title: Deleterious effects of osteoarthritis on the structure and function of the meniscal enthesis.
abstract: OBJECTIVE
  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 (SB). The goal of this study was to determine mechanical and structural changes in meniscal entheses after the onset of OA.
  
  
  METHODS
  Healthy and osteoarthritic meniscal entheses were evaluated for changes in histomorphological characteristics, mineralization, and mechanical properties. Glycosaminoglycans (GAG) and calcium in the insertion were evaluated with histological staining techniques. The extent of calcium deposition was assessed and tidemark (TM) integrity was quantified. Changes in the mineralized zone of the insertion were examined using micro-computed tomography (μCT) to determine bone mineral density, cortical zone thickness, and mineralization gradient. Mechanical properties of the entheses were measured using nano-indentation techniques to obtain material properties based on viscoelastic analysis.
  
  
  RESULTS
  GAG thickness in the calcified fibrocartilage (CFC) zone and calcium content were significantly greater in osteoarthritic anterior meniscal entheses. TM integrity was significantly decreased in OA tissue, particularly in the medial anterior (MA) 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.
  
  
  CONCLUSIONS
  These data suggest that significant changes occur at meniscal enthesis sites with the onset of OA. Mechanical and structural changes in meniscal entheses may contribute to meniscal extrusion, which has been shown to increase the progression of OA.
authors: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: acabraha@engr.colostate.edu.
authors: A C
authors: AC
authors: Abraham
authors: School of Biomedical Engineering, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: hmpauly1@gmail.com.
authors: H M
authors: HM
authors: Pauly
authors: Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: tammy.donahue@colostate.edu.
authors: T L Haut
authors: TL
authors: Donahue
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D015519:Bone Density / Q000502:physiology; D002118:Calcium / Q000032:analysis; D055119:Elastic Modulus; D006025:Glycosaminoglycans / Q000032:analysis; D006801:Humans; D008592:Menisci, Tibial / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000473:pathology* / Q000503:physiopathology; D014783:Viscosity; D055114:X-Ray Microtomography
chemical_list: D006025:Glycosaminoglycans; D002118:Calcium
keywords: Graded tissue interface; Histomorphometry; Mechanical properties; Root Insertions; Tidemark