Evaluation of ventilatory efficiency during exercise in patients with idiopathic scoliosis undergoing spinal fusion

Study Design. A prospective evaluation of ventilatory function following spinal fusion in adolescent idiopathic scoliosis. Objectives. To prospectively evaluate pulmonary function, maximal oxygen uptake, and ventilatory efficiency during exercise in patients with adolescent idiopathic scoliosis before surgery and a minimum of 2 years postoperation. Summary of Background Data. For reasons that are unclear, patients with untreated adolescent idiopathic scoliosis tend to avoid aerobic exercise. Their reluctance may be the result of low ventilatory efficiency, as they often approach their ventilatory ceiling at maximum oxygen uptake despite forced vital capacities that are near normal. This inefficiency of ventilation with exercise may explain the reluctance of patients with scoliosis to pursue aerobic fitness. No study has evaluated the effect spinal fusion has on the ventilatory function of patients with scoliosis during exercises. Methods. Forty-two patients with adolescent idiopathic scoliosis (36 female and 6 male) at an average age of 14 +/- 3 years (range 10-18 years) underwent spinal fusion. Twenty patients underwent a posterior spinal fusion alone, 20 an anterior spinal fusion alone, and 2 an anterior spinal fusion and posterior spinal fusion. The average Cobb measurement was 55degrees (range 40-85degrees). Pulmonary function values (forced vital capacity, total lung capacity, maximum voluntary ventilation), maximum oxygen uptake ((V) over dot O(2)max), and ventilatory efficiency were obtained before surgery and a minimum of 2 years postoperation. Results. For all patients, forced vital capacity percent predicted decreased from 88.1% to 81.4% (P<0.0001). Total lung capacity also declined from 90.5% to 88.5% but was not statistically significant (P=0.189). Percent predicted maximum oxygen uptake ((V) over dot O(2)max) declined from 93.6% to 85.1% (P = 0.00029). Ventilatory efficiency, as measured by V(E)max/maximum voluntary ventilation, improved from 0.76 to 0.68 (P = 0.005), whereas measured by V(E)max/FEV1 x 40 was unchanged from 0.69 to 0.70 (P = 0.172) postoperation. The choice of operative approach [anterior (n = 20) versus posterior (n = 20)] or whether rib graft was harvested (n = 33) versus iliac crest graft (n = 7) did not change these results. Conclusion. Improvement in ventilatory efficiency during exercise dies no occur in the majority of patients with adolescent idiopathic scoliosis following spinal fusion and thus cannot be relied on to foster increases in aerobic activity.