The peroneus brevis longitudinal split tear represents a specific and often underdiagnosed injury within the lateral ankle complex. This condition involves a vertical cleavage within the peroneus brevis tendon, typically occurring at its mid-substance or musculotendinous junction. Understanding the nuances of this injury is critical for clinicians managing lateral ankle pain, as it bridges the gap between simple tendinopathy and complete tendon rupture.
Anatomy and Biomechanics of the Peroneal Tendons
The peroneal tendons, housed within the fibular groove behind the lateral malleolus, are essential stabilizers of the ankle during weight-bearing activities. The peroneus brevis, originating on the distal fibula, inserts primarily on the base of the fifth metatarsal, making it a powerful evertor and plantarflexor of the foot. The longitudinal split tear occurs when the tendon fibers separate along the line of their collagen alignment, a process often initiated by repetitive stress rather than a single traumatic event.
Mechanisms of Injury and Predisposing Factors
Individuals with a high arched foot (cavovarus deformity) or generalized ligamentous laxity are at increased risk for developing a peroneus brevis longitudinal split tear. The injury mechanism often involves repetitive inversion and plantarflexion, such as during running on uneven terrain or rapid directional changes in sports. Over time, this repetitive microtrauma leads to degeneration within the tendon substance, creating a vulnerable zone that ultimately splits longitudinally.
Clinical Presentation and Diagnostic Challenges
Patients typically present with lateral ankle pain that is activity-related and often described as a deep, aching discomfort. Swelling and warmth may be present, but the classic finding is pain with resisted eversion or passive inversion of the foot. The challenge in diagnosis lies in differentiating this tear from other lateral ankle pathologies, such as osteochondral lesions or occult fractures, necessitating a high index of suspicion.
Physical Examination Findings
Palpable tenderness directly over the peroneal tendons just posterior to the lateral malleolus.
Positive "flick sign," where flicking the tendon longitudinally reproduces the symptoms.
Pain during resisted peroneus brevis contraction, often more pronounced than with the peroneus longus.
Assessment of ankle varus stress to evaluate for associated ligamentous injury.
Imaging Modalities for Confirmation
While clinical examination provides the initial framework, imaging is essential for confirmation and surgical planning. Magnetic Resonance Imaging (MRI) is the gold standard, clearly delineating the longitudinal nature of the tear, the degree of tendon retraction, and the integrity of the superior peroneal retinaculum. Ultrasound offers a dynamic, cost-effective alternative, allowing for real-time assessment of the tendon under load.
MRI Characteristics of a Longitudinal Tear
Conservative Management Strategies
Initial treatment for a symptomatic peroneus brevis longitudinal split tear focuses on reducing inflammation and modifying activity. A controlled period of immobilization in a walking boot can alleviate symptoms by allowing the tear edges to approximate. Following this, a structured rehabilitation program emphasizing eccentric strengthening of the peroneals and proprioceptive training is crucial to prevent recurrence.
