather than across its width. This injury often creates persistent, localized pain that requires targeted medical evaluation.
Anatomy and the Nature of the Tear
The peroneus brevis tendon originates from the fibula and extends downward behind the ankle’s outer bony prominence, known as the lateral malleolus. It is positioned in a narrow channel called the retro-malleolar groove, adjacent to the peroneus longus tendon. The primary role of the peroneus brevis is foot eversion—the movement that turns the sole of the foot outward—and it provides ankle stability, especially on uneven ground.
A longitudinal split tear is caused by mechanical friction, often occurring where the tendon is compressed against the sharp posterior edge of the fibula. Unlike a complete rupture, the tendon fibers are frayed and separated along their length, splitting the tendon into two or more sections. This chronic mechanical wear is exacerbated by a shallow fibular groove or laxity in the superior peroneal retinaculum, the ligamentous band that holds the tendons in place. If the retinaculum fails to secure the tendon, repeated rubbing against the bone leads to degenerative fraying and splitting.
Common Causes and Risk Factors
The injury often develops from a combination of anatomical predisposition and repetitive mechanical stress, making it common in athletes involved in running, jumping, and quick changes in direction. Chronic lateral ankle instability, often lingering after a previous ankle sprain, is a primary risk factor. Repeated inversion injuries, where the ankle rolls inward, can stretch or tear the surrounding ligaments and the superior peroneal retinaculum.
Once compromised, the retinaculum no longer holds the peroneus brevis tendon securely in its groove, allowing it to subluxate, or slip out of place, over the bony ridge of the fibula. This repeated friction wears down the tendon, causing the characteristic longitudinal split. Other anatomical variations, such as a shallow fibular groove or a low-lying muscle belly, can crowd the space behind the malleolus and increase friction damage. Systemic conditions like rheumatoid arthritis or diabetes may also predispose the tendon to injury.
Recognizing the Symptoms
Patients typically report pain localized to the lateral side of the ankle, with specific tenderness felt directly behind the lateral malleolus. This pain often worsens during physical activities that require the tendon to work, such as pushing off or turning the foot outward against resistance. Swelling along the tendon sheath in the outer ankle area is a common physical sign that raises suspicion of a tear.
A frequent complaint is a feeling of weakness or instability in the ankle, described as the joint “giving way,” particularly when walking on uneven surfaces. This symptom can mimic a simple ankle sprain, which often leads to misdiagnosis or delayed treatment for the underlying tendon tear. If the injury is acute, a popping sensation may be recalled, but chronic tears develop gradually with pain that fails to resolve despite traditional rest and ice treatments.
Diagnostic Procedures and Treatment Pathways
Confirming a longitudinal split tear begins with a thorough physical examination where the clinician palpates the area behind the lateral malleolus for tenderness and swelling. A specific test involves resisting the patient’s attempt to evert the foot, which engages the peroneus brevis and often reproduces the localized pain. Imaging studies are necessary to visualize soft tissue damage and rule out other contributing factors, such as a fracture.
Plain X-rays are useful for assessing bony anatomy, such as the depth of the fibular groove or the presence of a fracture, but they cannot visualize the tendon tear itself. Magnetic Resonance Imaging (MRI) or high-resolution ultrasound are the preferred diagnostic tools. These methods clearly demonstrate the longitudinal split in the tendon, assess its severity, and show the condition of the surrounding retinaculum. MRI has high sensitivity for identifying these tears, though ultrasound is also effective.
Treatment is tailored to the tear’s severity, the patient’s activity level, and the injury’s chronicity. Non-operative management is the initial approach for mild, partial tears. This typically involves a period of rest, immobilization in a walking boot or brace for several weeks, and anti-inflammatory medication. Once acute symptoms subside, physical therapy focuses on restoring strength, range of motion, and proprioception (the body’s sense of joint position).
If symptoms persist for several months or if the tear is significant, surgical intervention is often recommended to restore the tendon’s integrity and function. The most common procedure involves debridement, where the surgeon removes the frayed, damaged edges of the split tendon. The remaining healthy tissue is then repaired with sutures in a technique called tubularization. For severe tears damaging more than half the tendon’s cross-sectional area, the non-viable segment may be excised, and the remaining tendon can be attached to the peroneus longus tendon in a procedure called tenodesis. Surgical repair requires post-operative immobilization, followed by several months of physical therapy for a full return to function.