Quantifying the Relationship Between the Transverse Acetabular Ligament and the Radiographic Teardrop

The transverse acetabular ligament (TAL) has been described as an anatomic landmark to guide in the positioning of the acetabular component during total hip arthroplasty. On plain films, the radiographic teardrop (RT) has similarly been used as a measure of appropriate cup positioning. The goal of this study is to quantify the distance and location between the anatomic TAL and RT landmarks to aid in the positioning of acetabular component.

Sixteen randomly selected cadaveric pelvises (eight males, eight females) underwent dissection. Radiographic markers were placed bilaterally at the anteromedial insertions of the TAL, and true anteroposterior pelvic radiographs of the cadavers were obtained. Distances between the markers and the lateral borders of the RT were measured.

The mean distance between the anteromedial insertion of the TAL and the lateral border of the RT in the male specimens was 11.8 (99% confidence interval, 11.4-12.2) mm. In the female specimens, the TAL to RT distance was shorter, with a mean of 8.4 (99% CI, 7.2-9.6) mm. There was a statistically significant difference between male and female cadavers (P < .01).

The distance between the RT and TAL differs between males and females. Understanding the distance between these anatomic and radiographic landmarks should aid surgeons in obtaining a more accurate degree of acetabular component medialization and can serve as a guide to minimize overmedialization in order to achieve more accurate and reproducible placement of acetabular components during a total hip arthroplasty.