Is transverse acetabular ligament an anatomical landmark to reliably orient the cup in primary total hip arthroplasty?

SummaryIntroductionAccurate positioning of the acetabular cup in primary total hip arthroplasty is critical to decrease the rate of dislocation. Inaccurate orientation of the cup is the most common error during this procedure. Target acetabular orientation is still controversial. An original study found a dislocation rate of 0.6% when the cup was aligned with the transverse acetabular ligament (TAL).HypothesisTAL is a patient-specific anatomical landmark and a tool for cup orientation.Materials and methodsEight cadaveric pelves (14 hips included for study) were harvested in toto at our research laboratory. Anatomical versions of the TAL, labrum and horns were measured in relation to the anterior pelvic plane. A navigator sensor and an optoelectronic device (Motion Analysis™) were used.ResultsAnatomical versions of the TAL, horns and labrum averaged 1.9° (range, −8° to +13.3°), 3° (range, −12.2° to 14°), and 26.3° (range, 17.4° to 41.8°), respectively.DiscussionTo our knowledge, this is the first study to report the orientation of the periacetabular soft-tissues. TAL anteversion was outside the safe zone described by Lewinnek, while labrum anteversion was within this safe-zone. We discuss the reference used, Lewinnek's safe zone, and functional orientation of the implants. Lewinnek's safe-zone does not seem to be valid. The TAL seems to be a specific reference for each patient but its reliability must still be confirmed as an adequate reference for positioning the cup in total hip arthroplasty.Level of evidenceLevel IV Prospective study.