Normal MRI Anatomy
On MRI, the normal peroneal tendons typically appear dark on all pulse sequences. On axial sequences at the level of the ankle, the peroneal tendons are found posterior to the lateral malleolus within the peroneal or retromalleolar groove, which is sometimes deepened by a small fibrous ridge at the lateral fibular margin. The groove may alternatively be flat or convex, which can predispose to subluxation. At this level the peroneus brevis tendon is positioned anteromedial to the peroneus longus and is crescentic in cross-section (Figures D&E). The peroneus brevis myotendinous junction is lower in position than that of the peroneus longus, and may be seen at the level of the tibiotalar joint (Figure E). The SPR is seen as a thin dark band posterolateral to the tendons at the level of the lateral malleolus, attaching to the periosteum at the posterolateral margin of the fibula. The uninjured periosteum is thin and indistinct from the bone cortex. Distal to the lateral malleolus, the peroneus brevis courses anterior to the peroneus longus (Figures F&G). The peroneal tubercle is variable in size and projects laterally from the anterior process of the calcaneus, separating the positions of the peroneus brevis and longus tendons (Figure F). Normal variant anatomy in this region may include a peroneus quartus muscle, a low-lying peroneus brevis muscle belly, or an os peroneum.
On MRI, the normal peroneal tendons typically appear dark on all pulse sequences. On axial sequences at the level of the ankle, the peroneal tendons are found posterior to the lateral malleolus within the peroneal or retromalleolar groove, which is sometimes deepened by a small fibrous ridge at the lateral fibular margin. The groove may alternatively be flat or convex, which can predispose to subluxation. At this level the peroneus brevis tendon is positioned anteromedial to the peroneus longus and is crescentic in cross-section (Figures D&E). The peroneus brevis myotendinous junction is lower in position than that of the peroneus longus, and may be seen at the level of the tibiotalar joint (Figure E). The SPR is seen as a thin dark band posterolateral to the tendons at the level of the lateral malleolus, attaching to the periosteum at the posterolateral margin of the fibula. The uninjured periosteum is thin and indistinct from the bone cortex. Distal to the lateral malleolus, the peroneus brevis courses anterior to the peroneus longus (Figures F&G). The peroneal tubercle is variable in size and projects laterally from the anterior process of the calcaneus, separating the positions of the peroneus brevis and longus tendons (Figure F). Normal variant anatomy in this region may include a peroneus quartus muscle, a low-lying peroneus brevis muscle belly, or an os peroneum.
Peroneus brevis (red arrowhead), peroneus longus (red arrow), SPR
(green arrowheads), fibular periosteum (blue arrowhead), peroneal
tubercle (yellow arrowhead).
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