Musculoskeletal structures are long, striated and many times layered tissues. Due to the striated morphology of these tissues and their superficial location, high frequency, linear array transducers are best suited for this application. It is recommended that no less than 7.5 MHz transducers be used for musculoskeletal examinations of the extremities. Ideally, 8.0 MHz and above provide the highest resolution.
As in all ultrasound examinations, proper technical settings are vital to the diagnostic value of the images. Musculoskeletal images require adequate grayscale. Limited grayscale can lead to diagnostic challenges. Refer to the manufacturer of your equipment and their specific guidelines for optimal image settings.
It is very important to maintain accurate transducers placement in musculoskeletal sonography. Due to the close proximity of several distinct structures in a small area, a slight displacement of the probe can produce inaccurate images. If the image states it is a “midline” image be sure to be as close to midline as possible.
Image orientation is consistent throughout the manual. Regardless of right or left.
Longitudinal views: left side of the image is CEPHALAD.
Transverse views: left side of the image is the PATIENT’S RIGHT
Suggested Exam Protocol
The photographs in the manual clearly indicate patient and probe positioning. All examinations do not need to be bilateral studies that include identical images. It is not necessary to perform all images described for each extremity in this manual on every examination. Images may be performed specifically in the area of complaint. However, we recommend no less than 6 images per exam. 3 transverse images and 3 longitudinal images.
Tips For Clinicians
Optimize your system for proper grayscale. Almost all images have identifiable bony landmarks. Visualize the bony landmarks and the surrounding soft tissue should also be visible. Labeling of images in this manual are merely suggestions. Feel free to establish a system of labeling of images that is best for your facility. To avoid confusion, take care not to make abbreviations too short.
3 Steps to Successful Imaging
1. Image GENERATION
Patient & probe position, grayscale settings
- Image RECOGNITION
Identify Individual Interfaces from the bony cortex UP to the skin surface!
- Image INTERPRETATION
Determine abnormal findings by knowing normal!
Using a systematic, STANDARDIZED approach lets the clinician obtain highly accurate anatomic representation of the anatomy.
The anticipated length of the “learning curve” is shortened. Confidence and expertise is gained in a shorter time frame.
Ultrasound in Muskulo-Esqueletic pathologies. A medical revolution
This is a very basic introduction to normal musculoskeletal anatomy on ultrasound, which is intended to get novices started scanning quickly. For in-depth knowledge of normal and abnormal musculoskeletal anatomy.
On longitudinal views, the muscle septae appear as bright/echogenic structures, and are seen as thin bright linear bands. On transverse views, the muscle bundles appear as speckled echoes with short, curvilinear bright lines dispersed throughout the darker/hypoechoic background.
Subcutaneous tissue is isoechoic (equal brightness) with skeletal muscle. The difference between subcutaneous tissue and skeletal muscle visualized on ultrasound is the septa do not lay in lines or layers. More conspicuously; a thick, continuous, hyperechoic band usually separates subcutaneous fat from muscle.
On ultrasound examination, normal cortical bone appears as a continuous echogenic (bright) line with posterior acoustic shadowing (black).
Fascia is a collagenous structure that usually surrounds the musculotendinous areas of the extremities. The fascia is then encompassed by subcutaneous tissue. Many times, the fascia is seen inserting onto bone, and blending with the periosteum. Normal fascia appears as a fibrous, bright/hyperechoic structure.
Occasionally, a thin echogenic line running parallel with the cortical bone is demonstrated on ultrasound. This is likely the periosteum. However, in normal situations, the periosteum is not visualized by ultrasound. Injuries to the bone, especially those damaging the cortex, periosseous soft tissues, and periosteum will produce a periosteal reaction, which is visible.
A normal tendon on ultrasound examination is a bright/echogenic linear band that can vary in thickness according to its location. The internal echoes are described characteristically as having a fibrillar echotexture on longitudinal views. On ultrasound the parallel series of collagen fibers are hyperechoic, separated by darker/hypoechoic surrounding connective tissue. The fibers will be continuous/intact. Interruptions in tendon fibers are visualized as anechoic/black areas within the tendon. Tendons are known to be anisotropic structures.
On ultrasound examination, a normal ligament is also a bright echogenic linear structure. However ligaments have a more compact fibrillar echotexture. Individual strands/fibers of the ligaments are more closely aligned. Ligaments are composed of dense connective tissue, like tendons, but there is much variability in the amounts of collagen, elastin and fibrocartilage within a ligament, which makes its ultrasound appearance more variable than tendons.
In a normal joint, the bursa is a thin black/ anechoic line no more than 2 mm thick. The bursa fills with fluid due to irritation or infection. Depending on the extent of effusion, the bursa will distend and enlarge; internal brightness echoes are inflammatory debris.
High-frequency transducers allow the visualization of peripheral nerves that pass close to the skin surface. Peripheral nerves appear as parallel hyperechoic lines with hypoechoic separations between them.
On longitudinal views, their appearance is similar to tendons, but less bright/echogenic. On transverse views, the peripheral nerves’ individual fibers, and fibrous matrix, present with multiple, punctate echogenicities (bright dots) within an ovoid, well-defined nerve sheath.
An / iso / tropy. To not have equal properties/ characteristics/ appearances on all axes. The property of being directionally dependent. Produced when the probe is not perpendicular with the structure being evaluated. Most common artifact in musculoskeletal ultrasound.
US-guided injections can be performed using the method where the skin surface is marked after the detection of the most appropriate entrance point and the measurement of the depth of the target area, or under direct visualization of needle placement during real-time scanning
US-guided injection under direct visualization should be performed according to the following principles:
- Baseline US assessment to explore the target area and evaluate the indication for the planned injection therapy.
- Definition of the best US window to optimize visualization of needle placement within the target area.
- Antiseptic swabbing of both the injection site and the surface of the probe.
- Placement of a thin layer of sterile gel on the skin of the patient.
- Continuous monitoring of the needle progres- sion within the soft tissues on the screen with particular attention to the tip of the needle, which is placed within the target area.
- Visualization of the steroid suspension during and after the injection
- On longitudinal scans, when the needle is perpendicular to the US beam it appears as a sharply defined echoic band with strong posterior rever- berations. On transverse scan, the needle appears as a small hyperechoic round spot that can be easily identified by dynamic assessment (fine movements of the syringe).
Confirmation of the needle’s correct positioning can be obtained by direct observation by inject- ing air or under power Doppler control (the injected fluid is visualized as a patch of color).
Needle placement is quick and easy to perform when marked distension of the joint cavity is pres- ent. Optimal visualization of the needle depends on the correct alignment between the needle and ultrasound beam. Accurate positioning of the probe is critical to obtain a clearly defined image both of the needle and the target site.
Local injection therapy has a wellestablished role in patients with tenosynovitis.
The cost/benefit ratio largely depends on the correct placement of the needle into the widened ten- don sheath. An experienced rheumatologist should be able to perform a safe and accurate intra-lesion- al injection in most patients with tenosynovitis. The main problem is taking care to avoid contact between the tip of the needle and the tendon
The conventional blind approach to intra-lesion- al injection cannot avoid the theoretical risk of caus- ing damage to tendons and surrounding structures.
The injection of steroids within a widened tendon sheath under US control appears to be very effective in minimizing this risk.
The progression of the needle can be accurately controlled “step by step” on the monitor until the tip of the needle is properly placed within the tendon sheath.
Bursitis is a very common problem in rheumatological practice. Injection of steroid is an effective and safe procedure in non-responders to other conservative therapeutic options, including rest, local application of ice and anti-inflammatory medication. The US approach to patients with suspected bursitis serves three purposes: firstly, confirmation of the diagnosis; secondly, aspiration of synovial fluid for microscopic examination and thirdly, correct placement of the needle for steroid injection.
US is very useful for the detection of popliteal cysts and for careful assessment of their content. Once the inner structure of the cyst is established, it is possible to define an appropriate therapeutic approach that depends on the cyst characteristics. Needle aspiration of synovial fluid and steroid injection within a popliteal cyst under US control are indicated especially in patients with large cysts due to a valve effect of the synovial tissue. US control is critical to avoid puncture wounds of nerves and/or blood vessels and to ensure the correct position of the tip of the needle especially in patients with loculated cysts.
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