Ultrasonography-Guided Injections for Knee Osteoarthritis in Primary Care

Todd P. Stitik, MD; Nourma Sajid, MD; Patrick J. Bachoura, MD; Vivan Shah, MD; Laxminarayan Prabhakar, MD; and Leonard Introna, BS

Stitik TP, Sajid N, Bachoura PJ,  Shah V, Prabhakar L, Introna L. Ultrasonography-guided injections for knee osteoarthritis in primary care. Consultant. 2018;58(10):261-271.


ABSTRACT: Ultrasonography (US) is becoming a commonly used imaging modality for the musculoskeletal system, particularly in patients with knee osteoarthritis. It has several advantages, including the absence of ionizing radiation, the availability of real-time data, that it is relatively inexpensive, and that it typically yields increased patient satisfaction. This article discusses the use of US in the diagnosis and treatment of osteoarthritic knee pain. It also includes tips for image optimization, offers step-by-step instructions on performing US-guided aspiration and/or corticosteroid injection, and discusses the financial aspects of owning a US instrument.

KEYWORDS: Ultrasonography, knee osteoarthritis, effusion, joint aspiration, corticosteroid injection


Although the potential clinical applications of diagnostic ultrasonography (US) are diverse (Table)1 and of great potential utility for improving patient care, especially as it pertains to musculoskeletal medicine, this article focuses on the use of US for osteoarthritic knee pain, one of the most likely clinical pathologies to be encountered in primary care. This is especially pertinent to the primary care setting, given the growing incidence of knee osteoarthritis (OA) as the population ages. Specifically, knee pain affects approximately 25% of adults and accounts for an estimated 4 million primary care visits per year, making it the 10th most common reason for outpatient visits in the United States. The knee is the most frequent joint affected by OA, with a prevalence of 22% to 39% in the US population.2 Studies support initial nonsurgical management for common knee pathologies, including osteoarthritis.3 While the diagnosis of knee OA is generally relatively straightforward, optimal nonsurgical management can be more challenging, especially with respect to medication selection and the most favorable patient selection for injection procedures and the accurate performance of these procedures.

Ultrasound Table

In patients with knee pain who have radiographic evidence of OA, 90% will have imaging evidence of effusion, with 55% having a moderate to large effusion.4 It is especially these 55% who could experience the most immediate benefit from a knee joint aspiration/injection procedure. Depending on the patient’s body habitus, a knee joint effusion can be difficult to detect with certainty during physical examination. In contrast, effusions are typically easily detected using US.

Accurate identification of knee effusions can significantly influence medication selection. First-line analgesics for OA include acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs). As recommended by a systematic review of 5 randomized controlled trials,3 acetaminophen should be considered initial therapy because it can be effective and has fewer potential adverse effects than NSAIDs.3 However, in the case of OA associated with joint effusion, NSAIDs are the more logical choice, since they have both analgesic and anti-inflammatory properties at anti-inflammatory doses.

In cases where an effusion is absent or minimal but pain is still significant, the anti-inflammatory properties of oral or topical NSAIDs no longer offer an advantage; thus, the clinician could consider other analgesic medications typically used in knee OA, including non-NSAID and non-aspirin-based topical medications, duloxetine, tramadol, and other narcotic analgesics. It is this accurate detection of knee effusions that helps the clinician choose between anti-inflammatories and analgesics.

Furthermore, the presence of a knee effusion in patients in whom NSAIDs are poorly tolerated or contraindicated can help the clinician to decide on the need for a knee injection procedure. US can also help the primary care provider to perform this procedure confidently and accurately without the need to refer the patient to a musculoskeletal medicine specialist. In addition to corticosteroid injections, accurate injections are especially important for viscosupplementation or platelet-rich plasma injections, since inadvertent injection of these substances into soft tissue structures can be particularly irritating to tissues.

The American College of Rheumatology, the American Academy of Orthopaedic Surgeons, and the Osteoarthritis Research Society International have all published guidelines for the treatment of knee OA that focus on therapeutic exercise and weight loss.3,5 Optimizing pain reduction by selecting the best candidates for injections and by accurately conducting such injections should logically help the patient to participate in therapeutic exercise and exercise-related weight-loss efforts.

Another advantage to knee injection is that aspiration can be performed as needed to determine the etiology of a joint effusion in cases where a nonosteoarthritic origin for the arthropathy is suspected. Simple inspection of synovial fluid can provide insight as to etiology. For example, a slight cloudy aspirate might be a clue to underlying crystalline arthropathy, which could then be confirmed by formal synovial analysis. US is the diagnostic tool that could allow for more feasible sampling of synovial fluid.

Pain relief associated with the aspiration of large effusions is another benefit of injection. US-guided knee aspiration resulted in a 183% increase in aspirated synovial fluid volumes.6 Furthermore, real-time US visualization of the target and structures in the needle’s path should help decrease pain from the procedure and the potential for morbidity from needle trauma. Improvement in outcomes using US guidance for knee arthrocentesis included a 48% reduction in procedural pain.6

Numerous studies have demonstrated greater accuracy with visually guided methods compared with palpation-guided techniques for intraarticular knee injections. For the suprapatellar approach, US-guided injection resulted in greater accuracy rates (96%-100%) than palpation-guided injections (55%-84%). For the medial patellar portal approach, injection accuracy increased from 77% for blind injections to 96% for US-guided injections.6

NEXT: Ultrasonography Basics

Ultrasonography Basics

A US instrument typically consists of a transducer (probe) connected by a cable to a computer processor that is connected to a monitor. The US instrument generates electrical signals that are converted by a transducer into sound waves. The transducer is placed on the surface of the body region to be examined, along with US gel that is applied to the skin to acoustically couple the probe to the skin. The sound waves are transmitted into the body, with some of them absorbed into the tissue and some reflected back toward the transducer. The transducer detects sound waves that are reflected to it and converts them to electrical signals that are relayed to the computer processor, which converts them into images displayed on the monitor.

In general, the greater the tissue density (eg, bone) the brighter the signal appears on the US image, because more of the US waves are reflected to the transducer and fewer are absorbed by the tissue. In contrast, less-dense tissues (eg, knee effusion) produce darker images, because fewer of the US waves are reflected to the transducer. The US instrument can be adjusted in several ways to optimize the images depending on the anatomical structures of interest and the patient’s body mass index.

Ultrasonographic images in general should be acquired using 2 basic probe orientations relative to a given structure—the transverse/short-axis view and the longitudinal/long-axis view. Because these views are perpendicular to one another, a simple 90° rotation of the probe will orient the image in either a longitudinal or transverse view. For both views, it is important to keep the probe as parallel to the anatomical structure as possible so that the US beam encounters (or insonates) the tissue as perpendicular as possible. This perpendicular orientation of the US beam relative to the target structure produces a sharp image and reduces an artifact known as anisotropy (Figure 1).

Ultrasound Figure 1
Figure 1. By placing the probe perpendicular to the target structure, one can effectively reduce anisotropy and attain a clearer image.

NEXT: Injection Basics

Injection Basics

US-guided injection procedures provide the advantage over “blind” (ie, anatomically guided) injections of real-time visualization of the target, needle, and flow of injectate. It is this real-time visualization that greatly assists avoiding nontarget structures such as cartilage in the case of knee injections and blood vessels and/or nerves in the case of some of the various other injections.7 US-guided procedures in general are associated with increased accuracy, decreased discomfort, and decreased morbidity. Increased accuracy has been consistently shown for injections in general, including knee injections.6

The most basic and easily understood concept is that of the in-plane injection, whereby the needle is oriented as parallel as possible to the US probe so that the needle is seen in its entirety. The skin puncture site relative to the US probe is chosen to achieve this orientation. This is an important technical detail, because if the needle and the probe are not parallel to one another by more than approximately 30°, the needle may not be visible due to anisotropy, whereby the reflected sound wave does not return to the probe surface per se (Figure 1). Under such circumstances, it may be possible to selectively apply pressure to the distal end of the probe (“back pressure”) in order to decrease this angle (Figure 2). If this is not possible, the needle may need to be repositioned more parallel to the probe.


Ultrasound Figure 2
Figure 2. These images demonstrate how back pressure can make the angle between the US beam and the needle more perpendicular so that the needle can come into view.

To view a step-by-step video of an US-guided intraarticular knee injection/aspiration procedure, go to https://www.youtube.com/watch?v=Li_3S59IjYo.

Step 1. The patient typically is placed in a supine position with the target knee ipsilateral to the clinician, who is sitting next to the examination table and facing the US machine (Figure 3). It is generally helpful to place a buttress or rolled-up towels under the knee to partially flex it, since this maneuver often causes joint fluid to accumulate within the contiguous suprapatellar bursa. The US injection technique described here utilizes the suprapatellar bursa as the injection target, because it is anatomically directly connected to the knee joint, it allows for relatively easy detection of knee joint effusion, and the path of the needle is free of cartilage, thus avoiding the potential iatrogenic complication of needle injury to cartilage.

Ultrasound Figure 3
Figure 3. Correct positioning of the patient and the provider performing the US examination.

Step 2. The US probe is placed longitudinal to the knee, especially slightly lateral to the midline, given that fluid tends to accumulate laterally. If no suprapatellar bursal fluid is seen, the patient is asked to contract the quadriceps (“straighten the knee into the examination table”), because this maneuver can also help to expose fluid. A fluid collection will be present or absent (Figure 4). A conscious effort is made to avoid excessive probe pressure so as not to collapse the bursa and give the false impression that the suprapatellar bursa is empty.

Ultrasound Figure 4
Figure 4. US images of suprapatellar knee effusion in longitudinal view (left) and transverse view (right).

NEXT: Injection Basics (Continued)

Step 3. The US probe is then rotated 90° so that it is aligned parallel to the projected needle-entry site into the suprapatellar bursa. Again, a conscious effort is made to avoid excessive probe pressure so as not to collapse the bursa and give the false impression that the suprapatellar bursa is empty. If fluid is seen, the clinician estimates the needle-entry site so that it enters the skin as parallel as possible to the probe to allow for maximal needle visualization (Figure 5). This proposed needle-entry site can then be marked either by indenting it with the end of a plastic hypodermic needle cap or by drawing 2 perpendicular arrows to it using a permanent marker (Figure 6).

Ultrasound Figure 5
Figure 5. US images of no suprapatellar effusion (“dry knee”) in longitudinal view (left) and transverse view (right).


Ultrasound Figure 6
Figure 6. Proposed needle-entry site demarcated by perpendicular marker lines.

Step 4. An antiseptic solution such as chlorhexidine is applied to the skin using sterile gauze or a chlorhexidine stick. Chlorhexidine is preferred over povidone iodine solution given its superior antimicrobial coverage, its faster dry time of 30 seconds vs 2 minutes, and the fact that it does not visibly stain the skin, the US probe, or the clothing of the patient and the clinician.The probe can be “sterilized” by wiping it with chlorhexidine or covering it with a sterile probe cover. Sterile gel is then placed over the skin of the probe placement site.

Step 5. The clinician should inject local anesthetic (eg, lidocaine 1%, 2%, or 4%) through the needle as it penetrates the skin to make the procedure as painless as possible. It has been our consistent experience that an initial skin wheel of lidocaine followed by slow needle advancement with small boluses of lidocaine is significantly less painful than entering a given target structure without using local anesthetic. The choice of needle gauge depends on the amount of fluid in the bursa, with larger needle gauges (eg, 21-gauge) used for larger fluid collections.

Step 6. Once the suprapatellar bursa is reached, fluid aspiration can occur though the needle. A US image showing the effusion and the needle in the effusion is typically saved at this time. If the gauge of the needle used to enter the suprapatellar bursa is too small to allow for effective fluid aspiration of more than a few milliliters (as is often the case with 25-gauge needles), this needle can be removed, and a needle more appropriate for aspiration (eg, 18- to 21-gauge) can be advanced under direct US guidance into the suprapatellar bursa as it traverses the same tissue tract that was anesthetized with the lidocaine.

Step 7. After a sufficient amount of the fluid has been aspirated as judged by the clinician using real-time US visualization, the aspirating syringe can be unclamped, a syringe containing the appropriate injectate (eg, corticosteroid, viscosupplement, platelet-rich plasma) can be attached to the needle, and the injectate can be delivered. A postinjection US image is typically saved at this point to document that US was used to facilitate accurate injection after aspiration.

Step 8. The syringe/needle is then withdrawn, pressure is applied using a sterile gauze if needed, then an adhesive bandage is applied over the entry site. If fluid is not seen, the clinician either can decide not to conduct an injection procedure or can refer the patient for an injection procedure (preferably to a musculoskeletal medicine specialist who uses US, such as a physical medicine and rehabilitation physician).

NEXT: Return on Investment?

Return on Investment?

Would it be financially worthwhile to incorporate US into your practice? 

While buying a US instrument can cost upward of $10,000, other affordable options are available. Apple iPhone or iPad users can wirelessly connect and use the MSLPU35 US probe, which as of September 2018 cost a flat fee of $1203.8 For Android users, the Philips Lumify US probe, which can plug into any Android phone or tablet, costs $199 per month to rent with no long-term commitment as of September 2018.9 These probe-to-device options transform any compatible device into an US instrument without the need for traditional equipment.9 The additional cost of US gel is nominal.

Furthermore, considering Medicare’s average reimbursement for an office-based limited diagnostic US examination of an extremity (CPT code 76882) has risen from $36.61 in 2017 to $59.04 in 2018, and reimbursement for an arthrocentesis/injection of a major joint or bursa, which includes the knee (CPT code 20611) is $92.88 as of 2018, primary care providers have a good opportunity to generate a profit while providing patients with superior care during their office visit.10

Musculoskeletal US Training

Numerous in-person courses and conferences are offered by various organizations. These can vary widely in content and registration fee. Another option is an online musculoskeletal US course. One example is a knee musculoskeletal US course for $20 that covers normal views and common pathologies of the knee as seen on US, as well as tips on avoiding common mistakes during a US examination.11 US courses can also be supplemented with an anatomy and basic musculoskeletal US textbook.

It could be helpful to establish a rapport with a local interventional radiologist, pain management physical medicine and rehabilitation specialist, or anesthesia pain management specialist who is experienced in musculoskeletal US in order to have a resource if a question arises or if supervised hands-on practice of the techniques demonstrated in a training course is needed.

Since almost all primary care providers have patients with osteoarthritic knee pain, the potential for incorporating musculoskeletal US into clinical practice already exists. Although this article discussed the use of US specifically in the diagnosis and treatment of knee pain due to OA, many other US applications could also be useful to a primary care practice. The cost of bringing basic US instrumentation into one’s practice is feasible, and numerous training opportunities are available.

Todd P. Stitik, MD, is a professor and director of sports medicine in the Department of Physical Medicine and Rehabilitation at the Rutgers New Jersey Medical School in Newark, New Jersey.

Nourma Sajid, MD, is a resident physician in internal medicine at Nassau University Medical Center in East Meadow, New York.

Patrick J. Bachoura, MD, is a resident physician in family medicine, at PIH Health in Whittier, California.

Vivan Shah, MD, is a resident physician in physical medicine and rehabilitation at Beaumont Hospital in Royal Oak, Michigan.

Laxminarayan Prabhakar, MD, is in a preinternship position at Rutgers New Jersey Medical School in Newark, New Jersey.

Leonard Introna, BS, is pursuing a master’s of biomedical science degree from Rutgers University in Newark, New Jersey.


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