Abstract
Bone is a dynamic structure and is known to respond to changes in the load over time, in accordance with Wolff’s law. It states that the bone changes its shape and internal architecture in response to stresses acting on it [1]. Therefore, any structural changes in the spine may lead to bone remodeling due to changes in the optimal stress pattern. The changes in apparent density and thickness of the endplates following discectomy of varying amounts were analyzed. The study design coupled a bone remodeling algorithm based on strain energy density theory of adaptive remodeling with an experimentally validated 3D ligamentous finite element model of the spine. The apparent density and thickness of the index level endplates decreased above and below the region of discectomy. On the other hand, these parameters showed increases at the remaining regions of the endplate. There were no correlations between the amount of nucleus removed and the average percentage changes in apparent density and thickness of endplate above and below the discectomy region. However, the average percentage changes in apparent density and thickness at endplate in the other region increased with increase in amount of nucleus removed. These predictions are in agreement with the clinical observations [2-6].
Highlights
The vertebral endplate is a thin layer of dense subchondral bone which forms an interface between the intervertebral disc and the cancellous bone within the vertebral body [7]
There were no correlations between the amount of nucleus removed and the average percentage changes in apparent density and thickness of endplate above and below the discectomy region
For clarity the results are sub grouped in to two categories based on the region of endplate: 1) Endplate regions below and above the discectomy region: Region of the endplates directly above and below the dissected nucleus pulposus and annulus fibrosus, and
Summary
The vertebral endplate is a thin layer of dense subchondral bone which forms an interface between the intervertebral disc and the cancellous bone within the vertebral body [7]. Roberts et al found that the thickness of the subchondral vertebral bone is proportional to the amount of proteoglycan content of the adjacent disc [6] These studies supports the theory that endplate responds to the hydrostatic pressure and undergoes remodeling. These changes in endplate morphology due to structural changes in the disc are critical because of the accompanying alterations in the nutrient permeability of the endplates. Malinin et al studied the changes in the vertebral body adjacent to the acutely narrowed intervertebral disc in a baboon model [2]. Histological examination of Modic type 2 shows endplate disruption with yellow marrow replacement in the adjacent vertebral body.
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