Osteoarthritis Flashcards
What is osteoarthritis?
- wear and tear arthritis
- this is through damaged cartilage from modifiable or non-modifiable trauma that triggers down-stream events
- progressive joint disease (continually gets worse, therefore main age is in the elderly)
- occurs when damaged joint tissues are unable to normally repair themselves resulting in a breakdown of bone and cartilage
Epidemiology of OA
- 1 in 10 Canadians
- most prevalent kind of arthritis (more common than RA)
- prevalence rates vary depending on joint involved, ethnicity, age, and gender
- leading cause of disability in Canada and US
- 1 in 2 indivs will develop OA in their life
- increasing prevalence due to aging boomer pop, increasing life expectancy, increased rate of obesity
Etiology of OA
aka risk factors:
1) obesity
2) occupation, sports, trauma
3) Non-modifiable factors (genetics, age, gender)
Explain why obesity is a risk factor for OA
- it is the most important risk factor
- in obesity, weight loss of 5kg= 50% risk reduction for OA
- predictor for prosthetic joint replacement
- obesity increases joint stress, but sedentary lifestyle also decreases cartilage health as joints rely on adequa te joint usage for its nutrition source
Explain why overuse/trauma is a risk factor for OA
overuse: increased OA in occupations with repetitive motions (kneeling, squatting, etc) and heavy lifting (farming, sports, etc)
- injury to joint cartilage due to trauma= improper load bearing and stability= OA risk
- meniscal damage also increases the risk of knee OA b/c of loss of proper load bearing and shock absorption
disease: joint malalignment disorders
Occupations Associated with OA
Ankle: ballet dancers, soccer players (more rare)
Knee: miners, dockers, PE teachers, athletes, carpenters, concrete or shipyard workers
Explain the non-modifiable risk factors associated with OA
a) genetics- genetic link depends on joint (knee-hand-hip-spine)
-lower prevalence in Asian and Indian pops
b) Age- older you get the more prone to get OA
-blunted chondrocyte repair potential
-weakened muscles (joint protection)
-slower sensory nerve input (less effective muscle and tendon response
-ligaments stretch with increasing age (less effective absorption of force)
c) female gender more prone for OA than males
(flow chart of susceptibility to OA on slide 10)
OA Etiologic Classes
1) primary OA (idiopathic= unknown cause) -> most common form
- no identifiable cause
- localized-affecting 1 or 2 joints
- generalized-affecting 3 or more joints
2) secondary OA -> known cause or trigger
- RA, trauma, disease, obesity
Joint Protective Mechanisms
- joint capsule and ligaments
- synovial fluid
- mechanoreceptor sensory afferent nerves
- muscles and tendons
How do the joint capsule and ligaments protect the joint?
- provide a limit to excursion thereby fixing the range of joint motion
- ligaments attach bones to bones to give strength and stability to the knee
How does the synovial fluid protect the joint?
fills joint space to reduce friction between cartilage surfaces
How do the mechanoreceptor sensory afferent nerves protect the joint?
- these nerves are of the ligaments, overlying skin and tendons
- provide feedback so muscles and tendons assume the right tension at appropriate points
How do the muscles and tendons protect the joint?
- bridge the joint and contract at appropriate times to minimize the focal stress across the joint
- tendons are elastic tissues that connect muscles to bones
If there is no inflammation in OA, why is there pain?
- around the joint there are mechanoreceptors
- in OA, the joints are often discontented and twisted abnormally
- these mechanoreceptors sense these and this is what causes pain
What are bursae?
fluid-filled sacs around joints to reduce friction
Cartilage
- thin rim of tissue at the ends of 2 opposing bones
- lubricated by synovial fluid providing an almost frictionless surface across which these 2 bones move
- absorbs shock
- no nerve innervation (painless joint movement)
- no vascular supply to the internal joint (nutrition diffuses from synovial fluid; any fluid is external
- healthy cartilage is produced by chondrocytes
crepitus
-a grating sound or sensation produced by friction between bone and cartilage or the fractured parts of a bone
-this is the cracking sound you here when you get up and your joints are stiff and they crack
(in OA, the more you sit around, the more stiff your joints get, and the less you’ll want to get up)
Dual function of chondrocytes
1) make cartilage through type 2 collagen and aggrecan
2) breaks down cartilage through MMP-13 ADAMTS- 4 and 5 enzymes
- chondrocyte survival depends on adequate nutrition
Chondrocytes in formation of cartilage
produce 2 major macromolecules that make up cartilage:
1) type 2 collagen- provides cartilage with its tensile strength
2) aggrecan- proteoglycan linked with hyaluronic acid- highly negatively charged glycosaminoglycans
- tightly woven type 2 collagen constrains aggrecan forcing molecules together
- electrostatic repulsion gives cartilage its compressive stiffness
Chondrocytes in the break down of cartilage
- chondrocytes also produce enzymes that break down cartilage matrix:
1) matric metalloproteinases (MMP-13) breaks down Type 2 Collagen
2) ADAMTS 4 and 5 breaks down Aggrecan - they do this in a specific order
- some injury will activate the activate the chondrocytes that will begin the breakdown process
- homeostatic balance of synthesis and degradation is required to maintain and restore cartilage quality and volume
- if cartilage is injured, chondrocytes remove damaged areas and increase synthesis of matrix constituents to repair and restore
What are the forms of cartilage in the body?
1) hyaline (joint cartilage)
2) elastic (ear, epiglottis)
3) fibrocartilage
What is the difference between cartilage turnover between healthy cartilage and cartilage in OA?
- healthy cartilage is metabolically sluggish, with slow matrix turnover and synthesis and degradation in balance
- cartilage in OA or after an injury is highly metabolically active
Why is OA not just a “wear and tear” disease?
- it was previously thought that all cartilage damage was due to loss of support structures and subsequent mechanical damage
- NOW we know that:
1) mechanical wear/trauma acts as catalyst starting disease process
2) actual cartilage damage is a chemically-mediate disease process
3) complex cellular mechanisms involving increased catabolic responses and blunted anabolic mechanisms
Process of Osteoarthritic Cartilage
1) OA most commonly begins with damage to cartilage (e.g. trauma, excess joint loading, etc)
2) in response to damage, chondrocyte activity increases in attempt to remove and repair damage
3) balance between breakdown and re-synthesis of cartilage can be lost- increased breakdown can lead to further cartilage loss
Vicious cycle of increasing breakdown leading to further cartilage loss
(this is shown on slide 19)