Quantitative, 3D Visualization of the Initiation and Progression of Vertebral Fractures Under Compression and Anterior Flexion

Abstract

The biomechanical mechanisms leading to vertebral fractures are not well understood. Clinical and laboratory evidence suggests that the vertebral endplate plays a key role in failure of the vertebra as a whole, but how this role differs for different types of vertebral loading is not known. Mechanical testing of human thoracic spine segments, in conjunction with time-lapsed micro–computed tomography, enabled quantitative assessment of deformations occurring throughout the entire vertebral body under axial compression combined with anterior flexion (“combined loading”) and under axial compression only (“compression loading”). The resulting deformation maps indicated that endplate deflection was a principal feature of vertebral failure for both loading modes. Specifically, the onset of endplate deflection was temporally coincident with a pronounced drop in the vertebra’s ability to support loads. The location of endplate deflection, and also vertebral strength, were associated with the porosity of the endplate and the microstructure of the underlying trabecular bone. However, the location of endplate deflection and the involvement of the cortex differed between the two types of loading. Under the combined loading, deflection initiated, and remained the largest, at the anterior central endplate or the anterior ring apophysis, depending in part on health of the adjacent intervertebral disc. This deflection was accompanied by outward bulging of the anterior cortex. In contrast, the location of endplate deflection was more varied in compression loading. For both loading types, the earliest progression to a mild fracture according to a quantitative morphometric criterion occurred only after much of the failure process had occurred. The outcomes of this work indicate that for two physiological loading modes, the vertebral endplate and underlying trabecular bone are critically involved in vertebral fracture. These outcomes provide a strong biomechanical rationale for clinical methods, such as algorithm-based qualitative (ABQ) assessment, that diagnose vertebral fracture on the basis of endplate depression.

Is bone density associated with intervertebral disc pressure in healthy and degenerated discs?

“…Following the pressure measurements, the IVDs in these 26 spine segments were scored according to two grading methods that require dissection, Thompson (Thompson, et al, 1990) and the histological scoring method of Rutges et al (Rutges, et al, 2013) Finally, the IVD tissues of these 26 segments were processed to measure glycosaminoglycan (GAG) content and water content. The 35 spine segments not used for IDP measurements were not processed for histology and biochemical evaluation, because they had been subjected to mechanical testing to failure in a prior study (Jackman, et al, 2016); however, Thompson scoring was still performed for the IVDs in these spine segments, and thus Thompson scores were available for the IVDs in all 61 spine segments used in the present study.…”

Accuracy of finite element analyses of CT scans in predictions of vertebral failure patterns under axial compression and anterior flexion

“…Each segment was first imaged with QCT (GE Lightspeed VCT; GE Health-care, Milwaukee, WI; 0.3125 × 0.3125 × 0.625 mm 3 /voxel) and then placed in a radiolucent device for mechanical testing. Testing involved stepwise loading (0.5 mm per step at 0.25 mm/s for compression; 0.25 mm and 0.5° per step, at 0.25 mm/s and 0.5°/s, for flexion) applied via screws within the device (Jackman et al, 2015) (Fig. 1B; Supplemental material).…”

“…For flexion, the compressive force and flexion moment experienced by the spine segment were obtained using a calibration layer as a low-profile multiaxial load cell (Supplemental material) (Jackman et al, 2015). For compression, a load cell (LLB450, Futek Advanced Sensor Technology, Irvine, CA) measured the axial force.…”

Digital Volume Correlation: Review of Progress and Challenges

“…Other applications followed in the field of biomechanics (e.g., see Refs. [194,11,106,241,17,193,44,40,43,109]). At the beginning of the current decade, DVC was clearly identified as one technique very suited to biomechanical applications [239].…”