Changes in spino-pelvic alignment after surgical treatment of high-grade isthmic spondylolisthesis by a posterior approach: a report of 41 cases

Purpose To analyze changes in spino-pelvic parameters (SPPs) after surgery of high-grade lumbar isthmic spondylolisthesis (HDIS). Methods We analyzed 41 patients affected by HDIS operated upon by attempt of reduction and posterior spinal fusion with pedicle screw systems with or without inter-body fusion. Pelvic tilt (PT), lumbar lordosis (LL), pelvic incidence (PI), and sacral slope (SS) were measured, and patients were further divided into balanced and unbalanced pelvis subgroups. Results SS passed from 46.8 degrees +/- 9.8 degrees preoperatively to 50.1 degrees +/- 10.1 degrees (p = 0.02). PT passed from 26.7 degrees +/- 6.7 degrees preoperatively to 22.9 degrees +/- 7.5 degrees (p = 0.003). Unbalanced patients showed significantly higher PT and lower SS compared to the balanced patients preoperatively, and these corrected after surgery. Patients with instrumentation failure (n = 5) had significant increase in PT values post-operatively (p = 0.018). Conclusions We confirmed the positive effect of surgery on the SPPs in patients affected by HDIS, which showed different patterns of corrections with surgery for balanced and unbalanced pelvis patients.