Abstract
Background
Acetabular component malpositioning during hip arthroplasty increases the risk of dislocation, reduces range of motion and can be responsible for early wear and loosening. There have been numerous reports on the optimal orientation of the acetabular component in total hip arthroplasty (THA). Lewinnek et al recommended an abduction angle of 40°±10° and an anteversion of 15°±10° for cup alignment in THA. The purpose of the in vivo study was to compare computer assisted acetabular component insertion versus free-hand placement. The goal of the cadaveric study was to compare in vitro a new tool using ultrasound with the standard percutaneous manual methods for the anterior pelvic plane registration during computer-assisted total hip arthroplasty.
Methods
A controlled randomized matched prospective study was performed in two groups of 30 patients. In the first group, cup positioning was assisted by an imageless computer assisted orthopaedics system, based on Bone Morphingâ (CAOS+ group). In the control group, a free-hand cup placement was performed (CAOS- group). A same cementless cup has been used in the two groups. All the patients were operated by the same surgeon through an anterolateral approach. Cup anteversion and abduction angles were measured on three-dimensional CT-scan reconstruction postoperatively for each patient by an independent observer with special cup evaluation software. In vitro, four clinicians were asked to register ten times in a randomly change order the anterior pelvic plane landmarks in four different acquisition conditions: a cutaneous acquisition, a draped cutaneous acquisition, ultrasound acquisition and a direct bone acquisition on two cadavers. The mean and standard deviation of error for each anterior pelvic plane acquisition method were expressed as rotation and tilt about the relevant reference plane and compared.
Results
There were 16 males and 14 females in each group, the mean age was 62 years (24–80) and mean Body Mass Index was 25. Mean additional time of the CAOS procedure was 12 minutes (8–20). Intraoperative subjective agreement of the surgeon with the computer guidance system demonstrated a high correlation in 23 cases, weak correlation in 6 cases and a poor correlation in 1 case. There were no statistical differences between the CAOS+ group and the CAOS- group regarding means of the abduction and anteversion angles but a significant heterogeneity of variances, with the lowest variations in the CAOS+ group. In vitro, for the draped cutaneous acquisition method the mean of the rotation and tilt around the reference plane for the two cadavers and the four operators were respectively 3.8 °±0.21° and 19.25 °±4.1°, for the for the ultrasound acquisition method respectively 2.8 °±0.21° and 6.2 °± 4.1°, for the cutaneous acquisition method respectively 2 °±0.21° and 16.2 °±4.1°.
Discussion
The in vivo study has shown the accuracy of cup positioning using a CT-free navigation system in a prospective randomized controled protocol. Based on the number of the cadaveric study, ultrasound acquisition of the anterior pelvic plane is more accurate, reliable and reproducible in vitro than actual cutaneous digitization.
