Surface strain distribution on thoracic and lumbar vertebrae under axial compression - The role in burst fractures

Study Design. The surface strain distribution on the thoracic and lumbar vertebrae during axial compressive loading was examined. Objectives. To examine the general mechanical behavior of the thoracic and lumbar vertebrae to evaluate their role in burst fractures. Summary of Background Data. Burst fractures are generally characterized by injury to the middle column and fracturing of the superior endplate. However, results in previous biomechanical investigations have not shown how these fractures are initiated during compression. Methods. Twenty-one thoracic and lumbar vertebrae (5 T10, 10 L1, and 6 L4) with upper and lower vertebrae were studied. Three-axis rosette strain gauges were cemented to 11 sites on the vertebral surface. An axial compressive load was applied, and the strain was measured in each specimen. The strain recorded by each rosette gauge was converted into a tensile, compressive, and shear component. Results. The highest tensile and compressive strain was recorded at the base of the pedicle. Shear strain in the vertebral body was significantly higher than that in the lamina at all three spinal levels. At L1 and L4, the tensile strain at the superior vertebral rim was higher than that at the inferior rim. Conclusions. The high tensile and compressive strains found at the base of the pedicle of T10, L1, and L4 indicate that the base of the pedicle is the site of fracture initiation. The higher tensile strain at the superior vertebral rim of L1 and L4 supports the clinical observation of the thoracolumbar burst fractures.