Patients Undergoing Multilevel Thoracolumbar Fusions With Prior Total Hip Arthroplasty Are at Higher Risk for Prosthetic Dislocations

Background: – As the number of patients undergoing both total hip arthroplasty (THA) and lumbar spinal fusion rises, clinicians must gain a stronger understanding of the biomechanical and clinical associations between these two procedures. This study compared single versus multilevel spinal fusion on spinopelvic parameters, clinical outcomes, and THA dislocation rates in patients with existing THAs.Methods: – Patients with an existing THA undergoing elective spinal fusion were retrospectively identified at a single academic center. Cohorts were stratified by fusion construct length (single or multilevel) and outcomes were followed at least 1 year after surgery.Results: – A total of 392 patients (260 single level, 132 multilevel) were included. Patients who underwent multilevel fusion had less improvement in ∆ visual analogue scale (VAS) Back Scores at 1 year (−1.00 vs. −2.50, P = 0.039), greater hospital length of stay (5.00 vs. 3.00 days, P < 0.001), and lower rates of discharge home (48.5% vs. 81.4%, P < 0.001). They had higher dislocation (4.55% vs. 0.38%, P = 0.007), spinal revision (25.8% vs. 13.5%, P = 0.004), and 90-day readmission rates (12.1% vs. 3.46%, P = 0.002). Radiographically, patients with multilevel constructs had lower preoperative (40.4° vs. 49.1°, P < 0.001), postoperative (43.4° vs. 48.6°, P = 0.004), and 1-year lumbar lordosis (44.4° vs. 50.5°, P = 0.028) and higher postoperative mean anteversion (24.2° vs. 21.0°, P = 0.017). Single-level fusion was an independent predictor for lower VAS leg scores (odds ratio [OR] = −2.57, P = 0.011), fewer readmissions (OR = −0.13, P = 0.001), and fewer complications (OR = −0.25, P < 0.001). Male sex independently predicted increased spinal revisions (OR = 0.13, P = 0.026).Conclusion: – Patients with prior THA undergoing multilevel fusions experienced more dislocations, higher spinal revisions, less frequent discharge home, longer hospital length of stays, and higher 90-day readmission rates. They had less improvement in ∆VAS Back Scores at 1 year, lower lumbar lordosis, and greater anteversion. Patients with existing THA undergoing multilevel fusion have more abnormal spinal sagittal balance and higher risk of dislocation despite higher baseline and postoperative acetabular anteversion.