Advantages of Direct Insertion of a Straight Probe Without a Guide Tube During Anterior Odontoid Screw Fixation of Odontoid Fractures.

STUDY DESIGN A retrospective cohort study. OBJECTIVE The aim of this study was to compare the anterior odontoid screw fixation (AOSF) with a guide tube or with a straight probe. SUMMARY OF BACKGROUND DATA AOSF associates with several complications, including malpositioning, fixation loss, and screw breakage. Screw pull-out from the C2 body is the most common complication. METHODS All consecutive patients with type II or rostral shallow type III odontoid fractures who underwent AOSFs during the study period were enrolled retrospectively. The guide-tube AOSF method followed the standard published method except C3 body and C2-3 disc annulus rimming was omitted to prevent disc injury; instead, the guide tube was anchored at the anterior inferior C2 vertebra corner. After 2 screw pull-outs, the guide-tube cohort was analyzed to identify the cause of instrument failure. Thereafter, the straight-probe method was developed. A guide tube was not used. A small pilot hole was made on the most anterior side of the inferior endplate, followed by insertion of a 2.5 mm straight probe through the C2 body. Non-union and instrument failure rates and screw-direction angles of the guide-tube and straight-probe groups were recorded. RESULTS The guide-tube group (n = 13) had 2 screw pull-outs and 1 non-union. The straight-probe group (n = 8) had no complications and significantly larger screw-direction angles than the guide-tube group (60.5 ± 4.63 vs. 54.8 ± 3.82 degrees; P = 0.047). CONCLUSION Straight-probe AOSF yielded larger direction angles without injuring bone and disc. Complications were absent. The procedure was easier than guide-tube AOSF and assured sufficient engagement, even in horizontal fracture orientation cases. LEVEL OF EVIDENCE 3.