No Learning Curve of the Direct Superior Approach in Total Hip Arthroplasty.

OBJECTIVES: To assess the learning curve of the direct superior approach (DSA) for total hip arthroplasty (THA) and to compare surgical, clinical, and radiological results with a matched control group using the mini posterior approach (MPA). METHODS: A prospective cohort study was performed from October 2016 to May 2017 including our first 52 patients undergoing THA using the DSA. Patients with primary osteoarthritis or osteonecrosis and a body mass index (BMI) < 35 who were eligible for surgery were included. As a control group, 52 patients who underwent the MPA were included, matched based on age, BMI, and ASA classification. In the DSA group, damage to the iliotibial tract and the distal external rotators, including the external obturator and quadriceps femoris muscles, was avoided. Outcome measures were collected, including surgical time, blood loss, postoperative pain, length of stay, implant position, use of walking aids, patient reported outcome measures (PROM), and complications. Unpaired t-tests were used to analyze differences between the DSA and the MPA group in surgical time, blood loss, length of stay, and acetabular and femoral component position. χ2 -tests were used to analyze mobility and the number of complications. Two-way repeated measures ANOVA was used to analyze pain scores and PROM between the DSA and the MPA groups. RESULTS: The mean surgical time of 61 min (SD 8) in the DSA group was longer (P < 0.001) compared to that in the MPA group, 46 min (SD 12). No differences were found in blood loss, postoperative pain, or mean length of stay in the hospital. After 6 weeks, 94% of the patients in the DSA group were able to walk inside their home without walking aids compared to 90% in the MPA group. The mobility scores were not different after follow up of 6 weeks and 1 year (P = 0.12 and P = 0.36 respectively). All PROM improved postoperatively in both the DSA and the MPA group (P < 0.01). Acetabular cup and femoral stem position were not compromised by the DSA. Complications included two Vancouver B2 periprosthetic fractures in the DSA group, of which there was one surgical-related fracture and one fracture after a traffic accident. Complications in the MPA group included one periprosthetic fracture, two hip dislocations, and one ischial neuropathy. No infections or thromboembolic events were observed. The 1-year complication rate was not different between the MPA and DSA groups (P = 0.40). CONCLUSION: The DSA can be safely introduced as no learning curve in the prosthesis position or the complication rate was found.