What Is a Metatarsophalangeal Arthrocentesis?

Joint aspiration (arthrocentesis) of the metatarsophalangeal joint (in the foot) extracts synovial fluid to help diagnose arthritis.

Joint aspiration (arthrocentesis) of the metatarsophalangeal joint (in the foot) is a diagnostic procedure involving the extraction and analysis of the synovial fluid in the joints. A relatively quick procedure, it is an important component in diagnosing arthritis and differentiating an inflammatory arthritis from a non-inflammatory arthritis. 

An arthrocentesis can also be performed therapeutically (for pain relief, fluid drainage or injection of medications). It can be performed by any physician, physician’s assistant, or nurse who has the training and equipment in a clinic or hospital setting.

Any joint in the body can be aspirated, including for the following conditions:

• 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 that 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 along with injecting intra-articular medications such as corticosteroids or hyaluronic acid to improve efficacy. Steroid injections help reduce joint inflammation, reduce pain, and preserve joint structure and function. Hyaluronic acid lubricates the joint, reduces impact, delays joint aging, and reduces pain and stiffness.

A metatarsophalangeal arthrocentesis should be performed with caution in patients with bleeding disorders or those on anticoagulant drugs. Patients taking anticoagulant drugs may be advised to stop the medications for a few days before the procedure and resume again after the procedure.

Sometimes, a metatarsophalangeal arthrocentesis may be performed using radiological guidance because it may be required to confirm the presence of fluid before aspirating. Radiological guidance can also be helpful in aspirating other deep and technically difficult joints such as the hip joint or spine.

A metatarsophalangeal arthrocentesis is a relatively quick procedure, but may be performed under local anesthesia to avoid pain. A needle of an appropriate size and length is introduced into the joint, and the synovial fluid is collected in syringes. The fluid is then sent to the lab for analysis. 

Apart from microscopic analysis, the appearance of the aspirated synovial fluid can indicate certain features. Normal fluid is clear or light yellow and is viscous. Inflammatory fluid appears darker yellow to cloudy in appearance and loses its viscosity. Purulent fluid (pus in the fluid) appears brownish to whitish and opaque.

After the procedure, the patient would need to rest for a few minutes, soon after which they can resume normal activities. Patients may experience pain and bruising, which will resolve in a few days. Ice packs and pain killers can help reduce pain and bruising.

A metatarsophalangeal arthrocentesis is a relatively safe procedure, and complications are rare.

The common complications patients usually face are localized bleeding, pain, and swelling and sometimes a reaction to local anesthesia. Joint infection may occur, which is called septic arthritis.

If other medications such as 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 such as weight gain, puffy face, stretch marks, and easy bruising.