ABSTRACT
Transpedicular screw fixation of the spine in scoliosis is still not very popular. Although biomechanically superior, it carries the risk of wrong placement which may lead to serious complications. A modified method of screw insertion was suggested where the screw was put under vision and feeling. The aim of this study is to assess the accuracy of placement of transpedicular screws in scoliosis. Comparison between the traditional method of screw insertion [depending on anatomical landmarks] and the modified method will be conducted. Also the safest sites of screw placement will be studied trying to find the best sites of screw placement in adolescent idiopathic scoliosis for King I and II types. 248 screws were inserted in 45 patients of King I and II adolescent idiopathic scoliosis. Postoperatively, patients were evaluated clinically and radiologically for curve correction and neurological condition. Each vertebra instrumented was examined for degree of rotation, its location and its position in the curve. Also method of screw insertion was reported. Each screw was examined for its point of entry, direction, length and its containment inside the pedicle. Results were statistically analyzed. Percent correction of thoracic curve was 55.6%, while that of lumbar was 50%. Only two factors significantly affected correction: number of vertebrae included and number of sublaminar wires used. One patient developed irritation of L3 root that improved after removal of offending screw. The average number of screws used was 5.51 screws. Modified method was used to insert 67 thoracic screws out of 248 screws. Twenty three [9.7%] screws were misplaced while wrong point of entry was encountered in 31 occasions [12.5%] and inappropriate direction of the screws in 27 times [10.9%]. Most of these wrong screw applications were in the lower end of the curve. Inadequate screw length was encountered in 16 cases [6.5%]. The factors that affect accurate placement of screws were analyzed. The factors that significantly affect it include: level of instrumentation [higher incidence in lower lumbar], method of screw insertion [modified method gave significantly better results], type of the curve [King II gave better results] and number of screws inserted [the more the number of screws inserted in the patient, the more is the incidence of misplaced screws]