Updated: 6/5/2018

Articular Cartilage

Topic
Review Topic
0
0
Questions
30
0
0
Evidence
17
0
0
Videos
1
https://upload.orthobullets.com/topic/9017/images/cartilage layers.jpg
https://upload.orthobullets.com/topic/9017/images/encyclopedia[1]_moved.gif
Introduction
  • Articular cartilage is one of five forms of cartilage
    • hyaline or articular cartilage
    • fibroelastic cartilage (meniscus)
    • fibrocartilage (at tendon and ligament insertion into bone)
    • elastic cartilage (trachea)
    • physeal cartilage (growth plate)
Articular (hyaline) Cartilage Components
  • 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 
  • Composition
    • includes
      • extracellular matrix (water, 90% type II collagen, proteoglycans)
      • cells (chondrocytes)
    • % by weight
      • water > collagen > proteoglycan > noncollagenous protein > cells
  • Extracellular matrix 
    • water
      • makes up 65% to 80% of mass of the cartilage
        • accounts for 80% of the weight near the surface 
        • 65% at the deep zone
      • water content
        • decreases with normal aging
        • increases with osteoarthritis
          • increased water content leads to
            • increased permeability
            • decreased strength
            • decreased Young Modulus of elasticity
    • collagen
      • makes up 10 to 20% of total cartilage mass
      • type II collagen accounting for 90% to 95% of the total collagen content.
        • functions to provide cartilagenous framework and tensile strength
      • small amounts of types V, VI, IX, X, and XI collagen are also present
    • proteoglycans 
      • make up 10 to 15% of cartilage 
      • function to provide compressive strength and attract water  
      • aggrecan is most responsible for hydrophilic behavior 
      • produced by chondrocytes
      • proteoglycans composed of GAG subunits
        • chondroitin sulfate
        • keratin sulfate
    • noncollagenous protein
  • Cells
    • chondrocytes 
      • produce collagen, proteoglycans, and enzymes 
      • derive from chondroblasts that are trapped in lacunae and become chondrocytes
      • chondrocyte metabolism responds to both mechanical (mechanical load, hydrostatic pressure change) and chemical stimuli (growth factors, cytokines)  
      • immature articular cartilage has stem cells (mature articular cartilage does not)
Layers of Articular Cartilage 
  • Normal articular cartilage is composed of three zones and the tidemark 
    • zones based on the shape of the chondrocytes and the orientation of the type II collagen.
Zones of Articular Cartilage
Superficial zone (tangential zone) 

• Type II collagen orientation is parallel to joint 
• Has flattened chondrocytes, condensed collagen fibers, and sparse proteoglycans
• Has the highest concentration of collagen and lowest concentration of proteoglycans
 
• only zone where articular cartilage progenitor cells have been found 



Intermediate zone • Type II collagen has an oblique or random organization
• Is the thickest layer with round chondrocytes, and abundant proteoglycan content

Deep layer (basal layer)

• Type II collagen is perpendicular to joint and crosses tidemark;  has the highest concentration of proteoglycans
• Round chondrocytes arranged in columns                     


Tidemark • Is deep to the basal layer and separates the true articular cartilage from the deeper cartilage that is a remnant of the cartilage anlage, which participated in endochondral ossification during longitudinal growth in childhood.
 • The tidemark divides
- the superficial, uncalcified cartilage from the deeper, calcified cartilage
- division between nutritional sources for the chondrocytes
 • The tidemark is found only in joints 
 • Most prominently in the adult and nongrowing joint

Subchondral Bone  
 
Growth Factors
  • PDGF
    • thought to be involved with healing of articular cartilage lacerations
    • effects extrapolated from PRP (which contains it)
    • no adverse effects in normal joints
  • TGF-
    • stimulates proteoglycan and ECM synthesis
    • decreases catabolic activity of IL-1 and MMPs
    • causes synovial proliferation and fibrosis
    • induces osteophyte formation
  • b-FGF (Basic Fibroblastic Growth Factor)
    • stimulates DNA synthesis in articular chondrocytes
  • IGF-1 (Insulin growth factor -1)
    • stimulates DNA and cartilage matrix synthesis in adult articular cartilage
    • stimulates ECM synthesis
    • decreaes synovial thickening and chronic synovial inflammation
    • additive when combined with TGF-b
Nourishment and Metabolism
  • Cartilage is avascular
  • Nourished by 
    • synovial fluid at the surface
    • subchondral bone at the base
  • Relies on glycolysis for ATP production
Mechanical Stress Response
  • Physiologic stress stimulates matrix synthesis and inhibits chondrolysis 
    • cyclic stress (1-5 MPa)
    • moderate frequency (0.1-1 Hz)
    • low rates (<1000 MPa/s)
  • Excess stress suppresses matrix synthesis and promotes chondrolysis
    • excess stress (>5 MPa)
    • static load (<0.01 Hz)
    • high rates (>1000 MPa/s)
  • Cellular responses
    • primary cilia act as a mechanosensory organ on chondrocytes and osteoblasts
    • transduction of mechanical signals involves integrins
  • Repetitive loading
    • moderate running increases cartilage thickness and proteoglycan content
    • strenuous loading leads to cartilage thinning and proteoglycan loss
    • immobilization leads to cartilage thinning, softening and proteoglycan loss 
Wear Mechanics
  • Forms of lubrication
    • elastohydrodynamic
      • main mechanism during dynamic joint function
      • elastic deformation of articular surfaces
      • thin films of lubricant separate the surfaces
      • a fully congruent joint will not allow a fluid film to form 
    • boundary (slippery surfaces)
      • bearing surface is non-deformable
      • lubricant only partially separates surfaces
      • superficial zone proteins have a role in this lubrication mechanism
    • boosted (fluid entrapment)
      • concentration of lubricating fluid in pools 
      • trapped by regions of bearing surfaces that are making contact
    • hydrodynamic
      • fluid separates surfaces when one surface is sliding on the other
    • weeping 
      • fluid shifts out of articular cartilage in response to load
      • surfaces separated by hydrostatic pressure
  • Mechanisms of wear
    • adhesion
    • abrasion
    • transfer
    • fatigue
    • third body
Aging in Articular Cartilage
  • With age changes in articular cartilage include 
    • increases in
      • chondrocytes size
      • protein content
      • stiffness (passive glycation leads to increased stiffness of collagen) 
      • increase in ratio of proteoglycan keratin sulfate to chondroitin sulfate
    • decrease in
      • absolute number of cells (becomes hypocellular, despite the fact that individual chondrocytes are increasing in size)
      • water content (differentiates from osteoarthritis where water content actually increases)
      • solubility
      • proteoglycan size
      • elasticity
  • Advanced glycosylation end-products (AGEs)  
    • from spontaneous nonenzymatic glycation of proteins when sugars (glucose, fructose, ribose) react with lysine or arginine residues
    • because of the low turnover, articular cartilage is susceptible to AGEs accumulation. 
    • accumulation of AGEs has been thought to play a role in the development of OA of the knee and ankle.
    • effects of AGEs formation 
      • modification of type II collagen by cross-linking of collagen molecules
        • increasing stiffness and brittleness 
        • increasing susceptibility to fatigue failure
Factor
Aging
Osteoarthritis
Water
Decreased
Increased
Modulus/stiffness
Increased (less elastic)
Decreased (more elastic)
Chondrocytes
Fewer but increased size
Cells cluster (late stage)
Glycosaminoglycans
Increased keratan sulfate:chondroitin 4 sulfate ratio, constant chondroitin 6 sulfate
Increased chondroitin 4 sulfate:keratan sulfate ratio
Proteoglycans
Increased decorin, decreased proteoglycan size
Proteoglycans unbound from hyaluronate
Collagen
Increased collagen crosslinking/brittleness
 Collagen disorganized (increased collagenase)
Advanced Glycosylation End products (AGE) Increased Accumulation of AGE thought to lead to OA knee and ankle
 
Healing in Articular Cartilage
  • Deep lacerations (through tidemark)
    • leads to fibrocartilage healing
    • occurs when laceration travels through tidemark and penetrates subchondral bone
    • fibrocartilage produced by undifferentiated marrow mesenchymal stem cells
    • a healing response is initiated with hematoma, stem cell migration, and vascular ingrowth. 
    • This response produces type I collagen and resultant fibrous cartilage rather than desired hyaline cartilage as produced by chondrocytes. 
    • This repair cartilage has diminished resiliency, stiffness, poor wear characteristics, and the predilection for arthritis. 
  • Superficial laceration (not through tidemark)
    • leads to chondrocytes proliferation but no healing takes place because of avascular nature of cartilage

 

Clinical Conditions
  • Articular Defects of the Knee (Adults) topic
  • Osteocondritis dissecans topic
 

Please rate topic.

Average 4.3 of 40 Ratings

Thank you for rating! Please vote below and help us build the most advanced adaptive learning platform in medicine

The complexity of this topic is appropriate for?
How important is this topic for board examinations?
How important is this topic for clinical practice?
Questions (30)
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ06.210) Which of the following features of metal-on-metal total hip arthroplasty does not allow for improved fluid film lubrication between the components? Review Topic

QID: 221
1

Larger femoral head

11%

(315/2814)

2

Slight clearance of fit between the acetabular cup and the femoral head

16%

(461/2814)

3

Minimal surface roughness of the femoral head

2%

(64/2814)

4

Complete congruence of fit between the acetabular cup and the femoral head

68%

(1909/2814)

5

Minimal surface roughness of the acetabular cup

2%

(56/2814)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 4
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ04.3) Which of the following statements regarding articular cartilage is TRUE? Review Topic

QID: 114
1

Cartilage is an isotropic material

12%

(63/521)

2

Most of the water in articular cartilage exists in the deep layer next to the calcified cartilage

18%

(92/521)

3

Cartilage only heals if the injury does not pass through the tidemark

16%

(83/521)

4

Calcified cartilage is the only place that type IV collagen is found

5%

(28/521)

5

Cartilage exhibits stress shielding of the solid matrix components

48%

(251/521)

ML 4

Select Answer to see Preferred Response

PREFERRED RESPONSE 5
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ08.67) What part of the articular cartilage has the highest concentration of proteoglycans and the lowest concentration of water? Review Topic

QID: 453
1

Superficial

18%

(352/1967)

2

Transitional

8%

(155/1967)

3

Deep

56%

(1103/1967)

4

Tidemark

7%

(146/1967)

5

Calcified cartilage

10%

(202/1967)

ML 3

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK

(OBQ12.203) Which of the following best describes the appearance of chondrocytes and orientation of collagen fibrils in the superficial zone of articular cartilage? Review Topic

QID: 4563
1

Round chondrocytes oriented parallel with the tidemark and collagen fibrils oriented perpendicular to the tidemark

6%

(192/3325)

2

Round chondrocytes oriented parallel with the tidemark and collagen fibrils oriented parallel to the tidemark

6%

(214/3325)

3

Flattened chondrocytes oriented parallel with the tidemark and collagen fibrils oriented perpendicular to the tidemark

21%

(704/3325)

4

Flattened chondrocytes oriented perpendicular with the tidemark and collagen fibrils oriented perpendicular to the tidemark

9%

(293/3325)

5

Flattened chondrocytes oriented parallel with the tidemark and collagen fibrils oriented parallel to the tidemark

56%

(1876/3325)

ML 3

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ12.93) Which of the following contributes most to the ability of hyaline cartilage to attract water? Review Topic

QID: 4453
1

Aggrecan

88%

(3226/3678)

2

Biglycan

7%

(252/3678)

3

Decorin

2%

(66/3678)

4

Fibromodulin

2%

(60/3678)

5

Osteocalcin

1%

(46/3678)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(OBQ04.20) A 28-year-old marathon runner has a knee MRI done to evaluate medial sided knee pain. No meniscus tear is identified, but the articular cartilage of the femoral condyles is noted to be twice as thick as normal values. What is the most likely cause of this finding? Review Topic

QID: 131
1

Osteoarthritis

1%

(7/492)

2

Undiagnosed osteopetrosis

0%

(2/492)

3

Synovial cytokine sensitization due to excess running

11%

(52/492)

4

Extra-articular hydrostatic pressure changes

3%

(15/492)

5

Chondrocyte modulation via mechanotransduction

84%

(415/492)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ11.163) Figure A displays a schematic of the zones of articular hyaline cartilage. Which of the following zones has been shown to contain articular cartilage progenitor cells? Review Topic

QID: 3586
FIGURES:
1

A

30%

(706/2331)

2

B

13%

(309/2331)

3

C

31%

(730/2331)

4

D

7%

(158/2331)

5

E

18%

(419/2331)

ML 5

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(OBQ04.78) Which of the following biochemical changes are common to both aging cartilage and osteoarthritic (OA) cartilage? Review Topic

QID: 1183
1

Increased water content

9%

(232/2547)

2

Decreased collagen content and decreased modulus of elasticity

28%

(718/2547)

3

Decreased proteoglycan content

56%

(1430/2547)

4

Increased chondroitin sulfate concentration

3%

(65/2547)

5

Decreased keratin sulfate concentration

4%

(91/2547)

ML 3

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
Question locked
Sorry, this question is for
PEAK Premium Subscribers only
Upgrade to PEAK
ARTICLES (39)
VIDEOS (1)
Topic COMMENTS (28)
Private Note