The impact of bone graft volume on risk of pseudarthrosis, screw loosening, and rod breakage in surgical correction of adult spinal deformity.

BACKGROUND

Allograft bone and demineralized bone matrix (DBM) are important allogeneic sources of structural and biologic graft to support successful fusion in surgical correction of adult spinal deformity (ASD). Little is known about the contribution of graft type, volume, and ratio to successful fusion.

METHODS

A retrospective review of a single-institution database of ASD patients was reviewed to assess for postoperative pseudarthrosis, screw loosening, or rod breakage (PLB). Patients with ≥ 5 level fusion who had follow-up > 6 months were included in the analysis. Surgical records were reviewed to collect graft type and volume. Total allograft bone volume (TB), total DBM volume (DBM), and DBM: Bone ratio were assessed. TB and DBM per level were calculated. Univariate and multivariate analyses were performed. Receiver-operator curve (ROC) analysis was performed to identify cutoffs to minimize risk of mechanical complications.

RESULTS

A total of 310 patients were included in the analysis, with 13 (4.2%) demonstrating PLB. Univariate analysis demonstrated several significant risk factors for the study complications, including ASA class, male sex, and history of smoking, as well as TAB and TAB: Level. Multivariate analysis identified smoking, male sex, TB: Level, and DBM: Bone ratio as significant risk factors. ROC analysis identified a cutoff of 10.3 cc pf allograft bone per level, a DBM: bone ratio of 1.5, and a BMI of 25.1 kg/m2 as risk factors for failure.

CONCLUSIONS

In addition to demographic risk factors, total allograft bone per level and the ratio of DBM to allograft bone appear to be significant risk factors for pseudarthrosis after surgical correction of ASD. These values can be used to rationally select graft volume and graft composition in order to mitigate the risk of pseudarthrosis.