Utility of joint aspiration for rheumatological diseases

Joint aspiration (arthrocentesis) is a very important investigation for rheumatological diseases and is the most important initial investigation for people with suspected inflammatory monoarthritis. The aim of joint aspiration is to acquire a sample of synovial fluid for analysis of fluid colour, cells, crystals and most importantly, the presence of infection; see Synovial fluid analysis: typical findings in specific conditions for typical findings in synovial fluid. Aspiration should only be performed by those experienced in the procedure. Refer to a rheumatologist or other specialist if necessary.

If joint aspiration is indicated, consider the potential harms and benefits of the procedure, because in specific circumstances the risk of complications is increased. Before aspirating a joint, seek urgent specialist advice for cases that involve:

  • infection overlying a joint—perform imaging of the joint first to see if there is an associated effusion
  • extensive psoriasis over a joint—the risk of iatrogenic infection is increased when placing a needle through psoriatic plaques, which may be colonised with Staphylococcus aureus; see Plaque psoriasis for an image of psoriatic plaques
  • a prosthetic joint— always consult an orthopaedic surgeon if there is suspicion of infection, or if considering joint aspiration, of a prosthetic joint.

Key points on joint aspiration are shown in Key points on joint aspiration in rheumatological patients and key points on collection and synovial fluid analysis are shown in Key points on synovial fluid collection and analysis.

Figure 1. Key points on joint aspiration in rheumatological patients
  • Joint aspiration is the most important investigation in people with suspected inflammatory monoarthritis to rule out septic arthritis.
  • Joint aspiration enables diagnosis of infection, crystal deposition disease (eg gout) and haemarthrosis.
  • Joint aspiration should be performed by a clinician with appropriate expertise in the procedure.
  • The complication rate is low.
  • Ultrasound- or computed tomography (CT)–guided aspiration is recommended for deeper joints (eg hip joint), and joints that are difficult to access (eg metatarsophalangeal joints).
  • Aspirating the bulk of an effusion can offer therapeutic benefit (eg analgesia). Aspiration should be as complete as possible without compromising patient comfort or causing damage to the joint.
  • Do not aspirate if a fracture is suspected; there is an increased risk of developing osteomyelitis after aspiration of a fractured joint.
  • Do not aspirate through infected skin or psoriatic plaques; there is an increased risk of introducing skin bacteria (especially Staphylococcus aureus) into the joint.
  • Therapeutic anticoagulation is not a contraindication to joint aspirationConway, 2013.
  • Do not aspirate a prosthetic joint; always consult an orthopaedic surgeon.
Figure 2. Key points on synovial fluid collection and analysis
  • Collect 2 mL or more of synovial fluid in a plain sterile tube for Gram stain, culture and polarised microscopy; however, even a few drops of fluid may allow diagnosis.
  • An additional 1 mL of synovial fluid should be placed in a nonsterile anticoagulated tube (such as a full blood count tube) for accurate cell count and differential.
  • Synovial fluid should always be sent to a laboratory for examination.
  • Ideally, have the synovial fluid analysed within a few hours because, over time, changes can occur ex vivo (eg a drop in white cell count, reduction in the number of calcium pyrophosphate crystals, difficulty detecting monosodium urate crystals).
  • Direct inoculation of a blood culture bottle with synovial fluid improves the chance of a positive synovial fluid culture result.