Joint Pathology

False - epithelium lies on a basement membrane but the synovial membrane does not.  Therefore the synovial membrane is better described as a specialised connective tissue with secretory capacity.

Macrophages and fibroblasts

Lymphocytes

Plasma dialysate (fluid passed through a membrane) which is modified by secretion from cells in and around the joint and contains a small number of cells e.g. lymphocytes, monocytes and neutrophils.

• Lubrication - boundary lubrication of both of the synovial membrane and articular cartilage 
• Nutrient transport - as articular cartilage is avascular most of it is in close apposition to a synovial membrane which produces synovial fluid.  This synovial fluid helps to 'fill the gaps' where nutrients cannot be transported directly from tissue to tissue.

• Joint effusion 
• Suspect infection - sudden onset, pain, pyrexia, surgery
• Multiple joints
• Pyrexia of unknown origin

False - it should be done under GA or sedation.  After radiography is a good time to perform arthrocentesis.

• Blue (23g 0.6mm) or green (21g 0.8mm).  Length depends on the size of the joint.
• Dog - 2 or 5ml, Cat - 1 or 2ml

The stifle joint

EDTA

Make an air dried smear

Blood culture bottles - they provide bacteria with a friendly environment so they can be cultured and possibly identified

When the sample is still in the syringe barrel, if there is iatrogenic blood there will be distinct separation between blood and synovial fluid.  Whereas, if it is a pathological cause the blood will be mixed with the joint fluid and it will have a homogenous appearance.

• Cats = 0-1ml 
• Dogs = 0.1-1ml

increase

Clear/egg white in colour and it will form a gel in the sample tube.

• a) clear to pale yellow
• b) the turbidity of the fluid increases
• c) very abnormal in colour, blood is often present, often have a bad smell

~5cm

Reduced - normal joint fluid should not be watery

Put a small drop of synovial fluid on your slide.  Take another slide and place it on top of your sample.  Do not apply pressure - you just want to sit the two plates on top of each other or you will squash all the cells.  Swipe the top plate steadily across the bottom plate to evenly spread the sample.  The smear should be air dried very quickly to preserve all the cells.  The slide can be stained using Diff Quik, any standard Romanowsky stain or any routine haematology stain.

• Always eyeball the smear before putting it under the microscope
• First examine the background - the polysaccharides should be a pink haze 
• Assess the amount of red cells - high number indicates iatrogenic or pathological bleeding
• Platelet clumps will occur if there is bleeding at the time of sampling
• Count numbers of large mononuclear cells, lymphocytes, neutrophils and eosinophils.  
• Finally assess the nucleated cell count

• Acute haemorrhage - platelets
• Longstanding haemorrhage - no platelets, increased numbers of white cells, erythrophagocytosis, haematoidin crystals within macrophages and haemosiderin deposits within macrophages

• a) Inflammatory arthropathies
• b) Bacterial infective arthritis