Abstract
Introduction
The aim of this study was to assess the accuracy of aligning the cup with the transverse acetabular ligament (TAL) in total hip arthroplasty (THA) and the reproducibility of this procedure by using computer-assisted navigation.
Methods
Between January 2011 and March 2012, 75 patients (81 hips) underwent primary THA using the posterolateral approach at our hospital. We excluded 4 hips with a history of pelvic osteotomy; thus, the study included 77 hips. We measured the anatomical anteversion of the TAL intraoperatively by aligning the inferomedial rim of the cup trial with the TAL using computer-assisted navigation. We set the abduction to 45° at measure of the anteversion of the TAL. Measurements for each hip were independently performed thrice by 2 surgeons chosen among 1 expert and 6 non-experts. The surgeon performing the measurement was blinded during this process; the navigation screen was turned away from the surgeon's field of view. Anatomical inclination and anteversion were measured with reference to the functional pelvic plane. The intraclass correlation coefficient (ICC) was used to assess intra- and inter-observer reliability. The mean value of all 6 measurements was used to determine the anteversion of the TAL in each hip.
Results
The TAL was identified in 83% of the cases (64 of 77 hips). Intra-observer reliability was high for both the expert surgeon (ICC(1.1) = 0.851) and the non-expert surgeons (ICC(1.1) = 0.825). Inter-observer reliability was moderate (ICC(2.1) = 0.452). The mean difference in the anatomical anteversion measured by 2 surgeons was 7.0° (5.3°) (range, 0.3–21.3°). The mean anatomical anteversion of the TAL was 20.9° (7.0°) (range, 9.0–48.3°).
Discussion and Conclusions
Recently, reports have suggested that the TAL can be used as a reference for determining a patient's native acetabular anteversion; the position of the cup can then be customized so that the face of the acetabular component is parallel to the TAL. We measured the anatomical anteversion of the cup trial aligned with the TAL using computer-assisted navigation and assessed the reproducibility of the alignment. Intra-observer reliability was high, and each surgeon was able to align the cup according to his target for of the TAL anteversion. However, inter-observer reliability was only moderate. This is because the TAL is a short ligament with some thickness, and the methods employed to align the cup trial with the TAL may differ among surgeons. The smallest anteversion of the TAL was 9°, and retroversion was not observed in any of the cases. Therefore, in our opinion, the TAL is useful as a reference for not positioning the cup in retroversion. However, in some cases with an excessive posterior pelvic tilt, the anteversion of the TAL may have been excessive and not necessarily optimal. Therefore, aligning the cup with TAL may not be the ideal method for all cases.
