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-viscous and in all movable joints


reduce friction between bones
transport O2 and nutrients
lessen shocks


between articular cartilage on bones


ultrafiltrate of plasma
chemical components are in similar concentration to plasma
hyaluronic acid secreted by lining cells to give fluid viscosity


minimal (knee has 3.5 ml)
increased in diseased joints


Arthrocentesis- to remove fluid
-aids in diag of arthritis and other pathologies: pain and stiffness due to damage, infections, inflammation, metabolic disorders, trauma, age, stress


-<3.5 ml
-pale clear/yellow
-forms viscous string 4-6 cm
-<2000 RBC/ul
-<200 NUC/ul
-<25% neuts
-<75% lymphs
-<60-70% macro.mono
-no crystal
-<10 mg/dl lower glucose than blood
-<250 mg/dl lactate
-<3 g/dl total protein
-uric acid equal to PB

Groups of joint disorders

-noninflam: degenerative joint disorders, osteoarthritis
-inflam:RA, LE, pseudogout
-inflam (crystals): gout, CPPD
-septic: microbial
-hemorrhagic: trauma, coag deficiencies, tumors, anticoagulant OD

Noninflam: degenerative joint disorders

-increased macrophages and lymphs (<30% neut)
-no crystals
-no rbcs
-normal glucose, protein, viscosity, culture
-osteoarthritis, traumatic arthritis, sickle cells disease


-NUCs 2000-75000/ul (neuts >50%)
-no crystals, RBCs, bact
-decreased glucose and viscosity
-increased protein
-RA, SLE, rheumatic fever

Inflam: crystal induced

-NUCs up to 100,000/ul
-<70% neuts
-decreased glucose and viscosity
-increased protein and uric acid
-gout, pseudogout


-yellow to green, cloudy
-NUCs 50,000-100,000/ul (>75% neut)
-no crystals
-RBCs present
-glucose and viscosity decreased
-protein increased
-bacteria or fungal


-red/brown, xanthochromic
-many RBCs
-NUCs 50-10,000 (neuts predomin)
normal glucose
-increased protein
-decreased viscosity
-traumatic arthritis, anticoag therapy

Increased turbidity

-increased WBC
-Cellular debris


infla joint disease: depolymerizes complex causing watery fluid (arthritis)
-not a reliable test
-rated good, fair, poor.

Cell counts

-count may include lining cells
-hyaluronidase to break down hyaluronic acid
-do not use acetic acid for count- causes mucin clots
-norm <200

Abnormal Diff

-↑ neuts= sepsis
-↑ lymphs= non septic inflam
-↑eos= allergic rxn, rheumatic fever, parasites, metastatic carcinoma
-LE cells
-Reiter cells (vacuolated macros with ingested neuts)
-ragocytes (RA cells)- neuts with small dark granules of rheumatoid factor

Synovial lining cell

-covers non-articular surfaces of joint cavity
-round to oval shape
-dense chromatin, abundant cyto
-no significance

LE cell

-10% of LE patients
-can be in RA too
-hematoxalyn body- smooth chromatin completely ingested by neutrophil (never mono)


-lipid laden macros
-long standing RA, trauma, aseptic necrosis

Reiter Cells

-vacuolated macros with phagocytosed nuclear material
-indicates resolution of acute phase of inflam, not specific for reiters syndrome
-one or more neuts may be in varying phases of degeneratiion present in cytoplasm

Crystal evaluation

-need to ID crystals to treat
-factors for crystal deposition: increasing age, familial predisposition, joint damage, post medicine injection

Crystal examination

-perform soon after collection
-intracellular and extracellular
-observed on counting chamber, polarized and compensated light
-determine crystals birefrigence properties
-primarily to detect uric acid and CPPD

Monosodium urate (uric acid)

-diag of gout: disorder of purine metabolism, variable and raised blood levels, severe recurrent acute arthritis of sudden onset
-crystals in connective tissues and cartilage
-strong birefrigence: rotate light and appear very brigh against dark background
-intra (90% acute) and extracellular, needle shaped, 2-20 um
-yellow parallel to compensator, blue perpendicular

Calcium pyrophosphate (CPPD)

-pseudogout or degenerative arthritis (calcium leached from bones in degeneration), metabolic disorders with increased calcium
-weak birefringence: appear dim
-acute-intracell, chronic extracell
-pleomorphic: rhombohedral, plate-like, rod-like
-yellow perpendicular to polarized light, blue parallel


-flat, transparent and plate-like with notches.
-occurs in turbid thick specimen
- in RA of long duration

Corticosteroid crystals

- 1 month post injection

Polyethylene Crystals

artifact from joint replacement

Starch powder crystals

contamination from gloves
maltese cross under polarized light

Hematoidin crystals

post joint bleed

Chemistry tests

-approx same as serum


marked decreased- inflam or sepsis (<20)
compare to serum

Lactic acid

dif inflam or septic
>250 mg/dl in septic and sometimes RA

total protein

norm: <3 mg/dl (1/3 serum)
increased in inflam and hemorrhagic


infection secondary to inflam
bact most common, but can be fungal, TB, viral
gram stain and culture

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