Aims. Excellent outcomes have been reported following CT-based robotic arm-assisted total hip arthroplasty (rTHA) compared with manual THA; however, its superiority over CT-based navigation THA (nTHA) remains unclear. This study aimed to determine whether a CT-based robotic arm-assisted system helps surgeons perform accurate cup placement, minimizes leg length, and offsets discrepancies more than a CT-based navigation system. Methods. We studied 60 hips from 54 patients who underwent rTHA between April 2021 and August 2023, and 45 hips from 44 patients who underwent nTHA between January 2020 and March 2021 with the same target cup orientation at the Department of Orthopedic Surgery at Ozu Memorial Hospital, Japan. After propensity score matching, each group had 37 hips. Postoperative acetabular component position and orientation were measured using the planning module of the CT-based navigation system. Postoperative leg length and offset discrepancies were evaluated using postoperative CT in patients who have unilateral hip osteoarthritis. Results. The absolute differences in radiological inclination (RI) and radiological anteversion (RA) from the target were significantly smaller in rTHA (RI 1.2° (SD 1.2°), RA 1.4° (SD 1.2°)) than in nTHA (RI 2.7° (SD 1.9°), RA 3.0° (SD 2.6°)) (p = 0.005 for RI, p = 0.002 for RA). The absolute distance of the target’s postoperative centre of rotation was significantly smaller in the mediolateral (ML) and superoinferior (SI) directions in rTHA (ML 1.1 mm (SD 0.8), SI 1.3 mm (SD 0.5)) than in nTHA (ML 1.9 mm (SD 0.9), SI 1.6 mm (SD 0.9)) (p = 0.002 for ML, p = 0.042 for SI). Absolute leg length and absolute discrepancies in the acetabular, femoral, and global offsets were significantly lower in the rTHA group than in the nTHA group (p = 0.042, p = 0.004, p = 0.003, and p = 0.010, respectively). In addition, the percentage of hips significantly differed with an absolute global offset discrepancy of ≤ 5 mm (p < 0.001). Conclusion. rTHA is more accurate in cup orientation and position than nTHA, effectively reducing postoperative leg length and offset discrepancy. Cite this article: Bone Jt Open 2024;6(1):3–11

Introduction. Body mass index (BMI) is a topical area of interest in the field of lower limb arthroplasty. It has been well established that BMI can influence post-operative outcomes. This study compares post-operative outcomes, including satisfaction rates, length of stay (LOS) and radiographic findings in different BMI groups following total hip arthroplasty (THA). Methods. We retrospectively evaluated all non-navigated THAs performed at our institution from 2006–2016. Case-notes were reviewed for dichotomised satisfaction score, LOS and radiographic parameters including inclination, anteversion, limb length discrepancy (LLD) and offset discrepancy. Patients were classified into 4 groupings based on BMI (underweight (<24.5), healthy (24.5–30), obese (30–40), severely obese (>40)). Appropriate statistical analyses were performed to identify between group differences. Results. A total of 6874 patients were included for analysis, (Male=2807, Female=4067, Age = 68.1, BMI=29.60). Satisfaction rates at 3 months and 1 year and LOS according to BMI are displayed in Table 1. Radiographic findings grouped by BMI are displayed in Table 2. Discussion/Conclusion. Satisfaction rates for all categories of BMI were excellent at 3 months (96.90%-98.02%) and 12 months (95.94%-98.32%), with no clinically significant differences between groups. BMI was associated with a significantly longer LOS for the underweight and the severely obese compared to the healthy group. There was no clinically significant influence of BMI on any of the radiographic findings reported. The obese and severely obese groups were significantly younger than the underweight and healthy groups, indicating BMI does appear to have an effect on the age where THA is considered a suitable treatment option in this patient group. For any figures or tables, please contact the authors directly