Review peroneal tendon tear MRI signs, including peroneus brevis split tears, peroneus longus injury, tendon subluxation, sheath effusion, and chronic ankle instability.
The peroneal tendons (peroneus longus and brevis) run along the lateral ankle and are important for ankle stability and eversion. Injuries include tendon tears (longitudinal splits are most common in peroneus brevis), subluxation or dislocation from the fibular groove, and tendinopathy. These injuries are often associated with lateral ankle sprains and chronic ankle instability. Our AI consortium evaluates tendon morphology, position, and the integrity of the superior peroneal retinaculum.
Peroneal tendon tears are often missed when the search stops at a routine ankle sprain. The key MRI questions are whether the brevis tendon has a longitudinal split, whether the longus tear extends toward the cuboid tunnel, whether the superior peroneal retinaculum is stripped, and whether tendon instability explains persistent lateral ankle pain. Compare the broader ankle MRI reading guide when the report also mentions ligament edema, talar dome cartilage injury, or marrow contusion.
Axial PD-FS sequences at the level of the retromalleolar groove are the key diagnostic plane. Peroneus brevis split tears present as a C-shaped or bifid tendon with a longitudinal intrasubstance cleft on axial images, often with the peroneus longus wedged within the split. Peroneus longus tears more commonly occur at the cuboid tunnel or os peroneum level — a fragmented or enlarged os peroneum on lateral radiograph and a longitudinal hyperintense cleft on axial PD-FS confirms the diagnosis. Peroneal tendon sheath effusion and SPR signal disruption on coronal images indicate associated retinaculum injury.
Peroneal tendon subluxation occurs when the superior peroneal retinaculum (SPR) fails to contain the peroneus brevis and longus within the retromalleolar groove. MRI signs include SPR disruption or periosteal sleeve avulsion from the fibula on axial T2-FS, shallow or convex retromalleolar groove morphology, and tendon displacement anterior to the fibular tip. Dynamic ultrasound with real-time dorsiflexion-eversion stress directly visualises subluxation. AI review of axial MRI quantifies groove depth (normal >3 mm) and SPR continuity to stratify surgical versus conservative management.
Peroneal tendon involvement should be suspected when lateral ankle pain persists beyond 6–8 weeks following a sprain, when pain localises to the posterolateral fibula rather than the ATFL footprint, or when eversion strength is disproportionately reduced relative to inversion stability. Studies show that up to 25% of chronic lateral ankle instability cases have concurrent peroneal tendon tears on MRI. AI analysis of ankle MRI in post-sprain patients simultaneously screens ATFL, CFL, and the peroneal tendon complex, reducing rates of missed combined pathology.
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