A split tear of the peroneus brevis tendon is a specific type of injury affecting the ankle that can significantly compromise foot function. This condition involves damage to one of the two main tendons running along the outer part of the ankle, often causing persistent discomfort and instability. The injury is a mechanical failure of the tendon fibers under stress. It represents a common cause of chronic lateral ankle pain, especially in athletes and individuals with pre-existing ankle issues.
Defining the Peroneus Brevis Tendon and the Split Tear
The peroneus brevis is one of two peroneal tendons. It originates as a muscle in the outer lower leg and becomes a cord-like structure near the ankle. This tendon courses behind the lateral malleolus (the bony prominence on the outside of the ankle) and inserts into the tuberosity at the base of the fifth metatarsal bone. The primary function of this tendon is to evert the foot (turning the sole outward) and assist with plantarflexion.
A split tear, also called a longitudinal tear, is a partial disruption where the tendon fibers separate along their length, similar to a frayed rope. This is distinct from a complete rupture where the tendon separates entirely. The longitudinal nature allows the tendon to remain functional, but the damaged fibers often become inflamed and rub against surrounding structures. On imaging, the tear can cause the tendon to appear C-shaped as the fibers splay around the adjacent peroneus longus tendon. This degeneration usually occurs where the tendon passes through the narrow, high-friction groove behind the fibula.
Common Causes and Risk Factors
The development of a peroneus brevis split tear is usually a slow, degenerative process resulting from chronic mechanical irritation rather than a single traumatic event. A frequent initiating factor is chronic ankle instability, often stemming from repeated inversion ankle sprains where the foot rolls inward. These sprains force the peroneal tendons to contract sharply to stabilize the joint, creating excessive tension and friction. Over time, this repetitive stress causes the tendon to fray against the sharp posterior edge of the fibula.
Anatomical variations can predispose individuals to this injury by increasing mechanical stress. These factors include a shallow groove behind the fibula, which allows the tendons to subluxate or slip out of place, or the presence of a low-lying muscle belly of the peroneus brevis. Engaging in sports that involve frequent, sudden changes in direction, jumping, or running significantly increases the risk. Systemic health conditions like rheumatoid arthritis or diabetes are also associated with increased tendon vulnerability.
Identifying Symptoms and the Diagnostic Process
Patients typically report chronic or recurrent pain and tenderness along the outer edge of the ankle, often concentrated behind the fibula. This discomfort worsens with activity and may be accompanied by fluctuating swelling. Some individuals also experience a sensation of instability or the ankle “giving way,” especially when walking on uneven surfaces, due to the compromised stabilizing function. A clicking or popping sensation may occur if the tendon is subluxating.
The diagnostic process begins with a thorough physical examination. A clinician checks for tenderness directly over the tendon sheath and assesses ankle stability. They may test the strength of the eversion movement against resistance, which often reproduces the pain. Initial X-rays are ordered to rule out associated bony injuries, such as a fracture at the base of the fifth metatarsal, or to identify anatomical factors like a shallow fibular groove. To confirm the soft tissue injury, Magnetic Resonance Imaging (MRI) is the preferred modality. MRI provides detailed images of the tendon structure, clearly distinguishing the longitudinal split tear from other conditions like tenosynovitis or a complete rupture.
Treatment Pathways and Expected Recovery
Management is initially guided by the injury’s severity, with conservative non-surgical treatment attempted first for mild or partial tears. This approach focuses on reducing inflammation and protecting the tendon from further strain. Non-surgical options include the RICE protocol (rest, ice, compression, and elevation) and the use of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs). Immobilization with a walking boot or supportive brace is often used temporarily to allow the tendon to rest and begin healing.
Once the initial pain subsides, a structured physical therapy program is implemented to restore function and prevent recurrence. Physical therapy focuses on strengthening the peroneal muscles and surrounding musculature to enhance dynamic ankle stability and improve proprioception. Non-surgical recovery, which requires dedicated physical therapy, typically takes 6 to 12 weeks before a gradual return to full activity is possible.
Surgical intervention is reserved for high-grade tears, chronic tears that fail to improve after three to six months of conservative treatment, or cases involving persistent tendon subluxation. The most common procedure is a debridement and repair, where the surgeon removes the damaged tissue and sutures the longitudinal split back together (tubularization). If the tear is irreparable, a tenodesis may be performed, transferring the damaged tendon’s remaining fibers to the adjacent peroneus longus tendon. The surgeon may also deepen the shallow fibular groove or repair the superior peroneal retinaculum if anatomical issues are present. Post-surgical recovery involves a period of immobilization, typically two to four weeks, followed by rehabilitation. A full return to high-impact sports usually requires three to six months of structured physical therapy.