OBJECTIVETo evaluate and analyze the misplacement patterns of the pedicle screws in surgical correction of patients with adolescent idiopathic scoliosis.

METHODSFor this study, 70 consecutive cases of patients with adolescent idiopathic scoliosis treated by posterior instrumented spinal fusion with pedicle screws were investigated from July 2008 to September 2008. Postoperative CT scans were performed in all cases. The patients included 58 girls and 12 boys, with a mean age of 14.5 +/- 2.7 years at surgery (range 12 - 19 years). Pedicle screws were inserted using anatomic landmark with free hand technique. A number of parameters were measured using PacsClient software (PACS) on workstation, which included distances of the penetration of medial, lateral pedicle cortex and anterior vertebral cortex. The distance between edge of aorta and tip of screw should be measured if left pedicle screw penetrated lateral pedicle cortex or anterior vertebral cortex. Misplacement screws with > 2 mm of either pedicular cortex perforation and grievous screws with >4 mm of medial pedicle perforation or contour of aorta were defined. The influencing factors for misplacement screws were analyzed.

RESULTSA total of 1030 pedicle screws were inserted, 773 in thoracic pedicle and 257 in lumbar pedicle. There were 108 (10.5%) misplacement screws, 35 of which penetrated lateral pedicle cortex, 56 of which penetrated medial pedicle cortex, 33 of which penetrated vertebral anterior cortex. Misplacement screw rate of apical vertebra, 5 segments above apical vertebra (AV-5s) and 4 segments below apical vertebra (AV + 4s) were higher than other levels. Most of grievous screws were placed in apical vertebra region.

CONCLUSIONSThe risk factors for misplacement screws included Cobb angle > 90 degrees and vertebrae rotation extent up to III-IV. Care should be exercised during pedicle screw instrumentation in the apical region of the main thoracic curve, AV-5s region and AV + 4s region.