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. 2022 Apr 22;5(2):e1198. doi: 10.1002/jsp2.1198

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© 2022 The Authors. JOR Spine published by Wiley Periodicals LLC on behalf of Orthopaedic Research Society.

This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc-nd/4.0/ License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

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Microscopical evaluation showed intervertebral discs (IVD) degeneration changes in all defect types. Representative microscopical changes observed during histopathological grading from a sheep model of injured lumbar IVD using 3 different annulus fibrosus (AF) status (slit, cruciate, box‐cut AF defect) followed by a 0.1 g nucleus pulposus (NP) removal. (A‐B) Severe morphological changes in the AF and NP visualized by illumination with polarized light characterized by a disruption and de organization of the structured annular lamellae (delamination; arrowheads). Depletion of proteoglycan content of the AF and part of the NP regions demonstrated by markedly reduced Safranin O staining (asterisk) compared to a normal intensely stained region is also observed; scale bar: 1 mm. (C) Cleft formation visualized by illumination with polarized light characterized by complete discontinuation of fibrils leading to the formation of voids (open arrows); scale bar: 200 μm. (D) Changes in cell morphology characterized by the formation of differently sized clusters of rounded chondrocytic cells; scale bar: 100 μm. (E) Blood vessel ingrowth characterized by small capillaries in close vicinity of an IVD defect (not shown in the picture); scale bar: 50 μm. (F) Influx of inflammatory cells characterized by aggregation of round to oval lymphocytic cells in close vicinity of an IVD defect (not shown in the picture); scale bar: 50 μm. (nondecalcified, resin‐embedded, Safranin O‐Fast Green‐stained thick‐sections)