Joint Anatomy and Physiology

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Joint Anatomy and Physiology

• An articulation between 2 bones/cartilages
• 1. Fibrous
• 2. Cartilaginous
• 3. Synovial- majority of articulations of
  extremities
• Can be further subdivided based on shape, axes of
  movement

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Other synovium-lined spaces 1. Bursae 2.
Synovial tendon sheaths
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Synovial Membrane
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Synovial Membrane - anatomy

• 1-3 cells thick- synoviocytes lie loosely in a
  bed of hylauronate interspersed with collagen
  fibrils
• Type A synoviocytes macrophage derived
• Type B synoviocytes fibroblast derived
• Subsynovium
• Relatively avascular- scattered blood vessels,
  fat and fibroblasts extracellular matrix
• Gradually replaced by loosely organized
  connective tissue

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Synovial Membrane - function

• Low-friction lining for the joint during
  movements (well-lubricated)
• Formation of synovial fluid
• Regulation of matrix turnover in synovium and
  cartilage (via synovial fluid)
• Blood synovial barrier
• Negative intra-articular pressure joint stability

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Synovial Fluid

• An ultrafiltrate of plasma to which hyaluronate
  and other factors are added locally by
  synoviocytes
• Clear and viscous
• Low protein concentration
• Few cells

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Synovial Fluid - function

• Nourishment of articular cartilage (avascular)
• Role in joint stability adhesive seal
• Lubrication
• Lubricin - binds cartilage at surface and
  decreases friction
• Hyaluronate lubrication of synovium-on-synovium
  and synovium- on-cartilage

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Articular Cartilage
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Articular Cartilage
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Articular Cartilage - anatomy

• Cells Chondrocytes
• Matrix
• Water 70-80
• Solids 20-30
• Type II collagen 60
• Proteoglycans 30
• Non collagenous proteins 10

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Articular Cartilage - function

• Chondrocytes synthesize and maintain cartilage
  matrix
• Collagen - tensile strength and framework for
  chrondrocytes and proteoglycans
• Proteoglycans elasticity and hold water

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Articular Cartilage -function

• Low friction, protective, load-bearing tissue
• Absorbs impact by virtue of compressibility,
  elasticity, low hydraulic permeability and
  self-lubrication
• Note that protection of joint during impact
  loading is also dependent on muscle, bone

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Subchondral Bone - function

• Immediately beneath cartilage
• Supported by meshwork of underlying trabeculae
• Modifies the compressive forces to which
  articular cartilage is subjected

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Systemic Therapy Options for Acute Gouty Arthritis

• Nonsteroidal antiinflammatory drugs
• Use in full doses
• Avoid in patients with renal or hepatic failure
  and patients at risk for GI adverse effects,
  bleeding, congestive heart failure
• Systemic corticosteroids
• Prednisone 25-50 mg daily for 3-4 days, then
  taper by 5mg every 3-4 days until finished
• Avoid if sepsis has not been excluded

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Systemic Therapy Options for Acute Gouty Arthritis

• Colchicine
• Greatest benefit if given promptly at onset of
  attack
• 0.6-1.2 mg initially
• Then 0.5mg q1-2h until relief or side effects or
  maximum dose reached (6-8 mg)
• Alternate 1.2mg q12h X 3 doses only
• Avoid in patients with renal insufficiency,
  hepatic dysfunction watch for bone marrow and
  muscle toxicity

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Principles of management of septic arthritis

• 2 categories
• Gonococcal
• responds quickly,excellent prognosis
• Non-gonococcal
• may result in joint destruction, increased
  mortality
• Treatment of the infection includes
• Drainage of the joint (daily)
• Antibiotics choose based on clinical scenario or
  appropriate to gram stain once available