Radiographic Changes in Spinopelvic Alignment Following Single-Level Lumbar Total Disc Replacement

Study Design: Retrospective cohort study. Objective: To assess radiographic changes in spinopelvic alignment following single-level lumbar total disc replacement (LTDR), with particular focus on the L1-pelvic angle (L1PA) and distal lumbar lordosis (L4–S1). Summary of Background Data: Lumbar total disc replacement preserves segmental motion and may influence sagittal alignment; however, its effects on distal lumbar lordosis distribution and L1-pelvic angle remain incompletely characterized. Materials and Methods: Thirty-six patients who underwent single-level LTDR at L4–5 (n=14) or L5–S1 (n=22) were retrospectively evaluated. Preoperative and postoperative standing lateral radiographs were analyzed for changes in pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), global lumbar lordosis (L1–S1), distal lumbar lordosis (L4–S1), and L1PA. Univariable and exploratory multivariable linear regression analyses were performed to examine associations between patient- and implant-related factors and postoperative alignment changes. Statistical significance was defined as P <0.05. Results: Following LTDR, distal lumbar lordosis (L4–S1) increased significantly by a mean of 3.1° ( P =0.0007), and L1PA decreased by 1.6° ( P =0.005), resulting in closer approximation to calculated ideal L1PA values (preoperative deviation: +3.42°; postoperative: +1.85°; P =0.01). No significant changes were observed in global lumbar lordosis, pelvic tilt, sacral slope, or pelvic incidence. Exploratory multivariable analysis demonstrated associations between increased distal lumbar lordosis and greater implant-derived lordosis, older age at surgery, and smoking status. Subgroup analysis showed significant increases in distal lumbar lordosis at both L4–5 and L5–S1, while significant improvement in L1PA was observed only at L5–S1. Conclusion: Single-level lumbar total disc replacement is associated with increased distal lumbar lordosis and improvement in L1-pelvic angle while preserving global sagittal alignment. These findings suggest that LTDR may permit regional alignment changes without imposing fixed segmental correction. Further prospective studies incorporating clinical outcomes are needed to clarify the clinical significance of these radiographic changes.