Reducing unintended valgus deformity after supracondylar femoral derotational osteotomy: Influence of derotation amount and osteotomy method based on femoral antecurvature.

Abstract

Purpose: The purposes of this study were threefold: (1) to evaluate the influence of femoral antecurvature on coronal alignment changes following supracondylar femoral derotational osteotomy (FDO); (2) to investigate the combined effects of derotation angle and osteotomy orientation in relation to femoral antecurvature and (3) to propose a practical strategy for minimising valgus deviation after FDO based sagittal femoral bowing.

Materials and methods: Sixty-six cadaveric femoral computed tomography (CT) scans were analysed using three-dimensional (3D) simulation. Femurs were classified into three groups based on the degree of antecurvature using the distal diaphyseal angle (DDA). Virtual surgery was simulated at 7 cm above the joint line using two osteotomy methods (shaft-perpendicular and distal femur condylar line [DFC]-parallel) and two derotation angles (10° and 20°). Mechanical lateral distal femoral angle (mLDFA) was measured before and after simulation. Multivariable and stratified regression analyses were performed.

Results: Greater antecurvature led to larger mLDFA decrease, with more pronounced valgus shifts at higher derotation angles. Making DFC-parallel osteotomy significantly reduced valgus change regardless of bowing (β = -0.331, p = 0.005). A significant interaction was found between DDA and derotation angle (β = 0.015, p < 0.001). The combination of DFC-parallel osteotomy with 10° derotation provided the least valgus change (R² = 0.84). The allowable derotation angle to maintain <1° valgus shift decreased as DDA increased.

Conclusion: Femoral antecurvature significantly affects coronal alignment after supracondylar FDO. Although the optimal target angle for derotation remains a surgical choice, understanding the relationship between sagittal bowing and coronal alignment can help tailor patient-specific decisions. To minimise valgus shift after supracondylar FDO, aligning the osteotomy plane parallel to the distal femur condylar line can be effective. This method is simple and practical for standard surgical procedures.

Level of evidence: Level IV.