Validation of the intervertebral disc histological degeneration score in cervical intervertebral discs and their end plates.

BACKGROUND CONTEXT: Vertebral joints consist of intervertebral discs (IVDs) and cartilaginous end plates (EP) that lie superiorly and inferiorly to the IVDs and separate them from the adjacent vertebral bodies. With aging, both IVDs and EPs undergo degeneration. The Histologic Degeneration Score (HDS) is a grading system that microscopically evaluates the degree of degeneration in lumbar discs and predicts it with high accuracy basing on several histological markers of IVD and EP. There is currently a lack of validated histologic grading schemes for cervical spine degeneration.

PURPOSE: The aim of our study was to describe the changes in cervical IVDs and EPs with degeneration and to test the validity of the HDS in the cervical spine.

STUDY DESIGN: A histological study on degenerative changes in cervical IVDs and EPs was conducted.

METHODS: Thirty human cadavers were dissected to obtain 60 cervical IVDs from the lower half of C4 to the level of the upper half of C6. The IVDs were carefully excised along with EPs and then sectioned to obtain midsagittal samples for macroscopic examination according to a five-grade classification system. The samples were further dissected, fixed, and stained for histological examination according to HDS.

RESULTS: Thirty C4-C5 IVDs and thirty C5-C6 IVDs were macroscopically examined for degeneration. The averaged Thompson's grade was found to be 2.9±1.3. The mean HDS for IVDs was 13.1±5.8 and for EP was 10.2±5.2. The interrater reliability estimates indicated excellent reliability (κ values>0.81, percentage agreement 86.1%-96.1%). Spearman's rank correlation coefficients for IVD and EP scores showed good consistency in predicting macroscopic degeneration. No significant differences were found between the values for cervical IVDs and EPs in the present study and those for lumbar discs derived in previous studies.

CONCLUSIONS: The HDS was confirmed to be as accurate in predicting the degree of degeneration in the cervical spine as in the lumbar region. To our best knowledge, this is the first reported and validated histological classification system intended for assessing histological degeneration in the cervical spine. Therefore, HDS can be recommended for academic and pathologic purposes in cervical disc degeneration.