This study aimed to determine whether an isthmus-guided cortical bone trajectory (CBT) technique provides better clinical outcomes than the original cortical bone trajectory CBT technique for screw fixation. Methods A consecutive series of 21 patients with lumbar spondylolisthesis who had undergone CBT screw fixation using the original technique from June 2012 to February 2013 and 33 who had undergone the isthmus-guided technique from March 2013 to August 2014 was retrospectively reviewed. The number of screws inserted, interbody fusion and screw misplacements, amount of blood loss, and creatinine phosphokinase (CPK) ratios (postoperative day 1 CPK/preoperative CPK) were reviewed to evaluate clinical outcomes and compared between the original and isthmus-guided CBT techniques. Results Postoperative serum CPK concentrations were significantly lower with the isthmus-guided than the original CBT technique (P < 0.05). There were no significant differences in age, blood loss, or number of screws, vertebral interbody fusions and patients with history of previous decompression surgery at the same level. There was a trend to higher incidence of screw misplacement with the original than the isthmus-guided CBT technique; this difference was not significant (P = 0.53). There were no major intraoperative complications. In all the CBT procedures performed in our institution, almost half (47%) the screw misplacements have occurred at the level of L5, and most on the right side. Conclusions Right-handed operators should take care inserting screws on the right side. From the viewpoint of screw misplacement, isthmus-guided CBT provides superior or equivalent safety to the original CBT technique.
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