PURPOSE: The pathogenesis of adolescent idiopathic scoliosis (AIS) remains poorly understood. To date, potentially involved local changes in the deep paraspinal muscles still remain unknown. METHODS: Needle electromyography (EMG) and muscle biopsy of paraspinal muscles at convexity and concavity of the AIS main thoracic curve were performed in 25 subjects. In this group, EMG was performed in 16 AIS subjects (12 females, 12-27 years), muscle biopsy in 18 AIS subjects (15 females, 11-31 years) compared to 10 non-scoliotic controls (6 females, 12-55 years). Samples of muscle tissue were removed during corrective surgery and were examined histologically, enzyme histochemically and immunohistochemically. Both methods of EMG and muscle biopsy were performed in 9 subjects (7 women, 12-27 years). RESULTS: Right curve convexity was found in 24 AIS subjects. Amplitudes of motor unit action potentials (MUPs) were significantly increased on the AIS curve convexity versus concavity. Turns, duration and phases of MUPs were without any significant changes. In all 18 subjects, the histological examination revealed muscle fiber redistribution with numerical predominance of type I on the curve convexity which strongly correlated with the progression of the Cobb angle. CONCLUSION: Our findings demonstrate significant changes of muscle fiber redistribution in the paraspinal muscles of AIS with increased proportion of type I on the convexity corresponding to a significantly higher amplitude of MUPs on the same side. A possible explanation of this alteration is a secondary adaptation due to chronic high load demand.

Department of Neurology 3rd Faculty of Medicine Charles University Prague and Faculty Hospital Kralovske Vinohrady Ruska 87 100 00 Prague 10 Czech Republic

Department of Orthopedics and Traumatology 3rd Faculty of Medicine Charles University Prague and Faculty Hospital Královské Vinohrady Prague Czech Republic

Department of Pathology and Molecular Medicine 2nd Faculty of Medicine Charles University Prague and Motol University Hospital Prague Czech Republic

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