Peroneal Tendon Tear MRI Signs: Brevis Split, Longus Tear, and Subluxation

Peroneus Brevis Split Tear: Decoding the Report Wording

A “longitudinal split tear of the peroneus brevis” means one of the two tendons behind the outer ankle bone has split lengthwise, often into a C shape that partly wraps around the peroneus longus. It is a tear along the tendon rather than straight across it. Tenosynovitis and subluxation, often listed nearby in the report, are separate findings.

Peroneal phrases you may find in the report

• “Longitudinal split tear of the peroneus brevis tendon”
• “C-shaped” or “bisected peroneus brevis”
• “Intrasubstance signal” or “tendinosis of the peroneal tendons”
• “Peroneal tenosynovitis” or “fluid in the common peroneal sheath”
• “Subluxation of the peroneal tendons” or “stripped superior peroneal retinaculum”
• “Flat” or “convex retromalleolar groove”

Split, tendinosis, tenosynovitis and subluxation compared

A split tear shows on axial images as a cleft through the peroneus brevis, with the two halves forming a C around the peroneus longus. Tendinosis or intrasubstance signal means the tendon is abnormal inside without a clear split. Tenosynovitis means the tendon sheath is inflamed, with fluid around the tendons. Subluxation means the tendons slip out of their groove behind the fibula, usually because the superior peroneal retinaculum that holds them is torn or stripped.

Some appearances can mimic a tear. A normal peroneus brevis can look mildly crescent-shaped or bifurcated, the magic angle effect can brighten a healthy tendon, and an extra peroneus quartus muscle or a low-lying brevis muscle belly can crowd the groove. Radiologists still report these variants because they can predispose to tears.

How much the finding weighs in treatment

Peroneal tendon injuries should be considered in anyone with lasting outer ankle pain, and they are often linked with sprains and ankle instability. Treatment depends on symptoms and activity level more than on the exact wording: people with low physical demands usually do well with conservative care, while those with high demands may benefit from surgery if conservative care fails.

What to ask about the peroneal tendons

• Is the peroneus brevis split along its length, and is the peroneus longus intact?
• Do the tendons stay in their groove, or does the report suggest the retinaculum is torn?
• Could the split explain why my ankle still hurts after the sprain healed?
• Would you try physiotherapy or a brace first, and what would make surgery worth discussing?

Overview

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.