Late-onset idiopathic scoliosis is associated with a rib hump in the thoracic region, and surgery is indicated when this deformity becomes unacceptable. Fifty patients with this deformity were treated by the Leeds procedure, which consists of segmental wiring to a kyphotically-contoured square-ended Harrington rod; this procedure not only derotates the spine but restores the natural thoracic kyphosis, thus avoiding subsequent buckling. All patients were followed up for a minimum of two years. Forty-two of these, who had a pre-operative Cobb angle of less than 60 degrees, were treated by one-stage instrumentation and fusion, while the remaining eight with greater curves underwent preliminary anterior multiple discectomy to provide flexibility with shortening. Postoperative loss of correction was not observed and there were no neurological complications.

A study of 130 scoliotic children with curves measuring 10 degrees or more has been performed in order to elucidate the importance of stature, growth and development. Girls with adolescent idiopathic curves measuring 15 degrees or more were taller than girls with smaller idiopathic curves and taller than those whose scoliosis was secondary to leg-length inequality (pelvic tilt scoliosis). No differences were observed as regards growth velocity or development. The increased standing height may be genetic but the uncoiling effect of the normal kyphosis to give a flat lateral profile is a more likely cause. The familial trend in idiopathic scoliosis may therefore be explained by the genetically determined shape of the spine in the median (sagittal) plane.

A clinical, cadaveric, biomechanical and radiological investigation of the pathogenesis of idiopathic scoliosis indicates that biplanar asymmetry is the essential lesion. Many normal children have coronal plane asymmetry (an inconsequential lateral curvature of the spine), and certainly all have vertebral body asymmetry in the transverse plane, but when median plane asymmetry (flattening or more usually reversal of the normal thoracic kyphosis at the apex of the scoliosis) is superimposed during growth, a progressive idiopathic scoliosis occurs. Idiopathic kyphoscoliosis cannot and does not exist, from the mildest cases in the community to the most severe cases in pathology museums. Median plane asymmetry is crucial for progression and the lateral profile of the spine must be carefully scrutinised. Increased anterior vertebral height at the apex of the curve with posterior end-plate irregularity characterises the median plane asymmetry and suggests that idiopathic scoliosis is the reverse of Scheuermann's disease.