Are traditional spinopelvic risk factors relevant for young adults undergoing total hip arthroplasty?

Purpose: Traditional spinopelvic risk factors, including lumbar stiffness, sagittal imbalance and standing posterior spinopelvic tilt (SPT), are well-established predictors of impingement in patients undergoing total hip arthroplasty (THA). However, these parameters are related mainly to degenerative lumbar conditions. With the expanding indications for THA in young patients, the relevance of preoperative spinopelvic risk factor assessment and its association with the risks of adverse spinopelvic mobility and impingement in this group remain uncertain. Methods: We retrospectively analysed a cohort of 730 consecutive patients who underwent THA and had preoperative functional X-rays and computed tomography scans. The patients were divided into four groups: younger than 50 years, 55 years, 60 years and older than 60 years. We compared the prevalence of spinopelvic risk factors (SPT ≤ -10°, lumbar flexion ≤20°, pelvic incidence-lumbar lordosis mismatch ≥10°), the rate of adverse spinopelvic mobility (∆SPT ≥ 20°) and the in-silico risk of impingement with a cup orientation of 40° inclination and 20° anteversion. Hip flexion (flexed-seated pelvic femoral angle [(∆PFA)] was analysed in patients without risk factors across age groups. Results: Risk factors were absent in patients ≤50 (0%), rare in those ≤55 (4.2%) and ≤60 years (12.0%), but frequent in those >60 years (29.4%). In younger groups, risk factors were not significantly associated with a ΔSPT ≥ 20° or impingement, although both outcomes were observed in 10%-17% of patients. In contrast, in patients >60 years, risk factors were significantly associated with a ΔSPT ≥ 20° (31.6% vs. 15.0%, Conclusion: Traditional risk factor-based screening may underestimate adverse spinopelvic mobility or impingement risk in younger patients, where excessive hip motion and other factors may be drivers, highlighting the need for functional assessment even in younger patients. Level of Evidence: Level III, case-control retrospective analysis.