Chapter outline Physiology and Composition of Synovial Fluid Specimen Collection Laboratory Testing Macroscopic Evaluation Chemical Examination Microscopic Examination Classification of Joint Disorders
Synovial Fluid Synovial = syn (like) + ovia (egg). Synovial fluid is a thick, stringy fluid found in the cavities of synovial jointsWith its egg like consistency . The inner membrane of synovial joints is called the synovial membrane and secretes synovial fluid into the joint cavity This fluid forms a thin layer [roughly 50 milli microns] at the surface of cartilage.
composition Synovial tissue is composed of connective tissue that lacks a basement membrane. Two cell types [typeA and typeB ]are present. Type B produces synovial fluid & type A produces hyaluronic acid. Synovial fluid is made of hyaluronic acid and lubricin , proteinases and collagenases. Normal synovial fluid contains 3-4 mg/ml hyaluronan [hyaluronic acid ], a polymer of disaccharides .composed of D-glucronic acid and D-N –acetyl glucosamine joined by alternating beta-1,4 and beta-1,3glycosidic bonds.
composition Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity to increase the viscosity and elasticity of articular cartilages and lubricate the surface between synovium and cartilage. Synovial fluid also contains lubricin secreted by synovial cells. It is chiefly responsible for so called boundary layer lubrication, which reduces friction between opposing surfaces of cartilage. There is also some evidence that it helps regulate synovial cell growth.
functions Reducing friction by lubricating the joint . Absorbing shocks. Supplying oxygen and nutrients to removing carbon dioxide and metabolic wastes from the chondrocytes with in articular cartilage . It also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.
Synovial Fluid Synovial membrane from a normal knee joint showsjoint space, synovial membrane composed of synovial cells embedded in a loose connective tissue stroma overlying dense collagen (hematoxylin and eosin).
Synovial Fluid: Physiology andComposition Clear viscous ultra filtrate of plasma Glucose and uric acid equivalent to plasma Protein lower than plasma Hyaluronate protein complex containing mucin Moistens and lubricates joints
Bulge testThe Bulge test is used to determine if there is an abnormalamount of fluid surrounding a joint Bulge test of joint for the detection of synovial effusion
Synovial Fluid: Specimen Collection(cont.) Needle insertion Placement of needle in arthrocentesis of (A) elbow and (B) knee joints.
Laboratory Testing: Macroscopic Volume Color and Clarity Inclusions Viscosity Clotting Mucin Clot
Laboratory Testing: Macroscopic Volume Normal up to 4 mL of fluid Result usually recorded at bedside Some laboratories may include volume in reports
Macroscopic Analysis: Color and Clarity Colorless and clear normal Red, brown, or xanthochromic hemorrhage into the joint Yellow/clear noninflammatory effusions Yellow/cloudy inflammation White/cloudy crystals
Macroscopic Analysis: Inclusions Rice bodies. Free-floating aggregates of tissue appear as rice bodies. rheumatoid arthritis (RA) Degenarated synovium enriched with fibrin Ochronotic shards debris from joint prosthesis look like ground pepper A =ochronotic shards B= rice bodies
Macroscopic Analysis: Viscosity Evaluated using “String test” Normal = 5cm long before breaking Low viscosity indicates inflammation
Macroscopic Analysis: Clotting Clotting of synovial fluid = fibrinogen Damaged synovial membrane Traumatic tap Clots interfere with performance of cell counts
Macroscopic Analysis: Mucin Clot Estimation of hyaluronic acid–protein complex integrity the adding of acetic acid to normal synovial fluid, which causes clot formation. The compactness of the clot and the clarity of the supernatant fluid are the criteria on which the result is based. Evaluated using “Rope’s test” Good = tight ropey mass normal Poor = beaks easily haluronate destruction haluronate dilution
Chemical Analysis: Protein All proteins found in plasma Exception: various high–molecular weight proteins which may be present in very small amount Fibrinogen beta 2 macroglobulin alpha 2 macroglobulin Use common serum protein procedures
Chemical Analysis: Protein (cont.) Normal range 1-3 g/dl Increased protein ankylosing spondylitis arthritis Crohn disease Gout Psoriasis Reiter syndrome ulcerative colitis.
Chemical Analysis: Glucose Compare to serum glucose levels Normal synovial glucose is no lower than 10mg/dl less than serum glucose levels. Decreased – joint disorders Greater than 20mg/dl decrease may indicate infection
Chemical Analysis: Uric Acid Normal - 6 to 8 mg/dL Increased – gout May form crystals
Chemical Analysis: Lactic Acid Rarely measured in synovial fluid Can be helpful in diagnosing septic arthritis. Normal = less than 25 mg/dL Septic arthritis can show levels up to 1000 mg/dL
Laboratory Testing: LactateDehydrogenase May be elevated in synovial fluid, while serum levels remain normal. Increased in Rheumatoid arthritis (RA) infectious arthritis, gout. Neutrophils increased during the acute phase of these disorders contribute to this increased LD.
Laboratory Testing: Rheumatoid Factor RF is an antibody to immunoglobulins. Present in rheumatoid arthritis: Serum – most cases Synovial fluid - 50% Rarely elevated only in synovial fluid and not serum False positives in other chronic inflammatory diseases.
Microscopic Analysis: Differential(cont.) Elevated lymphocytes: tuberculosis Early stages of RA
Microscopic Analysis: Differential LE cells LE cells are neutrophils that have engulfed a nucleus of a lymphocyte that has been altered by antinuclear antibody Tart cells Tart cells, monocytes that have engulfed nuclearMaterial
Microscopic Analysis: Differential Reiter cellsReiter cells are neutrophil-laded macrophages
Microscopic Analysis: Crystals-Uric Acid Synovial fluid with acute inflammation and monosodium Synovial fluid with acute urate crystals. The needle-shaped inflammation and monosodium crystals demonstrate negative urate crystals. (Wright–Giemsa birefringence, because they are stain and polarized light). yellow when aligned with the compensator filter and blue when perpendicular to the filter (Wright– Giemsa stain and polarized/compensated light).
Microscopic Analysis: Crystals-other Synovial fluid with acute Synovial fluid with acute inflammation and calcium inflammation and calcium pyrophosphate dihydrate crystals. The pyrophosphate dihydrate crystals rhomboidal intracellular crystal (Wright–Giemsa stain and (center) demonstrates positive polarized light). birefringence, because it is blue when aligned with the compensator filter (Wright–Giemsa stain and polarized/compensated light).
Microscopic Analysis: Crystals-other Corticosteroid crystals :crystals are needle-shaped intra-articular injections Cholesterol crystals : chronic effusions from patients with osteoarthritis or RA Apatite crystals :(small chunky rods) calcific periarthritis osteoarthritis inflammatory arthritis
Laboratory Testing: Microbiology (cont.) Staining Smears prepared by centrifugation or cytocentrifugation Saline dilution reduces clustering of cells Gram’s stain most common Positive in only 50% of cases Culture Set up with positive or negative stain results Aerobic anaerobic
Review of Key Points Synovial fluid analysis Is a well-established procedure for evaluation of joint disease. Determines the presence of arthritis Assists in the classification of joint disorders Helps guides appropriate treatments