see: [Tintinalli - arthrocentesis](x-devonthink-item://A78A6685-C1F4-4E11-9859-5C21E4393390?page=1965&start=1309&length=15&search=ARTHROCENTESIS), [Robert and Hedges - arthrocentesis](x-devonthink-item://31ACDC98-D2CC-48C5-BE69-E9B37E53FA8C?page=1260) > **note** > I tend to get the fluid analysis confused between [[Spontaneous Bacterial Peritonitis#ascites tap|ascitic tap (paracentesis)]] criteria for peritonitis, [[Pleural effusion#Light's criteria|pleural effusion (light's criteria)]] for exudative/transudative, joint aspirate ([[Arthrocentesis]]), and [[Lumbar puncture#interpretation|LP interpretation]]. There isn't any clinical value in making a table comparing these results, but may be beneficial for studying. > > *memorisation cues for fluid analysis:* > - Lights - POS and LOG > - LPs - "rule of 5s" > - arthrocentesis - "rule of 2s" # Knee joint aspiration ## Causes of effusion - septic arthritis - gout - haemarthrosis ## indications and contraindications **Indications** - joint effusion of unknown cause -- exclude septic arthritis, dx of gout (diagnostic) - joint effusion with pain -- eg large tense effusion (therapeutic) **Contraindications** - local skin cellulitis - joint prosthesis -- perform in theatre - DOACS and warfarin are not specific contraindications, but appropriate to defer procedure in patients with severe coagulopathy or INR >4 likely appropriate **Complications** - failure - pain - infection (1:2,500 to 1:10,000) - bleeding - damage to articular cartilage ## Procedure - enter medial or lateral to patella - pt supine - fully extend knee and make quadriceps muscle relaxed - identify midpoint of patella - insertion point of the needle is 1cm inferior to patellar edge (lateral or medial) to the middle of the patella - direct needle posterior to the patella and horizontally toward the joint space - compress/"mil" to both sides of joint space ![[Pasted image 20240322232705.png]] ![[Pasted image 20240322233406.png]] # interpretation ![[Pasted image 20240322232019.png]] ![[Pasted image 20240322232054.png]] #tables | labs | normal | degenerative | inflammatory | septic/infective | haemorrhagic | | ----------- | --------------- | ----------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------- | | colour | clear or yellow | clear or yellow | yellow | cloudy / turbid, purulent | bloody, may have fat globules | | WBC /mm3 | <200 | <2,000 | 2k - 50k | > 50,000 | varies | | neutrophils | <25% | <25% | <90% (50-90) | 75 - 90% | <25% | | microscopy | neg | neg | crystals - uric acid, calcium pyrophosphate<br>gram stain -ve | bacteria +ve in 50-60% of confirmed cases | neg besides blood | | causes | n/a | osteo-arthritis, rheumatic fever | gout, pseudo-gout, spondyloarthopathy, [[Systemic rheumatic diseases\|RA]], SLE | S aureus, s pyogenes and pneumoniae, n gonorrhoea, [[Tuberculosis\|TB]], gram -ve | trauma, coagulopathy, [[Haemophelia]] | | mgmt | n/a | paracetamol<br>ibuprofen<br>physio<br>+/- ortho | d/w rheumatology<br>- pred po 15-30 mg od <br>- colchicine low dose 1mg → 0.4mg 1 hr later<br>still risks of septic joint<br>refer for intra-articular methylpred | - ortho washout<br>- +/- fluclox + gent +/- cef3 (ortho might want to wait if pt well) | ideally don't do an arthrocentesis if know haemorrhagic<br>+/- factor VIII or DDAVP | # OSCE - [Monash 2020 station 4 - knee](x-devonthink-item://678784CD-EDF6-4C75-89BD-6D54E291812F)