Instrument for distraction by limited surgery in scoliosis treatment

A principle for secondary instrumental spinal distraction by a rod appliance of the Knodt and Harrington types is described. The principle entails of the rotation of the screw rod by wire traction. The wire is, in a secondary procedure, unwound from a wire barrel mounted onto the screw rod in the primary operative procedure. The study describes the devices employed, modified according to the wire traction--instrument distraction principle. Previous results from intra-vital studies of the Harrington instrumentation have been reported from experiments performed. Thus, a final distraction force of 18 kp effected for correction of a scoliosis curvature, was taken as a value of distraction prior to secondary instrumental distraction by wire traction. In the extra vital study, the wire traction was adjusted to surmount a compressive force of 20 kpby means of a Bessmann weight scale. Wire traction created a distraction force of 39.5 kp, and a metric distraction, from the position resulting from 20 kp distraction to that resulting from 39.5 kp distraction, of 2.8 mm, which was considered to affect the prevailing scoliosis geometry to a considerable and sufficient extent.