Presentation
Lateral ankle pain with no history of acute trauma. Pain has not improved despite ice, pain killers, and physical therapy.
Patient Data
Fibula and peroneal tendons
A septated ganglion cyst lies immediately posterior to the tendons.
There is a split tear in the peroneus brevis tendon which is located adjacent and posterior to the lateral malleolus.
With dynamic maneuvers, the peroneus brevis tendon (PB) initially moves laterally towards the transducer and then the tendons flip, so that the peroneus longus tendon moves abruptly around the superficial lateral border of the PB and the PB moves away from the transducer.
Both tendons remain within the intact peroneal sheath which prevents the tendons subluxing anteriorly around the lateral malleolus, (posterior is to the right of the screen).
Key image from ultrasound with annotations: outlined in blue are the two pieces of the torn peroneus brevis tendon and outlined in green is the intact peroneus longus tendon.
Case Discussion
This case shows a split tear of the peroneus brevis tendon as well as intra-sheath subluxation of the peroneal tendons (type B) 1.
Dynamic ultrasound is necessary to diagnose intra-sheath subluxation which involves the peroneal tendons switching positions during specific movements of the ankle. Static imaging may result in a false negative result.
The patient is positioned prone on the examination table with the foot projecting beyond the table to allow dorsiflexion and eversion of the ankle. The transducer is oriented in the axial plane.
Case submitted by Mathew Illimoottil in collaboration with Shashank Gupta (medical student at Loyola University).
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