Mri-detected low-lying and hypertrophic muscle bellies are associated with the occurrence of peroneal tendons dislocation: A case-control study.

OBJECTIVE

To investigate the correlation between MRI-defined anatomical features and peroneal tendon dislocation (PTD) by comparing the characteristics of the peroneus brevis muscle belly (PBMB) in patients with those in a control group, with the hypothesis that an increased prevalence of enlarged and distally extended muscle bellies is associated with PTD cases.

METHODS

This case-control study included 33 patients in the PTD group and 33 matched controls in the normal control (NC) group. MRI scans were conducted to measure the peroneal tendons cross-sectional areas (PTCA) and peroneus brevis muscle belly cross-sectional areas (MBCA) at five levels: one at the ankle joint center and the adjacent proximal and distal slices (1 proximal, 3 distal), calculate the muscle belly ratio (MBR), and determine the height of the distal endpoint of muscle belly (HMB).

RESULTS

PTCA showed no significant differences between the two groups across five levels. The PTD group exhibited significantly larger MBCA and MBR at all levels, notably at level 1 (proximal slice), level 2 (ankle joint center), and level 5 (p < 0.001). Moreover, the PTD group exhibited a lower HMB compared to the NC group (1.3 ± 5.4 mm vs. 9.0 ± 6.5 mm, p < 0.001). HMB showed an AUC of 0.838 with an optimal cutoff of 8.20 mm; MBR at Level 1 showed an AUC of 0.843 with an optimal cutoff of 68.86 %. The recommended thresholds are 8.00 mm for HMB (sensitivity 0.909, specificity 0.667) and 69.00 % for MBR at Level 1 (sensitivity 0.788, specificity 0.788).

CONCLUSION

PTD is correlated with hypertrophied peroneus brevis muscle bellies and distally extended muscle bellies. Defining low-lying muscle belly (LLMB) as the PBMB positioned ≤8 mm proximal to the fibular tip with an MBR of Level 1 > 69 % enhances precise identification.