Direct Anterior Versus Anterolateral and Posterior Approaches to Total Hip Replacement: Comparative Accuracy of Acetabular Implant Placement and Early Clinical Outcomes

Background Different surgical approaches used in total hip arthroplasty (THA) include a direct anterior approach (DAA), anterolateral approach (AL), and posterolateral approach (PL). However, the acetabular cup position varies according to surgical view, surgical table, and patient position for each approach. This study is aimed to compare acetabular cup position in THA under different approaches, including surgical time, blood loss, and postoperative complications.


Introduction
Total hip arthroplasty (THA) is one of the most successful and widely used orthopedic procedures, featuring early recovery and shorter rehabilitation [1]. Several techniques have been developed for THA, including direct anterior approach (DAA), anterolateral (AL), and posterolateral (PL) [2].
Cup alignment plays a critical role in successful THAs due to complications associated with implant impingement, bearing wear, and dislocation [3]. However, different surgical approaches in uence the view cup placement. DAA for THA is an intermuscular approach with less surgical trauma, faster recovery, and more accurate prosthesis placement [4,5]. Historically, many surgeons have performed DAA THA with or without a speci c orthopedic table or intraoperative uoroscopy. Yuya et al. compared DAA with AL and showed that the AL group had a better safe zone than the DAA group [6]. Hu et al. reported that DAA allowed better cup orientation than PL [7], while Maeda et al. found no difference in cup alignment between DAA and PL [8]. Based on the above studies and the known advantages and disadvantages of the three surgical approaches, the ideal surgical approach for THA still remains controversial, and no direct comparisons exist in the literature. Therefore, the aim of this study was to compare and analyze differences in cup alignment among these three surgical approaches.

Materials And Methods
This study was a retrospective and comparative study using a database from the China Medical University which covered patients who underwent THA using DAA, AL and PL approaches for the period Jan 2017 to Dec 2018. We collected 231 primary THAs performed at our hospital. The inclusion criteria consisted of patients with avascular necrosis, osteoarthritis, infection, DDH and post-traumatic arthritis, such as acetabular fracture or hip fracture, and surgery performed by several experienced surgeons willing to partake in the study. Exclusion criteria consisted of prior revision surgery or cancer metastasis reconstruction. Post-operative follow up was at least one year.
The clinical evaluation retrospectively recorded operation time, blood loss, length of stay, and complications (postoperative infection, dislocation, and intraoperative fractures) for each group. Standing anteroposterior (AP) pelvic radiographs for hips and lateral radiographs of the proximal femur were routinely obtained on postoperative day 1 and at 3-12 months. The 3-month standing AP and lateral radiographs were used to evaluate cup inclination angle, while cup anteversion was assessed using the Cup Anteversion Inclination App (OrthoGate CC, Western Cape, South Africa) (https://itunes.apple.com/us/app/cupanteversioninclinationapp/id1448919739). The app is based on Widmer's method [9], which has been shown to be accurate compared with other methods [10]. Evaluation was performed by two independent junior orthopedic surgeons (Ying-Lin Chen and Shang Lin Hsieh) in a blinded fashion. Cup positioning within the safe zone was de ned following Lewinnek et al. [11], who found an increased dislocation rate in cups placed outside anteversion angles of 5°-25° and 30°-50° of inclination. Therefore, we de ned this range as the safe zone and all other ranges as outliers.
The surgical approach was assessed individually by each surgeon. However, we did not use DAA for cases with deformed femoral neck-shaft, hip contracture, stiff lower lumbar spine, Crowe grade III or IV hip dysplasia, any history of hip osteotomy or osteosynthesis.

Surgical technique for minimal invasive anterolateral (AL) approach
We placed patients in a lateral decubitus position, then exposed their hip joint using the Watson-Jones interva, as suggested by Rottinger et al, [12]. The anteversion and inclination of the cup were determined by aligning the guide rod [13]. Fluoroscopy was not used intraoperatively throughout this course.

Surgical technique for posterolateral (PL) approach
We rst placed patients in a lateral decubitus position and then made a posterior skin incision. Tensor fascia lata, piriformis tendon, and the short external rotator muscles were released to expose the joint capsule. After assessing the direction of the femoral axis using a canal nder, femoral rasping and trial stem insertion were performed. We checked the stability and lower limb length without uoroscopy. Cup anteversion and inclination were assessed using a mechanical acetabular alignment guide rod [13]. After cup and stem insertion, the muscle-capsular ap and short external rotators were repaired as suggested by Pellicci et al. [14].
Surgical technique for direct anterior approach All DAA patients were placed in a supine position on the Judet-type orthopedic table (Hana table, OSI, USA) and intraoperative uoroscopy was used for con rmation of the following steps: nal acetabular reaming, acetabular cup placement, trial stem insertion, con rmation of leg length discrepancy after temporary reduction, and nal implant placement, as suggested by Matta et al. and Nakamura et al. [4,15] (Fig. 1).

Statistical analysis
We compared implant alignment and clinical outcomes among DAA, AL, and PL groups. Data are presented as raw numbers and percentage (%), mean (SD), or odds ratio (OR), with 95% con dence interval (CI) where applicable. Continuous scales were compared with a one-way ANOVA followed by Scheffe's post hoc test and categorical variables were compared with a Fisher's exact probability test. A univariate logistic regression was performed to estimate the odds ratio of cup alignment in the safe zone among all groups. SAS version 9.4 (SAS Institute, Cary, NC, USA) was used for all analyses. A two-sided P value < 0.05 was considered statistically signi cant.

Results
We assessed 121 females and 110 males. The mean age at surgery was 60.2 years old (range: 20-92 years). The primary diagnosis was osteoarthritis in 102 cases, osteonecrosis in 68 cases, rheumatoid arthritis in 15 cases, traumatic arthritis in 7 cases, and Crowe type III/IV in 2 cases. DAA, AL, and PL were used for 64, 96, and 71 patients, respectively. The patient's demographic data, perioperative factor, and outcome for these different approaches are shown in Table 1.

Complications
We found two periprosthetic joint infections, one greater trochanteric fracture, two calcar fractures, one postoperative dislocation, one post-operative femoral fracture, and two symptomatic leg length discrepancies. For overall complication rate, PL showed the highest complication rate (9.9%), followed by DAA (3.1%) and AL (1%) groups ( Table 1). The larger complication rate in the PL group may be due to patients that were older, more likely to be female, had more traumatic arthritis, and more complicated Crowe type deformity compared with other groups.

Cup position
The  Table 2). The cup was in the safe zone in 96.7% of the DAA group, 74% of the AL group, and 56.3% of the PL group (Fig. 2). DAA, direct anterior approach; AL, anterolateral approach; PL, posterolateral approach Table 3 presents the odds ratio and 95% con dence intervals for cup alignment in the safe zone associated with all groups. Compared with DAA group, AL group had the odds ratio of 2.2 out of the safe zone (95% CI 1.1-4.2). Furthermore, the odds ratio of PL group falling outside the safe zone was 24 (95% CI 5.4-106.0).  Data were analyzed by univariate logistic regression.

Discussion
Our study indicates that DAA with a special table was a reliable approach to reduce variation in cup position during inclination, anteversion angle, and comparing lateral lying in PL and AL approaches. Acetabular component anteversion may vary among surgical approaches. Variable cup position for AL or PL approaches may be due to the oppy and tiling lateral lying posture [16]. The lateral lying position is the most common position during THA surgery and the patient should be well xed to limit intraoperative motion. However, it is di cult to accurately measure pelvic direction on the table [17]. Schwarzkopf et al. found that intraoperative roll resulted in implant placement outside the safe zone [18][19][20]. The supine position can provide a more predictable pelvic orientation, particularly when using uoroscopy to check the position of the pelvis and acetabular implants during surgery. Further, the acetabular alignment guide is not always accurate [21,22]. Minoda et al. tested 15 alignment guides from 7 manufacturers and found that alignment guides can decrease cup anteversion (mean of 6° and maximum of 12°) and increase cup abduction angle (mean of 2° and maximum of 4°).
We assessed DAA-THA using both a speci c orthopedic table and standard operation table. A systematic review conducted by Sarraj et al. [23] that collected 44 studies concluded that speci c orthopedic tables and standard operation tables present similar outcomes and complications. However, intraoperative blood loss, surgical time, and intra-operative fracture rate were greater in the speci c orthopedic table group than in the standard operation table group [23].
Intraoperative uoroscopy may play a critical role in in uencing cup position. Goodman et al. [24] showed cup position in DAA-THA results in lower cup angle variation in groups with intraoperative uoroscopy compared to those without. However, Joshua et al. evaluated acetabular cup position and limb length discrepancy in 265 patients who underwent surgery with or without uoroscopy and found no signi cant difference in acetabular inclination, anteversion, and postoperative limb length discrepancy (LLD) between the two DAA-THA groups [25]. Based on these ndings, the impact of uoroscopy usage on cup angle is still controversial.
A previous study found that DAA was associated with a larger percentage of acetabular cups placed within the "safe" zone of alignment when using uoroscopy [1], which corroborates our ndings. However, there is no clear hierarchy in clinical outcomes of surgical approaches to THA. Current evidence comparing outcomes with anterior versus posterior THA demonstrates no clear superiority of either approach [15]. A multi-center prospective cohort study by Meneghini et al. tested whether surgical approach was associated with early THA failure [26]. They found that early femoral component loosening was commonly associated with DAA and direct lateral approaches compared with the posterior approach. Although the differences were not signi cant, early femoral periprosthetic fractures were more common with DAA than posterior and direct lateral approaches [26]. In our study, there were fewer fracture occurrence which may be due to the continuous intraoperative uoroscopy which also lengthens DAA surgery time.
Experienced surgeons can improve THA surgery procedures, including exposure of the acetabulum and femur [16]. Therefore, an effective team familiar with the work ow, a stable position during operation, intraoperative imagery, such as uoroscopy or navigation to con rm implant position, and checkpoints for each surgical procedure can improve outcomes and reduce complications in hip arthroplasty.
A limitation of this study was that it was retrospective. Within the same group of surgeons, biased patient selection, lack of randomness, and varying learning curves in surgical techniques may have biased our results. For complex femoral or acetabular deformity, we chose the PL approach. Many professionals argue that posterior capsulectomy causes posterior dislocation, while skilled repairing of the capsule can lower dislocation rate [27,28]. Our data are somewhat contradictory to this notion since only one dislocation occurred in our group. Finally, our follow-up period was one year, which is relatively short to identify de nitive long-term outcomes.

Conclusion
We conclude that muscle preserving THA by DAA using a special table is a reliable procedure for