Other periarticular tissue

Other periarticular tissue

• Synovium

  • Loose connective tissue rich in capillaries

  • Lacks a basement membrane; no tight junctions

  • Type A synovial cells—macrophage-like

    • Involved in phagocytosis

  • Type B synovial cells derived from mesenchymal cells— fibroblast-like

    • Produce synovial fluid and lubricin

  • Lubricin

Mucinous glycoprotein that binds to hyaluronic acid

Also present in lamina splendens

Contributes to boundary lubrication

• Lubricant is present between two surfaces but its thickness is inadequate to prevent contact throughout the surfaces

Defect associated with camptodactyly-arthropathy–coxa vara–pericarditis (CACP) syndrome

• Elastohydrodynamic lubrication

  • Major mode of lubrication in joints

  • Lubricant pressure causes elastic deformation of the opposing surfaces.

  • This elastic deformation increases conformity.

Synovial fluid

• Ultrafiltrate of plasma

• Hyaluronic acid, lubricin, proteinase, collagenases, and prostaglandins

• Nourishes and lubricates cartilage

• Nonnewtonian fluid: shear thinning (thixotropic)

  • Viscosity decreases with increased shear rate.

• Normally contains no RBCs, WBCs, or clotting factors

• Joint fluid analysis

  • Noninflammatory arthritis

    • Clear, straw color, high viscosity

    • WBCs: fewer than 200 cells/µL, with 25% polymorphonuclear leukocytes (PMNs)

  • Inflammatory arthritis

    • Yellow-green tinged with low viscosity

    • WBC count: 2000–75,000 cells/µL, up to 50% PMNs

    • Complement is decreased in rheumatoid arthritis (RA) (normal in ankylosing spondylitis [AS])

    • Crystals seen in gout and calcium pyrophosphate (dihydrate crystal) deposition disease (CPDD)

  • Septic arthritis

    • Cloudy to opaque

    • WBC count above 50,000–80,000 cells/ µL

    • Low glucose and high lactate may also be seen

  • Traumatic

    • Increased RBC and protein values

    • Concern for intraarticular fracture if fat globules present

    • MRI neapolitan effusion—fat above plasma above RBCs

Meniscus (labrum in hip/shoulder)

• Increases contact area and distributes load

• Deepens the articular surfaces of various synovial joints

• 90% type I collagen

• Fibroelastic cartilage

• Fibrochondrocyte is responsible for meniscal healing

• More elastic and less permeable than articular cartilage

• Blood supplies only the peripheral 25% of the knee menisci.

• Nerve fibers found in peripheral two-thirds.