8.3 Types of Cartilage

  • Hyaline (most commonly thought of)
    • Lines synovial joints (joints that contain synovial fluid)
    • Dense, translucent, connective tissue
  • Fibrocartilage
    • Transitional cartilage found at the margins of some joint capsules
    • Joint capsules
    • Insertions of ligaments and tendons into bone
    • Menisci, Annulus fibrous (vertebral disc)
  • Elastic cartilage
    • External ear
    • Eustacian tube, epiglottis, and parts of the larynx

[ (slide credit: @OpenStaxAnatomy2020 Ch. 4 @Jastifer2010Cartilage) ]

  • Hyaline cartilage provides support with some flexibility. The example is from dog tissue.

@OpenStaxAnatomy2020 Ch. 4

  • Fibrocartilage provides some compressibility and can absorb pressure.

@OpenStaxAnatomy2020 Ch. 4

  • Elastic cartilage provides firm but elastic support.

@OpenStaxAnatomy2020 Ch. 4

(slide adapted from: @OpenStaxAnatomy2020 Ch. 4)

8.3.1 Cartilage sub-types

  • Physeal: growth plate
  • Fibrocartilage: tendon/ligament bony insertion
  • Elastic: trachea
  • Fibroelastic: meniscus
  • Hyaline: articular

[ ( slide credit: @Geeslin2016Cartilage ) ]

8.3.2 Hyaline Cartilage and Synovial Joints

@Geeslin2016Cartilage

  • Bartel refers to “articular cartilage”
  • Allows joints to have a wide range of motion
  • Joint surfaces covered with 2-4 mm of hyaline cartilage
    • Well suited to withstand rigors of joint environment, capable of handling cyclic loading
      • Distinct from bone
      • Devoid of blood supply, nerves
      • Cellular density less than any other tissue

[ ( slide credit: @Jastifer2010Cartilage ) ]

8.3.3 Articular cartilage

@Geeslin2016Cartilage

  • Millions of cycles required in a lifetime
  • Cartilage allows activity while minimizing wear to the joint surface

[ ( slide credit: @Jastifer2010Cartilage ) ]

8.3.4 Friction at articular surfaces

8.3.5 Exercise and cartilage wear (literature example)

@Geeslin2016Cartilage

8.3.5.1 Critique the abstract?

The effect of long-term exercise on canine knees was studied to determine whether an increased level of lifelong weight bearing exercise causes degeneration,or changes that may lead to degeneration, of articular cartilage. Eleven dogs were exercised on a treadmill at 3 km/hr for 75 minutes 5 days a week for 527 weeks while carrying jackets weighing 130% of their body weight. Ten control dogs were allowed unrestricted activity in cages for the 550 weeks. At the completion of the study all knee joints were inspected for evidence of joint injury and degeneration. …

Articular cartilage surfaces from the medial tibial plateau were examined by light microscopy, the cartilage thickness was measured, and the intrinsic material properties were determined by mechanical testing. No joints had ligament or meniscal injuries, cartilage erosions, or osteophytes. Light microscopy did not demonstrate cartilage fibrillation or differences in safranin O staining of the tibialarticular cartilages between the two groups. Furthermore, the tibial articular cartilage thickness and mechanical properties did not differ between the two groups. These results show that a lifetime of regular weight bearing exercise in dogs with normal joints did not cause alterations in the structure and mechanical properties of articular cartilage that might lead to joint degeneration.

Thoughts???

8.3.6 Fibrocartilage - enthesis

Apostolakos et al, Musc Lig Tend J 2014

  • The enthesis is the connective tissue between tendon or ligament and bone.
  • There are two types of entheses:
    • Fibrous entheses and
    • Fibrocartilaginous entheses
  • In a fibrous enthesis, the collagenous tendon or ligament directly attaches to the bone.
  • In a fibrocartilaginous enthesis, the interface presents a gradient that crosses four transition zones:
    • Tendinous area displaying longitudinally oriented fibroblasts and a parallel arrangement of collagen fibers
    • Fibrocartilaginous region of variable thickness where the structure of the cells changes to chondrocytes
    • Abrupt transition from cartilaginous to calcified fibrocartilage—often called ‘tidemark’ or ‘blue line’
    • Bone

(text adapted from Wikipedia, 2020)

8.3.7 Sidebar - Tendon healing (and its relationship to fibrocartilage)

@Geeslin2016Cartilage

  • Left: Normal supraspinatus tendon insertion site in a rabbit
  • Right: Fibrovascular (IF) scar tissue 4 weeks after repair
    • Note the repaired tendon (scar tissue) is much less organized

@Rodeo2007

[ ( slide credit: @Geeslin2016Cartilage ) ]

8.3.8 Perichondrium

  • Dense connective tissue that covers cartilage (except articular cartilage of joints.)
  • Contains blood, nerve supply, lymphatics.
  • Contains collagen fibers, fibroblasts

@Jastifer2010Cartilage

[ (slide credit: @Jastifer2010Cartilage) ]