HP11: THE USE OF TRANSVERSE ACETABULAR LIGAMENT (TAL) AS AN ANATOMICAL LANDMARK FOR ACETABULAR COMPONENT ORIENTATION IN PRIMARY TOTAL HIP REPLACEMENT

Abstract

Published data has shown that only 45% of acetabular components were in an acceptable position, where positioning was determined clinically by the surgeon intra-operatively. The aim of this study is to assess the accuracy of cup orientation, using computer tomography (CT), when the TAL is used as the intra-operative guide.

In this prospective study, the TAL was used as the anatomical reference for positioning the cup. The TAL was graded 1 to 4 based on visibility of the ligament. The version and abduction angles were estimated clinically and recorded by the surgeon after insertion of the cup. Post-operatively the true orientation of the cup was measured using CT. Statistical analyses were carried out to calculate the difference between the intra-operative estimation of cup orientation and the true cup position as measured by CT. Ethical approval was granted and informed consent was obtained for all the patients.

Forty-eight hips have been studied to date. The TAL was easily identifiable in the majority of cases. Overall, the cup version was under-estimated by the surgeon when the TAL was utilized as the anatomical landmark. The true mean acetabular component version was 26.5 degrees [range from 11 to 41 degrees]. The true mean abduction angle was 43.6 degrees [range from 35 to 55 degrees]. The mean difference between surgeon estimation and CT measurement for cup version was 4 degrees of underestimation [range from 14 degrees of underestimation to 11 degrees of overestimation]. The mean difference for abduction angle was 0.1 degrees [range from 14 degrees of underestimation to 10 degrees of overestimation]. When using TAL as an intra-operative guide, 64% of acetabular components were within the target range of 15 to 30 degrees of anteversion, as measured by CT, compared to 45% in previously published study (Wines, A & McNicol, D, J. Arthroplasty, 2006).

TAL improves the accuracy of acetabular component version, when utilized as an anatomical landmark during cup insertion in primary total hip arthroplasty. It is reliable and easily identifiable in the majority of cases.