How Is Knee Arthrocentesis Performed?

Knee arthrocentesis is a relatively quick procedure but may be performed under local anesthesia to avoid pain.

Arthrocentesis (joint aspiration) is a diagnostic procedure in which fluid is drained from a joint (synovial fluid) using a sterile needle and syringe. 

Knee arthrocentesis is an important procedure used for diagnosing arthritis and differentiating inflammatory arthritis from noninflammatory arthritis. Arthrocentesis can also be performed therapeutically for

• pain relief,
• drainage of fluid or
• injection of medications.

Any joint in the body can be aspirated. Joint aspiration is a relatively quick and inexpensive procedure to perform. It can be done in a clinic or hospital setting. Any trained physician, physician’s assistant, or nurse can perform the procedure.

Knee arthrocentesis may be indicated in the patients with inflamed knee joints without an established diagnosis. Inflamed joints are recognized by being

• red,
• warm,
• tender,
• swollen, and
• painful during movement. 

Some conditions that may require joint aspiration and analysis to establish diagnosis are:

• Monoarticular arthritis (inflammation of the joint)
• Septic arthritis (infection of the joint)
• Joint effusion (swelling due to fluid accumulation in the body)
• Intra-articular fracture (fractures which involve the joint space) 
• Crystal arthropathy (accumulation of calcium crystals in the joint and surrounding areas)

Joint aspiration may be performed as a treatment in certain conditions:

• Repeated aspirations can be part of the management of the septic joint to relieve discomfort and prevent joint damage.
• Aspiration can be considered in cases of hemarthrosis (blood in the joints) to prevent adhesions. 
• Aspiration can be performed while injecting intra-articular medications, such as corticosteroids or hyaluronic acid to improve efficacy. Steroid injections help reduce joint inflammation, reduce pain, preserve joint structure, and function. Hyaluronic acid lubricates the joint, decreases impact, delays joint aging, and reduces pain and stiffness. 

Knee arthrocentesis should be performed with caution in patients with bleeding disorder or those on anticoagulant drugs (blood thinners). Patients taking anticoagulant drugs may be advised to stop the medications a few days before the procedure and resume again after the procedure.

Occasionally, knee arthrocentesis can be performed using radiological guidance as it may require to confirm the presence of fluid before aspirating. Radiological guidance can also be helpful in aspirating other deep and technically difficult joints like the hip joint or spine. 

Knee arthrocentesis is a relatively quick procedure but may be performed under local anesthesia to avoid pain. 

• A sterile needle of appropriate size and length is introduced into the joint and the synovial fluid is collected in syringes. 
• The fluid is then analyzed microscopically. Apart from microscopic analysis, the appearance of the aspirated synovial fluid can indicate certain features. 
• Normal fluid is clear or light yellow and viscous. Inflammatory fluid appears darker yellow to cloudy and loses its viscosity. Purulent fluid (pus in the fluid) is brownish to whitish and opaque.
• After the procedure, the patient is asked to rest for a few minutes, after that they can resume normal activities. 
• Some patients may experience pain and bruising which resolves in a few days. Ice packs and pain killers can help reduce pain and bruising.

Knee arthrocentesis is a relatively safe procedure and complications are rare. The common complications patients usually face are

• localized bleeding,
• pain,
• swelling, and
• sometimes a reaction to local anesthesia.

Infection of the joint may occur, which is called septic arthritis. 

If medications like steroids are simultaneously injected, though rare, it may cause localized shrinkage or hypopigmentation of the skin. Long-term use of steroid injections may cause systemic side effects like

• weight gain,
• puffy face,
• stretch marks, and
• easy bruising.