Version May 2024
INTRODUCTION — Ultrasonography (US), sometimes referred to as ultrasound imaging or sonography, is an imaging modality that utilizes reflected pulses of high-frequency (ultrasonic) sound waves. Musculoskeletal US can be used to assess soft tissues, cartilage, bone surfaces, and fluid-containing structures and is becoming more widely available for diagnostic and therapeutic use in outpatient settings, including rheumatology practices [1].
Among the major uses of US in the management of joint disorders and related conditions are image guidance of glucocorticoid injections and aspiration of joint effusions and other fluid collections [2-5]. Among the possible advantages of US are the avoidance of the radiation exposure and inconvenience associated with use of fluoroscopy for procedures involving otherwise difficult-to-enter joints and other spaces, including the sacroiliac and hip joints, and small targets, including tendon sheaths, gouty tophi, and small effusions; procedures in patients with obscured surface landmarks such as in individuals with obesity; avoidance of critical structures like nerves or arteries; appropriate needle placement in particular conditions like hemophilia [6]; and direct aspiration of Baker's cysts [7].
The use of US imaging for joint, tendon, and bursal injections and for aspiration of fluid is discussed here. A review of the clinical applications of musculoskeletal US and the technical aspects of musculoskeletal US, including the validity and reliability of image acquisition and interpretation in rheumatic disorders, are addressed in detail separately:
●(See "Musculoskeletal ultrasonography: Clinical applications".)
The techniques and indications, medication regimens, and complications of joint aspiration or injection are also discussed separately:
●(See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?".)
●(See "Joint aspiration or injection in adults: Complications".)
●(See "Joint aspiration or injection in adults: Technique and indications".)
ACCURACY AND EFFICACY — Needle placement based upon external landmarks alone is often inaccurate [8-10]. The use of ultrasound (US) guidance for the injection and aspiration of joints and related structures improves the accuracy of such procedures, but evidence supporting improved efficacy and safety of therapeutic injections using US guidance is still limited and contradictory [11-17]. In addition, a paucity of data exist in the literature regarding the efficacy and safety of US-guided injections for small joints, entheses, and tendon sheaths [14,15]. Avoidance of vulnerable anatomic structures is facilitated by US visualization, and the use of US potentially reduces the likelihood of "dry taps" from the needle missing a small or sequestered fluid collection [3,18]. US is able to detect volumes of synovial fluid in cadaver knees as small as 7.4 mL [19], but modern devices visualize fluid collections in ankle joints as small as 2 mL [20].
Accuracy of needle placement — The inaccuracy of needle placement using external landmarks and palpation alone has been shown in a number of studies, and the accuracy obtained with US has been compared with injection without imaging and with other imaging techniques. In a study of 109 patients who received "blind" intraarticular injections of the shoulder or the knee, the accuracy was only 25 and 70 percent, respectively [8]. Another study, which examined the accuracy of blind glenohumeral (GH) joint and subacromial bursal injections into 38 shoulders, found 42 and 29 percent accuracy, respectively [9].
The use of US may improve the accuracy of needle placement. In one study, greater accuracy was found at multiple sites in a study comparing US- and landmark-guided needle placement in a total of 63 joints, including the shoulder, knee, ankle, and small joints [10]. Successful aspirations were more frequent using US guidance (97 versus 32 percent), although interpretation of the study data is limited by the fact that patients referred for US-guided aspiration who subsequently failed to show fluid were excluded from the study. In addition, a randomized trial including 44 patients presenting to an emergency department with a suspected moderate-size joint effusion (defined as elbow, wrist, or ankle) reported a greater number of successful aspirations with US guidance compared with landmark-guided aspirations (94.1 versus 60 percent) [21]. Notably, of the 14 landmark-guided aspirations for which arthrocentesis was initially unsuccessful, eight of the patients had no effusion when subsequently evaluated with US.
Accuracy of small joint aspiration from metacarpophalangeal or proximal interphalangeal joints is also greater with US-guidance than using a palpation-guided approach (96 versus 59 percent) [22]. Other studies have found comparable accuracy for US in comparison with computerized tomography (CT) or magnetic resonance imaging (MRI) for the aspiration of joints, including the hips, or soft tissue masses at various skeletal sites [23,24].
Effect of accuracy on outcome — Higher accuracy of needle placement may improve clinical outcomes for peritendinous, bursal, or intraarticular injections [13,25-28]. The following examples demonstrate the range of benefits from greater accuracy:
●A randomized trial compared US guidance and conventional palpation guidance for arthrocentesis and glucocorticoid injection in a variety of joints in 148 patients with osteoarthritis, rheumatoid arthritis, and other conditions; the US guidance resulted in significant reductions in procedural pain and pain scores at two weeks (by 43 and 59 percent, respectively) and increased the rate of response (reduction in pain score of at least 50 percent) by 26 percent [28]. US increased the detection of effusions threefold and the volume of aspirated fluid by 337 percent.
●A randomized trial of large and medium joint glucocorticoid injection in 184 patients showed greater accuracy using US guidance than with blind injection at multiple sites, including the knee (91 versus 82 percent), shoulder (63 versus 40 percent), wrist (79 versus 75 percent), ankle (85 versus 58 percent), and elbow (91 versus 64 percent) [13]. A significant improvement in joint function was noted for accurate injections compared with inaccurate injections, but, for other outcome measures, including pain and stiffness, no significant difference between the two groups was found.
●A randomized trial of US-guided intratenosynovial glucocorticoid injection versus a blind intramuscular steroid injection in patients with rheumatoid arthritis and active tenosynovitis showed a significantly better response to the US-guided injection compared with intramuscular steroid injection, both at 4- and 12-weeks follow-up [29].
●A retrospective study evaluating residents of Olmsted County, Minnesota, with carpal tunnel syndrome, showed that ultrasound-guided injections were associated with a reduced chance of retreatment compared with blind injections [30]. Another trial including patients with carpal tunnel syndrome found that the degree of symptom improvement following US-guided local glucocorticoid injection was better for patients who received an injection using the US-guided in-plane ulnar approach compared with the US-guided out-of-plane approach and/or blind injection [31].
Other studies have failed to show that greater accuracy improves outcomes. As an example, one study has shown that true intrasheath injection offers no advantage over subcutaneous injection in the treatment of trigger digits [32,33]. A study of 24 patients with recalcitrant plantar fasciitis did not show any difference in benefit between US-guided injections and conventional injection [34]. In addition, an MRI-based study of the accuracy of US-guided subacromial injections versus blind injections in a small number of patients did not show any difference between the two methods [35].
Further studies are needed to determine the degree of benefit, if any, regarding efficacy and improved clinical outcome from the use of US-guided needle placement for individual anatomic sites and indications. The other possible advantage (ie, avoidance of damage to critical structures), was demonstrated in a single study of 195 therapeutic soft tissue injections [18]. Again, compelling evidence from additional studies is required to corroborate these findings.
TRAINING — The use of ultrasound (US) guidance for injection and aspiration of joints and related sites requires education and training. Courses are available for practitioners who have not received such instruction during their postgraduate medical training. Recommendations for the use of US guidance in the performance of the procedures outlined below, particularly when used for direct visualization during needle insertion, assume a sufficient level of experience and competence [36].
REQUIRED EQUIPMENT — An ultrasound (US) machine with a 7 to 15 MHz linear array broadband probe and a 5 MHz convex array probe is adequate for most studies. Either sterile or nonsterile US gel may be used. Furthermore, an array of needles together with T-connectors should be prepared depending upon the puncture site or specific procedure requested.
TECHNIQUE OF ULTRASOUND-GUIDED INJECTIONS — There are two approaches to the use of ultrasound (US) guidance:
●In the skin marking or indirect approach, US is used to evaluate the anatomic characteristics of the area of interest prior to performing the procedure.
●In the direct approach, US visualization is used during the procedure.
The direct approach requires greater training and experience to obtain competency with needle/probe coordination. It also requires training in coordinated use of one hand for the US probe and the other for the needle and syringe. In addition, familiarity with the differences in the appearance of the needle in the longitudinal and transverse planes and the effects of needle positioning are required. The tip of the needle is clearly visible on the longitudinal image when the needle is parallel to the US beam (image 1), but it appears as a tiny bright spot when the long axis of the transducer probe is transverse to the needle (image 2). The ultrasonographer should not rely solely on the transverse image, as the tip often cannot be seen.
Skin surface marking or indirect approach
Indications for the indirect approach — The indirect approach is used to better define the anatomic location of an area to be injected or aspirated than can be accomplished by physical examination alone. It is most appropriate for procedures involving large effusions that are lying relatively close to the skin surface, such as Baker's cysts and large joint effusions. It may also be used for a large deeper seated joint such as the hip.
Techniques for the indirect approach — The midpoint of the US image on the screen corresponds to the middle point of the transducer probe. The intended needle insertion point should be identified using the probe in the same orientation that is anticipated for the needle and then marked. There are several commonly used options for marking this site, including compression of the skin surface with the point of a retractable ballpoint pen to leave a small dimple; producing a mark with pressure of an extended paper clip; and use of an indelible marker. If a paper clip is used, the metal of an extended paper clip induces lines of bright repetition echoes in the US image. Subsequently, the exact spot for puncturing can be delineated (picture 1).
The depth of the lesion should be measured to facilitate selection of a needle of sufficient length. The skin should be sterilized using standard techniques, and the needle should be inserted near the mark in the same direction as the probe was oriented. The entire procedure takes only a few minutes for the experienced clinician/ultrasonographer. (See "Joint aspiration or injection in adults: Technique and indications".)
Direct approach
Indications for the direct approach — The direct approach to use of US guidance is indicated for reaching otherwise difficult-to-locate anatomic sites or small collections of fluid or to avoid injury to particular structures, such as vascular structures, nerves, and tendons in a critical environment like the wrist. We prefer to perform injections or punctures of small effusions, small joints, and difficult-to-reach joints under direct guidance.
Techniques for the direct approach — When injecting under direct sonographic visualization, the needle should appear on the side of the US image where it is localized anatomically. Thus, it should appear in the image on the right side of the transducer probe if it is introduced from the right side of the probe. The clinician performing the procedure should be positioned facing the scanner, allowing a direct view of the screen. Most right-handed sonographers prefer to hold the US probe in their left hand and the needle in their right hand. The opposite positioning may be preferred by left-handed individuals.
Aseptic technique should be employed. We prefer the use of sterile US transmission gel and cleaning the probe surface with alcohol rather than a sterile sleeve for the transducer probe when the direct approach is used. An alternative approach preferred by some clinicians, or in countries where sterile gel is not readily available, is to envelop the probe in a sterile glove filled with gel.
When the sterile-gel US approach is used, the skin is wiped with an alcohol swab and the probe surface is also cleaned with alcohol. Although iodinated solution can be used on the skin, the transducer surface may be affected by iodine, and cleaning with a 70 percent alcohol solution or chlorhexidine solution is used for the transducer probe. The sterile gel is then placed over the skin and the probe. Alternatives to the use of sterile gel are use of a gel-filled sterile transducer sleeve or sterile hand glove placed over the transducer. The needle is then placed under the probe and slowly advanced to the target. The use of sterile gel allows the needle to be inserted through the gel into the skin if it is overlying the preferred injection site.
Needle visualization — The needle should be introduced adjacent to the footprint of the probe, and the introduction of the needle is directly visualized in real time. Several strategies are used to optimize needle visualization. The needle appears as a bright line if the probe is oriented in the same axis plane as the needle path. Thus, the tip of the needle is clearly visible on the longitudinal image when the needle is parallel to the US beam. Small movements of the needle can make it more visible so that the progression of the needle course can be followed on the screen. If the long axis of the transducer probe and US beam is transverse to the needle, only a tiny bright spot indicates the needle, which does not necessarily correspond with the needle tip; thus, we generally discourage relying upon transverse scanning alone for these procedures. The needle tip should ideally be identified as a moving deflector and visualized throughout the procedure.
Another technique for ensuring correct placement is to inject a small amount of air or a mix of air/glucocorticoid/saline into the joint through the needle. Air bubbles are clearly visible as a white line, white dots, or bright spheres. This is especially useful to ensure the needle position in the shoulder region or in difficult-to-enter joints such as the hip [37-39]. No resistance to injection should be encountered and quick dissipation should follow.
Contraindications and limitations — There are no medical contraindications to the use of musculoskeletal US. However, several factors may limit availability or use of this technique in clinical practice (eg, in rheumatology or orthopaedics). These include the time and cost of acquiring sufficient training, expertise, and, where applicable, credentialing to perform and interpret the musculoskeletal US examination in anatomic regions of interest; the cost of equipment; the need to comply with and expense of regulatory or clinical requirements for image documentation; and proper coding and billing. Other factors include any added time that may be required in the office setting and the cost to the patient.
APPROACHES TO SPECIFIC JOINTS — Our approaches to the most common procedures that benefit from ultrasound (US) guidance are outlined below. The directly visualized US approach is suggested for most of the regions described. The techniques and indications, medication regimens, and complications of aspiration or injection of joints and related structures are discussed in detail elsewhere. (See "Intraarticular and soft tissue injections: What agent(s) to inject and how frequently?" and "Joint aspiration or injection in adults: Complications" and "Joint aspiration or injection in adults: Technique and indications".)
The decision regarding which procedures to perform using US guidance depends upon multiple factors. These include the availability and cost of using US in the clinical, usually outpatient, practice setting; the expertise of the clinician in US and in performing musculoskeletal procedures without US; the specific joint or associated structure of interest; and other clinical factors (eg, lack of success of an initial "blind" procedure). Trial data to demonstrate which specific procedures provide significant benefit with respect to patient outcomes are limited. (See 'Accuracy and efficacy' above.)
US guidance is of greatest use for joints or other periarticular spaces that are especially difficult to enter based upon external landmarks alone. In our experience, these regions and the recommended US approach include:
●Carpal tunnel (direct or indirect)
●Metacarpophalangeal joints (direct)
●Hip joint (direct or indirect)
●Sacroiliac joint (direct)
●Subtalar joint (direct)
●Metatarsophalangeal joints (direct)
US guidance may be of benefit, depending upon multiple factors, including cost, expertise of the clinician in unguided musculoskeletal procedures, and the success of initially unguided procedures, in regions for which procedures guided by external landmarks are common practice. These areas and our recommended US approach include:
●Posterior glenohumeral (GH) joint (direct or indirect)
●Subacromial bursa (direct or indirect)
●Elbow joint (direct or indirect)
●Wrist (radiocarpal) joint (direct or indirect)
●De Quervain tendinopathy (direct)
●Trigger finger (direct)
●Baker's cyst (direct or indirect)
●Tibiotalar joint (direct or indirect, after failure of unguided procedure)
US guidance is generally not necessary in the following joints in our experience:
●Acromioclavicular joint
●Knee (except in individuals with obesity)
●Tibiotalar joint
Shoulder joint and subacromial/subdeltoid bursa — The subacromial/subdeltoid (SASD) bursa can be reached using either a posterior, lateral, or anterior approach (picture 2 and image 3). The GH joint can be reached most easily using a posterior approach, as the GH joint space is difficult to visualize anteriorly.
The posterior approach to the GH joint is described below:
●Probe – A 7.5 to 15 MHz linear array broadband probe is used for visualization of the shoulder.
●Positioning – The clinician should sit behind the patient. The probe should be aligned in the long axis of the infraspinatus tendon (picture 3), while the patient is seated (or semisupine) with the arm in slight external rotation [40].
●Field of view – The scan should show the deltoid muscle, the infraspinatus tendon, the convex contour of the humeral head, and the posterior glenoid labrum.
●Needle placement
•The needle tip should be followed into the SASD bursa.
•The trajectory to the posterior GH joint is deeper than for the SASD bursa, under the infraspinatus tendon and under the labrum, requiring a longer (eg, 8 cm) needle. The penetration of the joint capsule by the needle is felt as transient resistance, followed by a slight sensation of vacuum suction.
•Injection of a small amount of air or fluid should be used to confirm the correct position. Upon injection of the mixture, no resistance to injection should be encountered, and quick dissipation should follow. The needle should be repositioned if there is resistance or if fluid accumulates focally, which may occur if the needle tip is in the deltoid muscle or is abutting the hyaline cartilage of the humeral head or the fibrocartilage of the labrum.
Elbow — We perform injection or arthrocentesis of the elbow joint by direct visualization, although the indirect approach is sometimes used.
●Probe – A 7.5 to 15 MHz linear array broadband probe is used for visualization of the elbow joint.
●Positioning – For puncture of an effusion in the olecranon fossa, the patient is seated, with the arm in retroposition and the elbow semi-flexed [40]. The hand is on the table. The probe is aligned with the long axis of the upper arm and the triceps muscle (picture 4).
●Field of view – The scan should show the triceps muscle and tendon, the fat pad, and the contours of the distal humerus and posterior trochlea, the joint space, and the ulnar olecranon. A posterior effusion will lift the fat pad.
●Needle placement – The needle is directly visualized as it is placed into the posterior joint space. The needle tip is positioned just proximal to the probe and advanced under direct imaging into the effusion.
Carpal tunnel — We perform injection of the carpal tunnel under direct visualization to help avoid trauma to the median nerve, radial artery, or ulnar neurovascular bundle [40]. Alternatively, the indirect method can be followed using a paper clip to localize the exact position of the median nerve.
●Probe – Linear array broadband probe of 7.5 to 15 MHz
●Positioning and field of view – The probe is placed in a transverse and longitudinal scan position. The median nerve is visualized in the middle of the transverse screen next to the long flexor tendon of the thumb (picture 1).
●Needle placement – The needle is placed obliquely at an angle of 45 degrees to the skin ulnar or radial of the median nerve along the wrist crease at the entrance of the carpal tunnel. The needle tip should be directed at a spot between the nerve and either the flexor carpi ulnaris or the flexor carpi radialis tendon depending on the site of entry, using an in-plane transverse scan, and glucocorticoid should be injected adjacent to the median nerve.
Wrist — We perform injection or aspiration of the dorsal radio-carpal wrist joint under direct US guidance (picture 5).
In addition, injecting an extensor tendon compartment is feasible under direct US guidance (picture 6 and image 4).
Trigger finger — Injection of a trigger finger can be performed under indirect visualization, by locating the A1 pulley, skin marking the specific area, and injecting at the region of the A1 pulley [40]. (See "Trigger finger (stenosing flexor tenosynovitis)", section on 'Persistent symptoms'.)
de Quervain tendinopathy — Direct US guidance may be useful for injections for de Quervain tendinopathy. However, US guidance is generally not necessary for treatment of this condition, and there is no evidence that it improves patient outcomes. In patients with de Quervain tendinopathy, a single synovial sheath may either surround both involved tendons at the first extensor region of the wrist (the abductor pollicis longus and the extensor brevis tendons of the thumb), or the sheath may be divided into two separate compartments by a septum.
●Probe and positioning – A 7.5 to 15 MHz probe is positioned in the axial axis of the region of the radial styloid [40].
●Field of view – The transverse and long axis scan will permit visualizing the two tendons and the common sheath.
●Needle placement – The needle is inserted just proximal to the most tender spot and advanced into the tendon sheath, from radial to ulnar.
(See "de Quervain tendinopathy", section on 'Glucocorticoid injection'.)
Hand — We perform punctures of small joints, including the metacarpophalangeal and proximal interphalangeal joints, under direct visualization, with a 15 MHz frequency probe either in a long or a short axis position. The procedure is carried out in a similar fashion to that described for the wrist joint or carpal tunnel. Puncturing can be performed either from a transverse position or long axis position.
Hip — Although direct US guidance is particularly helpful for aspirating hip joint effusions, this joint can also be punctured using the indirect guided method [40,41]. The indirect method helps to detect the location of the effusion and its adjacent neurovascular bundle. Skin marking can then be done by placing the probe in two perpendicular planes over the effusion, putting ink dots on the skin at the two ends of the probe, and connecting the four dots by two straight lines, so that a "+" sign is made.
●Probe – A low-frequency probe (3.5 to 5 MHz), either linear or curved array, is used to visualize the fluid collection.
●Positioning and field of view – The patient is supine, and the curvilinear or linear array probe should be positioned in the line of the femoral neck, displaying the femoral neck, the capsule, and the overlying muscles.
●Needle placement – A long needle (eg, 3.5 inch spinal needle) is advanced under direct visualization (picture 7 and image 5), and, upon breaching the convexity of the bulging capsule, one should try to aspirate. If no fluid appears, it is best to inject a small quantity of air to ensure correct placement of the needle in the hip joint.
Sacroiliac joint — US-guidance is under evaluation as an aid for localizing the deep-seated sacroiliac joint for injection as an alternative to computed tomography (CT), but it is not widely used. In limited studies, the joints in patients or cadavers have been successfully entered approximately 77 to 90 percent of the time, but direct comparison with CT has not been performed [7,42,43]. One study has shown that image fusion of real-time US with previously obtained CT imaging is also a feasible approach but is not generally available [44].
We place the patient in the prone position and use a 5 MHz curvilinear probe. Posterior scanning in a transverse plane shows first the bony landmarks of the posterior superior iliac spine laterally and the spinous process of the fifth lumbar vertebra medially. We then proceed to move the probe in a caudal direction to identify the dorsal crest of the sacrum, the gluteal crest of the ilium, and the first posterior sacral foramen. We then move the probe more caudally to the level of the second sacral foramen. The sacroiliac joint is just lateral to the first and second sacral foramen. The long needle can only reach the superficial part of the sacroiliac joint, not the deeper cartilaginous part [7].
Knee — US guidance is generally not required for knee aspiration or injection, but it may be useful in individual cases [40]. We place the patient in a supine position with the knee extended when using US guidance. A 7.5 linear probe is used to visualize fluid collection or popliteal (Baker's) cysts. A popliteal (Baker's) cyst can be accessed using either an indirect or direct approach with the patient prone and the leg fully extended, as shown in the picture and US images (picture 8 and image 6A-B). (See "Musculoskeletal ultrasound of the knee", section on 'Posterior knee' and "Popliteal (Baker's) cyst", section on 'Imaging studies'.)
Ankle — Ankle joint effusions, which are most commonly located in the anterior recess and less often in the posterior recess, are more easily aspirated with US guidance. Particular care should be taken to avoid the dorsalis pedis artery and the adjacent deep peroneal nerve, which both run anteriorly. The direct approach is generally used, both coronally and transversely; in the latter case, the artery and nerve can be easily avoided. The subtalar joint should only be accessed using the direct approach [41,45].
●Probe – A 7.5 to 15 MHz probe is placed in the coronal plane of the tibiotalar joint [40]. The patient usually is supine with the knee flexed and the foot horizontally on the examiner bench (picture 9 and image 7).
ULTRASOUND-GUIDED SYNOVIAL BIOPSY — Ultrasound (US)-guided synovial biopsy is not (yet) widely used other than for the purpose of research or infrequently for establishing a difficult diagnosis. Blind biopsies using the Parker-Pearson needle have been the standard in clinical care for many years, and arthroscopic procedures have also been utilized. In addition, minimally invasive US-guided percutaneous techniques have been developed using a portal and rigid forceps that permit sampling of inflamed synovial tissue under indirect visual inspection [46,47]. A role for routine use of US guidance for synovial biopsy has not been established.
SAFETY OF ULTRASONOGRAPHY — There are no risks or contraindications to the use of musculoskeletal ultrasonography (US), but, when used in conjunction with arthrocentesis or injections, careful attention should be paid to an antiseptic approach.
ADDITIONAL ULTRASOUND RESOURCES — Instructional videos demonstrating proper performance of the ultrasound examination, related pathology, and ultrasound-guided procedures can be found at the website of the American Medical Society for Sports Medicine: introduction to ultrasound guided procedures. Registration must be completed to access these videos, but no fee is required. Another useful site for free instructional videos is sonoskills.com.
SUMMARY AND RECOMMENDATIONS
●Ultrasound (US) guidance of the injection and aspiration of joints and related structures improves the accuracy of such procedures and can improve the efficacy and safety of therapeutic injections. (See 'Accuracy and efficacy' above.)
●The indirect approach of US guidance is used to better define the anatomic location of an area to be injected or aspirated than can be accomplished by physical examination alone. The needle insertion site is marked with the help of such guidance, and the procedure is performed without direct US visualization. It is most appropriate for procedures involving large structures that are lying relatively close to the skin surface. (See 'Skin surface marking or indirect approach' above.)
●The direct approach to US guidance is indicated for reaching otherwise difficult-to-locate anatomic sites or to avoid injury to particular structures. (See 'Direct approach' above.)
●When injecting under direct US visualization, the needle should appear on the side of the US image where it is localized anatomically. The clinician doing the procedure should be positioned facing the scanner, allowing a direct view of the screen. (See 'Techniques for the direct approach' above.)
●The needle appears as a bright line if the probe is oriented in the same axis plane as the needle path. Small movements of the needle can make it more visible. If the US beam is transverse to the needle, only a bright spot indicates the tip of the needle. Small amounts of injected air or air/fluid mixtures can be visualized as a white line, dots, or spheres. (See 'Techniques for the direct approach' above.)
●Direct US visualization during needle placement may be of particular use for the injection or aspiration of the glenohumeral joint (GH), subacromial/subdeltoid (SASD) bursa, elbow, carpal tunnel, de Quervain tendinopathy, hip, and ankle. (See 'Approaches to specific joints' above.)
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