An overview of point-of-care ultrasound for soft tissue and musculoskeletal applications in the emergency department
© The Author(s). 2016
Received: 25 April 2016
Accepted: 12 July 2016
Published: 15 August 2016
The skin, soft tissue, and most parts of the musculoskeletal system are relatively superficial anatomical structures and ideal targets for ultrasound examination in the emergency departments. Soft tissue and musculoskeletal ultrasound applications are relatively underused compared to traditional emergency applications, such as trauma, abdominal aortic aneurysm, and chest and cardiovascular systems.
It is important to have knowledge about sonoanatomy and landmarks within the skin, soft tissue, and musculoskeletal systems. Portable machines equipped with high-resolution transducers are now available to fulfill this field of applications in many emergency departments. After needling practice, emergency physicians can not only diagnose and identify pathological findings but also provide interventional procedures and treatments. In this review, we will introduce point-of-care ultrasound (POCUS) applications regarding the soft tissue and musculoskeletal systems: soft tissue infections, joint effusions, foreign bodies, long bone fractures, muscle and tendon injuries, vascular occlusions, and procedures.
With POCUS, emergency physicians can visualize the structures beneath the skin and provide better and safer cares in the emergency departments.
During the previous 20 years, many emergency physicians (EPs) are using focused ultrasound at bedside to manage challenging problems while providing cares to emergent and critically ill patients. Nearly 10 years ago, soft tissue and musculoskeletal applications were listed as one of core emergency ultrasound applications . During the previous decade, most EPs are not familiar with soft tissue and musculoskeletal applications compared to other core applications, such as trauma, abdominal aortic aneurysm, deep venous thrombosis, central venous access, hydronephrosis, pneumothorax, and intrauterine pregnancy [2, 3].
The skin is the largest organ covering all the surface of the human body. The soft tissue and musculoskeletal structures beneath the skin are relatively superficial structures compared to visceral organs. Hence, the soft tissue and musculoskeletal systems should be easily observed under sonographic examination.
In this review article, we will introduce how to use point-of-care ultrasound (POCUS) for soft tissue and musculoskeletal applications in the emergency departments.
To optimize images, it is crucial to adjust gain, frequency, and focal zones . Comparison to the contralateral part in a dual image is important to differentiate normal from abnormal structures. For vascular structures, we can use a graded compression technique and Doppler functions to access the patency and flow status within the vessels. Dynamic examination is a hallmark of musculoskeletal ultrasound and can be used to evaluate joints and integrity of the muscles and tendons (Additional file 1: Video 1).
Three hyperechoic and continuous structures can be viewed as sonoanatomy landmarks for the soft tissue and musculoskeletal structures in the extremities. The superficial layer is the skin and dermis, the middle layer is the fascia, and the deepest layer is the cortical surface of the bone. The cortical surface can be further confirmed by rotating the transducer to create a hyperechoic surface with an acoustic shadow (Additional file 2: Video 2).
The subcutaneous tissue is located between the skin and fascia and composed with anechoic fat and discrete hyperechoic connective tissues. Most of the soft tissue infections can take place in this part.
The muscles are located beneath the fascia. Muscle fibers are elongated structures and wrapped up by an outer hyperechoic epimysium. The muscle elements are hypoechoic and surrounded by the echogenic connective tissue. Muscles appear as a spindle appearance in longitudinal scans and a speckled appearance in transverse scans.
The tendons, ligaments, and nerves have similar sonoanatomy: an echogenic, fibrillar pattern in long-axis scans and an echogenic, speckled pattern in transverse-axis scans. The neural elements are hypoechoic, and the surrounding connective tissues are echogenic. We can trace the nerve along its route from the distal to proximal part.
The tendons, ligaments, muscles, and nerves all have anisotropy and should be examined perpendicularly to avoid misinterpreting artifacts as abnormal pathologies.
The vessels have an anechoic, oval, or round pattern in transverse-axis scans and an anechoic, tubular pattern in long-axis scans. In contrast to the veins, the arteries have a thicker, hyperechoic, and consistent wall with a pulsatile nature.
The bones are highly echogenic on the cortical surface and have an acoustic shadow on transverse-axis scans. Disruption of the continuous cortical surface is the hallmark for fracture diagnosis.
Soft tissue infection
Cellulitis is the most common type of soft tissue infection and confined within the subcutaneous compartment. Cellulitis is a clinical diagnosis. Patients may have fever, chills, and leukocytosis in addition to redness, swelling, local heat, and swelling on the infected sites. A sonographic cobblestone-like appearance is composed of a hyperechoic, hyperemic pattern of the inflamed subcutaneous fat intersecting by anechoic fluid along the connective tissue (Additional file 3: Video 3). However, a cobblestone-like appearance only indicates inflamed tissue and is nonspecific for cellulitis.
Tender and swollen joints are common in the emergency departments. Different types of arthritis and injuries around joints are often complicated with joint effusions. Bursitis and arthritis with joint effusions are often difficult to differentiate at first encounter. Bursitis is the inflammation of a bursa and accompanied by fluid within the bursa. The joint effusion is located within the joint cavity and has different appearance on a dynamic examination.
POCUS is ideal for inflamed or fluid structures diagnosis. POCUS had changed the management in 65 % of patients with joint pain, erythema, and swelling and reduced the planned joint aspiration from 72.2 to 37 % . Early arthrocentesis can lead to early diagnosis and symptom relief . EPs can use POCUS to guide arthrocentesis in a safer and shortest route to reduce failed attempts and complications. EPs can also use POCUS to avoid blind needling into inflamed structures. Pediatric emergency physicians have been shown to use POCUS to diagnose hip effusion in pediatric patients in the emergency department . Operators can perform POCUS-assisted arthrocentesis in a static or dynamic manner based on their experiences and preferences. Operators can directly visualize the needling during the whole procedure. However, the dynamic POCUS-assisted arthrocentesis requires more practice and a sterile transducer covering for the procedure (Additional file 8: Video 8).
Foreign body-related injuries are often missing on the first encounter and the major reasons for malpractice. Radiopaque foreign bodies in soft tissues and muscles are easily identified by traditional radiography. EPs can use ultrasound as the initial screening modality to identify radiolucent foreign bodies to prevent wound complications and malpractice claims [19, 20]. In one experimental study, emergency doctors identified 29 of 30 foreign bodies and emergency trainees identified 60 of 70 foreign bodies . In one experimental study, nurse practitioners detected 47 of 60 foreign bodies after 2-h POCUS training session .
In addition to diagnose foreign bodies, POCUS can be used to assist foreign body retrieval [24, 25]. EPs can use POCUS-assisted in-plane needling to target the foreign body on both sides of the transducer and then explore the target under the needle guidance in traditional manners.
Long bone fracture
Muscle and tendon injuries
Muscle and tendon strains are not POCUS applications. However, POCUS can provide valuable information for major muscle tear and intramuscular hemorrhage. Major muscle tear may appear as irregular and disruption of fibrillar echo texture of muscle bundles and surround mixed echogenicity of hematoma. Dynamic examination of the injured muscle and comparison to the contralateral part can facilitate the diagnosis (Additional file 11: Video 11). Forceful coughing, direct trauma, or coagulopathy can cause intramuscular hemorrhage . The intramuscular hemorrhage can have mixed echogenicity, and Doppler function can aid the diagnosis for pseudoaneurysm formation (Additional file 12: Video 12).
Major tendons, such as Achilles tendon, quadriceps tendon, and patellar tendon, are superficial structures and hence the ideal targets of POCUS [34–36]. EPs can use POCUS to assess the integrity of the fibrillar echo texture of the tendons. Disruption of the typical fibrillar patterns of tendons under dynamic examination is the characteristic finding of tendon ruptures (Additional file 1: Video 1).
EPs use various emergency procedures for different purposes, such as diagnosis, treatment, monitoring, and resuscitation. Most EPs learn and perform procedures by identifying anatomic landmarks. Novice providers have more failure attempts and higher complications compared to experienced providers. For challenging cases, even experienced hands can encounter obstacles . With the aids of POCUS, EPs can visualize the targets and provide accurate critical procedures instead of anatomic or blind techniques [43, 44].
Echo-guided procedures can be static or dynamic. In static way, EPs use ultrasound guidance to identify the target and then perform the procedures in usual manner. In dynamic way, EPs use non-dominant hand to locate the target and then use dominant hand to insert the needle and advance the needle under real-time ultrasound guidance. The dynamic way is more accurate than static way by direct needling visualization, but required more psychomotor skill practices and aseptic preparations for the transducer. For novice providers, the static echo-guidance is easy and useful. With more practices, the real-time echo guidance should be the better choice for most invasive procedures.
Echo-guided needle advance can be off-plane or in-plane. Off-plane method is easy for novice providers, but to find the needle tip is the hardest part. To identify the needle tip, providers can gradually use tilting method to identify the strong echo of the needle tip and then decide whether to advance the needle or not. Providers can advance the needle and see the entire needle under in-plane ultrasound guidance. The hardest part for in-plane method is to put the needle in the middle part of the transducer throughout the procedures. The needle can be invisible if providers advance the needle in a skewed way.
The skin, soft tissue, and most parts of the musculoskeletal system are relatively the superficial anatomical structures and ideal targets for ultrasound examination. Familiar with sonoanatomy of different structures and psychomotor skills for needling are essential for various ultrasound applications. With POCUS, EPs can visualize the structures beneath the skin and provide better and safer cares in the emergency departments.
EP, emergency physician; POCUS, point-of-care ultrasound
Availability of data and materials
CKC conceived the study and participated in its design and coordination and helped to draft the manuscript. CCF helped to draft the manuscript and prepared the images and video clips. WTL conceived the study and helped to organize the study. LCM conceived the study, helped to organize the study, and edited the final manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Consent for publication
Written informed consent was obtained from the patient and participant for publication of their individual details and accompanying images in this manuscript. The consent form is held by the authors in the patients’ clinical notes and is available for review by the Editor-in-Chief.
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