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. Patient clinical outcomes were assessed using the Western Ontario and McMaster Universities Arthritis Index (WOMAC), imaging follow-up, and if any complications arose at one year post surgery. The modern uncemented cup (Trilogy Acetabular Hip) and M/L Taper Hip Prosthesis (Zimmer Biomet,Warsaw, IN, USA) were used for all hips.
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 , which has been shown to be accurate compared with other methods . 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 defined following Lewinnek et al. , who found an increased dislocation rate in cups placed outside anteversion angles of 5°–25° and 30°–50° of inclination. Therefore, we defined 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, . The anteversion and inclination of the cup were determined by aligning the guide rod . Fluoroscopy was not used intraoperatively throughout this course.
Surgical technique for posterolateral (PL) approach
We first 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 finder, femoral rasping and trial stem insertion were performed. We checked the stability and lower limb length without fluoroscopy. Cup anteversion and inclination were assessed using a mechanical acetabular alignment guide rod . After cup and stem insertion, the muscle-capsular flap and short external rotators were repaired as suggested by Pellicci et al. .
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 fluoroscopy was used for confirmation of the following steps: final acetabular reaming, acetabular cup placement, trial stem insertion, confirmation of leg length discrepancy after temporary reduction, and final implant placement, as suggested by Matta et al. and Nakamura et al. [4, 15] (Fig. 1).
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% confidence 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 significant.