Abstract:

BACKGROUND: Surgeons usually need to estimate the rod length according to the feature of the deformity and the length of the rod model made before the correction. But such estimation is not precise.
OBJECTIVE: To calculate preoperatively the length of the rod for patients with adolescent idiopathic scoliosis (AIS) using computer and to evaluate the validity and accuracy of this method.
METHODS: The spinal spiral CT of the patients with AIS was manipulated by the MIMICS software to reconstruct a three-dimensional model of all the vertebrae needing to be corrected. The vertebrae’s positions were adjusted to mimic the orthopaedic result of the operation, and the length of the orthopaedic rod can be calculated using short straight line by the software’s measuring tool. Seven patients were selected. The length of the orthopedic rod was calculated by MIMICS software and traditional method, anterior and posterior position X-ray of vertebral column were done postoperatively to measure the ideal length of the orthopaedic rod to evaluate the accuracy of the method.
RESULTS AND CONCLUSION: For validity evaluation, the interobserver variability was (2.492±2.089) mm, and r=0.986, P=0.000 for the intra observer variability. The rod length measured by the software was (4.23±3.84) mm longer than the ideal length, while the length measured by the traditional method was (9.32±5.23) mm longer. The P value was 0.021, and the difference was statistically significant. The method of calculating preoperatively the length of the orthopaedic rod for patients with AIS using MIMICS software has good validity and reproducibility; this method also has good accuracy, which can be put into practical use.