Background context: The vertebral augmentation procedures, vertebroplasty and kyphoplasty, can relieve pain and facilitate mobilization of patients with osteoporotic vertebral fractures. Kyphoplasty also aims to restore vertebral body height before cement injection and so may be advantageous for more severe fractures.
Purpose: The purpose of this study was to compare the ability of vertebroplasty and kyphoplasty to restore vertebral height, shape, and mechanical function after severe vertebral wedge fractures.
Study design/setting: This is a biomechanical and radiographic study using human cadaveric spines.
Methods: Seventeen pairs of thoracolumbar "motion segments" from cadavers aged 70-98 years were injured, in a two-stage process involving flexion and compression, to create severe anterior wedge fractures. One of each pair underwent vertebroplasty and the other kyphoplasty. Specimens were then compressed at 1 kN for 1 hour to allow consolidation. Radiographs were taken before and after injury, after treatment, and after consolidation. At these same time points, motion segment compressive stiffness was assessed, and intervertebral disc "stress profiles" were obtained to characterize the distribution of compressive stress on the vertebral body and neural arch.
Results: On average, injury reduced anterior vertebral body height by 34%, increased its anterior wedge angle from 5.0° to 11.4°, reduced intradiscal (nucleus) pressure and motion segment stiffness by 96% and 44%, respectively, and increased neural arch load bearing by 57%. Kyphoplasty caused 97% of the anterior height loss to be regained immediately, although this reduced to 79% after consolidation. Equivalent gains after vertebroplasty were significantly lower: 59% and 47%, respectively (p<.001). Kyphoplasty reduced vertebral wedging more than vertebroplasty (p<.02). Intradiscal pressure, neural arch load bearing, and motion segment compressive stiffness were restored significantly toward prefracture values after both augmentation procedures, even after consolidation, but these mechanical effects were similar for kyphoplasty and vertebroplasty.
Conclusions: After severe vertebral wedge fractures, vertebroplasty and kyphoplasty were equally effective in restoring mechanical function. However, kyphoplasty was better able to restore vertebral height and reverse wedge deformity.
Keywords: Anterior wedge fracture; Cadaver; Kyphoplasty; Spinal deformity; Spinal mechanics; Vertebroplasty.
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