Indications

• Refusal to weight bear
• Limp
• Painful joint
• Swollen joint

 

Equipment

• Ultrasound machine
• Linear array probe (the curvilinear may be required for deep joins such as the hip in larger patients)
• Ultrasound gel

 

 

Introduction

Children often present to the emergency department with a limp, a painful joint, or refusal to weight bear. The differential is broad, including transient synovitis, septic arthritis and trauma. Previously, a formal ultrasound done by the radiology department has been used to determine the presence or absence of an effusion in order to help narrow the differential. PoCUS has been increasingly used by pediatric emergency physicians to quickly assess for the presence of a joint effusion at the bedside. The rapid identification of an effusion can expedite necessary interventions, including consultation of subspecialists or arranging for arthrocentesis.

 

Why Ultrasound?

Currently, most children presenting with a limp, refusal to weight bear or joint pain and swelling receive some combination of x-ray, blood work and formal ultrasound in the radiology department. Ultrasound as an imaging modality has many advantages, including low cost and no radiation [1,2]. The use of ultrasound at the bedside provides many advantages in its ease of access, as well as speed and portability [1-2]. This is especially useful when children are presenting to the department outside the hours in which a formal ultrasound is readily available.

Physical examination for joint effusions can be limited by pain, patient cooperation or soft tissue changes. POCUS is superior to physical exam for the detection of effusions and can be used to differentiate swelling at a joint due to effusion and soft tissue change (e.g. cellulitis) [3]. From an imaging perspective, X-ray has been shown to have a sensitivity for identifying an effusion ranging between 20-28%, whereas the sensitivity of a formal ultrasound approaches 100% [4-5]. Many studies have shown that PoCUS can been used by emergency physicians to easily identify fluid or a joint effusion in the hip, knee and ankle [1,5,6,7]. For example, a study in 2010 comparing trained PEM physicians performing hip ultrasound to a formal ultrasound read by radiologists showed a sensitivity of 80% and specificity of 98%. Moreover, when the physician reported confidence in their exam, the specificity and positive predictive value improved to 100% [7]. In 2018 Cruz et al showed that PEM physicians were able to detect hip joint effusions with a sensitivity of 85% and specificity of 98% [2]. In 2010 Adhikari and Blavais examined the role of PoCUS in patients presenting with joint complaints. In patients with clinically suspected effusions in whom arthrocentesis was planned, management changed in 69.2% after PoCUS was performed. In those in whom arthrocentesis was not planned, management changed in 53.3% of cases after PoCUS was performed [8]. Clinically, the absence of a joint effusion can effectively rule out septic arthritis, which can prevent unnecessary interventions on patients.

Overall, the use of POCUS to identify joint effusions is safe, easy to perform, and a quick way to begin the work up for the child presenting to the emergency department with a limp.

Summary

• PoCUS is both sensitive and specific for the diagnosis of pneumothorax.
• Use the linear probe to scan the anterior chest in a supine patient.
• Absence of shimmering, comet tails and lung pulse indicate pneumothorax.
• Don’t forget to document your findings in the chart and save images fro QA.

 

Pearls & Pitfalls

 

• Ultrasound is meant as a diagnostic aid. Always rely on clinical information to guide management decisions. If it is unclear what you are seeing, obtain formal imaging.

 

• Vascular structures can mimic abscess. Be sure to accurately identify common abscess mimics. Always use color doppler before making an incision: abscess should never have central blood flow.

 

• Small foreign bodies may be difficult to see and can be time consuming to identify. The location of foreign bodies can also limit imaging if there is a hematoma or large wound around the object.

 

What is NOT normal?

Cellulitis

Cellulitis can have a highly variable appearance. In general, the subcutaneous tissue appears thickened and will have a “cobblestone” appearance. This is caused by subcutaneous edema and inflammation generated by the surrounding infection. Cobblestoning is not a specific finding to cellulitis but a finding in tissue edema, care must be taken to correlate to the clinical scenario. If uncertain, compare the area of interest to an unaffected area of skin.

 

Figure 3: Cobblestoning

Cobblestone appearance of cellulitis	Cobblestone sidewalk

 

Video 4: Soft tissue cobblestoning

 

Pitfalls

Edema from any source including:

• Insect bites
• Trauma
• Generalized edema due to systemic causes

Abscess

Abscesses appear as heterogeneous anechoic, isoechoic (gray) or hypoechoic fluid collections. Their appearance is often not uniform. Abscesses can be well-circumscribed or be irregularly shaped areas of fluid which may demonstrate posterior acoustic enhancement (bright white in the far field). As with cellulitis, measure the size of the abscess in both the transverse and longitudinal plane. There is some evidence from an immunocompetent pediatric emergency department population that abscesses larger than 5 cm in diameter predict need for hospitalization [14]. In addition, measure the depth from the skin and the width from the base in order to guide future attempts at incision and drainage. As part of the evaluation, apply firm and graded pressure with the probe over the abscess to look for fluctuance (often over a point of maximal tenderness) and the “swirl sign.” Swirl sign refers to the movement of fluid and debris within the abscess and is generated by compression over the area. Finally, always evaluate the abscess with color Doppler to look for internal blood flow and surrounding vasculature prior to making an incision.

 

Video set 5: Examples of soft tissue abscesses

Courtesy of EDSONOshare library

 

Video 6: Video illustrating a positive “Swirl Sign”

 

Practice Pearl: Prior to performing any incision and drainage of an abscess, use color Doppler to look for evidence of blood flow. In addition, color Doppler can be used to identify surrounding blood vessels in order to decrease the rate of procedural complications.

 

Figure 4: Color Doppler over a suspected abscess

This mass was a clinically suspected abscess but bedside PoCUS identified significant blood flow. Planned incision was aborted and the patient was referred to surgery for further management.

Pitfalls:

• Hematoma
• AV malformation
• Lymph nodes
• Cysts

Necrotizing Fasciitis

Due to the low incidence and high morbidity of necrotizing soft-tissue infections, it remains a diagnosis that requires physicians to maintain a high clinical index of suspicion. The use of bedside ultrasound should never delay surgical consultation for these patients but should instead be used to expedite diagnosis. There are three main sonographic findings in necrotizing fasciitis. These include subcutaneous air (often tracking along a fascial plane) with accompanying “comet-tail” artifact, diffuse subcutaneous tissue thickening (which often requires comparison to a contralateral side), and >5mm of fluid accumulation along a facial plane [10].

 

Figure 5: Sonographic findings suggestive of necrotizing infection

 

Video 7: PoCUS suggesting necrotizing infection

Courtesy of EDSONOshare Library

 

Foreign bodies

Research has shown that over one-third of hand foreign bodies are missed at the index visit. Bedside ultrasound can be used to both diagnose foreign bodies and plan removal by accurately identifying the depth of the target and surrounding structures which may need to be avoided (i.e., vasculature). Ultrasound is superior to plain films for radiolucent objects such as plastic, wood or plant matter. When using ultrasound to guide removal of a foreign body, be sure to measure the distance from the skin surface with the calipers and scan the object in 2 planes to fully characterize its length, depth and width.

Practice Pearl: When using ultrasound to guide removal of a foreign body, consider placing multiple high gauge needles to mark the location of the object prior to dissecting down to find and then remove the foreign body. This can save a lot of time and avoid unnecessarily damaging tissue.

 

Figure 6: Foreign bodies on bedside ultrasound

Wood	Glass	Metal
Wood often demonstrates attenuation artifact or acoustic shadow.	Glass often demonstrates reverberation or comet tail artifact.	Metal often demonstrates reverberation artifact on ultrasound.

 

Video set 8: Soft tissue foreign bodies

Wood

Glass

Metal

Courtesy of EDSONOshare library

 

Pitfalls:

• Fascia
• Bones
• Subcutaneous air

What is normal?

Normal skin has a highly organized structure. The most superficial structures are the epidermis and dermis, which are often difficult to distinguish from each other. They will appear as a hyperechoic line immediately superficial to the globules of relatively hypoechoic subcutaneous fat. Within the hypodermis you may visualize blood vessels, nerves, and lymph nodes of varying echogenicity. Deep to the subcutaneous fat, the fascial layer appears as a hyperechoic layer immediately superficial to the more organized hypoechoic and striated muscle fibers. Lastly, depending of the depth setting, a hyperechoic and smooth bone cortex may be visualized.

 

Figure 1: Anatomy of Normal Skin

Courtesy of Matt Tabbut @ mtabbut

 

Video 2: Video illustrating normal skin and soft tissue

 

Lymph nodes can often mimic abscesses as they can be well circumscribed with hypoechoic central areas. In children, in particular reactive lymph nodes are often clinically challenging to distinguish from abscess. However, sonographically lymph nodes, are more oval and organized in shape than abscesses. Classically, lymph nodes will display a central stalk or hilum that is hyperechoic (bright white). At the base of the stalk, there is accompanying vasculature which will demonstrate flow when color Doppler is applied. Lymph nodes should not have surrounding signs of cellulitis or cobblestoning. Lastly, there is less posterior acoustic enhancement in lymph nodes than in abscesses.

 

Figure 2: Sonography of a normal lymph node

 

Video 3: Lymph node video

 

Skin and Soft Tissue Ultrasound: A Stepwise Approach

Indications

• Evaluate soft tissue skin infection
• Differentiate cellulitis from abscess
• Evaluate for features of necrotizing fasciitis
• Identify foreign bodies

Equipment

• Ultrasound machine
• High-frequency linear probe (8-12 MHz)
• Water bath or step off pad – if needed
• Sterile probe sheath –if needed

Patient Positioning

1. Place the patient in a position of comfort and expose the area of interest.
2. Palpate the area of interest ± mark any areas of maximal tenderness or fluctuance.
3. Consider allowing access to the opposite side as a “normal” comparison

Ultrasound Machine Preparation

1. Ensure the ultrasound screen is positioned in order to be clearly seen.
2. Select the high-frequency linear ultrasound probe.
3. Consider whether use of a sterile sheath is clinically indicated.
4. Choose a vascular or soft-tissue pre-set on the ultrasound machine.
5. Select depth of field to between 4-6 cm.
6. Focus gain to clearly visualize the soft tissue structures of interest.

Scanning Principles

1. Place the linear probe gently over the area in question.
2. Adjust the depth and optimize the gain to ensure that the fascial plane is visualized.
3. Slowly and systematically scan across the area of interest.
4. Scan in both the transverse and longitudinal planes in order to not miss any findings.
5. Use color doppler to help identify and differentiate vascular structures

 

Clinical Pearl: The Dead Zone 

The “dead zone” prevents visualization of superficial structures in the near field. This is caused by the ultrasound machine’s inability to send and receive sound waves simultaneously. The depth of the dead zone decreases as frequency increases, and with higher quality send/receive function of the machine and probe. As technology improves the dead zone becomes less clinically significant.

 

Tips and Tricks: “What if my area of interest is very superficial?”
A water bath or standoff pad (such as an IV fluid bag or glove filled with water) can be used to alleviate patient discomfort and improve image quality of very superficial objects. Ensure that the probe is perpendicular to the skin at all times as an oblique angle can cause false hypoechogenicity.   Note: A recent study showed that although most (89%) new ultrasound probes have a “dead zone” of 0 mm, older probes have a “dead zone” of up to 3 mm [13].
Water Bath	Standoff Pad

 

Video 1: Video of normal finger in a Waterbath

From EDSonoshare Library

Introduction

Point-of-care ultrasound is a useful tool for evaluating patients with skin or soft tissue complaints. It can accurately differentiate between cellulitis and abscess, aid in the diagnosis of necrotizing soft tissue infections and assists in foreign body localization. In addition, the use of point-of-care ultrasound has been shown to decrease wait times and improve patient satisfaction with emergency department care [1,2].

Why ultrasound?

Patient presentations for soft tissue infections are common. Over the last 40 years, the number of children presenting to emergency departments with skin and soft tissue infections has doubled [3]. Ultrasound is invaluable when examining soft tissue and has much better test characteristics than physician judgement and physical exam combined for differentiating between abscess and cellulitis [4]. With the growing prevalence of MRSA and the need for different management plans for cellulitis versus abscess, being able to differentiate between the two entities is important for frontline providers.

PoCUS has been shown to have a sensitivity of 98%, specificity of 88%, positive predictive value of 93% and negative predictive value of 97% for the diagnosis of cellulitis this is significantly better than clinical exam alone which has a sensitivity of 86%, specificity of 70%, positive predictive value of 81% and negative predictive value of 77% [4]. Additional studies have shown that ultrasound can be used to identify abscesses with a positive likelihood ratio of 5.5 and negative likelihood ratio of 0.04 [5]. Test characteristics are similar among both adult and pediatric patients [6,7]. A prospective cohort study of adult patients presenting to an urban ED with clinical soft-tissue infection (but no obvious abscess) found that 48% of patients who were clinically thought to be cellulitis alone, were found to have abscesses requiring incision and drainage when examined with ultrasound [8]. A similar study in pediatric patients found the use of PoCUS changed management in 22% of patients [9]. Point-of-care ultrasound also helps differentiate abscess from other pathology, thereby decreasing the chance of complications arising from incision and drainage. In complicated cases, the completeness of abscess drainage can be assessed, reducing the rate of treatment failure.

PoCUS can also aid in differentiating necrotizing fasciitis from other infections. When compared to biopsy findings, PoCUS demonstrating diffuse subcutaneous tissue thickening and fluid accumulation along the fascial plane has a sensitivity of 88% and specificity of 93% for necrotizing fasciitis [10].

Table 1:

Diagnostic Accuracy of Ultrasound in Soft Tissue Infection
	Cellulitis	Abscess	Necrotizing Infection
Sensitivity	98%	97% (CI: 94-98%)	88.2% (CI: 63.6-98.5%)
Specificity	88%	83% (CI: 75-88%)	93.3% (CI: 81.7-98.6)
Positive LR	—	5.5 (CI: 3.7-8.2)	—
Negative LR	—	0.04 (CI: 0.02-0.08)	—
Positive PV	93%	—	83.3% (CI: 84.5-99.4%)
Negative PV	97%	—	95.4% (CI: 82.2-97.3%)

 

Ultrasound is also a useful tool for identification of soft tissue foreign bodies. Plain film radiography can only identify radiopaque objects, while ultrasound is able to identify both radiopaque and non-radiopaque foreign bodies. In addition, ultrasound can be used procedurally to guide foreign body removal and to confirm the success of the procedure. Ultrasound is superior to x-ray for radiolucent foreign bodies, with a sensitivity of 87% and specificity of 97% for wooden foreign bodies larger than 2.5 mm in length [11] However, sensitivity and specificity decreases compared to x-ray for radiopaque foreign bodies. A good general practice when faced with a patient concerned about a soft tissue foreign body is to start with bedside ultrasound and then move to further imaging if the result of the ultrasound is negative.

Table 2:

Diagnostic Accuracy of Ultrasound in Retained Soft Tissue Foreign Bodies
	Foreign Body	Radiolucent Foreign Body
Sensitivity	72% (95% CI: 57-83%)	96.7% (95% CI: 90.0-99.1%)
Specificity	92% (95% CI: 88-95%)	84.2% (95% CI: 72.6-92.1%)
Positive LR	3.2 (95% CI: 2.1-5.1)	5.5 (CI: 3.7-8.2)
Negative LR	0.11 (95% CI: 0.08-0.16)	0.04 (CI: 0.02-0.08)

[12]

 

 

 

 

 

Primary Author: Julia Brandt 

Secondary Author: Nicholas Packer 

Reviewer(s): Mark Bromley, Melanie Willimann 

 

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