Laboratory testing of segmental spinal instrumentation versus traditional Harrington instrumentation for scoliosis treatment.

The authors have tested 51 instrumented calf spines in vitro, using a scoliosis simulator, to evaluate the adequacy of fixation and nature of acute failure seen with various methods of scoliosis instrumentation. Tests were performed in compressive loading, rotation, and forward bending on the following instrumentation systems: (I) Harrington distraction, (II) Harrington distraction plus compression connected by transverse approximators, (III) Harrington distraction plus segmental laminar wires, and (IV) Luque double "L" rods plus segmental laminar wires. The study demonstrated that the addition of segmental fixation to scoliosis instrumentation provides improved stability because of (a) multiple fixation sites and (b) prevention of deformity, especially kyphosis, within the instrumented segment (an important contributor to hook cutout when a single Harrington distraction rod is tested). Failure with the Harrington rod was always by fracture at the metal-bone interface, while failure with the Luque method always occurred outside the instrumented segment.