Computer-assisted tomography of scoliosis operated with or without Harrington's rod. Biomechanics aspects of the fusion.

Forty-eight cases of posterior vertebral arthrodesis for scoliosis, performed with or without instrumentation, were examined using computed tomography (CT) scanning to study the evolving fusion mass. The authors observed that the fusion mass area is more voluminous in the cases performed without instrumentation than in the ones performed with instrumentation, and that 2 years after fusion the bone mass shows already a considerable increase. For the cases operated with Harrington's technique, the increase of the fusion mass is very slow and becomes considerable 5 years after operation. In both series, the section of the fusion masses at the apex of the curve is asymmetric (with prevalence on the concave side), with an area of central resorption that shows the structure of a long bone (box section).