Prediction of pelvic mobility using whole-spinal and pelvic alignment in standing and sitting position in total hip arthroplasty patients

Purpose: Dislocation is a major complication after total hip arthroplasty (THA), and pelvic stiffness is reportedly a significant risk factor for dislocation. This study aimed to investigate spinopelvic alignment, and identify preoperative factors associated with postoperative pelvic mobility. Methods: We enrolled 78 THA patients with unilateral osteoarthritis. The sagittal spinopelvic alignment in the standing and sitting position was measured using an EOS imaging system before and 3 months after THA. We evaluated postoperative pelvic mobility, and defined cases with less than 10° of sacral slope change as pelvic stiff type. The preoperative characteristics of those with postoperative stiff type, and preoperative factors associated with risk of postoperative stiff type were evaluated. Results: Sagittal spinopelvic alignment except for lumbar alignment were significantly changed after THA.A total of 13 patients (17%) were identified as postoperative pelvic stiff type. Preoperative lower pelvic and lumbar mobility were determined as significant factors for prediction of postoperative pelvic stiff type. Among these patients, nine patients (69%) did not have pelvic stiffness before THA. Preoperative factor associated with the risk of postoperative pelvic stiff type in those without preoperative stiffness was lower lumbar lordosis in standing position by multivariate regression analysis. Conclusion: Spinopelvic alignments except lumber alignment was significantly changed after THA. The lower pelvic mobility and lumbar alignment were identified as the preoperative predictive factors for postoperative pelvic mobility. Evaluation of preoperative lumbar alignment may be especially useful for the prediction in patients with hip contractures, for these patients may possibly experience the extensive perioperative change in pelvic mobility.