Metacarpophalangeal Arthrocentesis

Arthrocentesis, or joint aspiration, is the removal of synovial fluid from a joint cavity.[1, 2]  The fluid removed may be used for diagnostic or therapeutic purposes. Diagnostically, the procedure may be used to elucidate the etiology of acute arthritis, diagnose a septic joint, or identify an intra-articular fracture or effusion. Therapeutically, joint aspiration can alleviate pain secondary to intra-articular pressure from an effusion or drain septic fluid. It can also be used for a pharmaceutical trial of intra-articular pain medication.

Synovial fluid analysis provides pertinent information regarding the composition of fluid in an affected joint suspicious for arthritis, gout, or intraarticular infection. Analysis includes, but is not limited to, identification of crystals, white blood cell (WBC) count, and Gram stain.

Fluid may be aspirated from almost any joint. The metacarpophalangeal (MCP) joint is often aspirated when a clinical suspicion for monoarticular or polyarticular arthritis exists. Because the MCP joint is the principal joint for function of the fingers, arthritic destruction of this joint can have devastating deforming effects and can limit hand function.[3]  Early diagnosis of MCP pathology is important, whether it be arthritis, infection, or gout.

Aspiration of the MCP joint is indicated to evaluate the cause of arthritis[4]  or nontraumatic joint effusion. Analysis of the synovial fluid is essential for facilitating differentiation between inflammatory and noninflammatory etiologies of joint pathology. Synovial fluid analysis is beneficial in patients whose history and physical examination do not elucidate a clear diagnosis.[5]

Arthrocentesis may also be used as a therapeutic modality, relieving the pressure and subsequent discomfort associated with a large effusion. An effusion places undue stress on the joint capsule, resulting in pain and limited mobility. In the case of a septic joint, the aspiration of fluid not only alleviates pain but also decreases the bacterial load in the joint, theoretically limiting joint destruction.

Joint aspiration also has a role in traumatic arthritides. Joint aspirate may be bloody with many red blood cells (RBCs) or may contain fat globules. Both findings are associated with an intra-articular fracture into the marrow cavity or disruption of intra-articular structures.

No absolute contraindications exist for MCP arthrocentesis. All contraindications are relative. As with any procedure, the risks and benefits should be discussed with the patient and informed consent obtained. The two most pertinent risks are infection and hemorrhage.

Overlying cellulitis of the joint is a relative contraindication, in that contamination of the joint may result from the needle passing through the skin and seeding the joint cavity. The exception is a suspected septic joint; the benefit of joint aspiration outweighs any relative contraindications when compared to the morbidity of an undiagnosed septic arthritis. When the needle is passed through a potential or obvious infection source, antibiotic treatment should be initiated. Arthrocentesis should be avoided in patients with bacteremia or sepsis, except to rule out septic arthritis.

Anticoagulation, secondary to metabolic derangements or medicinal therapies, is a relative contraindication. When feasible, the coagulopathy should be reversed; however, this may not be possible or practical. In these instances, special care with needle selection (employing the smallest one possible) and technique are imperative in order to decrease the risk of bleeding complications. No matter the cause, MCP arthrocentesis is safe in patients with mild coagulopathies or therapeutic doses of anticoagulation medications.[5, 6]

Anatomy

The anatomy of the MCP joint is illustrated in the image below.

Metacarpophalangeal joint.

Patient body habitus—specifically, morbid obesity—may make joint aspiration technically difficult. In this patient population, anatomic landmarks may be skewed or difficult to identify.

For metacarpophalangeal (MCP) arthrocentesis, as for any nonemergency procedure, informed consent should be obtained from the patient or the patient's representative. During the consenting process, possible complications must be discussed in detail, including bleeding into the joint, infection of the joint or surrounding skin, nerve injury, pain, bruising, and impaired mobility. It is important to emphasize that these complications can be minimized with sterile preparation and appropriate procedural technique.

Documentation in the medical record is required in the form of either a signed consent form or a written account of the interaction by the physician.

The patient evaluation should begin with a thorough history and physical examination. A focused examination of the MCP joint should include documentation of the overlying skin for signs of infection or previous surgical procedures. Joint size and mobility should also be assessed. The joint in question should be palpated for signs of warmth, crepitus, deformity, or ligamentous instability.

Equipment used in MCP arthrocentesis includes the following:

• Sterile gloves
• Sterile gauze
• Local anesthetic (eg, 1% lidocaine)
• Skin cleansing agent (eg, chlorhexidine or povidone-iodine)
• 3- to 5-mL syringe
• 25-gauge needle for anesthetic injection
• 22- to 25-gauge needle for joint aspiration
• Hemostat
• Specimen tubes
• Bandages

The patient may be positioned sitting or lying down with the hand resting on a bedside table in the prone position. Expose the joint of interest, and identify the joint line and the extensor tendon as it passes over the MCP joint. Swelling of the joint makes identification of the extensor tendon difficult; have the patient extend the ray against resistance to help identify the tendon. Using a marking pen, mark the needle entry site at the MCP joint, either medial or lateral to the extensor tendon. Alternatively, make a depression on the skin with a pen cap or needle sheath.

Next, anesthesia is applied to the skin and subcutaneous tissue. Special care should be taken to stay within the subcutaneous tissue, avoiding the joint space; anesthetic in the joint cavity may interfere with fluid analysis and delay diagnosis. Debate exists whether injecting anesthetic is just as uncomfortable as aspiration without local anesthesia. For this reason, the choice of whether or not to inject local anesthetics is practitioner-specific.

After a thorough examination with or without anesthesia, the entire hand is prepared with a skin cleanser and draped in a sterile fashion, so as to allow repositioning and better control of the joint without sacrificing sterility.

Using the previously made marks on either side of the extensor tendon as guides, insert a 22- to 25-gauge needle briskly through the skin into the joint space, directing it toward the center of the joint space to a depth of 0.3-0.5 cm.[5]  If bone is encountered, slowly withdraw the needle without exiting the skin, then redirect it. Distal traction of the finger may produce a depression on either side of the extensor tendon. These depressions may be used to guide needle insertion into the joint cavity.

If no fluid is aspirated, reevaluate the joint for an effusion, consider another site for aspiration, or seek another physician's perspective.

Aspirate analysis (see the image below) can be performed on 1-5 mL of fluid. If therapeutic injection into the joint is planned or additional fluid aspiration is needed, do not remove the needle from the joint space. Using a hemostat, grasp the base of the needle, being careful not to change position of the needle, and remove the syringe. Attach the second syringe, and continue either aspirating or injecting.

Synovial fluid analysis.

At the completion of the procedure, withdraw the needle and apply a bandage. Transfer the synovial fluid into the appropriate specimen tubes. Finally, document the procedure in the medical record, making special note of the fluid consistency and color. A mention of the joint's condition after the procedure may also be made, especially if an effusion was drained.