The weighted optimal common shape technique improves identification of the hip joint center of rotation in vivo

Functional methods present a promising approach for the identification of skeletal kinematics, but their accuracy is limited by soft tissue artifacts (STAs). We hypothesized that consideration of the nonuniform distribution of STAs across the segment can lead to a significant improvement in the determination of the center of rotation at the hip. Twenty‐four total hip arthroplasty (THA) patients performed repetitions of a star‐arc movement. The location of the hip centers of rotation (CoRs) were estimated from the motion data using the Symmetrical Center of Rotation Estimation (SCoRE), both with and without procedures to minimize the effect of STAs. The precision of the CoR estimations was evaluated using the SCoRE residual, a measure of joint precision. Application of the newly developed weighted Optimal Common Shape Technique (wOCST) achieved the best CoR estimations with a precision of better than 3 mm, while the precision using raw data alone was up to seven times worse. Furthermore, consideration of the nonuniform distribution of STA across the surface of the skin using the wOCST produced an improvement of ∼24% over kinematics data processed using the standard OCST. Functional determination of the CoR at the hip using the newly developed wOCST can now identify the joint CoR with a precision of millimeters. Such approaches therefore offer improved precision in the assessment of skeletal kinematics and may aid in evaluating clinical treatment success and differentiating between therapy outcomes. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29: 1470–1475, 2011