Aspiration and injection of the knee joint is commonly indicated in primary care practice. Arthrocentesis may be required to establish a diagnosis, relieve discomfort, evaluate a hemarthrosis, drain off infected fluid, or instill medication. Because prompt diagnosis and treatment of a monoarthritis can provide significant patient benefit, this easy technique should be considered a first-line intervention.
Effusion of the knee often produces a detectable suprapatellar or parapatellar swelling and may be more evident if the tissues surrounding the knee are compressed during examination. Large effusions can be confirmed by ballottement of the patella. A variety of needle entry techniques have been described for the knee joint, and almost all are successful when large effusions are present. Smaller effusions are best approached from beneath the patella with the knee extended (i.e., patient is supine) to allow for greater ease in aspiration. This chapter describes the commonly used superolateral approach.
Corticosteroids appear to limit the action of inflammatory cells and inhibit destructive enzymes within the joint. Steroid injections can provide significant symptom relief and assist in the resolution of exacerbations of osteoarthritis (Table 61-1). Intrasynovial administration is designed to maximize local medication benefits while minimizing systemic effects. Diluting the steroid solution with a local anesthetic (usually 1% lidocaine) increases the benefits from added volume, and the anesthetic provides instant relief.
TABLE 61-1. CRITERIA FOR THE CLASSIFICATION OF OSTEOARTHRITIS OF THE KNEE USING CLINICAL AND LABORATORY FINDINGS
Steroids should not be injected into a joint with cloudy fluid or if infection is suspected or confirmed. The total white blood cell count (WBC) can help classify the type of effusion (Table 61-2). A WBC of less than 2,500/mm3 is found in noninflammatory fluid, a WBC between 2,500 and 25,000/mm3 is found in inflammatory fluid, and a WBC greater than 50,000/mm3 is found in infectious fluid. The introduction of infection from arthrocentesis is a rare phenomenon and is believed to occur in less than 1 in 10,000 procedures. Despite this reassuring information, practitioners should use sterile gloves and sterile technique when entering joints.
TABLE 61-2. RECOMMENDED TESTS FOR SYNOVIAL FLUID
Several adverse events can occur after steroid and lidocaine injection of the knee. The anesthetized knee is vulnerable to injury, and strenuous activity should
be avoided in the first 24 hours after injection, which also prevents a washout effect of the injected medications. The postinjection flare is a worsening of joint pain 12 to 72 hours after a steroid injection. The postinjection flare is caused by a reaction to the steroid crystals and occurs after 1% to 2% of all joint injections. The postinjection flare can be diminished or avoided by recommending nonsteroidal antiinflammatory drug (NSAID) therapy for 72 hours after steroid injection.
The flare reaction is different from the window period. The window period represents the time during which symptoms may recur; the lidocaine wears off in 1 to 3 hours, and the steroid effect begins in 6 to 24 hours. Patient satisfaction is enhanced by adequate education about these issues before and after the procedure.
Steroids can produce long-term degeneration of the articular surface if repeatedly administered. Although some physicians advise no more than three injections per year, more conservative recommendations include no more than three or four injections in any weight-bearing joint in an individual's lifetime. Injection of viscous agents such as hyaluronic acid have increased the therapeutic options for patients with degenerative disease.
The anatomic structure of the knee is detailed.
(1) Anatomic structure of the knee.
With the patient lying supine, the suprapatellar pouch can be milked with downward pressure to reveal fluid that may not be apparent during the initial examination (Figure 2A). Alternately, the patella can be balloted with direct downward pressure (Figure 2B).
(2) Checking for a joint effusion.
Direct injection into the joint can be achieved under the patella with the knee flexed 90 degrees.
(3) Direct injection into the joint can be achieved under the patella with the knee flexed 90 degrees.
PITFALL: This technique is discouraged, because the needle tip may cause damage to the articular surfaces or the menisci. This direct approach may be acceptable when administering therapeutic viscous solutions (e.g., hyaluronic acid), because the knee cartilage has previously received significant wear.
The superolateral technique uses an entry point 1 cm lateral and 1 cm superior to the upper lateral point on the patella (Figure 4A). This entry site can be approximated by measuring 1 fingerbreadth laterally and superiorly.
(4) The superolateral technique uses an entry point 1 cm lateral and 1 cm superior to the upper lateral point on the patella.
The needle is inserted through skin stretched with the nondominant hand to reduce the patient's discomfort. Alternately, some physicians infiltrate 1% lidocaine (without steroid) to the skin entry site before the arthrocentesis needle is inserted.
(5) The needle is inserted through skin stretched with the physician's nondominant hand to reduce the patient's discomfort.
The aspirating syringe (60, 20, or 10 mL) is attached to a 20- or 22-gauge, 1¼-inch needle. The needle is cross-clamped with a sterile hemostat (i.e., perpendicular to the long axis of the needle) at the needle base.
(6) The needle is cross-clamped with a sterile hemostat.
The needle is gently inserted beneath the patella at a 45-degree angle to the axis of the extremity, aiming the needle to the center of the joint at the inferior portion of the patella.
(7) Insert the needle gently beneath the patella at a 45-degree angle to the axis of the extremity.
PITFALL: The needle tip should pass easily and not touch nearby structures. Touching the needle to any structures within the joint can cause significant discomfort.
After aspiration of fluid, the needle is held steady with the hemostat. The Luer-lock syringe is detached from the needle using counter-clockwise rotation (Figure 8A), and the syringe with steroid and lidocaine is reinserted rapidly without contaminating the needle. The injecting syringe is locked onto the needle using a clockwise rotation (Figure 8B). Inject the 1 mL of steroid (6 mg of betamethasone or 40 mg of triamcinolone) with 3 to 7 mL of 1% lidocaine. The needle is then removed, and a sterile bandage is applied to the injection site.
(8) The Luer-lock syringe is detached from the needle, and the syringe with steroid and lidocaine is reinserted rapidly without contaminating the needle.
PITFALL: Avoid movement of the needle when removing or reapplying a syringe. Movement of the needle is very painful.
INSTRUMENT AND MATERIALS ORDERING
The following instruments and materials are needed:
All materials can be ordered through local surgical supply houses. Lidocaine solution, injectable steroid solution (e.g., Celestone), and injectable viscous agents (e.g., Hyalgan) are available from local pharmacies or surgical supply houses. Consult the ordering information inChapter 65. A suggested tray for performing soft tissue aspirations and injections is listed in Appendix D. Skin preparation recommendations appear in Appendix H.
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