Updated: 3/3/2018

Cartilage

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Questions
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Evidence
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https://upload.orthobullets.com/topic/9014/images/fibrocartilage.jpg
https://upload.orthobullets.com/topic/9014/images/elastic.jpg
https://upload.orthobullets.com/topic/9014/images/epiphysealplate001.jpg

                                        

Introduction
  • 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 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  
  • 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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Questions (3)
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(OBQ07.250) SOX-9 is a key transcription factor involved in the differentiation of which of the following cell lineages? Review Topic

QID: 911
1

Osteoclasts

8%

(145/1821)

2

Osteoblasts

16%

(287/1821)

3

Chondrocytes

59%

(1072/1821)

4

Fibroblasts

8%

(139/1821)

5

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

9%

(165/1821)

ML 3

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