20.9.1: Arthrocentesis

Question 1

This slide was produced from a joint tap. What is visible and what might be it suggestive of?

Answer 1

• Mixed cells including RBCs, but predominantly polymorphonuclear leucocytes (neutrophils)
• Can also see intracellular bacteria (indicated by arrow)
• This is synovial fluid from a septic joint

Question 2

What is visible on this slide, producing from a sample of synovial fluid? What might it be suggestive of?

Answer 2

• The predominant cell type here = polymorphonuclear leucocytes
• This dog has immune-mediated polyarthritis

Question 3

What cell count would you expect in a sample of synovial fluid from a normal animal? What cell type would be expect to be predominant in this sample?

Answer 3

Normal animal synovial fluid:
* Cell count <3 x 10⁹ cells/L
* Main cell type >90% monocytes

Question 4

What cell count would you expect in a joint tap from a septic joint? What would be the main cell type in this sample?

Answer 4

Septic joint:
* >5-10 x 10⁹ cells/L
* Main cell type: polymorphonuclear cells

Question 5

What cell count would you expect in a joint tap from an animal with osteoarthritis? What would be the main cell type from this sample?

Answer 5

Osteoarthritic joint:
* Cell count <5 x 10⁹ cells/L
* Usually >90% monocytes

Question 6

What cell count would you expect in a joint tap from an animal with immune-mediated polyarthritis? What would be the main cell type present?

Answer 6

Immune mediated polyarthritis
* Cell count = variable
* Predominantly polymorphonuclear cells

Question 7

What are polymorphonuclear leucocytes?

Answer 7

• Type of immune cell that has granules
• Neutrophils, eosinophils, and basophils are polymorphonuclear leukocytes

Question 8

What cell type is present here? If you found these in the majority in a joint sample with a slightly elevated cell count, what might you be suspicious of?

Answer 8

• Monocytes
• This is from an animal with osteoarthritis

Question 9

How is synovial fluid viscosity assessed? How does it change with pathology?

Answer 9

• Viscosity decreases with pathology (synovial fluid becomes more watery) e.g. due to dilution by effusion or reduced production due to synovitis

Question 10

What should you do if you suspect sepsis after arthrocentesis?

Answer 10

• Place synovial fluid in a blood culture medium to transport to lab
• Can culture to guide antibiotic choice

Question 11

How can you assess turbidity in synovial fluid?

Answer 11

• Synovial fluid should be transparent
• You should be able to read through it
• If you cannot, this may indicate an elevated cell count

Question 12

This is synovial fluid. What might you be suspicious of?

Answer 12

Sepsis