On the use of knee functibnal calibration to determine the medio-lateral axis of the femur in gait analysis: Comparison with EOS biplanar radiographs as reference

Accurate calibration of the medio-lateral axis of the femur is crucial for clinical decision making based on gait analysis. This study proposes a protocol utilizing biplanar radiographs to provide a reference mediolateral axis based on the anatomy of the femur. The biplanar radiographs allowed 3D modelling of the bones of the lower limbs and the markers used for motion capture, in the standing posture. A comprehensive analysis was performed and results from biplanar radiographs were reliable for 3D marker localization (+/- 0.35 mm) and for 3D localization of the anatomical landmarks (+/- 1 mm), leading to a precision of 1 degrees for the orientation of the condylar axis of the femur and a 95% confidence interval of +/- 3 degrees after registration with motion capture data. The anatomical condylar axis was compared to a conventional, marker-based, axis and three functional calibration techniques (axis transformation, geometric axis fit and DynaKAD). Results for the conventional method show an average difference with the condylar axis of 15 degrees (SD: 6 degrees). Results indicate DynaKAD functional, axis was the closest to the anatomical condylar axis, mean: 1 degrees (SD: 5 degrees) when applied to passive knee flexion movement. However, the range of the results exceeded 15 degrees for all methbds. Hence, the use of biplanar radiographs, or an alternative imaging technique, may be required to locate the medio-lateral axis of the femur reliably prior to clinical decision making for femur derotational osteotomies. (C) 2016 Elsevier B.V. All rights reserved.