Objective: Maintaining lumbosacral (LS) arthrodesis and global sagittal balance after long fusion to the sacrum remains an important issue in the surgical treatment for adult spinal deformity (ASD). The importance and usefulness of LS fixation have been documented, but the optimal surgical long fusion to the sacrum remains a matter for debate. Therefore, the authors performed a retrospective study to evaluate fusion on CT scans and the risk factors for LS pseudarthrosis (nonunion) after long fusion to the sacrum in ASD.
Methods: The authors performed a retrospective study of 59 patients with lumbar degenerative kyphosis (mean age 69.6 years) who underwent surgical correction, including an interbody fusion of the L5-S1, with a minimum 2-year follow-up. Achievement of LS fusion was evaluated by analyzing 3D-CT scans at 3 months, 6 months, 9 months, 1 year, and 2 years after surgery. Patients were classified into a union group (n = 36) and nonunion group (n = 23). Risk factors for nonunion were analyzed, including patient and surgical factors.
Results: The overall fusion rate was 61% (36/59). Regarding radiological factors, optimal sagittal balance at the final follow-up significantly differed between two groups. There were no significant differences in terms of patient factors, and no significant differences with respect to the use of pedicle subtraction osteotomy, the number of fused segments, the proportion of anterior versus posterior interbody fusion, S2 alar iliac fixation versus conventional iliac fixation, or loosening of sacral or iliac screws. However, the proportion of metal cages to polyetheretherketone cages and the proportion of sacropelvic fixation were significantly higher in the union group (p = 0.022 and p < 0.05, respectively).
Conclusions: LS junction fusion is crucial for global sagittal balance, and the use of iliac screws in addition to LS interbody fusion using a metal cage improves the outcomes of long fusion surgery for ASD patients.
Keywords: ALIF = anterior lumbar interbody fusion; ASD = adult spinal deformity; BMD = bone mineral density; BMI = body mass index; LDK = lumbar degenerative kyphosis; LL = lumbar lordosis; LS = lumbosacral; ODI = Oswestry Disability Index; PEEK = polyetheretherketone; PI = pelvic incidence; PLIF = posterior lumbar interbody fusion; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; S2AI = S2 alar iliac; SS = sacral slope; SVA = sagittal vertical axis; VAS = visual analog scale; adult spinal deformity; interbody fusion; lumbar degenerative kyphosis; lumbosacral fusion; rhBMP-2 = recombinant human bone morphogenetic protein–2; sacropelvic fixation.