Morphological classification and clinical significance of retromalleolar canal based on magnetic resonance imaging

Tarsal tunnel neurovascular vulnerability lacks robust anatomical classification. We established an MRI-based retromalleolar canal classification to assess its clinical utility for surgical approach guidance and pathology diagnosis.

This retrospective study analyzed normal ankle 3 T MRIs from 250 consecutive patients (2018-2023). Three musculoskeletal radiologists independently classified retromalleolar canal morphology using axial T2-weighted turbo spin-echo sequences (Siemens Skyra 3 T) acquired at a standardized plane 4 mm superior to the talar dome.

Three radiologists demonstrated excellent interobserver reliability in all measurements (ICC >0.85, P < 0.001). Based on morphological parameters including shape, dimensions, and angular relationships, we classified retromalleolar canals into four distinct types: R (predominant, 60.4 %), V (18 %), K (16.8 %), and L (4.8 %). Morphometric analysis revealed significant differences across all classification groups (P < 0.001), particularly in groove depth and medial malleolar angle measurements.

The novel morphological classification may complement existing methods, potentially improving posterior ankle arthroscopy safety and aiding in the understanding of pathologies such as posterior tibial tendon dislocation and tarsal tunnel syndrome.