Vertebral Endplate Cyst as a Predictor of Nonunion After Lumbar Interbody Fusion: Comparison of Titanium and Polyetheretherketone Cages.

STUDY DESIGN The bone union rate after lumbar interbody fusion (LIF) using titanium (Ti) or polyetheretherketone (PEEK) cages was investigated retrospectively. OBJECTIVE To assess whether the PEEK cage is superior to the Ti cage in terms of bone union after LIF. SUMMARY OF BACKGROUND DATA We previously reported that the formation of vertebral endplate cysts is useful for predicting nonunion after LIF using Ti cages. METHODS We examined 144 levels in 117 patients treated from March 2005 to July 2012 with transforaminal LIF using Ti (93 levels in 77 patients) or PEEK cages (51 levels in 40 patients) with pedicle screw fixation. Using computed tomography, vertebral endplate cyst (cyst sign) was evaluated at 3 months, and bone union status was evaluated at 1 and 2 years postoperatively. The relationship between cyst sign and union status was analyzed statistically. The bone union rate and the accuracy of the cyst sign were compared between the two groups. RESULTS The postoperative bone union rate was 75.2% and 74.5% at 1 year, and 82.8% and 80.4% at 2 years for Ti and PEEK groups, respectively. The rate of positive cyst sign was 17.2% and 13.7%, respectively. The nonunion rate with positive cyst sign was 100% and 100% at 1 year, and 56.2% and 71.4% at 2 years, respectively. Calculated for the cyst sign and union status, the sensitivity was 69.6% and 53.8%, and the specificity was 100% and 100%, respectively. There were no significant differences in bone union rate, rate of positive cyst sign, nonunion rate with positive cyst sign, sensitivity, and specificity between the two groups. CONCLUSION The cyst sign was useful for predicting nonunion after LIF using PEEK or Ti cages. The bone union rate after LIF did not differ significantly between the two groups. LEVEL OF EVIDENCE 3.