Correlation Between Collagen Alignment and Viscoelastic Properties of TMJ Disc

Objectives: The TMJ disc features regional-dependent and anisotropic mechanical properties associated with regional variations of the direction of collagen alignment. Previous histological and SEM analyses of the disc revealed that collagen fibers are predominantly aligned in circumferential and anteroposterior directions in the peripheral bands and intermediate zone, respectively. However as of yet, there has not been an attempt for a quantitative analysis of the collagen alignment in each region of the disc. Here, we quantitatively analyzed the degree of collagen alignment using automated imaging analysis and determined its statistical correlation with region-variant viscoelastic properties of the human TMJ disc.

Methods: Human TMJ discs (age 45 – 60) were obtained from the National Human Tissue Resource Center. Horizontal sections with Picrosirius Red staining were imaged under polarized microscopy, as per our established methods. Mean angle and angular deviation (AD) of collagen fibers in each region of the TMJ disc were analyzed using our generated automated image-processing with Matlab. Instantaneous and relaxation moduli of each disc region were measured under a stress-relaxation test. A Spearman correlation analysis was then performed between the AD and the moduli using SPSS.

Results: Our automated image-processing resulted in regionally variant directions of collagen alignment that were consistent with previous findings. Interestingly, the degree of collagen alignment, quantified by the AD value, was significantly different between the regions. AD of the anterior and intermediate regions were significantly lower than the posterior region. Medial and lateral regions displayed significantly higher AD values compared to all other regions. The regionally variant AD values showed statistically significant correlation with the instantaneous modulus but not the relaxation modulus.

Conclusions: These findings suggest that region-variant degrees of collagen fiber alignment likely contribute to heterogeneous mechanical properties of the human TMJ disc and may have significant implications in the engineering of functional replacements of the native disc.