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Aspiration and injection of the knee animated demonstration

How to aspirate synovial fluid from the knee and administer intra-articular medication using a medial approach.

Equipment needed

Prepare a sterile field using a non-touch technique with the following:

  • Sterile gloves

  • Sterile antiseptic skin preparation (povidone-iodine or chlorhexidine are most suitable)

  • Surgical swabs

  • Sterile syringes and needles (21-gauge or 23-gauge)

  • Sterile specimen pots (if aspirating for diagnostic purpose)

  • Medication for injection (for therapeutic purpose)

  • Adhesive dressing

  • Local anaesthetic (optional).

Contraindications

  • Joint replacement or prosthesis

  • Infection: broken skin at injection site, local skin infection, cellulitis, systemic infection, or osteomyelitis

    • If septic arthritis is suspected, aspiration is indicated and injection is contraindicated

  • Haemarthrosis, osteochondral fracture, or suspected intra-articular fracture

    • Patients with intra-articular fractures will need reduction and operative fixation to preserve joint function

  • Patient refusal.

Abnormal clotting (e.g., haemophilia), anticoagulation, or thrombocytopenia is considered a relative contraindication: there is theoretically an increased risk of bleeding into the joint. However, several studies have shown that there is not a significant increase in bleeding provided that the patient’s international normalised ratio is in the therapeutic range.[38] [39] If the patient is taking a direct oral anticoagulant, avoid injecting or aspirating the shoulder during the peak of the drug activity.[40] The relative risks and benefits of the procedure should be discussed with the patient.

Indications

The indications for performing diagnostic aspiration of the knee joint include clinical suspicion of:

  • Septic arthritis

  • Crystal arthropathy: gout and pseudogout

  • Seronegative arthropathy (e.g., reactive arthritis, gonococcal arthropathy, ankylosing spondylitis)

  • Monoarthropathy, or joint effusion of unknown cause.

On rare occasions, aspiration of the knee joint might be performed to provide symptomatic relief of a very tense and painful haemarthrosis or large tense effusion.

The knee joint may be injected with corticosteroids to provide symptomatic relief for patients with osteoarthritis or gout.

Complications of joint aspiration

  • Pain: should be short lived; after injection of medication there may be an initial flare of pain due to reactive arthralgia. This should resolve within 48 hours

  • Haemorrhage

  • No synovial fluid aspirated

  • Infection: using an aseptic technique helps to reduce the risk of introducing infection into a previously sterile joint space; further investigation and orthopaedic intervention may be necessary if there is suspicion of infection

  • Recurrence of effusion.

Complications of joint injection

In addition to the complications of aspiration, injection of corticosteroid into the joint may cause:[40]

  • Local or systemic hypersensitivity to the injected substance

  • Facial flushing: usually occurs 24-72 hours after injection. More common in women

  • Joint destruction: injecting a joint with corticosteroids may lead to osteonecrosis and destruction of the joint surfaces. This should be weighed against the benefit of intermittent symptomatic relief. Injections should be limited to three per year per large joint[41]

  • Tendon damage or rupture with inadvertent corticosteroid injection into a tendon: risk may be reduced by withdrawing the needle upon meeting resistance, or by using ultrasound guidance

  • Elevated blood sugar in diabetic patients

  • Tissue atrophy and depigmentation of skin.

Aftercare

  • Send synovial fluid from the diagnostic aspirate to the lab for urgent microscopy, cell count, Gram stain and culture, and crystals (for gout and pseudogout)

  • If the aspirate is frank pus, or if there is a clinical suspicion of septic arthritis, immediate orthopaedic assessment and intervention is necessary. Get blood cultures and start the patient on intravenous antibiotics following the local protocol. The patient will need to have a formal joint washout in theatre as soon as possible

  • For aspirates that are non-septic, base the management plan on clinical findings and the results from the analysis of the joint fluid.