Effects of bone cement on intervertebral disc degeneration

Abstract

Percutaneous vertebroplasty (PVP) is popular for the treatment of intractable pain due to vertebral collapse from various lesions, intervertebral disk leakage of cement is a frequent complication. The aim of this study was to determine whether bone cement causes disc degeneration, and to evaluate the degree of intervertebral disc degeneration (IDD) according to the time period following cement injection, and the type and volume of cement injected. Sixteen dogs were randomly divided into two groups that were sacrificed at 12 or 24 weeks following cement injection. Five intervertebral discs in each dog were studied, including one control untreated disc and four discs randomly injected with polymethylmethacrylate (PMMA) or calcium phosphate cement (CPC) in two quantities. Radiographic and magnetic resonance imaging (MRI) studies were performed prior to animal sacrifice. T2-weighted mid-sagittal images of the discs were qualitatively analyzed for evidence of degeneration by calculating the MRI index, and all harvested discs were studied histopathologically. IDD was not evident in control discs. Univariate analysis revealed significant differences in the MRI index and the histological grade of disc degeneration in terms of the time period following cement injection, as well as the type and volume of cement injected. Result indicate that direct contact with PMMA and CPC can lead to IDD. However, IDD induced by PMMA was more severe than that induced by CPC. The extent of IDD was found to correlate with the time period post-cement injection and the volume of cement injected into the disc. PMMA and CPC may lead to intervertebral disc degeneration. Intervertebral disc degeneration induced by PMMA is more serious than that of CPC. The degree of intervertebral disc degeneration is correlative to the time after operation and the doses of bone cement.

Keywords: calcium phosphate cement; degeneration; intervertebral disc; magnetic resonance imaging; polymethyl methacrylate; vertebroplasty.

Figure 1

Lateral view of the X-ray film prior to and following cement injection.

Figure 2

Images at 24 weeks after injection of 0.3 ml polymethylmethacrylate (A) T1-weighted image shows irregular and patchy low signals in the intervertebral space, where the intervertebral disc exhibited an abnormal shape. (B) T2-weighted images show that the area of relatively high signal declined. (C) Axial T2-weighted image shows the irregular shape of the nucleus pulposus, and the patchy high signals in the annulus fibrosus, which did not have a clear boundary with the nucleus pulposus.

Figure 3

Images at 24 weeks after injecting 0.1 ml polymethylmethacrylate. (A) T1-weighted images reveal irregularity in the intervertebral space. (B) T2-weighted images demonstrate that the area of relatively high signal declined. Note the region of relative high signal where the degeneration of the nucleus pulposus happened was outlined on the screen and the computer mouse was used to define the region of interest.

Figure 4

(A) MRI indexes for the PMMA and CPC subgroups in the 12- and 24-week groups. (B) MRI indexes for the various quantities of cement subgroups in the 12- and 24-week groups. MRI, magnetic resonance imaging; PMMA, polymethylmethacrylate; CPC, calcium phosphate cement.

Figure 5

Histological examination using hematoxylin and eosin. (A) Note the marginally interrupted border between the annulus fibrosus and nucleus pulposus, and the tortuosity of the annulus fibrosus. (B) Note the moderate rupture between the annulus fibrosus and nucleus pulposus (magnification, ×100).

Figure 6

Histological examination using hematoxylin and eosin. (A) The number of cells in the nucleus pulposus was reduced and the extracellular matrix was condensed within the adjacent polymethylmethacrylate. (B) The number of cells in the nucleus pulposus was reduced and the extracellular matrix was condensed slightly within the adjacent calcium phosphate cement (magnification, ×100).

Figure 7

(A) Pathology scores for the PMMA and CPC subgroups in the 12- and 24-week groups. (B) Pathology scores for the various quantities of cement subgroups in the 12- and 24-week groups. PMMA, polymethylmethacrylate; CPC, calcium phosphate cement.