KNEE ASPIRATION

Diagnosis

• Aspirate an acute hot joint of uncertain origin before starting any antimicrobials
• Often used in diagnosis of chronic and subacute articular pathologies

Treatment

• Recurrent aspiration in management of septic arthritis
• Aspiration of tense effusions of any cause
• Before therapeutic intra-articular corticosteroid injection

• No absolute contraindications to joint aspiration
• Caution in patient with clotting disorder/taking anticoagulants. Discuss with consultant
• Caution in patient with prosthetic joint. Discuss with orthopaedic surgeon
• Avoid passing needle into joint through skin lesion (e.g. psoriasis), as this can lead to joint sepsis

• Sterile dressing pack
• Gloves
• Skin antiseptic
• 20, 10 and 2 mL syringes, green and orange needles
• Lidocaine 1% plain

• Blood culture bottles for aerobic and anaerobic culture of synovial fluid
• 2 plain sterile universal containers:
• 1 for Gram staining
• 1 for crystals
• Heparin tube – for white cell count (orange top)

• If not competent in procedure, organise supervision by a clinician experienced in the procedure

Consent

• Explain procedure and reassure patient
• Obtain and record consent

Position of patient and site of insertion

• Ask patient to lie supine
• Make sure muscles around joint are relaxed to minimise any discomfort from procedure
• putting pillow under knee may help to relax it
• Identify margins of knee joint and patella
• Mark a point (e.g. with thumbnail) 1 cm below mid-point of medial aspect of patella

Aseptic technique and premedication

• Wash your hands, don gloves, prepare skin around knee
• Infiltrate skin with lidocaine 1% using an orange needle

Sampling

• Use no-touch technique
• Insert green needle with 10 or 20 mL syringe horizontally at previously marked point into gap between patella and femur and slightly upward towards suprapatellar pouch
• see Figure 1
• if there is only a small effusion, it can help to displace patella medially to increase gap between patella and femur (Figure 1)
• Aspirate while advancing needle and stop advancing if synovial fluid aspirated
• once fluid begins to appear, it can be ‘milked down’ by pressure with one hand over suprapatellar pouch
• Once syringe full, detach from needle, leaving needle in joint
• Empty syringe into specimen bottles
• 8–10 mL of fluid directly into aerobic bottle first, followed 8–10 mL into anaerobic bottle, rest into plain sterile universal container
• Re-attach syringe to needle and re-aspirate
• Aspirate joint to dryness
• When aspiration complete, withdraw needle
• An adhesive plaster or Micropore dressing to skin is sufficient

Documentation

• Record procedure in notes
• Document exact joint aspirated with:
• volume of fluid
• macroscopic appearance (‘frank pus’, ‘turbid straw-coloured fluid’, ‘frank blood’, ‘blood-stained synovial fluid’, etc.)
• viscosity (‘viscous’ or ‘thin’) of fluid

• Send synovial fluid in blood culture bottle and one plain sterile universal container to microbiology
• request urgent Gram stain