The rate of screw misplacement in segmental pedicle screw fixation in adolescent idiopathic scoliosis

Method We retrospectively evaluated low-dose spine computed tomography of 116 consecutive patients (aged 16 (12--24) years, 94 females) who were operated during 4 periods over 2005--2009 (group 1: patients operated autumn 2005--2006; group 2: 2007; group 3: 2008; and group 4: 2009). 5 types of misplacement were recorded: medial cortical perforation, lateral cortical perforation, anterior cortical perforation of the vertebral body, endplate perforation, and perforation of the neural foramen. Reslts 2,201 pedicle screws were evaluated, with an average of 19 screws per patient. The rate of screw misplacement for the whole study was 14%. The rate of lateral and medial cortical perforation was 7% and 5%. There was an inverse correlation between the occurrence of misplacement and the patient number, i.e. the date of operation (r == --0.35; p < 0.001). The skillfulness of screw insertion improved with reduction of the rate of screw misplacement from 20% in 2005--2006 to 11% in 2009, with a breakpoint at the end of the first study period (34 patients). Interpretation We found a substantial learning curve; cumulative experience may have contributed to continued reduction of misplacement rate.