Histological analysis of surgical lumbar intervertebral disc tissue provides evidence for an association between disc degeneration and increased body mass index

Abstract

Background: Although histopathological grading systems for disc degeneration are frequently used in research, they are not yet integrated into daily care routine pathology of surgical samples. Therefore, data on histopathological changes in surgically excised disc material and their correlation to clinical parameters such as age, gender or body mass index (BMI) is limited to date. The current study was designed to correlate major physico-clinical parameters from a population of orthopaedic spine center patients (gender, age and BMI) with a quantitative histologic degeneration score (HDS).

Methods: Excised lumbar disc material from 854 patients (529 men/325 women/mean age 56 (15-96) yrs.) was graded based on a previously validated histologic degeneration score (HDS) in a cohort of surgical disc samples that had been obtained for the treatment of either disc herniation or discogenic back pain. Cases with obvious inflammation, tumor formation or congenital disc pathology were excluded. The degree of histological changes was correlated with sex, age and BMI.

Results: The HDS (0-15 points) showed significantly higher values in the nucleus pulposus (NP) than in the annulus fibrosus (AF) (Mean: NP 11.45/AF 7.87), with a significantly higher frequency of histomorphological alterations in men in comparison to women. Furthermore, the HDS revealed a positive significant correlation between the BMI and the extent of histological changes. No statistical age relation of the degenerative lesions was seen.

Conclusions: This study demonstrated that histological disc alterations in surgical specimens can be graded in a reliable manner based on a quantitative histologic degeneration score (HDS). Increased BMI was identified as a positive risk factor for the development of symptomatic, clinically significant disc degeneration.

Figure 1

Histomorphological signs for disc degeneration. a increase of cell density (chondrocyte proliferation) with moderate clones of chondrocytes (arrows) in the NP of a 42 years old patient (score 4). b severe occurrence of granular changes (arrows) in the NP of a 67 years old patient (score 3). c structural alterations with tears and clefts (arrows) in the AF of a 54 years old patient (score 3). d severe increase in acid mucopolysaccharides (mucous degeneration) with dark blue staining areas around clones of chondrocytes (arrows) in the NP of a 77 years old patient. (a-c H&E stain; d Alcian blue-PAS stain/a-d scale bar 100 μm).

Figure 2

Distribution of both sexes in relation to the investigated years (relative numbers per year in percentage).

Figure 3

Age distribution of the patient population in absolute numbers.

Figure 4

Histologic Degeneration Score (HDS) of the annular (AF) and nuclear (NP) region in relation to gender (Box-Plot).

Figure 5

Distribution of male and female patients in relation to the Body mass index (BMI) (relative numbers in percentage).

Figure 6

Interrelation of the annular (AF) and nuclear (NP) HDS with the BMI (mean +/- 2 Stdev).

Figure 7

Correlation of the annular (AF) and nuclear (NP) HDS with patient age groups (mean +/- 2 Stdev).