The pathophysiology of osteoarthritis


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The pathophysiology of osteoarthritis

  1. 1. andpresentThe pathophysiology of osteoarthritisThe pathophysiology of osteoarthritis
  2. 2. A few useful definitions and remindersSociété Française de rhumatologie website: J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629. Osteoarthritis is characterised by cartilage loss combined with synovial tissuethickening and subchondral bone osteosclerosis Other than the spine, osteoarthritis most commonly affects the knees, hands and hips Osteoarthritis is a common complex disorder with multiple hereditary, constitutionaland environmental risk factors Cartilage degeneration is not simply an age-related process, osteoarthritis is anindividual disease entity and has both inflammatory and mechanical features. Obesity increases the risk of osteoarthritis in the legs and fingers2Spine Knee Hands Hip
  3. 3. 3Hip-femoral osteoarthritis. Righthip arthrography, frontal image.Cervical spine. T2 MRI.Internal and external femorotibialosteoarthritis. Knee CT-arthrography.MRI of the left hand, T2 weighted sequences,coronal image after saturation of the fat signal.
  4. 4. Cartilage and chondrocyteCartilage is a very specific type of dense connective tissue Non vascularised: it draws its nutrients by a process of diffusionfrom the synovial fluid secreted by the synovial membrane andthe subchondral bone. Not innervated: it cannot therefore be held directly responsiblefor the pain experienced by osteoarthritis sufferers Cartilage consists of a single type of cell, chondrocytes,embedded in the matrix they createSociété Française de rhumatologie website: normal conditions, chondrocytes have low metabolic activity whichis mainly confined to breaking down various elements in the matrix(proteoglycans and collagen) and to renewing these same matrix components4Healthy knee cartilage
  5. 5. Osteoarthritis: a separate disease entity Osteoarthritis is not simply the result of normal ageing and excessivepressure on a joint It is caused by a variety of factors: Local, mechanical factors General (heriditary) and systemic factors (e.g. adipokines) And in some cases, trauma It involves changes in all joint tissues: cartilage, the subchondral bone(which could play an even more important role in thispathophysiology), the articular capsule and the synovial membraneSellam J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.5
  6. 6. Osteoarthritis: the disease process (1) Excessive pressure on the cartilage: Chondrocytes are activated via pressure-sensitivemembrane receptors (mechanoreceptors) Inflammation mediators are released The cartilage matrix deterioratesSociété Française de rhumatologie website: J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.6
  7. 7.  The 3 features in osteoarthritis are: Degradation of the cartilage matrix Inflammatory reaction in the synovialmembrane, often accompanied by jointeffusion Reaction in the subchondral bone withproliferation of neosynthesised bone:osteophytes (hypertrophic formation)Société Française de rhumatologie website: J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.7Osteoarthritis: the disease process (2)Shoulder osteoarthritis withmoderate gleno-humeral joint spacenarrowing and osteophyte on thelower surface of the humeral head.Knee osteoarthritis, tibial edemaand synovial inflammation. FSE T2sagittal slices.
  8. 8. Mechanical osteoarthritis Excessive weight: obesity or frequent heavyload-bearing (workplace or sport [, weight-lifting]) Joint overload and repeated microtrauma Unevenly distributed pressure: dysplasia,meniscectomy, malalignement (genu varumor genu valgum) Knee instability: ligament hypermobility,cruciate ligament rupture, particularly of theanterior ligament, or a poorly managedsprain, etc.Société Française de rhumatologie website: cyst under the insertion ofthe posterior cruciate ligament. FSE T2sequence in sagittal plane.Some cases of osteoarthritis are mainlymechanical in origin (caused by excessivepressure on part or all of the joint):
  9. 9. Secondary osteoarthritis Diseases directly affecting the cartilage: for example:crystalline particles in the cartilage - urate crystals (gout)or calcium deposits (chondrocalcinosis); genetichemochromatosis; ochronosis (very rare); and geneticdisorders which weaken the structures in the cartilage(proteoglycans or collagen) Disease affecting other joint tissues with an indirectimpact on the cartilage, especially: disorders of the subchondral bone, such as asepticosteonecrosis, synovial membrane disorders, joint infections even once cured,or synovial inflammation, for instance rheumatoid arthritisSociété Française de rhumatologie website: of the femoralhead in a patient with hiposteoarthritis.
  10. 10. Osteoarthritis and Obesity Obesity is a predisposing factor for osteoarthritis: via mechanical constraints linked to excess weight whichtrigger chondrocyte activation (see following slides, 10 and 11) and no doubt also through the production of cytokines in thefatty tissue which enter the bloodstream and have an effecton the joint tissues. This could explain the higher incidence offinger osteoarthritis in obese patients This is best illustrated by osteoarthritis of the fingers,which is more common in overweight or obese patients The risk of knee osteoarthritis increases by 15% for everypoint increase in the BMISellam J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.10Frontal image of advancedpatellofemoral kneeosteoarthritis.
  11. 11. Osteoarthritis and fatty tissue Fatty tissue, particularly abdominal fat, plays a rolein systemic inflammation by secreting specific cytokinescalled adipokines (adiponectin, leptin and resistin) Adipokines have potent immunomodulating effects andare found in the synovial fluid of patients withosteoarthritis The Hoffa fat pad, located immediately behind the patellartendon, may also produce adipokines. These adipokinescan migrate directly into the synovial fluid11Sellam J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.
  12. 12. A new concept: "metabolic osteoarthritis"The concept of metabolic osteoarthritis emerged afterthe following were observed: There is an epidemiological link betweenosteoarthritis and type 2 diabetes andbetween osteoarthritis and metabolicsyndrome or each of its individualcomponents (abdominal obesity,hyperglycemia and dyslipidemia) The incidence of knee osteoarthritis is higherin obese patients concomitantly presentingwith one or more features of metabolicsyndromeTherefore, younger patients with osteoarthritis should be screened for acardiometabolic disease (metabolic syndrome or type 2 diabetes)12 Sellam J, Berenbaum F. Arthrose et Obésité. Rev Prat 2012;62:621-629.The concept of metabolic osteoarthritis(according to Sellam 2012)
  13. 13. Knee osteoarthritis and trauma In addition to age and excess weight, the riskfactors for knee osteoarthritis which must also betaken into consideration include trauma,particularly: Meniscus injury Anterior cruciate ligament rupture, causing anteriorknee placing undue mechanical stresson the medial tibio-femoral compartment and causingpremature wear Joint fracture Prevention: The most conservative possible treatment ofmeniscus injury, given the increased risk of kneeosteoarthritis after meniscectomy, therefore in thiscase, no meniscectomy after the age of 40 Surgical repair of the ACL will not prevent thesubsequent development of osteoarthritis13 La Revue du Praticien 2012; 62: 621-629, Situations à risque d’arthrose du genou. Charles-Henri Flouzat-Lachaniette.Bilateral femorotibial kneeosteoarthritis. Arthrography.
  14. 14. Osteoarthritis and physical exercise When repeatedly exposed to extreme stress, the knee maydevelop osteoarthritis Professions at higher risk of knee osteoarthritis: mainlyconstruction workers who often work in a crouched positionor kneeling (knee hyperflexion, leading to meniscal injury andosteoarthritis) Sport and osteoarthritis: moderate physical exercise does notincrease the risk of osteoarthritis. Intense sporting activity canincrease this risk through injury (joint fractures and meniscalor ligament injury) and repeated microtrauma14 La Revue du Praticien 2012; 62: 621-629, Situations à risque d’arthrose du genou. Charles-Henri Flouzat-Lachaniette.
  15. 15. CONCLUSION Osteoarthritis is not a simple age-related diseasecaused by wear and tear on weight-bearing joints.It is characterised by low-grade tissue inflammation It is a disorder with a demonstrated systemiccomponent in some forms, potentially involving thefatty tissue and the adipokines it secretes The main risk factors are age, obesityand repeated microtrauma15Femorotibial and patellarknee osteoarthritis.Arthrography.