Comparative analysis between shape memory alloy-based correction and traditional correction technique in pedicle screws constructs for treating severe scoliosis.

The three-dimensional correction of severe rigid scoliosis has been improved by segmental pedicle screw instrumentation. However, there can be significant difficulty related to the use of a rigid rod, especially in the apex region of severe scoliosis. This study is a retrospective matched cohort study to evaluate the advantages of Nitinol shape memory alloy (SMA) rod-based correction by comparing the clinical and radiographic results obtained from using a temporary SMA rod and those from a standard rod in the correction of severe scoliosis. From May 2004 to September 2006, patients with matched curve type, ages at surgery, operative methods and fusion levels in our institute and instrumented with either SMA rods (n = 14) or traditional correction techniques (n = 16) were reviewed. In SMA group, the SMA rods served as a temporary intraoperative tool for deformity correction and were replaced by standard rods. The blood loss at surgery averaged 778 +/- 285 ml in the traditional group and 585 +/- 188 ml in the SMA group (P < 0.05). Operative time averaged 284 +/- 53 min in the SMA group and 324 +/- 41 min in the traditional group (P < 0.05). In the SMA group, the preoperative major curve was 92.6 degrees +/- 13.7 degrees with a flexibility of 25.5 +/- 7.3% was corrected to 29.4 degrees +/- 5.7 degrees demonstrating a 68.4% immediate postoperative correction. In the traditional group, the preoperative major curve was 88.6 degrees +/- 14.6 degrees with a flexibility of 29.3 +/- 6.6% was corrected to 37.2 degrees +/- 7.3 degrees demonstrating a 57.8% immediate postoperative correction. There was a statistic difference between the SMA group and traditional group in correction rate of the major thoracic curve. In the SMA group, one case suffered from deep infection 2 months postoperatively. In the traditional group, 6 of 16 cases suffered pedicle screw pull out or loosening during placement of the standard rod at the apex vertebrae on the concave side. In three cases, the mono-axial pedicle screws near the apex were abandoned and in five cases replaced with poly-axial pedicle screws. This study shows that the temporary use of SMA rod may reduce the operative time, blood loss, while improve the correction of the coronal plane when compared with standard techniques.