Abstract
While THA is regarded as one of the most successful surgeries in medicine, recent studies have revealed that ideal acetabular cup implantation is achieved as little as 50% of the time. Malalignment of the acetabular component in THA may result in dislocation, reduced range of motion, or accelerated wear. Recently, robotic-assisted surgery has been introduced to reduce the errors in component placement. The purpose of this study is to longitudinally assess the accuracy of cup placement of a single surgeon at three points in time: directly following a total joint fellowship, after 10 years of experience with manual instrumentation, and directly after adopting robotic technology.
Three hundred patients received THA at a single center by a single surgeon representing three series of 100 consecutive patients in each series. The first series A included the surgeon's first 100 THA patients following graduation from joint fellowship (2/2000–5/2002). The second series B included the surgeon's last 100 THA patients before adopting robotic technology (12/2010–1/2012) and the final series C included the surgeon's first 100 THA patients using robotic assistance (4/2012–4/2013). The post-operative abduction and version of the cup was measured using PACS imaging software from the AP and cross-table lateral radiographs. Abduction was measured using a transverse line at the level of the teardrop and the lateral opening angle of the cup relative to this reference line. Anteversion was measured using the ischial method described by Schmalzreid on the crosstable lateral view and accounts for pelvic flexion.
The average inclination for the groups A, B, and C was 48.6 ± 7.6°, 37.4 ± 6.2°, and 39.6 ± 47.6°, respectively and for anteversion was 29.3 ± 10.3°, 26.6 ± 8.4°, and 23.6 ± 5.7°, respectively. The cup placement in the original series A was within the Lewinnek safe zone only 31% of the time. This increased to 45% in series B and up to 74% in series C (p < 0.05). With the robotic series C, the three-dimensional pre-operative plan was obtained from the software. The average error (final placement–plan) was −0.7 ± 2.1° for inclination and 1.1 ± 2.0° for version. 93% of the inclination measurements and 94% of the version measurements were within 5° of the plan and 100% of both measurements were within 10° of the plan. Of note, 8% of the robotic cases were actually planned outside of the Lewinnek safe zone to accommodate for patient deformity and optimize correction to achieve the targeted combined anteversion of the acetabular and femoral components.
Robotic assistance in THA leads to significantly more precise acetabular cup placement. As measured by the Lewinnek safe zone, 10 years of experience resulted in a 45% increase in precision, while adding robotic assistance resulted in a 139% increase in precision compared to the surgeon's initial performance. With greater knowledge of ideal acetabular cup position, highly accurate techniques may allow surgeons to decrease the risk of dislocation, promote durability and improve the ability to restore appropriate leg length and offset.
