Does spinopelvic motion change after total hip arthroplasty?

Area of Science:

• Orthopedics
• Biomechanics
• Surgical Outcomes

Background:

• Spinopelvic motion is crucial for functional acetabular cup positioning in total hip arthroplasty (THA).
• Sacral slope (SS) serves as a reliable indicator of spinopelvic motion.
• Understanding pre- and post-operative spinopelvic motion is key to optimizing THA outcomes.

Purpose of the Study:

• To statistically analyze spinopelvic motion changes after THA.
• To evaluate the impact of THA on sacral slope (SS) in supine, standing, and sitting positions.
• To characterize spinopelvic mobility (normal, stiff, hypermobile) before and after THA.

Main Methods:

• Assessed 76 patients (88 hips) undergoing THA.
• Defined spinopelvic mobility based on change in SS from standing to sitting (ΔSS_stand/sit): normal (10°–30°), stiff (<10°), and hypermobile (>30°).
• Compared SS measurements before THA and one year post-THA.

Main Results:

• Significant changes in SS were observed one year post-THA, particularly in the sitting position (±7° in 44.3% of hips).
• A significant shift occurred in the prevalence of stiff (11.4% to 22.7%) and hypermobile (23.9% to 12.5%) spinopelvic mobility (p<0.05).
• Postoperatively, 40% of stiff and 57.1% of hypermobile hips transitioned to normal spinopelvic mobility.

Conclusions:

• Spinopelvic motion exhibits high inter-subject variability after THA, especially when sitting.
• THA leads to a notable normalization of spinopelvic mobility in patients who were previously stiff or hypermobile.
• These findings highlight THA's positive influence on restoring functional spinopelvic dynamics.