MSK Mod 2 Flashcards
what is the outer layer of the joint capsule
fibrous capsule aka stratum fibrosum
characteristics of outer layer of joint capsule
poor blood supply but rich in joint receptors (sensory receptors)
CT of joint capsule (connective tissue?)
what is the inner layer of the joint capsule
synovium aka stratum synovium
functions of inner layer of joint capsule
synovial fluid production immune function secrete immunoglobulins secrete lysosomal enzymes secrete hyaluronate (hyluronic acid) secrete lubricating glycoproteins reduce friction in joint ingest debris
what is hyalurnate?
glycoaminoglycan gel to improve viscosity of synovial fluid
what is the joint space
enclosed by capsule and filled with synovial fluid
what is synovial fluid
- clear, viscous fluid
- provides lubrication for the joint surfaces to create “frictionless” surfaces bw bones
- thixotropic properties - viscosity varies inversely with velocity of movement
thixotropic properties at rest and movement
- rest - synovial fluid resists movement of the joint
2. movement - synovial fluid provides less resistance to movement
what is articular cartilage
hyaline articular cartilage
- thin covering on the ends of most bones
- reduces friction, absorb/disperse compressive forces
composition of articular cartilage
- cellular component: chondroblasts
2. extracellular matrix: fibrous vs nonfibrous
what are chondrocytes
produce and maintain extracellular matrix
- produce and secrete enzymes that assist in matrix turnover (collagen and PGs)
- forms 2% of cartilage
what is the nonfibrous component of matrix
proteins, proteoglycans (5-10% cartilage)
-regulate fluid flow in/outcartilage
water (60-80% of cartilage)
what is the fibrous component of matrix
collagen fiber (10-30% of cartilage)
- arranged to absorb mechanical stress
- collagen fibers play role in regulating amount of fluid flow in/out of cartilage and prevent proteoglycans from escaping out of cartilage
what is the cartilage-bone interface
zone 1: smooth surface, reduce friction of joint surface
zone 2&3: transitional zones, absorb compressive forces
trademark: interface bw uncalcified and calcified layers
zone 4: clacified cartilage, anchors cartilage to bone
what is matrix turnover
- optimal joint function requires consistent matrix turnover
- enzymes hormones and mechanical stimuli all play role in maintaining matrix turnover
3 things that assist in matrix turnover
- enzymes
- hormones
- mechanical load
how do enzymes help matrix turnover
chondrocytes - secrete enzymes to assist in breakdown and rebuilding of matrix
how do hormones assist in matrix turnover
GH (growth hormone) and IGF (insulin growth like factor) stimulate chondrocytes and play role in regulating matrix turnover
how does mechanical load assist in matrix turnover
normal weight bearing forces required to stimulate optimal matrix turnover
function of articular cartilage
allow cartilage to absorb forces and provide nutrition to cartilage
healthy cartilage and weight bearing activity
- wt bearing activity will push fluid (water/synovial fluid) out of cartilage
- fluid flow becomes slower and resistance becomes exponentially harder the more the cartilage is compressed
- proteoglycans are responsible for regulating fluid flow in/out of cartilage
- release of wt bearing force allows fluid to re-enter back into cartilage
net result of healthy cartilage
this cycle protects against compressive forces and allow for nutrients to pass in/out of cartilage to reach chondrocytes
what is the joint composed of
joint capsule (fibrous & synovial membrane)
joint space
synovial fluid
articular cartilage
does articular cartilage have any nerve or blood supply
no
can pain associated with joint injuries/pathology be from articular cartilage
no
what is pain from in joint injuries/pathologies
results from inflammation/swelling/irritation of pain sensitive tissues such as joint capsule/synovium, periosteum, increased subchondral bone pressures, tendon/ligament insertion sites and protective muscle spasm
healing ability of articular cartilage
has poor ability to regenerate after injury because of poor blood supply
what is osteoarthritis
degenerative joint dz
classified as non inflammatory joint dz however evidence exists that there is an inflammatory component in OA
what is the MC of joint dz
osteoarthritis
primary defect of OA
loss/disruption of articular cartilage
- multiple factors contribute to cascade of events leading to OA
- -matrix destruction involving chondrocytes, collage, and proteoglycans
gross articular cartilage changes in primary defect OA
smooth glossy surface becomes a dull yellow/brown gray color with surface flaking fissures and fibrillations
4 cellular changes in articular cartilage
- enzymatic
- hormones
- cytokines
- nitric oxide and apoptosis
what enzymatic changes occur in cellular changes in articular cartilage in OA
excessive enzyme secretion from chondrocytes to matrix breakdown
1. proteoglycans, collagen and glycoaminoglycnas broken down by lytic enzymes
2. loss of proteoglycans in cartilage disrupts fluid regulation (water flows in/out of cell too easily)
3. elevated PGs found in synovial fluid
enzymes produced from synovium also contribute to matrix collagen breakdown
what hormone changes in articular cartilage OA
chondrocytes becomes less sensitive to GH/IGF
cytokine role in cellular changes in OA
- excessive production of IL-1 from synovium and chondrocytes leads to inhibition of normal cytokine regulation of matrix turnover
- IL-1 facilitates NO synthesis
- IL-1 is an inflammatory cytokine
NO and apoptosis role in cellular changes of OA
NO not normally found in healthy joint but is found in synvovial fluid and synovium of pts with OA
NO facilitates chondrocyte death (apoptosis)
–cartilage calcification also facilitates chondrocyte death (apoptosis)
articular cartilage function in OA
disruption of cartilage matrix allows fluid to flow in/out easier
- fluid changes:
1. rest: (non weight bearing) - increased volume of water within cartilage
2. wt bearing activity: fluid pushed out of cartilage rapidly and cartilage is easily compressed without much resistance - release of wt bearing allows increased volume of fluid to re enter cartilage
net result of articular cartilage function in OA
cartilage has limited ability to absorb forces and provide adequate nutrients to chondrocytes
secondary gross pathological changes associated with OA
–OA effects surrounding structures and not just the articular cartilage
subchondral bone sclerosis and bone cysts
-may be asymptomatic unless severe
-potential to communicate with the fissures and release contents into synovial fluid of joint space
-osteophyte formation may lead to irritation of synovium may contribute to loss of gross movement
-synovial thickening - may contribute to loss of gross movement
etiologies of OA
- multifactorial
2. exercise
multifactorial etiologies of OA
- trauma & genetics = largest
- joint/ligament laxity
- inflammatory conditions
- neurological disorders - abnormal movements