Abstract
Numerous studies have examined the biomechanical properties of the vertebral body following PMMA cement augmentation for the treatment of osteoporotic vertebral body fractures. To date there is no published literature reporting the effects of Vertebroplasty on internal intervertebral disc biomechanics which in turn have been shown to reflect loading patterns of the vertebral column.
To study effects of PMMA cement augmentation of vertebral body fractures on intervertebral disc biomechanics using stress prolifometry to assess differential anterior and posterior vertebral column loading.
Eight cadaveric motion segments were individually loaded on a hydraulically powered materials testing machine under 1.5kN of axial compression. Following fracture induction the lower vertebral body underwent Vertebroplasty.
Profiles of the vertically acting compressive stress were obtained by pulling a pressure sensitive transducer along the mid-sagittal diameter of the intervertebral disc. “Stress profile” measurements were obtained before fracture, following fracture, and after vertebro-plasty both in extension and flexion.
Stress profiles were integrated over area to calculate the compressive force across the disc. The compressive load acting on the neural arch was calculated by subtracting the disc force from the applied 1.5kN load.
In flexed postures posterior column loading increased from 17.1% to 42.2% following fracture (p< 0.01) and then decreased significantly from 42.2% to 23.68% following vertebroplasty (p< 0.03). There was no significant difference between pre-fracture and post-vertebroplasty status (p=0.11). In extended posture, fracture produced increased posterior column loading 72.9% vs 51.8% (p< 0.005) and following vertebroplasty there was no significant change (p=0.2).
In moderate degrees of flexion, vertebroplasty produces normalisation of load bearing through the anterior vertebral column and hence offloads the posterior elements to a significant degree. This could be postulated, to partly account for the analgesic effect seen following vertebroplasty in the clinical setting.
The abstracts were prepared by Mr Richard Buxton. Correspondence should be addressed to him at Bankton Cottage, 21 Bankton Park, Kingskettle, Cupar, Fife KY15 7PY, United Kingdom
