Numerous approaches to hip arthroplasty have been established. The posterior approach (PA) remains widely used and is the most commonly performed approach reported in the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) [
]. The direct anterior approach (DAA) has gained interest because of its perceived advantages of earlier functional gains compared with the PA [ 1, 5, 26 ]. In the PA, the hip is accessed through the division of gluteus maximus and the short external rotator muscles [ 2, 31 ]. In the DAA, an internervous intermuscular plane between the sartorius and tensor fascia latae is used to access the hip joint anteriorly [ 26 ]. 26
Proponents of the DAA report earlier improvements in clinical and functional outcomes [
], earlier discontinuation of assistive ambulatory devices [ 2, 32 ], lower early postoperative pain levels [ 7, 30 ], lower postoperative opioid analgesia use [ 7, 32 ] with earlier discharge [ 6 ], potential for improved resource use [ 6, 7, 32 ], reduced muscle trauma [ 19 ], lower dislocation rates [ 32 ], and less variance in component placement [ 31 ]. However, DAA THA can be technically challenging and difficult to learn, with a learning curve associated with higher risk of complications such as fractures, dislocations, and nerve injuries [ 32 ]. The DAA has also been associated with some reports of longer operative times [ 8, 11, 21 ] and greater intraoperative blood loss [ 6, 29, 32 ] than the PA. Furthermore, a number of distinct complications associated with DAA have been reported, including intraoperative fractures, femoral nerve palsy leading to quadriceps weakness, and lateral femoral cutaneous nerve (LFCN) injuries [ 6, 32 ]. We previously reported the results of a randomized controlled trial (RCT) comparing the PA and DAA for THA at 3 months’ follow-up [ 6, 10, 24 ]. 6
To our knowledge, although the comparison between DAA and PA THA has been extensively evaluated during the early postoperative period, few RCTs have compared the approaches at a minimum follow-up of 5 years; doing so would be important to establish any differences in mid-term outcomes or complications. In the current study, we report the 5-year results in terms of (1) patient-reported outcome scores, (2) quality of life and functional outcomes as assessed by the EQ-5D and 10-meter walk test results, (3) radiographic analysis, and (4) survivorship and surgical complications.
Patients and Methods
The methodology of the initial trial, selection criteria, surgical technique, and perioperative and postoperative protocols were reported in detail in the index study [
]. Inclusion criteria were symptomatic unilateral osteoarthritis, Dorr femoral classification of A or B, American Society of Anesthesiologists score ≤ 3, BMI less than 35 kg/m 6 2, and age between 40 and 75 years. Patients with prior hip surgery or with anticipated complex primary surgery were excluded. Two senior arthroplasty surgeons (MSA, PJS), both of whom had experience in DAA and PA since 2010, performed all procedures. The implants for both approaches were identical (Smith & Nephew R3 acetabular system and Anthology femoral stem), with either ceramic-on-ceramic or oxinium-on-polyethylene bearing surfaces, according to surgeon preference, and minimal difference in short- to medium-term outcomes. A traction table and intraoperative fluoroscopy were used for the DAA procedures, and patients with a PA underwent an enhanced posterior capsule and short external rotator tendon repair. Patients
One hundred twelve patients on the elective THA waitlist were approached to participate in the study. Two hip surgeons out of 18 who worked at two multisurgeon hospitals were involved in the study. Based on the inclusion and exclusion criteria, 33% (37 of 112) of patients were excluded and 67% (75 of 112) were randomized. Thirty-seven patients were initially meant to receive DAA, but two did not and were excluded. Therefore, 48% (35 of 73) of patients had DAA THA and 52% (38 of 73) had PA THA.
Over 5-year follow-up, only one (3%) DAA patient was lost to follow-up, but none were lost in the PA THA group. A per-protocol analysis, rather than intention-to-treat analysis, was adopted, resulting in 34% (12 of 35) and 24% (9 of 38) of DAA and PA THA patients being excluded from analysis respectively, leaving 66% (23 of 35) and 74% (29 of 39) of DAA and PA THA patients, respectively, to be analyzed. Thirty-seven patients of one surgeon and 15 patients of the other surgeon were followed. Twenty-one patients were excluded from the primary and secondary outcome analysis; 12 patients had another lower-limb replacement, two patients had revision hip surgery (one in the DAA group for infection and another in the PA group for periprosthetic fracture), three patients died for reasons unrelated to the index THA, three patients were incapacitated (one had severe dementia, one had severe scoliosis, and one had terminal malignancy), and one patient was unable to travel long distances for follow-up (
Fig. 1). Implant survivorship of patients recruited in the study was 97% (71 of 73 patients) at the 5-year mark, with the AOANJRR having no records of further revision procedures for the excluded patients. At the 5-year follow-up interval, both groups appeared well-matched for demographic characteristics ( Table 1). Fig. 1.:
CONSORT flow chart for patient selection.
Table 1. -
Demographic characteristics of the participants by treatment group
DAA (n = 23)
PA (n = 29)
Total (n = 52)
Age in years
64 ± 11
66 ± 10
65 ± 10
BMI during recruitment in kg/m
27 ± 3
28 ± 4
28 ± 3
Data presented as mean ± SD or % (n); DAA = direct anterior approach; PA = posterior approach.
Participants were evaluated clinically at the 1-, 2-, and 5-year intervals after the index THA. A clinical evaluation at 1- and 2-year follow-up was performed by the second author (TEC), while the 5-year follow-up evaluation was conducted by the first author (MN).
The study’s primary outcome measures were the WOMAC and Oxford Hip Score (OHS) questionnaires [
]. The secondary outcome measures included assessments of health-related quality of life using the EQ-5D [ 4, 9 ] and functional performance using the 10-meter walk test. All outcome scores were performed preoperatively, 2 weeks, 6 weeks, 3 months, and 1, 2, and 5 years postoperatively. EQ-5D utility scores were calculated using United Kingdom weights. Standardized weightbearing Charnley AP pelvic and lateral radiographs were obtained for all participants at 6 weeks and 1, 2, and 5 years follow-up evaluations. A radiographic analysis was performed using the standardized terminology for reporting results according to Johnston et al. [ 12 ]. The proximal femur was divided into 14 zones according to Gruen et al. [ 18 ]. Each radiograph was assessed by two radiologists (JM, JT) for signs of cortical hypertrophy, stem loosening, calcar resorption, and femoral stem subsidence and compared with immediate postoperative radiographs. Stem loosening was defined as the combination of lucency > 2 mm at the implant-bone interface and subsidence > 2 mm, and acetabular loosening involved migration or change in inclination. Surgical complications assessed were those felt to be pertinent at 5 years of follow-up and included revision, infection, recurrent dislocation, and LFCN injury. Implant survivorship was calculated based on all-cause revision total hip replacement surgery at 5 years, consisting of the replacement of any component part. 14 Ethical Approval
Ethical approval for this study was obtained from Eastern Health, Box Hill, Victoria, Australia (approval number E11/1314), and informed consent was obtained from trial participants (trial registration number: ACTRN12614000131651).
The study was initially powered to detect a 10-point difference in the WOMAC score, which is equivalent to the minimum clinically important difference (MCID). We assumed an SD of 13.7 with 80% power and a two-tailed significance level of 5% [
]. Post-hoc analysis showed a 70% power with a two-tailed significance level of 5%. Allowing for 10% attrition, the initial study aimed to recruit 70 participants. The statistical analysis was conducted according to the per-protocol principle, with data analyzed according to group allocation. Missing outcome data were addressed via a restricted maximum likelihood estimation within linear mixed models. Linear mixed-effects models were used to analyze continuous outcomes at all timepoints. The outcomes (WOMAC, OHS, EQ-5D, and 10-meter walk test result) were categorized as the dependent variables. Group (DAA or PA) and timepoint (1-, 2-, and 5-year follow-up) were categorized as the predictor variables. Group and time were considered fixed effects with a random intercept term for each patient. Pairwise comparisons were made between treatment groups at each timepoint, and the associated p values are reported. Clinical parameters were compared between groups using the Fisher exact test for categorical outcomes and the t-test for normally distributed data. The incidences of adverse outcomes were compared using the Fisher exact test, with risk ratios and 95% confidence intervals calculated, if possible. Life table estimates of survivorship were computed using the method of Norrish et al. [ 13 ], with confidence limits computed by the method of Rothman et al. [ 22 ] by using the harmonic mean of the numbers at risk at each follow-up time point and the preceding follow-up timepoint. 27
All statistical tests were two-sided with a statistical significance level of 5%. No adjustments for multiple testing were made. Findings with p values of less than 0.05 were considered statistically significant. All analyses were performed using statistics software R (version 4.0.2, R Foundation for Statistical Computing).
OHS and WOMAC Scores
There was no difference in OHS (
Fig. 2) and WOMAC scores ( Fig. 3) across time points. 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) ( Table 2). Fig. 2.:
This box plot represents the Oxford Hip Score across all timepoints.
This box plot represents the WOMAC scores across all timepoints.
Table 2. -
Comparison of WOMAC, OHS, and secondary outcomes between treatment groups at 1-, 2-, and 5-year time points
EQ-5D VAS (0-100)
WOMAC function (0-68)
WOMAC stiffness (0-8)
WOMAC pain (0-20)
WOMAC total (0-96)
10-meter walk test, fast, in m/s
2 ± 0.2
2 ± 0.2
2 ± 0.3
2 ± 0.2
2 ± 0.3
2 ± 0.2
10-meter walk test, normal, in m/s
2 ± 0.1
1 ± 0.2
1 ± 0.2
1 ± 0.1
1 ± 0.2
1 ± 0.2
Data presented as median (range) except for 10-meter walk tests, which are mean ± SD; DAA = direct anterior approach; PA = posterior approach.
EQ-5D Scores, EQ-5D VAS Scores, and 10-meter Walk Test
At the 5-year follow-up interval, there were no differences between the groups in the EQ-5D scores, EQ-5D VAS scores, and 10-meter walk test (
Table 2). Additionally, no difference was observed between scores at the 1- and 5-year follow-up intervals.
The median (range) EQ-5D result was 1 (0.1 to 1) in the DAA and 1 (0.5 to 1) in the PA groups (p = 0.45). The median EQ-5D VAS score was 85 (60 to 100) in the DAA and 95 (70 to 100) in the PA groups (p = 0.29). The mean 10-meter walk test fast speeds were 2 ± 0.3 m/s in the DAA and 2 ± 0.2 m/s in the PA group (p = 0.94), and normal speeds were 1 ± 0.2 m/s for both the DAA and PA groups (p = 0.17).
There was no acetabular or femoral implant migration greater than 2 mm between 1 and 5 years of follow-up. One patient in the DAA group had calcar resorption (Zone 7). Three patients in the PA group had cortical hypertrophy of the proximal femur. No radiographs suggested femoral stem or acetabular component loosening.
Survival and Complications
There was no difference in implant survival between groups at all time points, with all-cause revision as an endpoint (
Table 3). At 5 years, implant survival was 97% (95% CI 85% to 100%) for the DAA group and 97% (95% CI 87% to 100%) for the PA group ( Fig. 4). Other than LFCN injury, there were no differences in complications between groups from the 3-month to 5-year follow-up period. One late infection occurred at 5 years post–index operation, resulting in revision surgery. Eight of 23 patients in the DAA group reported decreased sensation over the LFCN distribution at 5 years’ follow-up. One of these patients had not reported any symptoms in previous follow-up evaluations. The LFCN symptoms of four patients had resolved since the 2-year follow-up evaluation.
Table 3. -
Life table estimates of implant survivorship
% (lower-upper limit)
% (lower-upper limit)
DAA = direct anterior approach; PA = posterior approach.
Implant survival graph.
Patient outcome and experience of THA is influenced by the recovery process, and the surgical approach may play a role in these outcomes. Although studies have demonstrated earlier recovery in the DAA group compared with PA, there is a paucity of longer-term RCTs that compare both groups of patients. This paper aims to provide 5-year follow-up information for patients enrolled in an RCT. Such longer-term information may be relevant not only for patient education but also in guiding a surgeon’s choice of approach during primary THA. RCTs offer the prospect of comparing surgical approaches while limiting other potential sources of bias. This study reports on the 5-year follow-up results of an RCT comparing the DAA and PA for THA, expanding on our previously published early results [
]. At 1, 2, and 5 years of follow-up, there were no differences in clinical outcomes, radiographic analyses, or implant survival between the groups. Despite resolution of LFCN hypoesthesia in some patients, there was still a higher prevalence of persistent nerve injury in the DAA group than in the PA group at the 5-year follow-up interval. 6 Limitations
A key limitation of our study is patient assessment for eligibility. Only 112 patients were assessed for eligibility. This was approximately half of the 205 patients who received elective THA at our institutions during the study period. This was due to a combination of logistical issues, patient factors, and our selection criteria. Given that only 2 of 18 hip arthroplasty surgeons were involved in the study, assessing half of the primary elective THA patients may be considered a greater proportion than expected. The other hip arthroplasty surgeons in our institutions were not proficient in both approaches. Logistically, both the study surgeons and research team were required to assess patients before the intervention. Some patients were unwilling to attend additional outpatient review before recruitment, while other patients preferred to remain under the care of the initial consulting surgeon. Patient factors that automatically excluded patients without requiring further assessment included patient age, previous lower limb arthroplasties, and inflammatory or posttraumatic arthritis. Furthermore, there was a lack of patient blinding because of the difference in surgical incision sites and postoperative management protocols relating to differing hip precautions for the approaches. Although these cannot be avoided in a study of this design, it introduces a potential bias that patients may have toward a certain approach and/or the perceived benefits of the DAA. Selection criteria for the study may have also reduced the postoperative complications due to the exclusion of patients with increased BMI and medical comorbidities. Limiting BMI in the study may have favored the DAA group, since increased BMI is associated with increased complications in DAA THA [
]. Although 95% (69 of 73) of the original patients were evaluated at the 2-year timepoint, only 71% (52 of 73) were evaluated at the 5-year timepoint. This was because of the strict exclusion of patients who underwent further lower limb arthroplasty, those with other joint pathologic conditions, and those with medical morbidities that arose during the 5-year follow-up period. 28 Clinical Outcomes
We did not find a difference in primary patient-reported outcome measure scores such as OHS or WOMAC, nor in the secondary outcome scores of EQ-5D and EQ-5D VAS or 10-meter walk test between the approaches at 5 years. These results are consistent with another 5-year follow-up report by Barrett et al. [
], who compared 43 DAA patients and 44 PA patients and found no difference between approaches in terms of Harris hip score, University of California Los Angeles activity score, and Hip Disability and Osteoarthritis Outcome Score. The authors also reported similar 7-year survivorship rates and no implant loosening at 5-year follow-up. Comparing results from Cheng et al. [ 3 ] and Barrett et al. [ 6 ], it appears that gains derived from the DAA in terms of clinical outcomes during the early postoperative period are negated within 6 weeks. A recent meta-analysis of seven RCTs comparing DAA and PA THA reported better Harris hip scores at the 6-week timepoint in the DAA group than PA group, but no difference at 3, 6, and 12 months postoperatively [ 3 ]. Ultimately, although there appears to be some potential early benefits in clinical outcome scores with DAA, the intermediate and longer-term results are comparable. Hence, other factors should influence the decision to perform either approach. 25 Radiologic Analysis
We found no difference in the proportion of patients who experienced stem or cup loosening in both groups. However, the AOANJRR and Dutch Arthroplasty Registry reported an increased risk of major revisions for aseptic loosening and fracture in DAA compared with PA and lateral approaches [
]. In those studies, aseptic femoral stem loosening was postulated to be caused by difficulties with exposure, leading to inadequate femoral preparation and component undersizing. This theoretically results in implant subsidence, a lack of osseointegration, and subsequent aseptic femoral stem loosening [ 15, 33 ]. Aseptic loosening could also be the result of implant type, especially in cementless femoral stems. Janssen et al. [ 16 ] reported a stem-approach interaction, with shoulder stems having a greater risk of early aseptic loosening than anatomically shaped stems in DAA THA. Reports of femoral stem loosening may increase as longer-term results are available. 17 Survival and Complications
Our study found no difference between the groups with a 5-year implant survivorship of 97%, with revisions for one periprosthetic hip fracture and one prosthetic joint infection. This contrasts with the 5-year results reported by the AOANJRR on a much larger registry population comparing DAA and PA THA [
]. The AOANJRR identified that a greater proportion of revision surgeries were performed for implant loosening in DAA THA than in PA THA, while a greater proportion of revision surgeries were performed for recurrent dislocations in PA THA [ 1 ]. 1
The only notable difference in surgical complications between both groups was the incidence of LFCN injury in the DAA approach, where the nerve is at risk during the procedure. Our earlier report noted that 83% of patients in the DAA group developed LFCN hypoesthesia at 3 months postoperatively [
]. At 5 years of follow-up, only 35% of patients in the DAA group had persistent hypoesthesia compared with the contralateral thigh. These results were consistent with those of Ozaki et al. [ 6 ], who investigated the incidence of LFCN injuries in 122 patients who underwent DAA THA and had self-reported questionnaires at two timepoints (first survey: 12.8 months postoperative; second survey: 26.2 months postoperative). The authors found that 96% of patients had spontaneous improvement of symptoms, and the incidence of LFCN symptoms decreased from 32% to 11% (p < 0.001) during the 14-month period between surveys. The impact of LFCN symptoms on clinical outcomes is less clear. Although our earlier report did not show any correlation between LFCN injuries and worse WOMAC, OHS, or EQ-5D scores [ 23 ], Ozaki et al. [ 6 ] revealed correlations between improvement in LFCN symptoms and better quality of life in terms of the Forgotten Joint Score-12. 23 Conclusion
Both DAA and PA for THA yield good functional and radiographic outcomes and implant survivorship at 5-year follow-up. This RCT demonstrates that differences in the immediate rehabilitation period observed in our earlier study were negated in longer-term follow-up. The choice between these two THA approaches should be based on patient and surgeon preferences and surgical experience. Our results must be interpreted in light of the study limitations, especially with regard to a potential for selection bias and the lack of blinding, which may favor the DAA approach. Future studies should further stratify patient groups with regard to patient selection, perhaps by indication for THA and BMI class to aid subgroup analysis.
We thank the generous donations from the Bulley Fellowship and the Box Hill Golf Club. We also acknowledge the support of Professor Ian Davis and the Eastern Health Clinical School (Monash University). This body of research is dedicated to the work and memory of the late Mr. Michael Armstrong, who passed away while serving as the Director of Orthopaedic Surgery, Eastern Health in April 2015.
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