Preoperative Hip Flexion and Extension Range of Motion and Global Sagittal Alignment Affect Sagittal Spino-Pelvic Alignment in Patients Undergoing Total Hip Arthroplasty.

Abstract

This study aimed to determine how preoperative hip flexion-extension range of motion (ROM) and sagittal vertical axis (SVA) affect postoperative ROM recovery, changes in sagittal spino-pelvic alignment, and patient-reported outcomes (PROMs) following total hip arthroplasty (THA). We retrospectively reviewed 416 patients who underwent primary cementless THA. Spino-pelvic parameters in standing and sitting positions and PROMs were evaluated preoperatively and at six months, one year, and two years postoperatively. Patients were divided into four groups based on preoperative hip flexion-extension ROM and SVA: the limited ROM (hip flexion ≤ 60° and/or extension less than 0°) and high SVA (≥ 50 mm) group (LR-H group; n = 60), the limited ROM and normal SVA (less than 50 mm) group (LR-N group; n = 77), the preserved ROM (flexion greater than 60° and extension ≥ 0°) and high SVA group (PR-H group; n = 56), and the preserved ROM and normal SVA group (PR-N group; n = 223). All groups showed significant improvement in hip flexion-extension ROM postoperatively; however, the LR-H group maintained significantly lower values than the other groups at two years. This group showed the lowest sacral slope and lumbar lordosis in both standing and sitting positions, the highest SVA in both positions, and persistent highest spino-pelvic mobility. Longitudinally, this group showed minimal improvement in global sagittal alignment. The LR-H group showed significantly lower achievement rates of minimal important change for PROMs compared to other groups. Preoperative limited flexion-extension ROM combined with high SVA significantly affects ROM recovery, sagittal spino-pelvic alignment, and PROMs following THA, suggesting that preoperative evaluation of both factors may be important for understanding postoperative outcomes and informing treatment strategies.