Arthrocentesis and Therapeutic Joint Injection: An Overview for the Primary Care Physician

Indications and clinical evidence

Multiple indications exist for arthrocentesis. Synovial fluid aspiration may be indicated in any joint with an effusion, or even in a normal-appearing joint when the diagnosis is in doubt. There are many causes for joint effusions in adults and children (Table 1). When evaluating a synovial effusion of unknown origin, aspiration is indicated.¹ Arthrocentesis is essential for the diagnosis and management of the acute hot red joint, which may be a medical emergency secondary to the morbidity and

Contraindications

Diagnostic arthrocentesis has few contraindications. Periarticular cellulitis or infection is considered an absolute contraindication to joint aspiration. The concern is that the joint might be seeded by organisms of the overlying skin infection during percutaneous access. However, if the joint is believed to be the cause of the infection, diagnostic aspiration should be performed. The attempt should be made through an area of appropriately prepared uninvolved skin. Joint access through an area

Complications of arthrocentesis

Generally, the most feared complication of arthrocentesis is iatrogenic infection. Although there is a lack of recent large studies, iatrogenic infection after arthrocentesis seems rare but remains a possible complication. In studies in which injection sites were stained before percutaneous needle access of a joint, investigators were able to arthroscopically identify transferred fragments of the stained skin within the joint in most cases.⁵ Although iatrogenic infection seems rare, these

Synovial fluid and effusions

There are numerous causes for joint effusions. The gross appearance of synovial fluid can provide clues related to the type and degree of joint pathology.

Historically, 1 step in clinical diagnosis has been to assign results of synovial fluid visual inspection to 1 of 5 categories: normal, inflammatory, noninflammatory, hemorrhagic, or septic (Table 2). Each category can have an association with a specific disease process.

On visual inspection, inflammatory-appearing fluid may suggest crystalline

Laboratory analysis of synovial fluid

Laboratory analysis of synovial fluid is the single most important assessment technique when investigating an effusion of unclear etiology. It is essential in any investigation of a suspected septic joint. Synovial fluid analysis also allows for diagnosis of specific crystalline arthropathies, and helps to determine whether the cause may be inflammatory or noninflammatory.

For formal study, collected synovial fluid can be divided into 4 aliquots. One of the 4 should be a sterile tube with

Cytology

Normal synovial fluid should be nearly free of cells. Samples indicating an inflammatory cause show increasing numbers of leukocytes, with the WBC cutoff of 2000 cells/μL generally accepted as distinguishing noninflammatory from inflammatory conditions. The widely accepted WBC count defining septic synovial fluid has classically been greater than 50,000 WBC/μL.⁶ However, in one recent study of culture-positive synovial fluid aspirates, 39% had synovial WBC counts of less than 50,000 cells/μL.⁷

Crystal detection

Synovial fluid analysis is useful in establishing a diagnosis of crystal-induced arthritis. The CPPD of pseudogout appear as positively birefringent rhomboid crystals under polarized microscopy. Definitive diagnosis of CPPD generally requires the addition of characteristic joint findings on imaging. The monosodium urate crystals of gout are negatively birefringent under polarized light microscopy, and their presence is diagnostic of gout.

Gram stain and culture

Studies to evaluate for microbes are essential in the evaluation of an effusion of unknown cause. The sensitivity of the Gram stain in bacterial arthritis is generally 50% to 70%, with the exception being gonococcal arthritis (perhaps <10%).9, 10 Cultures are generally positive in most cases of bacterial arthritis, the exception again being gonococcal arthritis (<50%).11, 12 Even in joint aspirates from patients with confirmed crystal-induced arthritis, one study reported that 1.5% had

Bacterial arthritis

Intraarticular corticosteroid injection is contraindicated in cases of suspected bacterial arthritis. Corticosteroids inhibit the ability of the immune system to fight off infection. The patient with septic arthritis generally requires inpatient care with intravenous antibiotics and orthopedic specialist consultation. Specifics and management are discussed elsewhere in this issue.

Injection in inflammatory arthritis

Intraarticular corticosteroids injections are commonly used to treat inflammatory joint conditions such as the rheumatoid and crystal-induced arthropathies. Much of the experience in this area has been with conditions such as rheumatoid arthritis, juvenile idiopathic arthritis, psoriatic arthritis, and reactive arthritis. There are anecdotal reports of use in less common conditions such as sarcoidosis and systemic lupus erythematosus, but there seem to be no large-scale studies using

Injection in noninflammatory arthritis

Osteoarthritis is typified by gradual degeneration of articular cartilage with the development of joint pain, stiffness, and losses in range of motion. The knee is the most commonly affected joint. When standard therapies such as physical therapy and oral analgesics do not provide adequate relief, intraarticular corticosteroids are commonly used to treat pain and swelling associated with osteoarthritis. Generally, in those who show a response, maximum benefit seems to last from 1 to 6 weeks,

Corticosteroid preparations

There seems to be no consensus on the type of steroid that is best used for therapeutic joint injection. Commonly used agents are triamcinolone preparations (Kenalog, Aristospan), methylprednisolone (Depo-Medrol), and betamethasone (Celestone Soluspan). There seems to be significant regional variation in choice of steroid.¹⁹ There is anecdotal evidence that use of betamethasone (Celestone Soluspan) may result in better outcomes (Box 1). Table 4 identifies how much volume of this preparation

Risks and complications

Although the incidence is low, iatrogenic infection is considered the primary risk associated with intraarticular injection. Estimates of actual risk vary by an order of magnitude from 1 in 10,000 to 1 in 100,000.20, 21 This risk, as well as warning signs and symptoms, should be included in an informed consent discussion with the patient before the procedure.

Redness and swelling that can be mistaken for signs of infection rarely occur after the procedure. This phenomenon, termed postinjection

Technique

Injection of the shoulder, elbow, or knee can be considered an adjunctive therapy. Generally, it may be used after other appropriate therapeutic interventions have been undertaken. These interventions include oral pain relievers, physical therapy, and in the case of rheumatoid arthritis should not replace disease-modifying agents.

Arthrocentesis and injection are best performed using sterile surgical gloves and aseptic technique. An 18- to 22-gauge needle should be used for medium to large

Knee

The knee is the most commonly and easily aspirated joint. There are many different successful techniques. It may be accessed via a lateral, medial, or anterior approach, with the patient either supine and the joint in nearly full extension, or with the patient sitting upright with the leg dependent and knee in 90° flexion. Many find that a lateral approach is easiest. Position the patient supine in near full knee extension with a rolled towel under the popliteal space for support when

Shoulder

The glenohumeral joint is the most mobile joint of the body. It is supported by the joint capsule and several ligaments and muscles. Therapeutic injection of the shoulder can be used in treatment of various systemic processes, overuse syndromes, and injuries. A suspected tear in the rotator cuff is a relative contraindication. The glenohumeral joint is a small space and accessing it can prove more challenging than the knee. Landmarks for the procedure include the acromion, the head of the

Elbow

The elbow joint comprises the articulations of the humerus, the radius, and the ulna. There is 1 commonly used approach to aspiration and injection of the joint, and success depends on proper landmark identification. For this procedure the patient may be placed in a semirecumbent position with the elbow flexed at 45°.

The lateral epicondyle of the humerus, the lateral aspect of the olecranon, and the head of the radius describe a triangle, the center of which allows percutaneous access to the

Technique

If additional syringes are needed during aspiration or if therapeutic injection is to be performed, the intraarticular needle may be secured and held steady by application of a sterile hemostat or other device. This procedure allows changeover of the syringes while maintaining needle positioning and minimizing excess movement within the joint space.

On withdrawal of the needle the area should be dressed. Joints with large effusions may benefit from pressure dressings to decrease reaccumulation

Summary

Athrocentesis and therapeutic joint injection is a safe, useful, and perhaps underused primary care procedure. Fluid collection and analysis from a joint with an effusion of unclear cause is an important part of appropriate management. Treatment with therapeutic joint injection can give patients significant, rapid, localized pain relief.