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[CLINICAL TECHNIQUES]

Knee Aspiration and Injection

William O. Roberts, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 26 - NO. 1 - JANUARY 98


Injection and aspiration of a knee joint is a useful procedure for the office, especially in a practice involving many physically active patients. Common reasons for aspirating or injecting a knee include local anesthesia, diagnosis of an unexplained effusion, evacuation of a painful effusion, and injection of a corticosteroid.

The "cortisone" injection is the most frequent reason to enter the knee joint with a needle. Patients with osteoarthritis who are trying to stay active and are not inclined or ready to undergo a partial or total joint replacement often get some relief from the use of intra-articular steroid. Steroid injections should not be used if infection is suspected, and they generally are not used in patients under age 40 because of the risk of cartilage degeneration. An intra-articular cortisone injection in the knee should be followed by at least 1 to 2 weeks of relative rest with no impact loading. The relative potencies of various steroids are shown in table 1 (not shown).

To date, the most common applications of knee aspiration in younger athletes are the analysis of joint fluid in the suspected septic joint and the removal of joint fluid to confirm a loss of extension in the presence of a traumatic effusion. The latter rationale has become less common, as has aspiration for the presence of blood in suspected anterior cruciate ligament (ACL) disruptions; reasons for this include improved evaluation techniques in general, the use of magnetic resonance imaging, and the current tendency to wait a few weeks rather than do ACL surgery immediately.

Injection Procedure

There are many approaches to aspirate or inject the knee joint. One of the easiest methods in the office is an anterior approach medial or lateral to the infrapatellar tendon with the patient in a sitting position as shown in figure 1. The injection point in the joint fossa is palpated and marked with a "fingernail cross" or a "pen-point dimple." An injection mark is essential when a joint effusion masks the joint line, but it may not be necessary in the thin patient with well-defined anatomy and no effusion. The patient's skin is prepped with an antiseptic solution.

[FIGURE 1]

If aspiration is not necessary, local anesthesia at the injection site may be omitted and the joint may be injected using a 25-gauge needle that is 1.25 to 1.5 in. long. A 16- or 18-gauge needle is required to aspirate thick joint fluid or purulent exudate; thus, if the joint is to be aspirated for culture, crystals, or blood, use local anesthesia (1% lidocaine mixed with 7.5% sodium bicarbonate in a 9:1 ratio) to permit use of the larger needle. Change needles after drawing up the injection medications.

Generally, the patient should sit in a chair or on the exam table with the back rest up. To prevent inadvertent extension of the leg while the needle is in the joint space, block the patient's foot with your foot before inserting the needle. As the needle is inserted through the skin, feel for the changes in resistance as it passes through the tissue layers. A "pop" can usually be felt as the needle passes into the joint space. An unexpected increase in resistance may indicate entry into ligamentous tissue.

Before injecting into the joint, aspirate to ensure a return of joint fluid and not blood. If there is unexpected flow resistance to the aspiration or injection, withdraw the needle slightly to see if the flow resistance decreases. The smaller 25-gauge needle will generate greater resistance to injection than a larger 18-gauge needle, and it takes practice to get the feel of "normal" injection flow.

There is usually minimal or no bleeding following withdrawal of the needle. If there is no bleeding, cover the site with bacitracin ointment and an adhesive strip. If there is bleeding, use sustained pressure on the site and cover with an oversized gauze pad and compression tape.

Potential Complications

Possible complications include allergic or toxic reaction to the medications and injection into the incorrect space. Be prepared for the unexpected and have the necessary equipment on hand to handle an emergent reaction to the medication. Vasovagal or syncopal reactions also occur and are a reason not to use the sitting approach to the knee injection or aspiration. If the patient has a history of vasovagal reactions, the procedure can be done with the patient supine and the knee flexed 90°.

A common pitfall in aspiration of suspected septic prepatellar bursitis is to attempt aspiration from the joint space rather than from the prepatellar bursa space. In bursa aspirations, aspiration should target the fluctuant area.

Coding for this procedure is confusing. If the injection is part of a diagnostic workup or a treatment procedure associated with an evaluation or reevaluation, the appropriate coding should include an evaluation code, a management code, and a 25- modifier to correctly document the service.

Dr Roberts is a family physician at MinnHealth SportsCare in White Bear Lake, Minnesota, and medical director of the Twin Cities Marathon. He is a fellow of the American College of Sports Medicine, a charter member of the American Medical Society for Sports Medicine, and an editorial board member of The Physician and Sportsmedicine.


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