Peroneus brevis tear.

Longitudinal partial tear of the peroneus brevis tendon, "peroneal splits". On this T2-weighted fat-suppressed axial image, the peroneus brevis tendon (red arrowheads) is partially longitudinally torn at the level of the lateral malleolus, creating an inverted U shape. The peroneus longus tendon (red arrow) is seen between the split portions of the peroneus brevis tendon. The partial tear can progress to a complete tear, in which case three tendinous structures would be seen posterior to the lateral malleolus, the peroneus longus tendon interposed between the split portions of the peroneus brevis tendon.