Muscle dysfunction and exercise limitation in adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) can lead to ventilatory restriction, respiratory muscle weakness and exercise limitation. However, both the causes and the extent of muscle dysfunction remain unclear. The aim of our study is to describe muscle weakness and its relationship to lung function and tolerance to exercise in AIS patients. Lung and muscle function, together with exercise capacity, were assessed in 60 patients with pronounced spinal deformity (>40 degrees) and in 25 healthy volunteers. Patients with AIS had only mild to moderate abnormal ventilatory patterns, the most frequent of which were restrictive abnormalities. The function of respiratory and limb muscles and exercise capacity were below normal limits in AIS patients, and were significantly lower than in controls. Exercise capacity was found to correlate with the function of inspiratory, expiratory, upper limb and lower limb muscles which, in addition, were reciprocally interrelated. Multivariate analysis showed that lower limb muscle function is the main contributor to exercise intolerance. There appeared to be no connection between spinal deformity and lung function, muscle function or exercise capacity. We conclude that AIS patients show generalised muscle dysfunction which contributes to the reduction in their exercise capacity, even in the absence of severe ventilatory impairment.