A preliminary investigation of shape memory alloys in the surgical correction of scoliosis

Nitinol, a shape memory alloy, is flexible at low temperatures but retains its original shape whan heated. This offers interesting possibilities for scoliosis correction. Of the shape memory alloys, nitinol is the most promising medically because of biocompatibility and the ability 10 control transition temperature. In vivo: Six goats with experiments scoliosis were Instrumented with 6-mm nitinol rods, The rods were transformed, and the scoliosis corrected, in the awakened goats by 450-kHz radio frequency Induction floating. The curves averaged 41° before instrumentation, 33“ after instrumentation, and 11° after rod transformation. The animals tolerated the heating without discomfort, neurologic injury, or avidence of thermal Injury to the tissues or the spinal Lord. !r\ vitro: Nitinoi rods were tested under both constant deflection and constant loading conditions and plotted temperature versus either force or displacement. The 6-mm rod generated forces of 200 N, The 9-mro rod generated up to 500 N, We safely coupled shape memory alloy transformation to the spine and corrected an experimental spinal deformity In awake animals. The forces generated can be estimated by the rod's curvature and temperature, The use of shape memory alloys allows continuous neurologic monitoring during awake correction, true rotational correction by rod toraion, and the potential option of periodic correction to take advantage of spinal viscoelasticity and the potential of true rotational correction by rod torsion.