Computation of hip rotation kinematics retrospectively using functional knee calibration during gait

Hip rotation kinematics during gait is a key parameter to support clinical decision making, for example in children with lower limb torsional deformities. However, hip rotation kinematics is also one of the least repeatable parameter because it is difficult to locate the position of the medio-lateral axis of the femur. Functional knee calibration provides an alternative to locate the medio-lateral axis of the femur and may be performed retrospectively, using the movement of the knee joint during gait. Although not necessarily more anatomically accurate, functional calibration may lead to increased repeatability between sessions, which would be useful to compare gait analysis data from sessions pre- and post-treatment, or to reprocess data in large gait databases.

This study presents a workflow to perform knee functional calibration using knee kinematics during gait and update hip rotation kinematics accordingly. The workflow was applied to investigate the inter-subject, inter-session and inter-trial variance components of multiple calibration methods in a group a 10 typically developing children.

Results indicated that one or two degrees of freedom functional calibration methods were more repeatable inter-session (SD: 1.8°) than conventional calibration using the knee alignment device (SD: 4.7°). However, simulated reduced range of movement at the knee during gait increased inter-session variance for the functional calibration algorithms. Functional calibration did not provide any improvement over the conventional calibration when knee range of movement was reduced and flexion greater than 20° during gait, i.e. 'crouch gait'.

The workflow presented allows the re-processing of gait analysis data using knee kinematics during gait only. The workflow may also be used to investigate functional axes of other joints, for example the ankle.