Voll, Sandra K. MS, FNP, WHNP, CNM; Walsh, Joseph MS, ACNP-BC, CEN
Over 60 million Americans suffer from chronic knee pain. The vast majority of these complaints are related to osteoarthritis (OA). The knee is both a weight-bearing joint and the largest synovial joint in the human body, making it prone to OA-related pain. Arthrocentesis is the puncture of a joint for diagnostic or therapeutic purposes. Synovial fluid can be aspirated and collected for analysis and/or removed to relieve pain, and medication can be instilled into the joint space.
Patients present with knee difficulties more than any other joint, and NPs in primary care practice will frequently manage musculoskeletal problems. The knee itself has three articular faces: the medial joint, the lateral condylar joint (femoral and tibia), and the patello-femoral joint. It has a wide range of motion: flexion, extension, internal and external rotation, abduction, and adduction.1
One in seven people over the age of 60 suffer from chronic knee pain, and knee pain accounts for 6% of visits to primary care practices.2 The prevalence of knee pain as a chief complaint confronting healthcare providers will likely continue to grow as society ages and obesity rates increase.3
A detailed history is an important first step toward a differential diagnosis. It is helpful to categorize knee complaints into two categories: pain/instability and age group. Pain is associated with injury to the articular surface, OA, inflammatory arthritis, torn meniscus, tendon tears, bursitis, fracture, or infection. The location and character of the pain is important to note as well. Instability can be caused by an episodic injury to the quadriceps patellar extensor mechanism or to the cruciate ligaments.3
Acute knee complaints are more often seen in patients under 50 and are usually caused by ligamentous injury, resulting in immediate swelling and instability. Skiers, basketball, and football players are especially prone to spraining or tearing the anterior cruciate ligament or medial collateral ligament with any sudden change of direction. Initial treatment for knee pain consists of ice, rest, and nonsteroidal anti-inflammatory drugs (NSAIDs).4 Gout affects middle-aged men and menopausal women. OA is associated with degenerative changes, and often, the pain is localized in the medial or anterior portion of the knee, typically after age 50. Patients with degenerative processes complain of stiffness, knee pain that is worse with exercise, going up stairs, rising from a chair, or getting in and out of a car. Rheumatoid arthritis involves symmetrical polyarticular involvement. Symptoms may vary in severity, and usually wax and wane.2 Any knee that is acutely warm, tender, or swollen without a history of trauma is suspect for infection. Other causes of joint inflammation would include a patient history of gout, pseudogout, symptoms of rheumatoid disease, sickle cell disease, hemophilia, or methicillin resistant Staphylococcus aureus (MRSA) infection. Radiographs of the knee (anterioposterior and lateral) are most often nonspecific. If the patient continues to have pain after a week or more, further magnetic resonance imaging evaluation may be indicated.
Risks and benefits
Written consent detailing the benefits and risks should be obtained prior to performing an arthrocentesis. Important benefits to discuss with the patient include improved mobility, reduced pain, and possible identification of pathology via joint fluid analysis. Major risks and complications include introduction of bacteria into the joint space (0.1%), pain during the procedure, increased joint pain for a few days after the injection (5%), and reoccurrence of the effusion.5
Significant complications are rare with arthrocentesis and include iatrogenic infection, allergic reaction, and cortisone-related complications. To prevent infection, the NP must maintain sterile technique and avoid inserting the needle through infected skin or tissue. The risk of infection with arthrocentesis is reported to be 1/10,000.4,5 Bleeding complications resulting in hemarthrosis are rare. If any bleeding occurs, it can be a result of nicking a small synovial blood vessel and is usually inconsequential. Allergic reaction can be prevented with thorough history taking and results from sensitivity to the local anesthetic used for the procedure. Fainting during the procedure is not unusual and is thought to be a result of a vasovagal response. To avoid fainting or complications of fainting during the procedure, have the patient sitting or lying with a support behind their back, and instruct them to take slow, deep breaths during the procedure. Other complications after the procedure can include swelling, pain, or in rare circumstances, persistent drainage from the injection tract.6
Indications and contraindications
An arthrocentesis is indicated for any knee with unexplained synovial effusion or a suspected septic joint. Diagnostically, aspiration of synovial fluid can aid in the evaluation of infectious (septic joint), traumatic (hemarthrosis), crystal-induced (gout/pseudogout), OA, or rheumatoid arthritis etiologies. Therapeutically, aspiration of excessive joint fluid will greatly reduce discomfort and improve range of motion and mobility almost immediately. As a general rule, as much synovial fluid or blood as possible should be removed during the arthrocentesis. Finishing the procedure with an injection of a mixture of an anesthetic and a corticosteroid into the joint space can provide longer-term pain relief.
Avoid the procedure in patients with a prosthetic joint; a specialty referral is more appropriate. Periarticular cellulitis (trauma, tendonitis, bursitis, contusion, cellulitis, or phlebitis) is considered an absolute contraindication to arthrocentesis. However, if the joint is believed to be septic, consultation with an orthopedic specialist is paramount. Use caution in patients with bleeding disorders or those on anticoagulant or antiplatelet therapy. Medications such as warfarin, dabigatran, rivaroxaban, and clopidogrel need not be stopped before the procedure.7,8 Consider using a smaller gauge needle for aspiration, and pressure should be maintained over the injection site for several minutes after withdrawing the needle. Patients with bleeding disorders, such as hemophilia presenting with tension hemarthrosis, may have an arthrocentesis to relieve pain after the appropriate clotting factors have been administered.9 Septicemia is considered a contraindication due to the risk of potentially introducing organisms into the joint space; however, the risk/benefit of the procedure must be considered. The consequences to untreated septic joint are significant, and joints with a high suspicion for bacterial infection warrant arthrocentesis.10 Patients who have undergone arthrocentesis in the past without relief of pain should receive other treatment modalities.
The basic supplies and equipment should be obtained prior to the procedure (see Equipment and supplies for knee arthrocentesis).
The patient should be placed in the semi-Fowlers position with the affected knee flexed approximately 15 to 20 degrees. Placing a towel roll beneath the knee will help achieve an appropriate degree of flexion, thus, opening the joint space for easy aspiration. The knee is comprised of two functional joints: the femoral-tibial and the patello-femoral. A recess can be palpated approximately 1 to 2 fingerbreadths superior and 1 to 2 fingerbreadths lateral of the superior margin of the lateral patella. Tense patients often contract their quadriceps muscles. This narrows the space between the patella and femoral bones, greatly hindering entry into the joint. Encourage the patient to relax these muscles before the injection. Remember good body mechanics—the NP should bring the tray table with supplies near the bedside and raise the stretcher to a comfortable working height.
The knee's joint space is quite large, and the NP may utilize four different approaches (see Medial view of the knee showing the parapatellar approach to knee arthrocentesis). NPs have different preferences, but the most common approach is the superior lateral aspect of the patella. With the patient comfortable and properly positioned, identify landmarks by first palpating the patella. Palpate to the superior-lateral third of the patella; then, thumbnail a point about 1 cm inferior to the patella—this is the injection site. Once the injection site has been identified, the area should be cleaned with an antiseptic solution. The sterile drape is positioned and sterile gloves should then be applied (see Right knee arthrocentesis).
With the 5 mL syringe of 1% lidocaine, start with a small, superficial wheal at the previously identified injection point. Withdraw the needle, and pause for about 1 minute as the lidocaine takes effect. Using the remaining lidocaine, inject deeply toward the joint space, and infiltrate the lidocaine into the tissue, as this will be the track of the larger aspiration needle. Obtain the 60-mL syringe with an 18-gauge needle attached, advance behind the patella into the joint space via the anesthetized track, and start to aspirate the synovial fluid. If the effusion is quite large and the first 60-mL syringe is filled, stabilize the 18-gauge needle with a hemostat, luer-lock off the first syringe, and change out the initial syringe to the back-up 60-mL syringe. Assess the aspirate, and if indicated, place samples in the appropriate sterile containers for lab analysis (see Characteristics of synovial fluid). Continue to aspirate by gently pulling back on the plunger until unable to draw any more fluid out of the joint space. At this point, use the hemostat to stabilize the 18-gauge needle again, remove the 60-mL syringe, and then luer-lock the corticosteroid/anesthetic syringe onto the needle. Inject the medication mixture into the joint space (see Sample medications for knee arthrocentesis injection). The contents should flow freely with little resistance. Once injected, remove the needle, and cover the injection site using a bunched gauze (44) and tape.
If no fluid is obtained initially during the procedure, needle position should be verified or repositioned. If contact is made with the bone during needle insertion, withdraw the needle only slightly, and reposition the angle of insertion; there is no need to withdraw the needle completely. Ultrasound can be used to facilitate needle placement for arthrocentesis, especially for joint aspiration.4
Figure. Medial view ...Image Tools
Figure. Right knee a...Image Tools
Prior to dispatching samples of the joint fluid to the lab, a brief visual analysis of the fluid at the bedside by the NP can provide some basic data. Normal synovial fluid should be amber or nearly transparent. This finding may indicate arthritis—osteoarthritis, rheumatoid, or gouty—as a cause of the pain and effusion. Bloody synovial fluid (hemarthrosis) is usually related to recent trauma, a coagulopathy, or a traumatic aspiration. Opaque, cloudy fluid indicates increased inflammation and perhaps infection as seen in septic joints. Important lab studies to obtain on the synovial fluid include cell count with differential, crystals, Gram stain, and culture and sensitivity. Results of these basic studies will assist in determining any other therapies required.
Table Characteristic...Image Tools
Injections into the articular space usually include both a local anesthetic agent for immediate analgesia and a corticosteroid for its anti-inflammatory properties, resulting in longer-term pain relief, except in those with a possible septic joint. Lidocaine 1% or 2% without epinephrine is most frequently used for intra-articular injection.11 Lidocaine has duration of action of 1.5 to 2 hours. Bupivacaine 0.25% and 0.5% has longer duration of 3 to 6 hours and is another alternative. Both agents have an onset of action of 2 to 5 minutes.
A corticosteroid injection can provide effective relief of acute crystal-induced arthritis in gout and pseudogout as well as OA.12 The choice of an injectable corticosteroid is provider dependent. No rigorous research has shown definitive efficacy and safety favoring one agent more than another.13 Knowing the properties of individual formulations assists in the selection process. Use only the depot formulations for injecting joints, since they have increased duration of action and a more localized effect. Depot corticosteroid action is not completely understood. The agents locally decrease inflammation in synovial tissues, affecting edema and the number of lymphocytes, macrophages, and mast cells.8 The solubility of the cortisteroid also influences the duration of action, with water-soluble agents wearing off sooner.
Corticosteroids are not without adverse reactions, but they are rarely seen. Corticosteroids injected intra-articularly are capable of suppressing the hypothalamic-pituitary-adrenal (HPA) axis. Patients can experience fatigue, depression, anxiety, anorexia, insomnia, and an inhibited immune response. If present, the suppression is usually resolved within 72 hours. Corticosteroids can potentially affect hepatic glucose metabolism and interfere with insulin effects, but observed changes in serum glucose levels have been minimal. Patients with diabetes should be instructed to monitor for increased blood glucose levels for 2 weeks after injection. Other potential adverse reactions include skin hypopigmentation, fat atrophy, and facial flushing.7 Postinjection flare can occur within 2 to 3 hours and up to 2 days after injection of corticosteroids. This is thought to be a result of an inflammatory reaction to the crystalline nature of the corticosteroid injected. The incidence is 1% to 6%.5 Using ice packs and oral NSAIDs for several days help resolve this adverse reaction.
Table CPT codes...Image Tools
The patient will likely have some clinical improvement after the procedure within 2 to 6 hours. Instruct the patient to elevate the knee and apply ice for 15 minutes every hour on the day of injection. Suggest the use of NSAIDs for postprocedure pain relief for patients without cardiovascular or gastrointestinal risk factors that would preclude drug use. Pain should continue to decrease even over the next few days as the corticosteroids take effect. Relief may last for 3 to 4 months, particularly if the pain and effusion appear to be arthritic in nature. Some patients experience increased pain for a few days (steroid flare) followed by a reduction in pain. A follow-up appointment should be made 2 weeks post procedure or sooner as clinically indicated to review lab results and assess patient function. A highly suspicious septic joint will require immediate orthopedic consult and admission to the hospital. The need for repeated arthrocentesis to control knee pain and effusions may prompt consideration of viscosupplementation therapy—several separate injections of hyaluronic acid into the joint in hopes of supplementing the synovial fluid/reducing pain—or joint replacement.
Arthrocentesis is within the NP scope of practice, and NPs should follow state and specialty practice regulations. Specialized training can be obtained at orthopedic conferences, during procedure preparatory course instruction, or with on-the-job training. In the hospital setting, the credentialing for the specific procedure must be followed for each institution. It is important to use the appropriate CPT codes for billing the arthrocentesis procedure (see CPT coding).
Arthrocentesis is a safe and fairly quick procedure that can provide both therapeutic and diagnostic results. Mastering this procedure can either identify a significant joint-threatening disease process or improve a patient's quality of life almost immediately. Subsequently, a properly executed aspiration and injection can provide significant relief for several months. Knee pain is a large and growing issue seen in urgent care centers, primary care clinics, orthopedic clinics, and EDs, and arthrocentesis is an important procedure in the diagnostic workup and treatment of knee pain that NPs can effectively perform.
Equipment and supplies for knee joint arthrocentesis
The following is a basic list of supplies and equipment for knee joint arthrocentesis:
* Towel roll
* Chlorhexidine or povidone-iodine × 3
* Sterile drape and sterile gloves
* Eye protection, goggles, or face shield
* 18 gauge, 1 ½ in. needle (occasionally a 3 in. spinal needle is required for large knees)
* 60 mL syringe × 2
* 10 mL syringe prefilled with chosen corticosteroid/anesthetic agent
* 5 mL syringe filled with 1% lidocaine
* 22-gauge 1 ½ in. needle
* Specimen collection tubes
* 4×4 sterile gauze and tape
Sample medications for knee arthrocentesis injection
* 1% Lidocaine
* Bupivacaine 0.25% or 0.5%
* Betamethasone 6 mg/mL as: betamethasone sodium phosphate 3 mg/mL and betamethasone acetate 3 mg/mL
* Methylprednisolone 40 mg/mL
* Triamcinolone acetonide 40 mg/mL
Source: Hellmann DB, Stone JB. Arthritis and Musculoskeletal Disorders. In: Tierney LM, McPhee SJ, Papadakis MA, eds. Current Medical Diagnosis and Treatment. 45th ed. New York, NY: McGraw-Hill, Medical; 2006:808-810.
1. Simon RR, Sherman SC. Knee. In: Simon RR, Sherman SC, eds. Emergency Orthopedics: The Extremities
. 6th ed. New York, NY: McGraw-Hill Medical; 2011 [chapter 20].
2. Alan Goroll, Albert Mulley Jr. Primary Care Medicine
. 6th ed. Philadelphia, PA: Williams & Wilkins; 2009.
3. Huddleston JI, Goodman SB. Hip and knee pain. In: Firestein GS, Budd RC, Harris ED Jr, McInnes IB, Ruddy S, Sergent JS, eds. Kelley's Textbook of Rheumatology
. Vol 1. 8th ed. St. Louis, MO: W.B. Saunders; 2008 [chapter 42].
4. Hellmann DB, Stone JB. Arthritis and musculoskeletal disorders. In: Tierney LM, McPhee SJ, Papadakis MA, eds. Current Medical Diagnosis and Treatment
. 45th ed. New York: McGraw-Hill, Medical; 2006:808–810.
5. Barkdull TJ, O'Connor FG, McShane JM. Joint and soft tissue aspiration and injection (arthrocentesis). In: Pfenninger JL, Fowler GC, eds. Procedures in Primary Care
. St. Louis, MO: Mosby; 2011:1302–1321.
6. Stulberg D. Knee joint aspiration and injection. In: Mayeaux EJ, ed. Essential Guide to Primary Care Procedures
. Philadelphia, PA: Lippincott Williams & Wilkins; 2009:816–823.
7. Bereznicki LR, et al. The risks of warfarin use in the elderly. Expert Opin Drug Safety
8. Salvati G, et al. Frequency of the bleeding risk in patients receiving warfarin submitted in arthrocentesis of the knee. Reumatismo
9. Parrillo SJ, Morrison DS, Panacek EA. Arthrocentesis. In: Roberts JR, Hedges JR, eds. Clinical Procedures in Emergency Medicine
. St. Louis, MO: WB Saunders; 2009:971–985.
10. Bennecourt RB, Linder MM. Arthrocentesis and therapeutic joint injection: an overview for the primary care physician. Primary Care: Clinics in Office Practice
11. Whittich CM, et al. Musculoskelatal injection. Mayo Clinic Proceedings
12. Wise CM. Arthrocentesis and injection of joints and soft tissue. In: Firestein GS, et al, eds. Kelly's Textbook of Rheumatology
. Philadelphia, PA: Saunders/Elsevier; 2009:721–739.
13. Cole BJ, Acher HR. Injectable steroids in modern practice. J Am Acad Orthopedic Surg