# Impact of Supine, Standing, and Sitting Postures on Acetabular Component Orientation in Total Hip Arthroplasty

## TL;DR

This study shows that hip implant placement varies with posture, suggesting the need for dynamic assessments during total hip arthroplasty.

## Contribution

The study demonstrates significant posture-related changes in acetabular component orientation, advocating for dynamic pre-operative evaluations.

## Key findings

- Acetabular component orientation varies significantly between supine, standing, and sitting postures.
- Sitting posture showed a mean anatomical acetabular anteversion of 30.93°, significantly higher than standing (13.07°) and supine (11.04°).
- Dynamic assessments using standing and sitting radiographs are recommended to improve implant placement accuracy.

## Abstract

Introduction: Total hip arthroplasty (THA) is a highly effective surgical procedure aimed at relieving pain and restoring function in patients with severe hip joint disorders, such as osteoarthritis, osteonecrosis, and developmental dysplasia of the hip (DDH). The primary goals of THA are to alleviate pain, improve joint function, and enhance the quality of life by providing a stable and well-functioning hip joint. Accurate orientation of the acetabular component is critical for the success of THA, ensuring optimal joint mechanics, reducing the risk of complications such as dislocation and wear, and enhancing implant longevity. Postural changes significantly influence the orientation and stability of the acetabular component. Traditional supine evaluations may not accurately reflect the functional alignment during daily activities, necessitating more dynamic assessment methods.

Materials and methods: The study was conducted at a tertiary care hospital in Chennai, Tamil Nadu, India, from March 2018 to October 2019. It was a prospective study involving 27 patients who underwent primary THA. Exclusion criteria included bilateral or revision THA, a history of spine or hip surgery, neurological or musculoskeletal disorders, or lower limb deformities. Computed tomography scans were performed in supine, simulated standing, and sitting postures. Pre-operative and post-operative evaluations included standing and sitting lateral lumbosacral spine radiographs. Measurements at the spinopelvic junction evaluated spinal balance and pelvic compensation. The anatomical acetabular anteversion (AAA) was determined in supine, standing, and sitting positions using CT scans.

Results: The study included 27 patients aged 19 to 66 (mean age 37). Most patients (17, 63%) were between 21-40 years old. Osteoarthritis was the most common indication for THA (15, 55.6%), followed by osteonecrosis (six, 22.2%), DDH (four, 14.8%), and post-traumatic arthritis (two, 7.4%). Spinopelvic mobility assessment showed 15 (55.6%) participants with normal mobility, eight (29.6%) who were hypermobile, three (11.1%) stiff, and one (3.7%) who were severely stiff. Significant variability in acetabular component orientation was observed across postures: mean supine AAA was 11.04° (SD 14.44°), standing AAA was 13.07° (SD 14.38°), and sitting AAA was 30.93° (SD 14.28°). The mean difference between sitting and standing AAA was 17.85° (SD 11.83°). Statistical analysis revealed significant differences in acetabular component orientation across different postures (p < 0.05).

Conclusion: This study highlights the critical need for dynamic and individualised approaches in THA. The findings underscore the importance of dynamic pre-operative assessments, including standing and sitting radiographs, to optimise component placement. Clinical recommendations include tailoring surgical techniques based on individual spinopelvic mobility, utilising advanced intraoperative tools for precise placement, and developing customised post-operative rehabilitation programs.