Abstract: BACKGROUND: Halo gravity traction is a pre-operative traction method recognized by many scholars, but most of them rely on clinical observation and lack finite element analysis.
OBJECTIVE: To explore the best traction force of Halo gravity traction on Lenke 3 scoliosis by finite element method and to provide a theoretical basis for clinics from a biomechanical point of view.
METHODS: The CT images scanned by patients with scoliosis were processed by reverse modeling, and a finite element model was established. The validity of the model was verified by taking normal segments (T1-T4 vertebral bodies). Five groups of different stress conditions were set on the lumbar-thoracic scoliosis model to simulate the correction of patients under different traction forces. In all five groups, the lower surface of L5 was completely restrained, and different traction forces were applied to the upper surface of T1 along the positive direction of the Z axis (the opposite direction of gravity), which were 50, 100, 150, 200, and 250 N, respectively. The displacement of the scoliosis spine, Cobb angle change of the main bending, elongation of the spine, and Von Mises stress were compared under different traction forces.
RESULTS AND CONCLUSION: (1) When the Halo gravity traction force was 150 N to 200 N, the reduction of the Cobb angle of the main bending was 69.4% to 88.9% of the maximum reduction; the elongation of the Z axis was 69.4% to 85.9%, and the stress was 63.6% to 82.9% of the maximum stress. (2) When the traction force was greater than 200 N, the reduction of the Cobb angle and the elongation of the Z axis did not change obviously, but the stress value increased sharply. At this time, the distance from the centroids of T6, T7, and T8 to the vertical line of L5 was the most obvious. (3) When the Halo gravity traction force was 150 N to 200 N, the correction effect on this type of patient was the best—the reduction of Cobb angle and the elongation of the Z axis were better without the sharp increase in stress. (4) It has certain theoretical support for clinical correction and can ensure the safety of patients when scoliosis is corrected to a large extent.

Key words: spinal scoliosis, Halo gravity traction, Cobb angle, finite element