The biomechanics of 1, 2, and 3 levels of vertebral augmentation with polymethylmethacrylate in multilevel spinal segments.

Abstract

Experimental biomechanics of multilevel segments with 0, 1, 2, and 3 vertebral levels of polymethylmethacrylate augmentation. To compare multilevel spinal segments with different numbers (0, 1, 2, and 3) of vertebral levels augmented with polymethylmethacrylate. The stiffness and strength of single-level polymethylmethacrylate augmentations in individual and multilevel vertebrae treated by kyphoplasty and vertebroplasty have been studied, but the biomechanics of multilevel segments with more than 1 vertebral level augmented with polymethylmethacrylate are lacking, yet this is clinically relevant in multilevel compression fracture treatment. A total of 48 multilevel segments (T3-T5, T6-T8, T9-T11, T12-L2, and L3-L5) from 12 spines with known bone mineral density (BMD) were allocated into 6 groups based on the number of vertebral levels augmented: 0 levels (n = 13), control group; 1 level (n = 7), group 2; 2 levels, groups 3, 4, and 5 (n = 7 in each); and 3 levels (n = 7), group 6. They were compressed to failure, disarticulated into individual vertebrae, and retested. Stiffness and strength were statistically analyzed using a univariate analysis of variance comparing the main effects, using least significant difference comparisons with 0.05 probability level. Strength was dependent on BMD (P < 0.001 multilevel segments, P < 0.001 individual vertebrae), with no differences among the 6 different augmentation groups, and no significant differences between augmented and nonaugmented individual vertebrae. Stiffness was dependent on BMD (P = 0.009 multilevel segments, P < 0.004 individual vertebrae), with no significant differences among the 6 different augmentation groups, and no significant differences between augmented and nonaugmented individual vertebrae. Multilevel segment biomechanics are dependent on BMD and not the pattern of augmentation, so the augmentation of fractured vertebrae can be extended to adjacent levels at risk for fracture to maintain stiffness and strength, thus preventing further fractures.