Abstract
Recent findings suggest that vertebral osteophytes increase the resistance of the spine to compression. However, the role of vertebral osteophytes on the biomechanical response of the spine under fast dynamic compression, up to failure, is unclear. Seventeen human spine specimens composed of three vertebrae (from T5-T7 to T11-L1) and their surrounding soft tissues were harvested from nine cadavers, aged 77 to 92 years. Specimens were imaged using quantitative computer tomography (QCT) for medical observation, classification of the intervertebral disc degeneration (Thomson grade) and measurement of the vertebral trabecular density (VTD), height and cross-sectional area. Specimens were divided into two groups (with (n = 9) or without (n = 8) substantial vertebral body osteophytes) and compressed axially at a dynamic displacement rate of 1 m/s, up to failure. Normalized force-displacement curves, videos and QCT images allowed characterizing failure parameters (force, displacement and energy at failure) and fracture patterns. Results were analyzed using chi-squared tests for sampling distributions and linear regression for correlations between VTD and failure parameters. Specimens with substantial vertebral body osteophytes present higher stiffness (2.7 times on average) and force at failure (1.8 times on average) than other segments. The presence of osteophytes significantly influences the location, pattern and type of fracture. VTD was a good predictor of the dynamic force and energy at failure for specimens without substantial osteophytes. This study also showed that vertebral body osteophytes provide a protective mechanism to the underlying vertebra against severe compression fractures.
Highlights
Vertebral body osteophyte is a common form of osteoarthritis defined as an abnormal bony growth or bone spur that forms along intervertebral joints [1]
A substantial osteophyte can be found in 20–25% of spines aged 20–45 years and in 73–90% of spines aged over 60 years [2,3,4, 6]
All bony ribs and non-ligamentous soft tissues were removed from the specimens and quantitative computed tomography (QCT) images were taken using a clinical scanner (SIEMENS Somatom Sensation Cardiac 64: 120 kV, 300– 350 mAs, contiguous slices of 0.6 mm thickness) for medical observation, classification and measurement of the osteophytes, which were observed at all vertebral levels
Summary
Vertebral body osteophyte is a common form of osteoarthritis defined as an abnormal bony growth or bone spur that forms along intervertebral joints [1]. Complications associated with osteophyte formation are numerous (dysphagia, thoracic aortic compression, vena cava obstruction, nerve root compression) and affect most structures located in close-proximity to the spine. As a consequence, they are generally viewed as a degenerative condition and can be removed surgically by traditional or minimally invasive techniques during spinal surgery, when they lead to a disability or neurological symptoms [1, 7]. If osteophytes provide stability by adding bone and increasing the cross-sectional area of the vertebrae, they might provide a protective mechanism against vertebral fractures despite the generalized osteopenia observed in most aging spines
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