MRI evaluation of peroneus brevis tendon position: Anatomical variants in individuals with normal peroneal tendons to improve recognition and prevent misdiagnosis.

BACKGROUND

An accurate assessment of the peroneal tendon position is essential in ankle MRI, yet classical anatomical descriptions may not reflect the full range of normal anatomical variation. This study aimed to classify anatomical variants in peroneus brevis position and assess associations with tendon shape, size, and the presence of the peroneus quartus muscle and low-lying peroneus brevis muscle.

METHODS

This observational cohort study included 230 ankle magnetic resonance examinations (3 T) with normal peroneal tendons. Peroneus brevis position relative to the peroneus longus was categorized into four types based on axial MRI: medial (no overlap), overlap with medial protrusion (extension beyond the medial margin of the longus), overlap with lateral protrusion (beyond the lateral margin), and overlap with both. Tendon shape was classified as general flat, flattened convex medially, flattened convex laterally, or oval. Associations between position and shape were tested using chi-square. Differences in cross-sectional area (mm²) and width (mm) across groups were assessed with analysis of variance and Tukey's post hoc test. A regression model identified predictors of tendon overlap.

RESULTS

The most common position was overlap with medial protrusion (72.0 %), followed by medial, lateral, and combined protrusions. Position was significantly associated with shape (p < 0.001); oval tendons were typically medial, while flattened tendons overlapped. Width and cross-sectional area differed significantly across positions (p = 0.0088), with the largest area in tendons protruding medially and laterally (16.9 mm²). Width correlated strongly with overlap (r = 0.79, p < 0.001) and was the strongest predictor in regression (β=0.51, p < 0.001). Peroneus quartus was independently associated with increased overlap (β=0.22, p = 0.03), while low-lying peroneus brevis muscle showed no significant effect.

CONCLUSION

Peroneus brevis position is highly variable and depends on its shape, width, and the presence of peroneus quartus. These variants are significantly related to tendon shape and width and may mimic peroneal instability on imaging.