Morphological changes in disc herniation in the lower cervical spine: an ultrastructural study

Abstract

Introduction: The basis of disc degeneration is still unknown, but is believed to be a cell-mediated process. Apoptosis might play a major role in degenerative disc disease (DDD). The aim of this study was to correlate the viability of disc cells with the radiological degeneration grades (rDG) in disc herniation.

Materials and methods: Forty anterior IVD's (C4-C7) from 39 patients with DDD were studied histologically and ultrastructurally to quantify healthy, "balloon", chondroptotic, apoptotic and necrotic cells. Patients were classified to their rDG, as having either prolapse (P: DGII + III) and/or osteochondrosis (O: DGIV + V). Similar studies were undertaken on eight control discs.

Results: Cell death by necrosis (mean 35%) was common but differed not significantly in both groups. All patients with a disc prolapse DGII + III revealed balloon cells (iAF: mean 32%). All appeared alive and sometimes were hypertrophic. However, significantly less balloon cells were found in the O-Group. Control samples revealed no evidence of "balloon" cells in DGII and only a minor rate in DGIII.

Conclusion: According to the different rDG, quantitative changes were obvious in healthy and "balloon" cells, but not for cell death. At the moment it can only be hypothesized if "balloon" cells are part of a repair strategy and/or cause of disc herniation.

Fig. 1

Box and whisker plots of the incidence of total cell counts per mm² identified by light microscopic appearance in the outer and inner annulus fibrosus and nucleus pulposus of human discs with different degeneration grades (DG II–V) and for the control discs. The boxes show the 25 and 75% percentile and median (horizontal line) values. Bars show the upper and lower extremes

Fig. 2

Box and whisker plots of the incidence of cell death (trypan blue positive cells, TUNEL positive cells) identified by light microscopic appearance in the outer and inner annulus fibrosus and nucleus pulposus of human degenerated discs with different degeneration grades (DG II–V) and for the control discs. The incidence of trypan blue-positive cells and TUNEL positive cells identified by light microscopy, fluorescence microscopy, respectively, of the same groups is shown equally for the different disc regions. The boxes show the 25 and 75% percentile and median (horizontal line) values. Bars show upper and lower extremes

Fig. 3

Box and whisker plots of the incidence of different cell morphologies identified by ultrastructural appearance in the outer and inner annulus fibrosus and nucleus pulposus of human degenerated discs with different degeneration grades (DG II–V) and for the control discs. The incidence of different disc cell morphologies of the same groups is shown equally for the different disc regions. The boxes show the 25 and 75% percentile and median (horizontal line) values. Bars show the upper and lower extremes

Fig. 4

a A healthy cell in the iAF at a magnification of 8,000×. Patient (No 18 P) and DG III: Note the intact cell membranes of rough endoplasmic reticulum. Evidence of glycogen storage (black arrow). Intact disc matrix where the cell is aligned in between the collagen bundles. b A cross-section of a healthy cell cluster in the iAF at a magnification of 1,600×. Patient (No 2 O) aged 47 years with severe osteochondrosis/DG IV (C5/6). No obvious glycogen storage in those healthy-appearing cells. Note the fine collagenous fibres of inner AF next to the lacuna. Cell residuum is pointed with a black arrow. c Necrosis in a patient of the osteochondrosis group at a magnification 8,000×. Patient (No 10 O) aged 46 years DG IV (C6/7) oAF. The nucleus without a visible double layer membrane surrounded by necrotic cell cytoplasm (black arrow). Note also dissolution of the matrix. d A chondroptotic cell at a magnification 8,000×. Cell from the iAF. Patient (No 20 P) aged 42 years DG III (C6/7). A dense cell matrix with osmiophilic stained organelles with some vacuolization. The nucleus shows many areas of condensed darkly staining heterochromatin (white arrow). e A ‘balloon’ cell in a patient of the prolapse group at a magnification of 8,000×. Patient (No 9 P) aged 55 years DG II (C5/6) in the iAF. The nuclear matrix stains entirely homogeneously with evidence of euchromatin (black arrow). Next to the nucleus the Golgi Apparatus (white arrow). There is evidence of organelle structure and heavy osmophilic cytoplasmic inclusions that may be glycogenic. f A ‘balloon’ cell cluster in the NP at a magnification of 2,000×: Patient (No 3 P) aged 36 years with disc prolapse DG II (C6/7). Again, the nucleus stains homogeneously. Also here evidence of glycogen storage. Note the huge lacuna with thin collagen fibres (black arrow)