Does using the direct anterior approach with a standard table for total hip arthroplasty reduce leg length discrepancies? Comparative study of traction table versus standard table

Introduction: Primary total hip replacement (THR) comes with a risk of leg length discrepancy (LLD), which occurs in 25 % of cases, especially when the surgery is done using an anterior approach on a traction table, since it is not easy to verify the lengths of the legs. By doing the anterior approach on a standard table an intraoperative visual evaluation of leg lengths can be done after the trial implants are in place. As far as we know, the ability to set the leg length has not been compared between procedures done on a standard table or a traction table. This led us to carry out a retrospective comparative study to determine whether using a standard table for anterior THR will 1) allow better control over leg length, 2) increase the risk of incorrect implant positioning, 3) increase the surgical complication rate.

Hypothesis: Anterior THR on a standard table will allow better control over leg length than anterior THR on a traction table.

Material and methods: This single center retrospective study included 266 THRs done between January 1, 2018 and November 2, 2019 for primary (n=219) or secondary (n=47) hip osteoarthritis. The 137 cases done with a traction table were compared to the 129 cases with a standard table. The two groups were comparable in terms of age, sex, body mass index, indication and bilateral implants. They were not comparable in the surgeon experience (more junior surgeons in the standard table group [p<0.001]) and types of implants used (more cementless cups and stems in the standard table group [p=0.001]). Radiographs were used to measure the LLD, cup inclination, and femoral stem placement in the frontal plane. Any early complications were documented. The target was for the operated leg to be the same length as the contralateral leg, which was defined as within 10mm of each other.

Results: The mean postoperative LLD was comparable between the traction table group 1.56±7.32 mm (min -15.6 max 17.2) and the standard table group 0.53±6.93 mm (min -16.4 max 13.7) (p=0.24). In the traction table group, 81 % (111/137) of patients had legs of the same length, versus 84 % (109/129) in the standard table group (p=0.7). Cup inclination was comparable with a mean of 40.4±7.1 degrees (min 23.4; max 58.5) in the traction table group versus 39.3±7.5 degrees (min 19.9; max 60.9) in the standard table group (p=0.21). The frontal position of the femoral stem was comparable between groups with a mean of 0.09±0.45 degrees (min -1; max 3.98) in the traction table group versus 0.08±0.59 degrees (min -4.97; max 1.93) in the standard table group (p=0.86). There were 5 complications (3.7 %) in the traction table group versus 11 (8.5 %) in the standard table group (p=0.16).

Conclusion: Use of a standard table to carry out THR by the direct anterior approach does not provide better control over leg length than using a traction table, subject to preoperative planning. When doing the procedure on a standard table, the implant placement is at least comparable, with a similar risk of complications.

Level of evidence: III; case matched study.