Detection of the center of the hip joint in computer-assisted surgery: An evaluation study of the Surgetics algorithm

Abstract

Objective: The aim of this paper is to assess the accuracy of an algorithm implemented by PRAXIM™ in the SURGETICS™ navigation station for detection of the hip center. This study will assess the robustness and accuracy of the algorithm in various clinical situations such as those involving non-sphericity of the femoral head, motion of the pelvis during hip center detection, and restricted range of motion.

Materials and Methods: The localization of the hip center, based on kinematics, relies on the recording of n successive positions of the femoral rigid body in the localizer reference system during a passive circumduction motion of the hip joint. Therefore, the shape of the clouds of points acquired may vary from one acquisition to the next. To allow a comprehensive study of the consequences of these variations for hip center detection, we developed a simulator to generate numerous clouds of points. Results given subsequently for each test are the values of the difference between the femoral mechanical axis computed with C_c, the computed hip center, and the same axis computed with C_o, the reference hip center.

Results: Test 1: Sensitivity to noise. The errors ranged from 3.33 E − 12 (SD 3.29E − 12) for a noise of 0 mm to 8.18E − 1 (SD − 7.05E − 1) for a noise of 15 mm. Test 2: Sensitivity to the shape of the acquisition motion. All trajectories gave an error < 1°. Test 3: Sensitivity to restricted range of motion. No value > 1° was found during this test. Test 4: Sensitivity to the distance between two points of the cloud. No value > 0.5° was found during this test. Test 5: Sensitivity to the number of points included in the cloud. No value > 1° was found during this test.

Conclusions: The Surgetics algorithm is robust to noise, can compensate for pelvic motion, and can be used even in the case of restricted range of motion.

• Hip center
• kinematic
• accuracy
• robustness
• assessment
• navigation