No Difference in Functional, Radiographic, and Survivorship Outcomes Between Direct Anterior or Posterior Approach THA: 5-Year Results of a Randomized Trial
Authors: Nambiar Mithun , Cheng Tze E. , Onggo James R. , Maingard Julian , Troupis John , Pope Alun , Armstrong Michael S. , Singh Parminder J. 
Published: July 2021

Abstract

Background
Both the direct anterior approach (DAA) and posterior approach (PA) to THA have known advantages and disadvantages. The comparison between DAA and PA THA has been widely explored during the early postoperative period. However, few randomized trials have compared these approaches at a minimum follow-up of 5 years; doing so would be important to establish any differences in mid-term outcomes or complications.

Questions/purposes
We performed a randomized trial comparing DAA and PA in THA in terms of (1) patient-reported outcome scores, (2) quality of life and functional outcomes assessed by the EQ-5D and 10-meter walk test results, (3) radiographic analysis, and (4) survivorship and surgical complications at a minimum of 5 years follow-up.

Methods
Two hip specialist surgeons performed both DAA and PA THA using the same THA components at two hospital sites. One hundred twelve patients on the elective THA surgical waitlist were invited to participate in the study. Thirty-four patients did not meet the study's inclusion criteria and were excluded, and three patients declined to participate in the study. The remaining 75 patients who were eligible were randomized into DAA and PA groups. Thirty-seven patients were initially randomized to receive DAA THA, but two did not and were excluded, resulting in 48% (35 of 73) of patients who received DAA THA; 52% (38 of 73) of patients were randomized into and received PA THA. Over a minimum 5 years of follow-up, 3% (1 of 35) of DAA patients were lost to follow-up, and none of the patients undergoing PA THA were lost. A per-protocol analysis was adopted, resulting in further patients being excluded from analysis. Of the 73 study patients, 99% (72; DAA: 35, PA: 37) were analyzed at 1 year, 95% (69; DAA: 34, PA: 35) were analyzed at 2 years, and 72% (52; DAA: 23, PA: 29) were analyzed at 5 years. The primary outcome was the Oxford Hip Score (OHS) and WOMAC score. Secondary outcomes included the EQ-5D and EQ-5D VAS scores, 10-meter walk test results, radiographic evidence of loosening (femoral: lucency > 2 mm at the implant-bone interface, subsidence > 2 mm; acetabular: migration or change in inclination), 5-year survivorship analysis from all-cause revisions, and surgical complications. The study was powered to detect a 10-point difference in the WOMAC score, which is equivalent to the minimum clinically important difference (MCID).

Results
There were no differences in primary outcomes (OHS and WOMAC scores) or secondary outcomes (EQ-5D scores, EQ-5D VAS scores, and 10-meter walk test result) between the DAA and PA groups at the 5-year follow-up interval. The median (range) OHS at 5 years was 46 (16 to 48) for DAA and 47 (18 to 48) for PA groups (p = 0.93), and the median WOMAC score was 6 (0 to 81) for DAA and 7 (0 to 59) for PA groups (p = 0.96). The median EQ-5D score was 1 (0.1 to 1) for DAA and 1 (0.5 to 1) for PA groups (p = 0.45), and the median EQ-5D VAS score was 85 (60 to 100) for DAA and 95 (70 to 100) for PA groups (p = 0.29). There were no cases of component loosening on radiographs. There was no difference in component survival between the two approaches at 5 years (DAA: 97% [95% CI 85% to 100%] versus PA: 97% [95% CI 87% to 100%]). Eight of 23 patients in the DAA group reported decreased sensation in the lateral femoral cutaneous nerve distribution.

Conclusion
DAA and PA are both effective approaches in performing primary THA. Each approach has its associated risks and complications. The choice of THA should be based on individual patient factors, surgeon experience, and shared decision-making. Early registry data indicate DAA and PA THA are comparable, but longer-term data with larger numbers of patients will be required before one can safely conclude equal survivorship between both approaches.

Level of Evidence
Level I, therapeutic study.