The Transverse Acetabular Ligament: Optimizing Version

Abstract

In total hip arthroplasty (THA), excessive retroversion is associated with posterior instability, anterior impingement, and resultant groin pain. Excessive anteversion can lead to anterior instability and posterior impingement. The transverse acetabular ligament straddles the inferior limit of the bony acetabulum. It is a strong load-bearing structure and, in the normal hip, in association with the labrum, provides part of the load-bearing surface for the femoral head. It is our hypothesis that the transverse acetabular ligament defines normal version for the acetabulum. In Belfast, we found that using the transverse acetabular ligament helped reduce our primary dislocation rate from 3.7% to 1%. The key is good intraoperative exposure. A grading of 1 to 4 was based on 1000 consecutive cases: (1) normal transverse acetabular ligament easily visible on exposure of the acetabulum, 49%; (2) covered by soft tissue, 35.1%--cleared by blunt dissection; (3) covered by osteophytes, 15.6%--cleared using an acetabular reamer; (4) no transverse acetabular ligament identified, 0.3%. As can be seen, the transverse acetabular ligament is only immediately visible in 49% of cases. In the other 51%, soft tissue or bone must be cleared to define the ligament. The advantages of the transverse acetabular ligament are many. It is independent of patient positioning. The cup version can be individualized by the patient. The surgeon can avoid estimating version angle of 15° to 20° intraoperatively. It is easy to teach and consistently present. It is valuable in minimally invasive surgery. Using the transverse acetabular ligament provides an acceptable dislocation rate with the posterior approach. If the cup is cradled by the transverse acetabular ligament, it helps restore acetabular joint center. However, the transverse acetabular ligament does not help with inclination. We recommend 35° of operative inclination when using the posterior approach.