Incidence of pars defect associated with idiopathic scoliosis has been reported as 6% based on roentgenographic evaluation in previous studies. (Fisk et al, 1978). We aim to present our results in an MRI based study.

224 patients of adolescent idiopathic scoliosis (AIS) who had an MRI scan over a period of three years (2006-2008), performed either as a preoperative investigation or due to other symptoms were reviewed. All MRI scans were reviewed by two experienced musculoskeletal radiology consultants independently.

Among 224 patients 13 (5.8%) patients were found to have pars defect. Mean age-group of patients were (19 years, range-11-40). 84.6% (n=11) patients were female and 15.3% patients were male. There was varying severity of curve patterns. We have noted two lumbar/thoraco-lumbar curves (Lenke 5), King Type I-6, King Type II-2 and three King Type III curves. All scoliotic deformities were non-structural. Bilateral pars defect was noted in nine (69%) patients.

Previous studies (Fisk et al, 1978; Mau H 1981) have described the incidence of pars defect as approximately 6.2%. Recent studies have emphasized use of MRI to diagnose pars defect based on signal changes in the pedicle (Sairyo et al.). Our study reveals the incidence of pars defect in AIS to be 5.8 % based on MRI diagnosis which does not seem to be different to previous roentgenographic studies.