Influence of Midfoot Deformities on Hindfoot Alignment Measurement – Comparison of Second Ray, Midfoot or Mortise Alignment on Weight-Bearing CT

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Hindfoot malalignment is linked to various foot and ankle pathologies. Accurate assessment is paramount for surgical planning. Traditional plane radiographic methods are limited by malrotation and superimposition, while weight-bearing CT (WBCT) provides precise spatial information. One established measurement method uses the second metatarsal as reference axis. This reference may be unreliable in the presence of foot deformities, potentially affecting hindfoot alignment measurements. The aim of this study was to assess how referencing of WBCT by second-ray, midfoot or ankle mortise, influences hindfoot alignment measurements in the presence of midfoot deformities. Methods: WBCT and standard foot radiographs of 136 patients were examined. Hindfoot alignment (isolated 3D hindfoot angle, I3HA) was measured comparing three reference axes: the established second metatarsal axis, the midfoot and the ankle mortise. Sgarlato angle (SA) was measured on standard radiographs as an indicator of midfoot deformity. I3HA measurements were compared between feet with normal or pathological SA values. Results: I3HA varied significantly across different reference systems (second metatarsal: 10.0°, midfoot: 12.7°, ankle mortise: 15.2°; p< 0.001). When comparing feet with normal versus pathological SA (>20°), I3HA showed significant differences when using the second metatarsal as reference (p < 0.001). Referencing to midfoot or ankle mortise remained stable, with no significant difference. Conclusion: Midfoot pathologies significantly influence hindfoot measurements when using the second metatarsal as reference axis, potentially leading to inaccurate results. In contrast, midfoot and ankle mortise referencing resulted in more stable hindfoot alignment measurements. Hindfoot alignment values have a direct influence on surgical technique and execution, making accurate measurements crucial for appropriate surgical correction.