Association between flat variants of the peroneus brevis tendon and split tears on magnetic resonance imaging.

Objectives: To determine whether the peroneus brevis tendon shape, cross-sectional area, and patient age are associated with split tears on magnetic resonance imaging.

Methods: This retrospective cross-sectional study included 358 patients (179 with and 179 without split tears), with sample size based on an a priori power calculation (Cramér's V = 0.186, 80% power, α = 0.05). Musculoskeletal radiologists assigned patients to split tear or no-tear groups based on MRI findings 8 weeks before independent shape classification and area measurements. Tendon shape was visually assessed on transverse proton density images and categorized as oval, general flat, flattened with medial convexity, or flattened with lateral convexity. Associations with split tear were evaluated using multivariable logistic regression.

Results: Flat-shaped tendons were more common in the split tear group (91.6%) than in controls (82.1%), while oval tendons were less frequent (8.4% vs. 17.9%, p = 0.007). The flattened with lateral convexity shape was most strongly associated with split tear. In the multivariable analysis, flat shape (odds ratio [OR] = 2.26, p = 0.021), larger cross-sectional area (OR per mm² = 1.04, p = 0.059), and older age (OR per year = 1.03, p < 0.001) are independently associated with split tear. No significant differences were observed between right and left ankles. Inter-rater agreement was substantial for shape (κ = 0.71, AC1 = 0.74) and excellent for area (intraclass correlation coefficient = 0.95).

Conclusions: A flat-shaped peroneus brevis tendon, an increased cross-sectional area, and older age are associated with an increased likelihood of peroneus brevis split tears. These features may serve as anatomical imaging biomarkers for early risk identification.