Cartilage Flashcards
Articular Cartilage
Aka Hyaline cartilage
60-80% water – Fluid filled sponge
Contains collagen & proteoglycan (Water affinity)
Covers joint ends at articulations
Reduces friction
Aneural (not-innervated)
Most slippery
Fibrocartilage
Functions
Improve fit between bones
Intermediary between hyaline cartilage and other connecitve tissues
Meniscus, articular disc: fibrocartilage structure
Intervertbral disc, jaw, knee
Also used to “fill in” an area of articular cartilage damage – technique is called “microfracture”
Mechanical behavior of Cartilage
Cartilage displays viscoelastic behavior and biphasic response
Displacement due to water loss
-Rapid: Elastic response
-Slow: Plastic response
Water does not squeeze completely out, acts like a tight sponge, takes most of load
Creep is sustained with compressive loads
Small vascular supply as a child, goes to almost nothing as an adult
Gets stiffer as fluid comes out
Cartilage Healing
Poor blood supply, poor healing
Nourished by synovial fluid exchange
-Need loading to maintain healthy tissue
What is microfracturing?
Surgeon goes in and purposefully puts holes in the cartilage to stimulate bleeding. The purpose is to create a scab over top. Very slow recovery process.
Cartilage and Meniscus
Loss of 1/3 of the meniscus leads to an increase in contact stress by 65%
-Pressure=Force/Area
Having meniscus distributes force, loss of meniscus concentrates it at very high levels, cartilage can’t handle it
Meniscus is fibrocartilage
Joint Deterioration Theory
Cartilage deterioration
Enzymatic degradation, loss of proteoglycan, mechanical wear
As we age blood supply moves deeper
Fissures can break off and lead to locking or clicking of bone
Steps
1.Increased load to bone ->
2.Subchondral bone “injury”, increased remodeling ->
3.Bone healing, increased bone stiffness (Wolff’s law) ->
4.Increased load to articular cartilage -> Back to 1
Bone remodels much quicker than cartilage (Poor blood supply)
What is autologous chondrocyte implantation (ACI)?
Grow cartilage patch or harvest cartilage from other areas and implant it
Can’t handle loading, progressively apply little loading, Passive machine moves patient
What are the two ways for Chondral injury management?
Microfracture surgery OR
ACI
Cartilage and Aging
As you age the amount of load a specimen can handle decreases with age
Amount of cartilage generally varies by joint type, bony geometry and generally by the amount of loading
Less OA associated with ankles rather than knees and hips
What is a proteoglycan?
Protein
Helps in compressive forces
Intervertebral Discs
Nucleus Pulposus
Mostly water, many hydrophilic proteoglycans
Absorbs shock and distributes load
Annulus Fibrosus
More fibrous rings of collagen, less water, fewer proteoglycans
Able to resist multidirectional load
What is hoop stress?
Axial loading compresses entire disk; results in “hoop stress”
How do disc injuries occur?
Bending and Rotation
Bending creates compression on one side and tension on other
Which direction are herniations most often and why?
Posterior
Occurs during forward bending.
Annulus fibrosis is thinner posteriorly and lacks structural support from the anterior or posterior longitudinal ligaments.
