Knee Injections and Aspirations

Aspiration

• Diagnostic: Used to rule out septic arthritis and obtain fluid for crystals to confirm gout.
• Therapeutic: Used to relieve symptoms. Aspiration of tense effusion for pain relief. However, depending on the underlying cause, the effusion may quickly reaccumulate.

Injections

• Steroids:
  • Acute inflammation of knee joint e.g. rheumatoid arthritis, osteoarthritis, crystal deposition diseases (e.g. gout, pseudogout) and medical conditions with joint manifestations (e.g. inflammatory bowel disease, psoriasis, Reiter's syndrome and ankylosing spondylitis.
  • For patients with osteoarthritis, injecting steroids into the knee joint reduces pain only temporarily and usually only for up to 4 weeks.¹
• Hyaluronic acid:
  • There is some evidence to suggest intra-articular hyaluronic acid is effective and gives more prolonged pain relief than intra-articular corticosteroids.^1,2
  • However it is not used by most UK rheumatologists and is NOT recommended in current NICE guidance.³

Injection of steroids should be performed no more than once every three months:

• Acute trauma or fracture
• Increased risk of causing knee joint infection, e.g. immunosupressed, cellulitis over the injection site, septic periarticular bursa, bacteraemia unless the joint is the suspected source, broken skin over the injection point
• Bleeding disorder or taking anticoagulation therapy (if INR uncontrolled)
• Unstable joint: multiple steroid injections may aggravate instability in a Charcot joint
• Prosthetic joints should only be aspirated by an orthopaedic specialist.

• Increased pain may occur in 5-10% of patients. This usually starts within the first 24 hours after injection and then settles in a few days. This is sometimes called a 'steroid flare'.
• Injecting into a joint may introduce infection, but this is rare.
• Bleeding is rare, but risk is increased if bleeding disorder or taking anticoagulant therapy.
• Septic arthritis may be aggravated.
• Steroid arthropathy can occur.
• Tendon rupture has been noted after tendon injection.⁴
• Osteoporosis has been seen when high doses are used over a long period of time.
• Superficial structures can be affected e.g. skin atrophy and depigmentation.
• Subcutaneous fat atrophy is also seen.
• Hypersensitivity reactions and adverse drug reactions have also been reported.

• The patient should lie still on a couch with their leg slightly flexed and a pillow under the knee.
• Using aseptic technique entry can be made from either the lateral or medial side of the patella.
• Insert the needle horizontally into the joint, in the gap between the femur and the patella.
• Aspiration and injection can be performed through the same needle.
• When the needle is behind the patella, it is in the joint space.
• After aspiration and/or injection, the joint should be rested for 24 hours.⁵

• Send joint aspirate for microscopy and analysis if suspicious, or need to confirm diagnosis.
• Clear viscous fluid from a cool knee (and suitable clinical picture) does not require analysis.

Aspirate analysis