Changes in shape of the adolescent idiopathic scoliosis curve after surgical correction

The effect of spinal instrumentation in idiopathic scoliosis was studied in 21 patients who had Harrington instrumentation and 15 who had Wisconsin-Drummond instrumentation.

Radiographs were analyzed to determine if the frontal and transverse plane shape of the scoliosis curve was changed by surgery, with and without segmental fixation.

Previous reports were based on frontal plane measurements of the curve (Cobb angle). The study reports correction in the frontal plane (Cobb angle) and transverse plane (apical vertebral rotation), as well as the regional distribution of the correction.

Radiographs before surgery, soon after, and between 5 and 48 months after surgery were marked and digitized to measure the regional distribution of the frontal plane shape and transverse plane vertebral rotation.

Despite improvement in the magnitude of the deformity, the scoliosis curve shape remained almost constant postoperatively. There was minimal correction of the apical vertebra axial rotation in either group.

This study documents that although the Harrington and Wisconsin-Drummond instrumentation systems decrease the Cobb angle, they do not change the shape of the curve or correct apical vertebra axial rotation. Newer instrumentation designs need to look beyond the Cobb angle as the only measure of outcome.