K. M. Cheung, K. Yeung, W. W. Lu, K. D. Luk, The University of Hong Kong, Hong Kong, Hong Kong; J. C. Chung, P. K. Chu, City University of Hong Kong, Hong Kong, China; C. L. Chu, Southeast University, Nanjing, China
Introduction: Full scoliosis correction rarely achieves due to visco-elasticity of spinal tissues. Use of excessive force in attempting 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 once, but will apply a constant and predictable correction force following surgery, allowing progressive and continuous deformity correction without inducing neurological problems or compromise of implant-bone interface. By using goat models, this study aims to demonstrate that the new implant using super-elastic NiTi can be used as an internal fixator to safely overcome the viscoelasticity 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.
Summary: Full scoliosis correction rarely achieves due to visco-elasticity of spinal tissues. Use of excessive force in attempting 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 once, but will apply a constant and predictable correction force following surgery, allowing progressive and continuous deformity correction without inducing neurological problems or compromise of implant-bone interface. By using goat models, this study aims to demonstrate that the new implant using super-elastic NiTi can be used as an internal fixator to safely overcome the viscoelasticity of the spine and progressively change the spinal curvature.
