Updated: 6/17/2021

Cartilage

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  • Types of cartilage
    • Main types of cartilage include
      • articular (hyaline) cartilage
      • fibrocartilage (tendon/ligament junction with bone) and fibroelastic cartilage (menisci)
      • elastic cartilage (trachea)
      • epiphyseal cartilage (growth plates)
  • Cartilage biology
    • Cartilage contents (avascular, aneural, and alymphatic)
      • cells
        • chondrocytes
      • extracellular matrix
        • water
        • collagen
        • proteoglycans
        • noncollagenous proteins
    • Cell differentiation
      • cartilage is formed from mesenchymal stem cells designated towards the cartilagenous lineage
        • multi-step process involving activation and migration of cells to necessary sites
        • SOX-9 is a key transcription factor involved in the differentiation of cells towards the cartilage lineage
        • parathyroid hormone (PTH) may have chondroprotective effects
          • thought to be related to influence on indian hedgehog (IHH) signaling pathways affecting cartilage growth
    • Metabolism
      • regulated through mechanical stimulation
      • pH of cartilage is 7.4
        • disruption in pH can lead to an abnormal cartilage structure
    • Nutrition
      • oxygen and other nutrients supplied to cartilage from synovial fluid diffusion
    • Loading
      • physiologic loading is chondroprotective
      • underloading leads to cartilage thinning, tissue softening, and reduced proteoglycan content, leading to cartilage fibrillation, ulceration and erosion
      • overloading leads to cartilage damage (in vitro only)
        • has not been shown in clinical setting
  • Articular (Hyaline) cartilage
    • Complete Topic
    • Location
      • articular surfaces
      • ribs
      • nasal septum
    • Composition
      • water > collagen > proteoglycan > noncollagenous protein > cells
        • water = 65% to 80% of mass of the cartilage
        • Type II collagen = provides cartilagenous framework and tensile strength
        • proteoglycans = function to provide compressive strength and attract water
        • chondrocytes = produce collagen, proteoglycans, and enzymes
    • Function
      • decreases friction and distributes loads
      • cartilage exhibits stress-shielding of the solid matrix components due to its high water content, the incompressibility of water, and the structural organization of the proteoglycan and collagen molecules
  • Fibrocartilage
    • Location
      • tendon/ligament junction with bone
      • pubic symphysis
      • annulus fibrosis of the intervertebral disc
      • menisci
    • Composition
      • fibrous cartilage
        • Type I collagen (predominantly)
        • extracellular matrix
          • proteoglycans
        • chondrocytes
        • water
      • fibroelastic cartilage
        • fewer proteoglycans and glycoproteins compared to hyaline cartilage
    • Function
      • healing response to injury of articular cartilage including
        • chondroplasty microfracture
        • drilling
        • abrasion arthroplasty
      • compressive strength
  • Elastic Cartilage
    • Location
      • auricle of external ear
      • epiglottis
      • auditory tube
    • Composition
      • chondrocytes surrounded by a thin collagenous network
        • Type II collagen (predominantly)
        • elastin fiber network
        • extracellular matrix
          • proteoglycans and glycoproteins
        • chondrocytes
        • water
    • Function
      • highly elastic
      • designed to tolerate repetitive deformation
  • Epiphyseal cartilage
    • Location
      • also known as the epiphyseal plate or epiphyseal ossification center
      • between the epiphysis and metaphysis at each end of long bones
    • Composition
      • stacked chondrocytes are divided into different zones of maturation
      • proteoglycans and growth factor (e.g.BMP-2) are found in the extracellular matrix between chondrocytes
      • progressive chondrocyte maturation and calcification of the extracellular matirix
      • infiltration of osteoprogenitor cells to produce osteoblasts and osteoid
    • Histology of Epiphyseal cartilage
      • Reserve zone
      • Proliferative zone
      • Hypertrophic zone
      • Primary spongiosa
      • Secondary spongiosa
    • Function
      • linear growth via endochondral ossification
      • can allow extensive bone deformity remodeling potential
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(OBQ07.250) SOX-9 is a key transcription factor involved in the differentiation of which of the following cell lineages?

QID: 911
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Osteoclasts

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Osteoblasts

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Chondrocytes

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Fibroblasts

7%

(174/2346)

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SOX-9 is not a transcription factor, it is a transmembrane tyrosine kinase receptor

9%

(212/2346)

L 3 C

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