Anterior pelvic plane registration accuracy and cup position measurement using ultrasound- and pointer-based navigation in primary total hip arthroplasty

Abstract

BACKGROUND:

Incorrect cup positioning in primary total hip arthroplasty is known as a risk factor for early implant failure. The use of navigation systems leads to more accurate cup positioning.

OBJECTIVE:

The aim of this study was to compare the registration accuracy of the anterior pelvic plane and the measurement accuracy of the definite cup position for a pointer computer-assisted orthopaedic navigation system (P-CAOS) and an ultrasound-based navigation tool (US-CAOS) in an intra-individual study design.

METHODS:

Anterior pelvic plane registration was performed in 44 patients receiving a primary total hip arthroplasty with P-CAOS and US-CAOS. The cup implantation was performed using US-CAOS. Intraoperatively, the cup position was assessed using P-CAOS and US-CAOS. The postoperative cup position was determined via CT scan. Inclination and anteversion errors were calculated using intraoperative values and CT data. All operations were performed by a single, high-volume surgeon using a minimally invasive anterolateral approach.

RESULTS:

The mean inclination error was 0.9 ${}^{\circ }$ in the US-CAOS group and $-$ 1.1 ${}^{\circ }$ in the P-CAOS group. This was not statistically significant. The mean anteversion error was significantly reduced ( $p<$ 0.001) in the US-CAOS group (1.4 ${}^{\circ }$ ) compared to the P-CAOS group ( $-$ 8.0 ${}^{\circ }$ ). Significantly more cups (23 of 44; 52%) in the P-CAOS group were outliers regarding to the defined anteversion error range of 15 ${}^{\circ }$ $\pm$ 10 ${}^{\circ }$ . Outliers in the US-CAOS group amounted to two (of 44; 5%) ( $p<$ 0.001). The number of outliers regarding the inclination error range of 40 ${}^{\circ }$ $\pm$ 10 ${}^{\circ }$ , did not differ significantly between the P-CAOS (2; 5%) and US-CAOS (1; 2%) group.

CONCLUSION:

We were able to show a systematic anterior pelvic plane registration error in this intraindividual study design. US-CAOS based APP landmark registration showed to be significantly more precise compared to P-CAOS registration. The anteversion error of the cup using US-CAOS showed to be significantly reduced compared to the P-CAOS method.