Introduction: Current scoliosis surgery rarely achieves full correction due to visco-elastic properties of spinal tissues. Use of excessive force in attempting a full correction may result in bony fractures or neurological deficit due to spinal cord damage. Our new correction approach is to establish a correction force over the scoliotic spine that may not completely straighten the deformity at the time of operation, but will apply a constant and predictable correction force following surgery, allowing progressive and continuous correction of the deformity without inducing neurological problems or compromise of the implant-bone interface. This study aims to demonstrate in a goat model that the new implant using super-elastic nickel titanium alloy can be used as an internal fixator to safely overcome the viscoelastic properties of the spine and progressively change the spinal curvature.

Methodology: Lumbar spine segments of 5 goats were exposed posteriorly. A pre-contoured super-elastic rod, with a curvature of 60°, is first cooled to 20°C, straightened and then implanted. After implantation, the rods were warmed to body temperature and the rate of scoliosis development initially observed clinically, and then after wound closure by daily radiographs.

Results: Only a 15° curve was induced immediately after surgery. Scoliosis between 25° and 30° developed by 2 days, and progressed to between 45° to 50° by 1 week.

Discussion and conclusion: The results demonstrated that super-elastic rods can be used to progressively create scoliosis. The reverse should also be true, and their use should allow more complete correction of spinal deformities. Previous concerns with Ni release by NiTi alloys have been overcome by recent advances in nanotechnology surface treatment. A new generation of super-elastic spinal implants will help improve safety and efficacy of spinal deformity surgery.

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