Asymmetry of premotor time in the back muscles of adolescent idiopathic scoliosis

Study Design. In 38 patients with adolescent idiopathic scoliosis ( AIS), the correlation between left and right differences in premotor time ( D- PMT) of back muscle and clinical findings were analyzed. Objective. To investigate the clinical relevance of back muscle D- PMT in AIS. Summary of Background Data. There have been numerous studies investigating back muscle asymmetry of AIS by EMG, but to date, no studies have measured D-PMT in back muscles. Materials and Methods. D- PMT in the back muscles measured in a similar manner as that in the extremity muscles was assessed in 10 nonscoliotic teenaged girls and 38 AIS patients. The correlation between back muscle D- PMT and four factors ( age, Risser sign, Cobb angle, and progression of deformity) was investigated. Results. The D- PMT values of back muscle at all levels in the control group were within +/- 5 ms, but those in 20 of the 38 AIS patients were more than 5 ms. D- PMT at the lower- end vertebra level was strongly correlated with progression of deformity, but not with age, Risser sign, and Cobb angle. All five patients with D- PMT of more than 10 ms at the lower- end vertebra level had progressive deformity. Conclusions. D- PMT in back muscle at the lower end vertebra level in AIS correlated closely to the progression of scoliotic deformity, thus suggesting that this phenomenon is associated with the progression in AIS.