Biomechanical, biochemical, and histological characterization of canine lumbar facet joint cartilage: Laboratory investigation

Object. Tissue engineering appears to be a promising strategy for articular cartilage regeneration as a treatment for facet joint arthritis. Prior to the commencement of tissue engineering approaches, design criteria must be established to determine the required functional properties of the replacement tissue. As characterization of the functional properties of facet joint cartilage has not been performed previously, the objective of this study was to determine the biomechanical, biochemical, and histological properties of facet joint cartilage. Methods. The in vitro testing was conducted using 4 lumbar spinal segments obtained from skeletally mature canines. In each specimen, articular cartilage was obtained from the superior surface of the L3-4 and L4-5 facet joints. Creep indentation was used to determine the compressive biomechanical properties, while uniaxial tensile testing yielded the Young modulus and ultimate tensile strength of the tissue. Additionally, biochemical assessments included determinations of cellularity, glycosaminoglycan (GAG) content, and collagen content, as well as enzymelinked immunosorbent assays for collagen I and II production. Finally, histological characterization included H & E staining, as well as staining for collagen and GAG distributions. Results. The means ± standard deviation values were determined. There were no differences between the 2 spinal levels for any of the assessed properties. Averaged over both levels, the thickness was 0.49 ± 0.10 mm and the hydration was 74.7 ± 1.7%. Additionally, the cells/wet weight (WW) ratio was 6.26 ± 2.66 × 10⁴ cells/mg and the cells/dry weight (DW) ratio was 2.51 ± 1.21 × 10⁵ cells/mg. The GAG/WW was 0.038 ± 0.013 and the GAG/DW was 0.149 ± 0.049 mg/mg, while the collagen/WW was 0.168 ± 0.026 and collagen/DW was 0.681 ± 0.154 mg/ mg. Finally, the aggregate modulus was 554 ± 133 kPa, the Young modulus was 10.08 ± 8.07 MPa, and the ultimate tensile strength was 4.44 ± 2.40 MPa. Conclusions. To the best of the authors' knowledge, this study is the first to provide a functional characterization of facet joint articular cartilage, thus providing design criteria for future tissue engineering studies.