An experimental evaluation of spinal flexibility with respect to scoliosis surgery.

Lateral flexibility of the spinal column was investigated by mechanical analysis and by experiments on fresh cadavers. The work was undertaken with the aim of improving the surgical treatment of scoliosis by quantifying the effects of ribs and transverse processes on lateral spinal flexibility. To this end, flexibilities before and after removal of the bony elements in cadavers' spines were compared. A portable instrument was built to apply loads to the spines. Generally, the spines were tested in the following sequence of conditions: intact, resected ribs on one side, resected ribs and transverse processes on the same side. The results from nine cadavers indicate that only rib resection on the tension side of the induced curve (scoliotic concavity) significantly increased spinal flexibility. It is concluded that the surgical correction of scoliotic curves with instrumentation and fusion is maximized with rib osteotomy or resection.