A computed tomographic graphical approach to guide correction of femoral torsion

Objective To report geometric methods to assess femoral transverse bone morphology and develop a virtual method to guide the surgical correction of femoral torsional deformities. Study design Observational study. Sample population Sixteen client‐owned dogs comprising 14 normal femurs and 14 femurs with angulation‐rotation bone deformities. Methods Femoral torsion angle was measured with computed tomographic (CT) three‐dimensional (3D) multiplanar reconstruction. Distal femoral transverse morphology was estimated with geometric methods and compared to direct measurements to span a target 20° angle on 3D reconstructions. A virtual correction of 20° was performed, and 3D‐printed bone models were created. Femoral torsion of corrected bone models was compared to precorrection. Results Geometric estimates with an arc and chord of the metaphyseal area and chord of a best fit circle did not differ from direct measurement of femoral cortical length along the cranial cortex. Femoral torsion differed between normal femurs (25.8° ± 6°) and those with deformity (36.9° ± 8.4°, P < .001). Torsion that was measured on corrected 3D bone models did not differ from the expected torsion (preoperative +20°). Conclusion Geometric methods provided an accurate estimate of distal femoral transverse bone morphology. Rotation of the distal femur based on geometric methods resulted in an accurate correction of torsion. Clinical significance Femoral bone diameter can be measured on a CT cross‐section, and rotation distance can be calculated to achieve a desired correction of torsion. This approach provides a simple and accurate method to guide the correction of femoral torsion.