Adam C. Abraham, Hannah M. Pauly, Tammy L. Haut Donahue
The ability of menisci to prevent osteoarthritis (OA) is dependent on the integrity of the complex meniscal entheses, the attachments of the menisci to the underlying subchondral bone. The goal of this study was to determine mechanical and structural changes in meniscal entheses after the onset of osteoarthritis.
Healthy and osteoarthritic meniscal entheses were evaluated for changes in histomorphological characteristics, mineralization, and mechanical properties. GAG and calcium in the insertion were evaluated with histological staining techniques. The extent of calcium deposition was assessed and tidemark integrity was quantified. Changes in the mineralized zone of the insertion was examined using micro-computed tomography to determine bone mineral density, cortical zone thickness, and mineralization gradient. Mechanical properties of the entheses were measured using nanoindentation techniques to obtain material properties based on viscoelastic analysis.
GAG thickness in the calcified fibrocartilage zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. Tidemark integrity was significantly decreased in OA tissue, particularly in the medial anterior enthesis. The mineralized zone of osteoarthritic meniscal entheses was significantly thicker than in healthy entheses and showed decreased bone mineral density. Fitting of mineralization data to a sigmoidal Gompertz function revealed a lower rate of increase in mineralization in osteoarthritic tissue. Analysis of viscoelastic mechanical properties revealed increased compliance in osteoarthritic tissue.
These data suggest that significant changes occur at meniscal enthesis sites with the onset of osteoarthritis. Mechanical and structural changes in meniscal entheses may contribute to meniscal extrusion, which has been show to increase the progression of OA.