The purpose of this study was to determine whether or not patients undergoing unilateral total hip arthroplasty (THA) experience changes in spinal sagittal and coronal alignment, patients experiencing changes in spinopelvic parameters following THA, and patients were experiencing differences in spinopelvic alignment between those who are sagittally balanced and those who are imbalanced. When a patient has a spinal sagittal imbalance, correcting it surgically can affect their spinopelvic alignment and pelvic tilt. To what extent THA impacts spinopelvic, spinal sagittal, and coronal alignment is unknown at this time. Biplanar stereoradiography in the standing position was used for preoperative and postoperative evaluations in 153 THA patients. C7-sagittal vertical axis, pelvic incidence-lumbar lordosis (PI-LL) mismatch, lumbar lordosis (LL), C7-central sacral vertical line, lumbosacral pelvic oblique angle, intra-pelvic oblique angle, pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), anterior plane pelvic tilt (APPT), and pelvic femoral angle (PFA). The effect of sagittal misalignment on spinopelvic alignment was analyzed for the C7-SVA and PI-LL subgroups. When comparing preoperative and postoperative values for the spinopelvic parameters studied (spinal stiffness (SS), physical therapy (PT), anterior pelvic tilt (APPT), and posterior femoral angle (SS, PT, APPT, and PFA; P<0.000) (d=−0.394; d=0.609; d=−0.481; d=0.431). statistically significant changes were found. No major variations were seen in the measures of coronal alignment and pelvic obliquity. The misaligned groups (C7-SVA; PI-LL) showed significantly higher PI and PT and lower LL than the groups with normal sagittal alignment. Sagittal misaligned groups with normal sagittal alignment were evident in 66/153 (C7-SVA) and 46/153 (PI-LL) of the THA patients before surgery. There was a significant decrease in postoperative PT, suggesting that THA had an effect on sagittal spinal and spinopelvic alignment, but no effect on coronal alignment was found. Notably, there are notable variations between the misaligned groups, which may be classed as a risk population and may biomechanically lead to a higher risk of posterior impingement and anterior THA dislocation. The high prevalence of sagittal misalignment in THA patients highlights the importance of multidisciplinary teamwork.
