More cups likely to be in safe zone with transverse acetabular ligament as a THA landmark

Issue: April 2013

CHICAGO —Transverse acetabular ligament aids placement of acetabular cups during total hip arthroplasty and limits variability in cup anteversion, according to investigators from Belgium and the Netherlands.

Perspective from Steven T. Woolson, MD

Although some authors with published research on this topic argue that the transverse acetabular ligament (TAL) is hard to find intraoperatively, Geert Meermans, MD, of Bercham, Belgium, disagreed with them in comments he made during a presentation at the American Academy of Orthopaedic Surgeons Annual Meeting, here.

“It is always there. It is patient specific. It is independent of patient position during the operation. It is easy to use,” Meermans said. “You don’t need any external instrumentation and you don’t need expensive navigation.”

Geert Meermans

In the randomized controlled trial performed in 2009, 80 patients were randomized to have their acetabular cups placed either freehand (FH) or via the method that uses the TAL location to determine cup placement. They were all operated on in the lateral decubitus position via a posterior approach and underwent cemented total hip arthroplasty (THA) with a 28-mm head.

“At the end, we used transosseous suture to repair the posterior capsule,” he said.

If the TAL was not visible, as occurred in three cases, Meermans said he got a better view of the ligament using a small reamer to clear any small osteophytes before he began reaming the acetabulum.

Investigators who were blinded to the surgical technique used measured cup position intraoperatively and postoperatively on radiographs taken 6 weeks, 3 months, 1 year and 2 years postoperatively.

For purposes of this study, the safe zone was defined as cup anteversion of 15° and abduction of 40°, plus or minus 10° for both measurements. According to Meermans, the mean anteversion was measured at 23° in the FH group and 18º in the TAL group, a difference that was significant, however the differences seen in the abduction angles for both groups was not significant.

“Nine cups were placed outside the safe zone for the FH group. All the cups were in the safe zone in the TAL group,” he said, showing a slide of a scatter plot of cup abduction results in both groups. “You can see more outliers in the FH group,” he said.

One patient in the FH group whose anteversion angle was 33° dislocated anteriorly, which was the only dislocation in the series.

Reference:

Meermans G. Paper #34. Presented at: American Academy of Orthopaedic Surgeons Annual Meeting; March 19-23, 2013; Chicago.

Disclosure: Meermans has no relevant financial disclosures.

Perspective

Steven T. Woolson, MD

I actually published on this and my partner and I tried to find the transverse acetabular ligament in a consecutive series of patients and he was not able to find it, I think, in two thirds or half of the patients. I couldn’t find it because of spurs — inferior osteophytes in about 15% to 20% [of patients]. But if you are able to find it, it is helpful.

Reference:

Epstein NJ. Clin Orthop Relat Res. 2011. doi:10.1007/s11999-010-1523-1.

Steven T. Woolson, MD

Session moderator

Palo Alto, Calif.

Disclosures: Woolson is on the speaker’s bureau for and is a paid consultant to Medical Compression Systems and Johnson & Johnson, has stock/stock options with Medical Compression Systems and receives research/institutional support as a principal investigator for Johnson & Johnson.