Correction of scoliosis with shape-memory alloy.

Using NiTi shape-memory alloy, we devised an instrument for correction of scoliosis. Our instrument is characterized by gradual correction of the spine. Restoration power of the alloy was 25 kgcm in a rod with a diameter of 3 mm, 45 kgcm in a 4-mm rod, and 110 kgcm in a 5-mm rod. Spinal cord injuries on heating the rod were observed at an epidural temperature of 48 degrees C or more, suggesting that 48 degrees C is the critical temperature. The blood Ni concentration after implantation of the NiTi alloy rod reached a level twice normal after 6-9 hours. After 4 weeks, the Ni concentration increased 4-fold in the kidneys, 2-fold in the liver, and 10-fold in the urine. Alloy rods were attached to a scoliosis monkey and heated gradually. Scoliosis with a Cobb angle of 43 degrees was completely corrected.