Does the Formation of Vertebral Endplate Cysts Predict Nonunion After Lumbar Interbody Fusion?

Study Design. A retrospective study was conducted to investigate the impact of vertebral endplate cyst formation on union status after lumbar interbody fusion. Objective. To assess the impact of cyst formation at the vertebral endplate in the early detection of nonunion after lumbar interbody fusion. The relationship between vertebral endplate cyst formation and subsequent union status was evaluated retrospectively using dynamic x-ray and computed tomography (CT) and multiplanar reconstruction. Summary of Background Data. Although many studies have reported on the assessment of bony union after lumbar interbody fusion, no study has reported on the radiological risk factors for nonunion in the early postoperative period. The meaning and importance of vertebral endplate cyst formation have not been reported and should be clarified. Methods. Radiological vertebral endplate changes at 93 levels were assessed in 76 patients after transforaminal lumbar interbody fusion, using a titanium cage with pedicle screw fixation. Computed tomographic findings for the vertebral endplate at 3 months were compared between nonunion and union cases. The relationship between vertebral endplate cyst formation and union status was tested statistically. Results. Fifty-nine union cases were compared with 17 nonunion cases. The overall union rate was 75.2% at 1 year and 82.8% at 2 years. At 1 year, the sensitivity of cyst formation for subsequent nonunion was 69.6%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 90.9%. Multivariate logistic regression analysis showed that a multioperated back was a significant predictor of cyst formation (odds ratio [OR]: 3.8; 95% confidence interval [CI]: 1.1-13.1) and that cyst formation and multioperated back were significant predictors of nonunion (OR: 12.3; 95% CI: 1.8-133 and OR: 116; 95% CI: 22.4-infinity, respectively). Conclusion. These findings show a relationship between vertebral endplate cyst formation in the early postoperative period and nonunion after lumbar interbody fusion. Endplate cyst formation is a useful early predictor of subsequent nonunion.