Postoperative spinopelvic changes are associated with increased dislocation risk following total hip arthroplasty (THA). The aim of this study was to identify preoperative patient and radiographic factors associated with high-risk postoperative spinopelvic parameters. A retrospective review of consecutive THA patients who received preoperative and postoperative sitting and standing lateral lumbar spine-hip radiographs with minimum radiographic and clinical follow-up of 10 months was performed. Patient demographics were recorded and preoperative standing and sitting sacral slope (SS), anteinclination, pelvic femoral angle (PFA), and combined sagittal index (CSI) were measured. High-risk patients were defined by decreased spinopelvic motion (∆SS from sitting to standing of >10°), increased hip motion (∆PFA from sitting to standing of >10°), or decreased CSI of >10° at final follow-up compared with preoperative measurements. Univariate and multivariate regression analyses were used to identify preoperative demographic and radiographic factors associated with these high-risk categories. One hundred and fifty-three patients were included with an average age of 62 years, average body mass index of 27.8 kg/m2 , and average follow-up of 16.2 months. At 1-year follow-up, 43 (28.1%) patients demonstrated a decreased ∆SS > 10° and 67 (43.7%) patients demonstrated an increased ∆PFA > 10° compared with preoperative values. Sitting CSI decreased by >10° in 17 (11.1%) patients. Preoperative increased sitting PFA (adjusted odds ratio [aOR] 1.057, p < 0.001) and decreased preoperative hip motion (∆PFA) were associated with decreased sitting CSI of >10° at 10-month follow-up. Increased spinopelvic motion (∆SS) and decreased hip motion (∆PFA) preoperatively are associated with postoperative radiographic changes that be associated with increased dislocation risk.
Keywords: instability; spinopelvic biomechanics; total hip arthroplasty.
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