Accuracy of Ultrasound-Guided Injections and Conventional Approaches

The use of ultrasound to visualize the joint space was recommended to improve the accuracy of intra-articular injections of the small joints of the hand, the acromioclavicular joint, and the knee. Ultrasound guidance significantly increased injection accuracy into the first or second tarsometatarsal joint compared with palpation alone (64% versus 25%). Metatarsophalangeal, ankle, Achilles, flexor hallucis longus, and posterior tibial tendon sheath injections were found to be 100% accurate, and subtalar injections were 90% accurate. Ultrasound-guided intra-articular injections of the hip from an oblique sagittal approach, using contrast-enhanced fluoroscopy as a reference standard, yielded an accuracy rate of 97%. Although high-resolution ultrasound allowed exact localization of the joints, other observers could not determine significant differences between the conventional and ultrasound-guided method.

A randomized study conducted to assess the outcomes of emergency physicians performing conventional landmark versus ultrasound-guided knee arthrocentesis revealed no difference in success rates. No difference was found in accuracy between the blind and ultrasound-guided injection of the subacromial-subdeltoid bursa in 20 consecutive patients with impingement syndrome of the shoulder. However, the study authors conclude that ultrasound-guided injections may offer a useful alternative in difficult cases, such as postoperative changes in anatomy or lack of clinical outcome. A prospective, double-blind, randomized, controlled study involving 60 patients with rheumatoid arthritis and wrist synovitis failed to reveal any difference in the accuracy of blind versus ultrasound-guided wrist injection performed by an experienced rheumatologist and confirmed with postprocedural contrast radiography.

Outcomes of Ultrasound-Guided Injections and Conventional Approaches

Improved accuracy and outcomes have been demonstrated for ultrasound-guided procedures compared with conventional methods. Balint and colleagues reported success rates of 97% and 32%, respectively. Sibbitt an coworkers reported that sonographic guidance resulted in a 43% reduction in procedural pain, 58.5% reduction in absolute pain scores at the 2-week outcome, and a 25.6% increase in response rate (reduction in Visual Analog Scale score ≥ 50% from baseline). They also observed a strong trend for sonographic guidance to detect more effusions and permit greater mean fluid aspiration. In a randomized, blinded study assessing shoulder function and pain following conventional or ultrasound-guided subacromial injection of depot steroid, significantly greater improvements in shoulder function and pain were observed in patients who had received ultrasound-guided corticosteroid injections, and this finding was accompanied by greater accuracy of needle placement. Patients reported less pain with ultrasound guidance in a randomized study comparing conventional landmark versus ultrasound-guided knee arthrocentesis. Providers thought that the ultrasound-guided technique was easier to perform. The total procedure time was also shorter with the ultrasound-guided technique. Although there was no difference in the amount of fluid obtained with the techniques, a subgroup of novice practitioners thought that the ultrasound-guided technique was easier to perform and obtained more fluid using ultrasound guidance.

Successful treatment of de Quervain’s tendinitis could be predicted on the basis of the accuracy of the intrasheath injection of depot steroid. In contrast, ultrasound guidance for injection into the tendon sheath for trigger finger did not seem to be necessary for effective pain relief. Similarly, ultrasound guidance failed to show superiority in outcomes over palpation guidance for steroid injection of recalcitrant plantar fasciitis in a randomized trial involving 24 patients. A prospective study enrolling 20 patients, who were randomized for blind or indirect ultrasound-guided corticosteroid injection into the acromioclavicular joint, also failed to reveal any difference in outcomes (i.e., clinical examination at multiple time points after treatment) between the two groups. However, accuracy was assessed by evaluating the widening of the joint space by ultrasound only in the ultrasound group.

These findings suggest that we should not automatically assume that guided injections lead to greater clinical benefits. Most available studies retrospectively correlated clinical outcomes with steroid placement. Although these studies suggest an association between accuracy and outcome, they do not provide definitive proof of a causal relationship. Other factors might have influenced outcome, because although they incorporated a blinded outcome assessor, many studies did not always blind the participants, which could have biased results. Some patients may expect that their rheumatologist will correctly position the injection, whereas others may assume that imaging will increase its accuracy. Any decision about the cost-effectiveness of such injections must rely on data provided by well-randomized, controlled trials with long-term follow-up, which are unavailable. Until data demonstrate that ultrasound guidance improves long-term outcomes, it seems reasonable to conclude that although ultrasound guidance is useful for some joints, such as the hip and midtarsal joints, for accuracy of steroid placement, for most joints that have conventionally been injected by rheumatologists, image guidance should be reserved for patients who have not responded to injection using the conventional approach.

Practical Aspects of Ultrasound-Guided Injection in Difficult Joints

One study showed that puncture of the glenohumeral joint guided by ultrasound at the rotator interval space using an endocavitary transducer was easy and quick, even when performed by radiologists with no experience in arthrographic procedures. Ultrasound guidance was also used to visualize hard targets such as facet joints during injection in a randomized, controlled trial; the procedure was characterized by shorter duration times and less radiation compared with the CT-guided approach.

Ultrasound can detect inflammatory activity in the dorsal sacroiliac joint and is suitable for image-guided sacroiliac joint injection. Ultrasound-guided sacroiliac joint injection in cadavers and patients has been assessed at two puncture levels (i.e., upper level defined at the level of the posterior sacral foramen 1 and lower level at the level of the posterior sacral foramen 2) and was found to be feasible at both levels when defined sonoanatomic landmarks were used. CT confirmed correct intra-articular needle placement in cadavers by showing the tip of the needle in the joint and intra-articular diffusion of contrast media in 16 (80%) of 20 sacroiliac joints. In all four cases in which needle insertion failed, intra-articular sacroiliac joint injection at the other level was successful. In these patients, 100% of ultrasound-guided injections were successful (i.e., eight lower level and two upper level).

A comparison between ultrasound- and fluoroscopy-guided glenohumeral injections demonstrated that the ultrasound-guided approach was significantly less time consuming and more successful on the first attempt. It also caused less patient discomfort and obviated the need for radiation and iodine contrast. Intra-articular injection of the hip joint through a biopsy guide from the anterosuperior approach was more economic and faster compared with CT or fluoroscopy guidance.

Infections after arthroplasty and resection arthroplasty are notoriously hard to manage and may represent diagnostic challenges. Ultrasound guidance may offer significant aid in arthrocentesis, which is the compulsory procedure in suspicious cases in which effusion is present.

Additional Benefits of Ultrasound Guidance

Ultrasound examination can lead physicians to change their anatomic diagnosis of involved structures in certain musculoskeletal conditions and consequently their plan for joint injections and overall treatment. Such modifications were associated with a trend toward improved short-term symptomatic treatment by rheumatologists.

Various specialties use and request musculoskeletal sonographic examinations, which influence clinical decisions. There are considerable differences about the role of sonography as regarded by rheumatologists, musculoskeletal radiologists, and orthopedic surgeons. A report comparing the musculoskeletal ultrasound practices of a rheumatologist and a radiologist working within the same National Health Service Trust found that musculoskeletal ultrasound was predominantly requested by rheumatologists to aid in the diagnosis of synovial and tendon inflammation and to guide injections, whereas musculoskeletal ultrasound performed by the radiologist was predominantly requested by orthopedic surgeons to aid in the diagnosis of structural pathology. Ultrasound guidance may also be used to guide injections containing analgesic compounds into painful joints or soft tissue areas to differentiate localized (i.e., articular or focal) from radiating or projected pain (i.e., arising in other structures).

Safety of Ultrasound-Guided Injections

Although corticosteroids remain the most often used intra-articularly injected drugs, many other compounds have been used, including biologic agents. For many of these agents, such as viscosupplements, radioactive compounds, and destructive agents used for chemosynovectomy, safety and accurate needle positioning are particularly important, highlighting the significance of image guidance. Ultrasound-guided needle placement spares surrounding structures, such as vessels, nerves, and tendons, from deleterious effects. Accidental pannus injury, which may cause extensive intra-articular bleeding, is also avoided. Ultrasound-guided injection of trigger points in myofascial pain syndrome of the cervicothoracic spine, a common medical problem, may help to prevent misguided or misplaced injections that can result in a pneumothorax and to improve efficacy of the trigger point injections.

A large study of therapeutic soft tissue injections in which ultrasound guidance was used to inject corticosteroid into the tendon sheaths of various anatomic regions (upper and lower extremities), plantar fascia, iliopsoas tendon entheses, and bursae clearly showed that ultrasound-guided interventions avoided direct injection of steroids into structures such as fascia and tendons, which would inevitably result in degeneration and rupture.

In terms of potential infections, the direct ultrasound-guided technique (discussed later) is argued to be safe for patients and operators with ordinary antisepsis. Some studies even go so far as to suggest that the use of sterile gels or liquids in combination with sterile sheaths, condoms, or gloves may be an unnecessary procedural effort. Caturelli and associates observed no infections when the ultrasound transducer was cleaned with a 70% alcoholic solution before each intervention. No drapes or covers were needed, and no needles were contaminated. No patient or operator presented with fever or sepsis or with negative viral or hepatitis markers that became positive during follow-up. A larger study based on 8000 ultrasound-guided, mainly abdominal interventions that included fine-needle and large-bore needle biopsies, nephrostomies, and fluid collection aspirations revealed a complication rate of 0.187% and a mortality rate of 0.038%. These studies, however, were primarily based on abdominal punctures of solid organs. There are no studies investigating the infection rate in joint aspiration that has been directly guided by imaging techniques.

Certain skin conditions may influence the safety of ultrasound-guided interventions, in a fashion similar to conventional approaches. They include most skin conditions, primarily psoriatic plaques, local skin or subcutaneous tissue infections, and open wounds. Ultrasound machines have been implicated as potential sources of infection, but the results of these limited studies remain controversial.

Approach to Intervention

Intervention is best conducted in a step-by-step manner ( Table 23-2 ). After the medical history is obtained and the physical examination performed, a conventional radiographic evaluation of the targeted area should be performed to assess structural damage and anatomic variations that may influence the intervention. Before any ultrasound-guided procedure, an ultrasound examination is recommended.

Before the examination, the most appropriate ultrasound transducer for the area and the lesion must be selected. Small-footprint transducers with a higher frequency range are used to assess and guide interventions of small joints and superficial structures, whereas large-footprint transducers with a lower frequency range are used for larger joints and deep structures (see Chapter 5 ). Ultrasound can be used to assess echogenicity, structure, location, shape, contour, size, and vascularization of the lesion, which are critical parameters required for performing a safe and successful intervention. Ultrasound allows real-time examination of the lesion and reveals its relation to the bone surface and to normal, uninvolved soft tissue structures. It can visualize lesions under dynamic conditions, in motion or when pressure and shear forces are applied. Ultrasound helps to differentiate between intra-articular (intracapsular or intrasynovial) and periarticular lesions, as well as between complex lesions with intra-articular and extra-articular distributions that may show evidence of anatomic or pathologic communication between various structures.

The best entry point or portal must be selected. This decision is determined by anatomic and pathologic findings and should be done on a case-by-case basis. For multiloculated lesions (e.g., separated by septa or plicae) the largest or the closest chamber should be selected (based on the diagnostic or therapeutic value). The depth of the lesion from the skin usually determines the route and the size of the needle. The shortest possible route that also avoids vulnerable structures (e.g., nerves, blood vessels, cartilage) and muscles (painful contraction may change position of the needle) should be chosen. The best route should involve the penetration of as few layers and tissues as feasible.

The relationship between the skin and the lesion usually determines the angle and position of the needle with respect to the transducer. For instance, if the distance between the skin and the joint capsule is small, the needle usually should be positioned in the transverse plane relative to the transducer. However, if the capsule is bulging or there is a level difference between the bone endings, a longitudinal approach is favored (see “Direct Technique: Real-Time Visualization”. With the exception of rare cases (e.g., inflammatory or noninflammatory effusion, pus or hematoma, large concentration of crystals), ultrasound examination alone does not allow differentiation between different types of fluid. Selecting the appropriate needle always requires a certain amount of luck, because pus, thick fluid (e.g., rice bodies), and the myxoid content of ganglia can easily block small-bore needles. For cystic lesions and fluid collections, care should be taken to avoid hitting the synovial layer, which may block the needle during aspiration. Whenever possible, the needle should rest bevel up in a fluid-filled cavity, rather than on the wall of the structure ( Fig 23-1 ).

The scan shows the optimal position of the needle within a fluid-containing lesion. The echogenic needle rests bevel up (arrow) in the anechoic area corresponding to the fluid-filled cavity.

The position of the patient and the joint or other target must also be selected, followed by selection of an operator who is experienced in the appropriate technique and an ultrasound machine that is capable of performing the required task. Nurses, technicians, sonographers, and other colleagues may be asked to help in difficult or cumbersome cases. The best arrangement for performing any ultrasound-guided intervention involves a layout that allows the operator a clear view of the ultrasound screen; the patient or the target area should be situated between the operator and the screen in such way that does not hinder the examiner’s view of the screen. The arrangement also should provide ample space for the operator to perform the intervention. In case of direct visualization, appropriate disinfection and sterilization of the area may be performed. The area of interest is then rescanned and the target (region of interest) is positioned in the middle of screen. Final adjustments (e.g., focus, gain) may be undertaken to enhance image quality.

The intervention is performed according to the techniques discussed later. In the case of a single operator, the dominant hand should hold the syringe while the nondominant hand performs the scanning. The operator should focus on the position of the needle, maintaining the appropriate angle and position relative to the transducer. The moment the needle enters the skin, the operator’s attention should shift immediately to the ultrasound screen, following the route of the needle to the lesion. The transducer must not be moved during the intervention after the target is appropriately visualized.

Injection Methods

Guided-Injection Technique

Several companies, including ultrasound system manufacturers, produce needle guide kits and biopsy kits along with other equipment (e.g., sterile gel, transducer covers) required for ultrasound-guided intervention. Many of these devices can be attached to the transducer to guide needle placement ( Fig. 23-2 ). Certain transducers have built-in concentric channels for needle placement, but attachable guide kits have proved to be more popular. The need for needle guidance is explained by the difficulty in finding and following the needle tip, particularly with narrow-caliber needles. A major limitation of most attached needle guides is that they require the needle to be passed at a specific or fixed angle relative to the transducer and plane of imaging. Deep structures are more readily assessed with guidance kits (explaining the predominant use of kits for hip injection). Because of the relatively or completely fixed angle of the kit, superficial structures and lesions are harder or sometimes impossible to assess. The more widespread freehand technique excludes this particular problem. It does, however, require considerable practice and experience to master the hand-eye coordination necessary for needle visualization and targeting. Devices that provide graphically displayed guidance information obtained from small sensors positioned within a weak magnetic field generated by a base unit may be used to allow the sonographer to approach the lesion from any angle relative to the transducer.

Guided injection is demonstrated. A, Attachable guided-injection device (GE injection kit). B, Ultrasound-guided intervention of the hip (anterior approach) uses the guided-injection technique (GE injection kit).

Freehand Technique

Needle puncture procedures of joints and soft tissues are usually performed using the freehand technique. The indications and contraindications for ultrasound-guided joint and soft tissue injections are essentially the same as for conventional injection, although most operators also use a combination of antiseptic liquids (also used for conventional injections) and sterile gels, and they cover the transducer with sterile gloves, sheaths, or condoms. Some operators, however, refrain from using a sterile covering on the transducer, arguing that the transducer does not come into close contact with the needle. There are two common freehand methods using ultrasound guidance.

Indirect Technique: Prerecorded Visualization

Also known as the semiguided or skin surface marking method, the indirect method involves performance of a standard ultrasound examination of the selected region, during which the appropriate target, approach, direction, and inclination are determined and the proposed entry site marked by an indelible pen or metal clipper. This is easy to do. As before any interventional procedure, a baseline ultrasound scan of the involved tissue should be performed. Ultrasound provides valuable information on the extent, volume, and consistency of joint effusions and can detect a variety of additional musculoskeletal lesions, such as synovitis, tenosynovitis, or cysts. Access for the injection should be determined not by predefined anatomic regions but by the ultrasound-selected location of maximal fluid accumulation and specific localization of the target.

The middle of the transducer corresponds to the middle of the ultrasound image on the screen. It is important to measure the depth of the lesion to select the correct needle length. The skin is then disinfected with an appropriate agent, in the same way as done for conventional injections, and the needle is inserted exactly on the mark. This method is quick and convenient because it requires no disinfection of the transducer nor the use of transducer sleeves and covers or sterile gel. Another major advantage of this method is that it does not require an additional operator to hold the transducer, although an experienced sonographer may attempt to perform the injection under direct guidance (discussed later) without external help. The principal disadvantage of the indirect technique is that the performer is unable to see the needle after it enters the skin.

This method is suitable for most joint injections, with the exception of the hip joint, the small joints of the hand and feet, and small fluid collections. In such cases and for most soft tissue targets that are harder to reach due to the relative lack of anatomic landmarks, direct ultrasound-guided needle placement may be preferable. The examiner may easily switch to a direct procedure if the indirect approach fails.

Direct Technique: Real-Time Visualization

Direct visualization of the needle is considered to be the superior technique because it confirms the appropriate placement of the needle. Direct visualization is preferred when the planned route of the needle is close to nerves, vessels, tendons, cartilage, or other vulnerable structures and when the target is small or deeply located.

The skin and transducer are disinfected, followed by application of sterile gel between the skin and the transducer. An alternative approach is to apply sterile gel to the transducer and then cover it with a sterile sleeve or cover. Sterile gel between the transducer and the sleeve is necessary to prevent contamination if the sleeve is ruptured. Regardless of the preparation method used, the transducer is then placed on the area of interest, and an appropriate image of the target is acquired. The needle is then placed under the transducer. The movement of the needle in tissue can be followed by ultrasound during the procedure. The image of the needle on the screen depends on the relationship between the transducer surface and the needle ( Table 23-3 ). In most cases, the needle is parallel to the long or short axis of the transducer. When introduced longitudinal to the transducer (i.e., parallel to the long axis of the transducer (also referred to as being in plane), the needle appears as a highly hyperechoic line causing strong reverberation artifacts ( Fig. 23-3 ) inferior to the image. If the ultrasound beam is transverse to the needle (also referred to as being out of plane), with the needle parallel to the short axis of the transducer, the tip can be visualized as a bright echoic dot as it enters the target ( Fig. 23-4 ). Reverberation artifacts may also appear when the needle is in the transverse position.

Table 23-3

Needle Position Relative to the Ultrasound Transducer Surface

• Parallel to the long axis of the transducer • Parallel to the short axis of the transducer • Perpendicular to the transducer from the opposite side of the scanning surface • Angled relative to the long axis of the transducer • Angled relative to the short axis of the transducer

 

The metallic needle is parallel to the long axis of the transducer and appears as a highly hyperechoic line (arrow). It causes strong reverberation artifacts (arrowhead) within a Baker cyst.

The metallic needle is parallel to the short axis of the transducer and appears as a bright echoic dot (arrow) , representing the tip entering a Baker cyst and causing strong reverberation artifacts (arrowhead) .

After a good image of the target is acquired, the transducer should not be moved. If the needle is not visible, it should be adjusted until an appropriate image of the needle can be visualized ( Fig 23-5 ). Moving the transducer may localize the needle, but the target lesion may easily be lost, resulting in an incorrect intervention. In the transverse position, care should be taken to avoid overrunning with the needle (i.e., advancing the needle so that the ultrasound beam passes through the shaft, not the tip of the needle), which may not be apparent by simply looking at the image because the tip and the shaft of the needle appear quite similar from this aspect. Table 23-3 summarizes the relationship between the transducer surface and the needle. The needle can be more easily seen within a fluid collection when the capsule is distended.

Ultrasound-guided intervention is demonstrated. For an intra-articular injection, the shaft and tip of the needle are visible, with the tip located within the joint space (arrow) . The needle is parallel to the long axis of the transducer.

Air arthrography has been proposed for ultrasound-guided joint aspiration. In this procedure, a small amount of highly echogenic atmospheric air (0.5 mL) is injected to confirm the exact intra-articular position of the needle. Alternatively, a crystalline steroid suspension or a mixture of air, steroid, and physiological saline can be used as contrast medium. The injection of air or crystalline steroid suspension can be supervised on the screen as fine hyperechoic clouds or spots ( Fig. 23-6 ). This allows the examiner to observe whether the injected drug is going into the right place in real time. A major disadvantage of this method is the appearance of ring-down artifacts, a form of localized reverberation that appears when two reflective interfaces and their sequential echoes are closely spaced. Later echoes may show decreased amplitude because of attenuation, displayed as decreased width and resulting in a dense, tapering trail of echoes (see Fig. 3-14 in Chapter 3 ). Such artifacts are commonly caused by gas bubbles or bubbles forming in liquid, and they may hinder visualization of structures located behind the injected material until it is absorbed or dissipates.

A crystalline steroid suspension is injected into tissue. The injected steroid appears as fine, hyperechoic clouds or spots (long arrows). The reverberation artifact makes the needle (short arrows) appear larger than its actual size.

Superiority of air or crystalline steroid arthrography over conventional ultrasound-guided joint aspiration has not been investigated. Air or crystalline steroid arthrography with or without power or color Doppler imaging can lead to the appearance of flow at the tip of the needle, which may also facilitate visualization ( Fig. 23-7 ). Alternatively, this method can be used to verify the presence of drug in the target after a blind or indirect injection and may be used for evaluating injection techniques in clinical practice. A third use is to show the pathologic anatomic connections of adjacent structures. However, a study investigating an intra-articular distribution pattern after ultrasound-guided injections by contrast-enhanced MRI follow-up failed to reveal specific patterns in active rheumatoid arthritis wrist joints.

Air arthrography uses power Doppler imaging. The Doppler jet (arrow) appearing at the tip of the needle is caused by the injection of air into the fluid-filled cavity and facilitates the visualization of the needle. The Doppler signal in other areas of the image corresponds to increased blood flow caused by inflammation.

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