Patient-specific ROM and load-based Target Zone for Total Hip Arthroplasty and its Application in a retrospective Analysis

Abstract

The outcome of total hip arthroplasty (THA) depends on multiple alignment and design parameters. Unsuitable parameter settings could lead to impingement, dislocation, increased wear, and loosening. This work introduces a method for calculating a patient-specific target zone based on range of motion (ROM) related and load related criteria. Possible bone or prosthesis impingement are analyzed. The resulting hip force is calculated and compared to the pre-operative situation. The edge loading risk is analyzed. Pelvic tilt is considered for the calculation of the ROM and the load. THA parameters fulfilling all criteria are included in the target zone.The above described method has been applied to 30 cases retrospectively. All cases had been planned and navigated on the basis of CT data. From each patient, pre- and post-operative CT and EOS data and Harris Scores were acquired. The pre-operative data served as the input data for the target zone calculator. We hypothesized that cases with post-operative THA parameters inside the target zones have higher scores than other cases.The patients whose implants are within the target zones had higher scores than the remaining patients. Especially patients inside both target zones (combined target zone) had higher scores. The results also show that for 19 out of 30 patients, conventional CT-based planning and navigation does not provide optimal placement regarding the combined target zone. A further validation of the method with a larger sample size is part of our ongoing work.