osteo- means â€œboneâ€, and -arth- refersto â€œarthronâ€ which means joint, and -itis means â€œinflammationâ€, so osteoarthritisis a disease involving inflammation of the bone and joint cartilage. it was once thought that the â€œitisâ€ partof osteoarthritis was a misnomer, and that inflammation didnâ€™t play a role in its development,and that it was mostly a degenerative disease resulting from simple â€œwear and tearâ€. nowadays, itâ€™s thought that inflammationdoes indeed play an important role in the development of osteoarthritis. alright, so a healthy joint consists of twobones, each with its own layer of articular
cartilage, which is a type of connective tissuethat allows the two bones to glide against each other essentially without friction. with osteoarthritis, weâ€™re really talkingabout one particular kind of joint which is a synovial joint. along with articular cartilage, another importantcomponent of synovial joints, and where they get their name from, is the synovium, whichalong with the surface of the articular cartilage, forms the inner lining of the joint space. the synoviumâ€™s composed of loose connectivetissue, blood vessels, lymphatic vessels, and on the surfaceâ€”â€type aâ€ cells thatclear cellular debris and â€œtype bâ€ cells
that produce components of synovial fluid,which helps lubricate the two articular surfaces. one of the main issues in osteoarthritis isthe progressive loss of this articular cartilage, which means thereâ€™s not much separatingthe two bones anymore, which adds a significant amount of friction between them, which thengenerates inflammation, and triggers pain through the nerve endings in this joint space. maintaining healthy articular cartilage isthe chondrocyteâ€™s job, a specialized cell responsible for maintaining everything cartilage-related. the chondrocytes produce and are embeddedwithin a strong gel or extracellular matrix which contains type ii collagen, a proteinthat provides structural support, as well
as proteoglycans, which are aggregates ofprotein and sugar molecules like as hyaluronic acid, chondroitin sulfate, and keratin sulfate. all of these extracellular components givethe cartilage elasticity and high tensile strength, which help weight-bearing jointsdistribute weight such that the underlying bone absorbs the shock and weight, and theseare joints like the knees, hips, and the lower lumbar spine. okay, so chondrocytes are important for thearticular cartilage, got it. that makes sense. in healthy people, chondrocytes maintain adelicate balance between breaking down old
cartilageâ€”called catabolic activity, andproducing new cartilageâ€”called anabolic activity, through the use of both degradativeenzymes and synthetic enzymes. when something causes an increased expressionof degradative enzymes, then the balance tips toward a net loss of cartilage, via loss ofproteoglycans and collagen. what sort of something though can cause anincreased expression of degradative enzymes? thatâ€™s the million dollar question, right? and the answer isnâ€™t super straight forward. the biggest risk factor for osteoarthritisseems to be age, and often the cartilage degrades over longer periods of time, which makes itreally hard to pinpoint one single culprit.
as i mentioned earlier, inflammation alsoseems to be involved, and there are a number of proinflammatory cytokines like il-1, il-6,and tnf, among others, that seem to play a role. some of these are more involved in breakingdown cartilage through proteolysis, meaning increased catabolism, whereas others are moreinvolved in blocking the formation of new cartilage (meaning decreased anabolism). also, joint injury, which brings with it alot of inflammation, seems to be a major risk factor for osteoarthritis, as well as mechanicalstress and obesity. other risk factors include neurologic disorders,genetic factors, and even certain medications,
suggesting there are other mechanisms at playas well. whatever the initial cause of articular cartilagedamage is, it gets the chondrocytes to start trying to repair the cartilage. they initially start making less of the proteoglycansand more type ii collagen, but soon switch over to making a different collagen type,type i collagen. unfortunately, type i collagen doesn't interactwith the proteoglycans in the same way and there is an overall decrease in elasticityin the cartilage matrix, allowing it to breakdown. eventually though, over the course of years,chondrocytes arenâ€™t able to keep up, and they become exhausted, and can undergo apoptosis,or programmed cell death.
the cartilage gets softer, weaker, and continuesto lose elasticity, and starts to flake off into the synovial space, called joint mice. as â€œtype aâ€ cells in the synovium attemptto remove the debris, immune cells like lymphocytes and macrophages are recruited into the synovialmembrane, which produces proinflammatory cytokines that ultimately cause inflammation of thesynovium as well, called synovitis. also, fibrillations form, essentially thesecracks or clefts, on what used to be a smooth articular surface. the cartilage continues to erode away untilthe boneâ€™s exposed, allowing it to rub with the other bone, which causes bone eburnation,making it look like polished ivory.
finally, on the edges, bone grows outward,called osteophytes, which makes the joints look wider, something thatâ€™s most obviouswhen seen in the distal and proximal interphalangeal joints, or the finger joints, called heberdennodes in the distal joint and bouchard nodes in the proximal. osteoarthritis is really common, and nearlyeveryone knows someone that suffers from it. people with osteoarthritis often feel stiffnessin the morning, which usually lasts less than 1 hour but comes back at the end of the day. this is an important difference between rheumatoidarthritis, an inflammatory disease that also affects the joints.
with rheumatoid arthritis, morning stiffnessusually lasts longer than 1 hour. the pain in osteoarthritis is usually a sharpache or burning sensation, which also gets worse with prolonged activity, but usuallythe joints donâ€™t swell, whereas rheumatoid arthritis typically involves painful swelling. finally, management and treatment of osteoarthritiscan involve non-pharmacological approaches, like losing weight or moderate exercise, aswell as physical therapy. this can be especially important for large-weightbearing joints like the hips and knees. pharmacological treatments focus on reducingpain and inflammation. if neither of these approaches are successful,sometimes people might benefit from injections
of hyaluronic acid into the joint or may needsurgery to replace the affected joint.