Tubes for synovial fluid analysis

1. Chemistry tube for glucose.

2. Hematology tube [with ethylenediaminetetraacetic acid (EDTA)] for cell count and differential.

3. Sterile tube for cultures and smears.

4. Heparinized tube for crystal analysis. Ascertain that a powdered anticoagulant, which may interfere with crystal indentification, is not used.

5. Cytology bottle (if neoplasm is suspected).

IV. Technique. The most important maneuver before aspirating a joint is to locate the appropriate landmark and mark it with an indelible felt pen. Generous local anesthesia of the overlying skin and subcutaneous tissues is recommended. Long-acting intraarticular steroid preparations may induce a crystal synovitis 24 hours after the injection, which soon abates spontaneously or with application of ice and pain medications. Further, the needle itself may traumatize the joint, especially if the joint is small; for this reason, the patient should be warned of possible short-term aggravation of symptoms in the injected joint and receive appropriate instructions regarding analgesia.

A. Shoulder. The shoulder can be entered either anteriorly or posteriorly.

1. Anterior approach (Fig, 4-1). With the patient's hand in the lap and the shoulder muscles relaxed, the glenohumeral joint can be palpated by placing the fingers between the coracoid process and the humeral head. As the shoulder is internally rotated, the humeral head can be felt turning inward and the joint space can be felt as a groove just lateral to the coracoid. When the skin over this area is anesthetized, a 20- or 22-gauge needle can be inserted lateral to the coracoid. (Avoid the thoracoacromial artery, which runs on the medial aspect of the coracoid.) The needle is directed dorsally and medially into the joint space. The needle should be directed slightly superiorly to avoid the neurovascular bundle.

FIG. 4-1. Arthrocentesis of the shoulder, anterior approach.

2. Posterior approach (Fig 4-2). The posterior aspect of the shoulder joint is identified with the patient's arm internally rotated maximally. This position is achieved by placing the patient's ipsilateral hand on the opposite shoulder. The humeral head can then be palpated by placing a finger posteriorly along the acromion while the shoulder is rotated. The needle is inserted about 1 cm inferior to the posterior tip of the acromion and directed anteriorly and medially.

Posterior Shoulder Arthrocentisis

FIG. 4-1. Arthrocentesis of the shoulder, anterior approach.

Shoulder Arthrocentesis
FIG. 4-2. Arthrocentesis of the shoulder, posterior approach.

B. Elbow (Fig 4-3). The elbow joint can be identified by placing the patient's relaxed arm in the lap. With the palm facing the patient, flex the elbow to a

45-degree angle. Place your finger on the lateral epicondyle and note the shallow depression distal to it, which represents the elbow joint. A 22-gauge needle is introduced perpendicular to the joint.

Joint Aspiration The Hand
FIG. 4-3. Arthrocentesis of the elbow.

C. Wrist (Fig, 4-4). Wrist aspiration is performed on the dorsal aspect just distal to the radius or ulna as indicated by clinical examination.

Arthrocentesis Wrist
FIG. 4-4. Arthrocentesis of the wrist, medial and lateral approaches.

1. Radial entry. The hand and wrist are relaxed in a slightly flexed position. The joint space can be located by palpating the edge of the distal radius just medial to the thumb extensor tendon. A 22-gauge needle should be directed into the joint from the dorsal aspect.

2. Ulnar entry. Keep the wrist in the same relaxed position. The joint space can be identified by palpating just distal to the distal ulna. The 22-gauge needle is directed in a volar and radial direction.

D. Ankle (Fig 4-5). The ankle may be difficult to enter. For both approaches, the foot is first placed at about a 45-degree angle of plantar flexion.

Arthrocentesis
FIG. 4-5. Arthrocentesis of the ankle, medial and lateral approaches.

1. Medial approach. A 22-gauge needle is placed about 1 in. proximal and lateral to the distal end of the medial malleolus. The flexor hallucis longus tendon is just lateral to this point. The needle is directed 45 degrees posteriorly, slightly upward, and laterally.

2. Lateral approach. A 22-gauge needle is placed about 1/2 in. proximal and medial to the distal end of the lateral malleolus. The needle should be directed 45 degrees posteriorly, slightly upward, and medially.

E. Knee (Fig 4-6). The knee is the largest and easiest joint to enter. It may be entered either medially or laterally. The patient should be supine with the knee comfortably extended to relax the quadriceps muscle. If one can gently rock the patella medially and laterally, relaxation is adequate. By grasping the medial and lateral margins of the patella, a skin mark can be made that corresponds to the inferior plane of the patella. It is generally easier to aspirate at the medial aspect of the joint. After the skin and subcutaneous tissue are anesthetized, a 19-gauge needle is introduced in a direction parallel to the plane of the posterior surface of the patella. With thick exudative effusions, a larger-bore needle may be required. Drainage of the knee bursa can be facilitated by compressing the suprapatellar pouch during aspiration. With large knee effusions, the distended suprapatellar pouch can be aspirated directly from either the medial or lateral aspect of the quadriceps muscle mass.

Knee Synovial Fluid Analysis

F. Small joints of the hands and feet may be difficult to enter. Occasionally, the effusion bulges and facilitates aspiration. Often, a corticosteroid injection can be performed just adjacent to the joint rather than within; this results in an equivalent clinical response.

1. The metacarpophalangeal (MCP) joint can be easily palpated on its dorsal, lateral aspect with the finger slightly flexed and relaxed. The joint is entered on the dorsal-lateral aspect with a 22-gauge needle. Because this is a ball (distal metacarpal) and cup (first phalanx) joint, the needle should not be directed at a 90-degree angle but rather distally at about a 60-degree angle.

2. The metatarsophalangeal (MTP) joint is aspirated in a fashion similar to that for the MCP joint.

3. The proximal interphalangeal (PIP) joint margin is barely palpable but may be felt on its dorsal aspect just distal to the skin crease. The joint is entered from the dorsal aspect with a 25-gauge needle that is directed slightly distally.

4. The distal interphalangeal (DIP) joint is extremely small and difficult to enter. The technique is the same as for aspirating the PIP joint.

G. Other joints. There are external landmarks that can direct aspiration and injection of the hip joint, but success in this venture requires some experience. When the goal of aspiration is to secure synovial fluid for diagnostic studies, arthrocentesis should be performed under fluoroscopic or ultrasound control. The spinal and sacroiliac joints often demand fluoroscopic or CT guidance.

V. Intraarticular medications. At our institution, we use methylprednisolone acetate, a long-acting, insoluble corticosteroid preparation. The dose varies with the size of the joint. Doses and appropriate needle sizes are summarized in Table^i-l,.

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Table 4-1. Intraarticular therapy regimens

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