Adolescent Idiopathic Scoliosis. The Role of Low Dose Computed Tomography

Sammanfattning: Continuous implementation of new operative methods for correction and stabilization of spinal deformities in young patients with AIS demands a detailed morphological analysis of the vertebral column. CT spine according to protocols available in daily clinical practice means high radiation dose to these young individuals. All examinations included in this thesis were performed on a 16-slice CT scanner. Examination of the chest phantom in paper I showed that the radiation dose of the spine (including 15 vertebrae) was 20 times lower than that of routinely used protocols for CT examination of the spine in children (0.38 mSv vs 7.76 mSv). In paper II the radiation dose and the impact of dose reduction on image quality were evaluated in 113 consecutive examinations with low-dose spine CT and compared with that of 127 CTs after trauma and 15 CTs performed according to a previously used ANV-protocol of a limited part of the vertebral column. The effective dose of the low-dose spine CT (0.01 mSv/cm scan length) was 20 times lower than that of the standard CT for trauma (0.20 mSv/cm scan length). The absorbed doses to the breasts, genital organs, and thyroid gland in the low-dose spine CT was 8, 265, and 22 times lower than the corresponding doses in CT for trauma. This significant dose reduction conveyed no impact on image quality with regard to answering the clinical questions at issue for the preoperative CTs and for the postoperative CTs after posterior corrective surgery. In paper III the low-dose CT showed to be a reliable method in the evaluation of screw placement in patients with AIS after posterior scoliosis surgery with titanium implants, using the new grading system for screw misplacement. Our proposed grading system for screw misplacement has shown to be feasible, practical, and easy to perform and is in line with the general agreement about the harmlessness of misplacement with minor pedicle breach. In paper IV the evaluation of the clinical and radiological outcome of 49 patients with AIS operated on with titanium “all-pedicle screw construct” showed an overall misplacement rate of 17 %. No evidence of neurovascular complications was reported. In parity with most of the reports in the literature the lateral- and medial cortical perforation were the most common types of screw misplacement (8 % and 6.1 % respectively).