Evaluation of the accuracy of acetabular cup orientation using the accelerometer-based portable navigation system

Background: Accurate orientation of acetabular and femoral components is important during total hip arthroplasty (THA). In recent years, several navigation systems have been developed. However, these navigation systems for THA are unpopular worldwide because of their high cost. We assessed the orientation accuracy of cups inserted using a disposable accelerometer-based portable navigation system for THAs. Methods: This was a prospective cohort study. We analyzed 63 hips with navigation prospectively and 30 hips without navigation retrospectively as historical control. The patients underwent THA via the mini anterolateral approach in the supine position using an accelerometer-based portable navigation system. We compared the preoperative target angles, intraoperative cup angles using navigation records, postoperative angles using postoperative CT data, measurement errors of cup angles, and clinical parameters such as sex, treated side, age at surgery, and body mass index (BMI). Results: The average absolute error (postoperative CT-navigation record) was 2.7 +/- 2.1 degrees (inclination) and 2.7 +/- 1.8 degrees (anteversion), and the absolute error (postoperative CT-preoperative target angle) was 2.6 +/- 1.9 degrees (inclination) and 2.7 +/- 2.2 degrees (anteversion). The absolute error between postoperative CT and target angle with navigation was significantly lower than the error without navigation (inclination; p = 0.025, anteversion; p = 0.005). Cup malalignment (absolute difference of inclination or anteversion between postoperative CT and preoperative target angle of over 5 degrees) was significantly associated with BMI value (OR: 1.3, 95% CI: 1.1-1.7). The absolute measurement error of cup inclination and anteversion was significantly correlated with patients' BMI (inclination error: correlation coefficient = 0.53, p < 0.001, anteversion error: correlation coefficient = 0.58, p < 0.001). Conclusions: The clinical accuracy of accelerometer-based portable navigation is precise for the orientation of cup placement, although accurate cup placement was affected by high BMI. This is the first study to report the accuracy of accelerometer-based portable navigation for THA in the supine position. (C) 2019 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.