Arthrocentesis

Arthrocentesis or joint aspiration is an interventional procedure done for the collection of synovial fluid.

History

The existence of liquid inside joints was first mentioned in the Corpus Hippocraticum, later in the 16^th century, Paracelsus coined the name “synovia” for synovial fluid.

Indications

Typical indications of synovial fluid aspiration include the following:

• septic arthritis
• confirmation of inflammatory arthritis (e.g. crystal arthropathy, spondyloarthropathy)
• aspiration of hemarthrosis

Contraindications

Extensive cellulitis around the respective joint preventing any sterile approach is the only absolute contraindication.

Relative contraindications include:

• bacteremia
• coagulopathy

Procedure

Preprocedural evaluation

The preprocedural evaluation serves to confirm the indication, to exclude possible contraindications to plan the procedure including the approach. It includes the following.

• present symptoms: type, nature, severity, duration and location of pain
• relevant medical and surgical history
• review relevant laboratory results: INR, aPTT, thrombocytes, leukocytes, c-reactive protein etc.
• review of prior imaging
• obtaining informed consent

Positioning/room set up

Positioning will vary in relation to the specific joint, which is to be aspirated.

Equipment

The exact equipment can vary according to in

• sterile drape and gauze/dressing pack as well as sterile gown and gloves
• skin marker e.g. biopsy grid (CT)
• 5 mL syringe with a hypodermic needle (25G) for local anesthetic (e.g. lidocaine)
• 10 mL to 20 mL syringes with 18-22G (spinal) needle for fluid aspiration
• collecting tubes for laboratory analysis
• connecting tubing
• forceps or hemostat for needle stabilization
• optional: small-bore pigtail catheter 7-8 Fr for septic joint drainage in larger joints (shoulder, hip knee) ³

Technique

Specific techniques vary with respect to the joint punctured and the imaging technique used for guidance. Before the puncture the approach should be planned transversing the needle through areas of inflammation or other skin lesions should be avoided ². As much synovial fluid as possible should be aspirated in particular if the joint aspirate contains pus ².

US-guided

• review consent, coagulation parameters
• patient positioning
• inspection of the skin for possible signs of infection or other skin diseases
• shaving if necessary
• a quick ultrasound scan for procedure planning
• antiseptic skin preparation and drape
• subcutaneous infiltration of local anesthetic
• advance the puncture needle under US guidance into the targeted joint space
• retrieval of synovial fluid, in case of pus as much as possible, should be retrieved
• optional: intra-articular injection of a small amount of contrast for documentation
• dress puncture site and apply pressure to stop bleeding

CT-guided

• review consent, coagulation parameters
• patient positioning
• inspection of the skin for possible signs of infection or other skin diseases
• shaving if necessary
• CT scan with overlying biopsy grid
• planning of the needle approach
• antiseptic skin preparation and drape
• subcutaneous infiltration of local anesthetic
• advancement of the puncture needle under CT guidance into the targeted joint space
• retrieve of in case of pus as much as possible should be retrieved
• optional: intra-articular injection of a small amount of contrast for documentation
• dress puncture site and compression of the puncture site to stop bleeding

Postprocedural care

Postprocedural care includes the following:

• patient reassurance
• observe for 30 minutes for any immediate complications
• forward synovial fluid samples to the laboratory
• commonly performed laboratory testing includes microbiology (gram stain and cultures), cell count, crystal analysis, protein and glucose levels

Complications

Complications are very rare and include the following:

• infection, including septic arthritis
• bleeding 
• allergic reaction to local anesthetic or contrast agent (if used)

Outcomes

Arthrocentesis plays an important role in the diagnosis of septic arthritis and in that setting rapid diagnosis is crucial to prevent delay and possibly associated irreparable joint damage. Aspiration of synovial fluid and/or pus of a swollen joint will lead to decompression and alleviates discomfort and pain.

A  study performing ultrasound-guided aspiration and drainage for septic arthritis in a small number of joints achieved complete evacuation on the first attempt in 5/8 joints ³. 

Practical points

• for fast CT guided puncture one can think about one short control scan after administration of the local anesthetic with the needle in place (can save subsequent control scans)
• if the amount of aspirated fluid is insufficient the needle might be rotated before another aspiration attempt, if the desired amount is still not obtained the needle might need repositioning