Knee Joint Aspiration and Injection

Daniel L. Stulberg, MD, FAAFP

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Subject: Knee Joint Aspiration and Injection

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Aspiration and/or injection of the knee joint are useful procedures for the office-based or hospital-based practitioner. Arthrocentesis may establish a diagnosis, relieve discomfort, detect hemarthrosis, drain off infected fluid, or instill medication. Even with the increased frequency of advanced imaging including magnetic resonance imaging (MRI), arthrocentesis can be very time and cost-efficient as well as therapeutic. This simple procedure can be a useful diagnostic and therapeutic tool for the practitioner. 
Therapeutic injection of the knee joint may be performed without the presence of an effusion. Aspiration of fluid from a knee effusion can temporarily relieve pressure and reduce discomfort, but the fluid usually recollects unless the underlying process is self-limited or treated. Therefore, aspiration is more useful when the etiology of the effusion is unclear and analysis of the fluid will help the clinician treat the patient. The differential diagnosis includes osteoarthritis, injury, infection, rheumatic disorders, gout, and other less common disorders, so cell counts, Gram stains, cultures, and analysis for crystals are often performed based on the clinical situation. 
Effusion of the knee initially causes a rounder, full appearance to the knee with a loss of the “hollows” medially and laterally at the inferior portion of the patella. Larger effusions will cause swelling seen superiorly. With compression of one or two of these areas, the fluid will shift to the other areas and appear more prominent. The patella may even be ballottable (having a bouncing or floating feel) when compressed posteriorly. A variety of needle entry techniques have been described for the knee joint, and almost all are successful when large effusions are present. Common approaches are the superolateral or the medial from a supine position or the inferolateral from the sitting position with the knee flexed to 90 degrees. 
As with any invasive procedure and the injection of medications, the clinician should weigh the risks and benefits of the procedure with the patient prior to proceeding. Corticosteroids can temporarily help with the pain and inflammation of osteoarthritis (Table 106-1) or help with a flare of gout. Viscosupplementation with hylan or hyaluronan (Synvisc and Orthovisc respectively) is approved for the treatment of osteoarthritis with longer-lasting reduction in pain versus corticosteroids based on a Cochrane database analysis. They are given as a series of three weekly injections. Intra-articular administration is thought to maximize local medication benefits while reducing systemic effects, but patients should be counseled regarding the risks of viscosupplementation and the risks of steroids as appropriate, including the risk of aseptic necrosis of the femoral or humeral head with the latter. 
TABLE 106-1.
Criteria for the Classification of Osteoarthritis of the Knee using Clinical and Laboratory Findings
Steroids should not be injected into a joint if infection is suspected or confirmed. The total synovial white blood cell count (SWBC) can help classify the type of effusion. Typically, a SWBC of <2,500/mm3 is found in noninflammatory fluid, and a SWBC between 2,500 and 25,000/mm3 is found in inflammatory fluid. A 2007 systematic review of the literature by Margaretten et al. showed that a SWBC differential of 90% or higher segmented neutrophils has an increased likelihood ratio of 3.4 versus a likelihood ration of only 0.34 if the differential was <90% segmented neutrophils. The review also found increasing likelihood rations of 7.7 and 28 for SWBC >50,000/mm3 and >100,000/mm3 respectively. 


  • Sterile gloves are preferred by some; others use nonsterile gloves and a “no touch” sterile technique.

  • Skin preparation agent: 70% isopropyl alcohol, povidone-iodine (Betadine), or chlorhexidine gluconate with 70% isopropyl alcohol (ChloraPrep) pads or applicator.

  • Viscosupplementation agent or steroid for injection as indicated, most commonly 40 to 80 mg of methylprednisolone acetate (Solu-Medrol), 10 to 40 mg of triamcinolone hexacetonide (Aristospan), or 10 to 40 mg of triamcinolone acetonide (Kenalog).

  • Syringe (3 to 10 mL, for administering medication).

  • Syringe (20 to 60 mL, for aspirating effusion).

  • One or two 21- to 22- gauge, 1.25-inch needles (to draw up injecting solutions, with the option of a second needle for performing arthrocentesis).

  • Straight hemostat for stabilizing the needle if planning to aspirate first and then exchange the medication syringe for the aspiration syringe to inject without entering the joint a second time.

  • 1% lidocaine for use as a local anesthetic as needed and for injection with cortico-steroids.

  • Red-top tube or vial for laboratory analysis and culture swab with medium for testing as indicated.

  • Postprocedure bandage.


  • Diagnostic evaluation of the cause of an effusion or an unexplained monoarthritis

  • To limit joint damage from infected or inflamed joint fluid by serial removal of fluid

  • Symptomatic relief by removing a large effusion or treatment of joint pain or inflammation (usually temporary)

  • Diagnosis or treatment of a crystal-induced arthropathy

  • Administration of viscous agents for symptomatic improvement of osteoarthritis

  • Administration of glucocorticoids for symptomatic improvement of osteoarthritis


  • Bacteremia or cellulitis overlying the joint

  • Bleeding diathesis or coagulopathy

  • Uncooperative patient

  • Injection of steroids if septic arthritis is suspected or present

  • Clinician is unfamiliar with the correct approach to the joint

  • Presence of a joint prosthesis

  • Lack of response to previous injections or aspirations

  • Steroid injections should usually be limited to three to four times per year

  • Poorly controlled diabetes or systemic illness (diabetes or illness may be more difficult to control with injection of steroids)

  • Therapeutic injection for children and conditions other than those listed previously warrant consideration of a specialty evaluation or recommendation

The Procedure

Step 1

In skilled hands, injection into the knee joint can be completed in only a few seconds, so a local anesthetic is not usually used. For aspiration, for the patient with difficult anatomy, or for the less experienced clinician, a local anesthetic of 1% lidocaine plain injected subcutaneously at the injection site and toward the joint may be useful. See Appendix F. Some practitioners believe that a larger volume gives greater distribution of the medication and will use up to 10 mL or more of local anesthetic injected into the joint with the corticosteroid, and some studies have shown that injection of a volume of anesthetic alone can reduce symptoms. 
  • PITFALL: Limit the use of local infiltration to 1 to 2 mL to avoid causing swelling that would distort the usual landmarks and the ability to palpate the joint.

  • PEARL: Marcaine can be mixed with the lidocaine to extend the anesthetic effect from approximately 1 hour to between 3 and 4 hours.

  • PITFALL: Some experts recommend a new needle for each multidose vial and for the actual injection as well as using single-dose vials of unpreserved anesthetic to avoid possible precipitation of the steroid due to the preservative.

Step 2

If aspiration and then injection is planned, draw the medication into a syringe, remove the needle, and place where the tip will remain sterile (optimally have an assistant hold it). Attach a 21- or 22-gauge needle to a 10- to 60-mL Luer lock syringe based on anticipated volume. Have a straight hemostat available to grasp and stabilize the needle after the aspiration. 
  • PITFALL: This can be done without an assistant, but make sure that sterility is maintained and that the needles are securely on the syringes with a Luer lock to prevent leakage or dislodgement but not so tight that they are difficult to remove during the procedure.

Medial Approach (Supine Position with the Knee Slightly Flexed)

Step 3
Place a gloved hand around the patella with the thumb on the medial aspect and the fingers on the lateral edge of the patella. 
Step 4
Pull the patella medially with the fingers at the same time as the thumb is used to slightly elevate the patella on the medial aspect, opening up a space under the patella and palpating the injection site at the midpoint of the medial aspect of the patella. 
Step 5
Back the thumb inferiorly from the intended injection site by 1 cm, using the thumb as a pointer for the injection. Use one of the listed prep agents to clean the injection site and allow it to dry. 
Step 6
Do not touch the area or move the positioning hand to maintain a sterile area for the “no touch” technique. With the other hand, guide the needle quickly through the skin at a 45-degree angle to the anterior plane of the knee and under the patella. The depth of insertion should be approximately 1 inch. If the needle hits bone or other firm structures, then pull back slightly and then angle slightly more superficial or deep to the anterior plane based on reassessment of the anatomy. 
  • 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.

Step 7
For aspiration, withdraw the desired amount of fluid. If the effusion is small, pressure applied by an assistant at the inferior and superior aspects of the patella at its medial and lateral margins can displace the fluid toward the aspirating needle. To avoid a second puncture and inject at the same time, grasp the hub of the needle with a straight hemostat, rest that hand against the patient, and stabilize the needle while unscrewing the syringe and then screwing on the medication syringe. Maintain the sterile condition of the connections by not allowing them to touch any other surfaces. 
To inject the medication, push the plunger. There should be no resistance. If there is any resistance, then the needle is not in the joint space and should be repositioned. When there is no resistance, the medication can be injected in less then a second, and the needle removed very quickly to the relief of the patient, who is usually nervous but then pleased that the procedure was brief. Place a gauze pad or cotton ball over the site for any skin bleeding, and then apply an adhesive bandage. If lidocaine is used, the patient will usually note a reduction in pain in a matter of only a few minutes. 
  • PITFALL: Avoid movement of the needle when removing or reapplying a syringe. Movement of the needle is very painful.

Superolateral Technique

Step 8
In the same “no touch” sterile technique and setup as described previously, palpate the superolateral aspect of the patella. Insert the needle quickly through the skin 1 cm (approximately one fingerbreadth) superiorly and laterally to the patella. Then gently guide the needle beneath the patella at a 45-degree angle to the axis of the extremity, aiming the needle to the center of the joint toward the inferior portion of the patella. 

Anterior (Sitting Flexed Knee) Technique

Step 9
With the patient sitting, the foot facing forward, and the knee flexed at 90 degrees, insert the needle slightly medially or laterally to the palpable infrapatellar tendon at its insertion on the inferior portion of the patella. Advance the needle posteriorly and slightly toward the midline. 
  • 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.


  • Infection from arthrocentesis is rare and is believed to occur in <1 in 10,000 procedures.

  • The knee is vulnerable to injury, and strenuous activity should be avoided in the first 24 hours after injection.

  • Postinjection flare is a worsening of joint pain 12 to 72 hours after a steroid injection; nonsteroidal drugs may help.

  • Theoretically, steroids may cause degeneration of the articular surface; limit them to three to four injections per year.

Pediatric Considerations

This is rarely used in pediatrics patients. 

Postprocedure Instructions

Cautions regarding the risks and benefits of the procedure should have been discussed prior to the procedure but may be reinforced after the procedure. Even though the patient will likely feel better, the patient should rest for 1 to 2 days and avoid overusing the knee. The patient should watch for signs of infection, which could include fevers, increasing pain, warmth, or redness of the knee. The knee will usually feel much better for one to a few hours after the injection if an anesthetic was injected. This will wear off, and it will take 1 to 2 days before the steroid or viscosupplementation effects start. With steroids or viscosupplementation, there can be a flare and increased pain initially. This can be helped by icing the knee and taking a nonsteroidal anti-inflammatory drug (NSAID) if the patient can tolerate one. Flexible gel ice packs are commercially available, or a bag of frozen peas or corn can be molded over the knee (but should be discarded instead of consumed if used as an ice pack). Steroids and viscosupplementation will not help all patients, and the improvement in symptoms is useful, but only temporary, especially with steroids. If an effusion was tapped, there is a high likelihood that it will at least partially return. 

Coding Information and Supply Sources

All materials can be ordered through local medical supply companies. Lidocaine solution, injectable steroid solution (e.g., Celestone), and injectable viscous agents (e.g., Hyalgan) are available from local pharmacies or medical supply companies. A suggested tray for performing soft tissue aspirations and injections is listed in Appendix I: Suggested Tray for Soft Tissue Aspiration and Injection Procedures. Skin preparation recommendations appear in Appendix E


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Bellamy N, Campbell J, Robinson V, et al. Intra-articular corticosteroid for treatment of osteoarthritis of the knee. Cochrane Database of Systematic Reviews 2006:2. University of Queensland, Centre of National Research on Disability and Rehabilitation Medicine, Brisbane, Queensland, Australia. Cochrane Database of Systematic Reviews 2006, Issue 2. Art No.: CD005328. DOI: 10.1002/14651858. 2.
Bellamy N, Campbell J, Robinson V, et al. Viscosupplementation for the treatment of osteoarthritis of the knee. Cochrane Database of Systematic Reviews 2006:2. University of Queensland, Centre of National Research on Disability and Rehabilitation Medicine, Brisbane, Queensland, Australia. Cochrane Database of Systematic Reviews 2006, Issue 2. Art No.: CD005321. DOI: 10.1002/14651858. 2.
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