101 - When the Brevis Breaks: A Case Report on Subacute Peroneus Brevis Rupture Detected by Ultrasonography

A 55-year-old male with a subacute peroneus brevis rupture.

Case Description: A 55-year-old male ultramarathon runner with bilateral pes cavus and a history of lumbar radiculopathy presented with persistent left lateral ankle pain and instability for six weeks following a hiking injury, without a distinct traumatic event. Initial plain radiographs were negative for acute fracture. On examination, there was localized tenderness over the distal peroneal tendons and calcaneofibular ligament, with pain and weakness on resisted foot eversion. Musculoskeletal ultrasound revealed discontinuity of the distal peroneus brevis tendon and hypoechoic swelling proximal to the tear, consistent with a full-thickness rupture. The peroneus longus tendon and anterior talofibular ligament appeared intact. The clinical and ultrasonographic findings supported a diagnosis of subacute peroneus brevis rupture.

Discussions:

Peroneal tendon injuries are a frequent cause of lateral ankle pain and instability in athletes. Both ultrasound and magnetic resonance imaging (MRI) are effective for detecting peroneal tendon tears, with MRI generally considered the reference standard for preoperative evaluation. However, ultrasound offers several advantages: it enables dynamic assessment of tendon movement, real-time interpretation, and is safe, accessible, and cost-effective. Surgical correlation studies demonstrate that ultrasonography has high sensitivity and specificity for peroneal tendon tears, and the American College of Sports Medicine and the American Medical Society for Sports Medicine state that ultrasonography can be as precise as MRI for tendinous and ligamentous injuries, but emphasize the importance of operator expertise. Early and accurate diagnosis is critical in facilitating timely intervention, optimizing functional outcomes, and minimizing chronic pain and instability.

Conclusions: Ultrasonography enabled prompt and accurate diagnosis of subacute peroneus brevis tendon rupture in a high-demand athlete, facilitating timely surgical management. This case highlights the value of dynamic ultrasound as a reliable, accessible imaging modality for peroneal tendon pathology, supporting its role in the diagnostic pathway for lateral ankle pain and instability.