A radiographic comparison between threaded cage and box cage in MIS-TLIF

Abstract

Introduction: In MIS-TLIF, the cage is likely placed in the center of the vertebral endplates where the regional strength is weak. We have selected threaded cages (TC) for immediate improvement of stability. The purpose of this study was to compare the radiographical differences between TC and the box cages (BC).

Methods: The subjects were 44 patients who underwent MIS-TLIF at L5/S1 and were followed for at least 1 year after surgery (19 TC patients, 25 BC patients). We observed bone union, screw failure, cage displacement and local lordosis angle of L5/S1 using X-ray for lumbar lateral view.

Results: The percentage of bone union in the TC group was significantly poor compared with the BC group (TC 47.4%, BC 84.0%, P=0.011). Screw failure occurred in 3 cases in the TC group and 0 case in the BC group, cage displacement occurred in 0 case in the TC group and 10 cases in the BC group. The local lordosis angle was 6.7 degrees before surgery and 4.9 degrees at final observation in the TC group, and 6.7 degrees before surgery and 6.6 degrees at final observation in the BC group, and no significant difference was observed between preoperatively and at final observation in either group.

Conclusion: As TC was good for stability in the anteroposterior direction, there was no cage displacement. However, the percentage of bone union was poor in the TC group due to instability for forward or back bending. Neither group achieved enough local lordosis, hence it is necessary to draw up a surgical plan for having local lordosis such as increasing the number of cages, or insertion of cages to the rim of the vertebral endplate.