General Principles of Musculoskeletal Ultrasound

Alice Chiu SPT DKCH 3 July 2012

Basic considerations Equipment Selection

◦ High Frequency, linear array transducers are best for

tissues with striated morphology of tissues e.g mm,

ligt in superficial location. (5-14MHz) (7.5MHz)

◦ Adequate greyscale is necessary for accurate

diagnostic interpretation-optimal image settings.

Probe Placement

◦ If the image states is a midline image, be sure to be

as close to midline as possible

Image Orientation

◦ Longitudinal view: left side of image is CEPHALAD

◦ Transverse view: left side of the image is the

PATIENT’s RIGHT

Suggested Exam Protocol◦Bilateral studies not absolute

necessary◦Not necessary to perform all images

for each extremity: selection◦Usually perform images in the area

of complaint◦Usual practice: no less than 6 images

per exam with 3 transverses and 3 longitudinal images

Identification of bony landmarks during imaging is key success for

accurate soft tissue labeling.

Reflectivity-echogenicityHigh reflective pattern: whiter and

brighter-hyperechoicLow reflective pattern: darker and less

bright-hypoechoicNo reflectivity-clear fluid-anechoicSame reflectivity surrounding tissue-

isoechoic

HyperechoicHypoechoic

Anechoic Isoechic

Basic Normal Musculoskeletal Ultrasound Anatomy Skeletal Muscle

◦Long view: muscle septae appear as bright/echogenic structures and are seen as thin bright linear band.

◦Transverse views: muscle bundles appear as speckled echos with short curvilinear bright lines dispersed throughout the darker/hypoechoic background

Subcutaneous Tissue◦Isoechoic( equal brightness) with

skeletal muscle. ◦Main difference: septa do not lay in

lines or layers. ◦It usually appears as a thick

continuous, hyperechoic band usually separate subcutaneous fat from muscle.

Cortical Bone◦Appears as a continuous echogenic

( bright ) line with posterior acoustic shadowing ( black)

Fascia◦Collagenous structure that usually

surrounds the musculotendinous areas of the extremities.

◦The fascia is encompassed by subcutaneous tissue.

◦Fascia is seen inserting into bone, blending with periosteum.

◦Appears as a fibrous, bright/hyperechoic structure.

Periosteum◦A thin echogenic line running parallel

with the cortical bone.◦Not usually not visualized by US

except after cortex damages, periosseous soft tissues and periosteum will produce a perisoteal reaction visible by US.

Tendons◦A bright/echogenic linear band that can

vary in thickness according to its location.◦Tendons are known to be anisotropic

structures in US nomenclature.◦On Longitudinal views: fibrillar

echotexture.◦The parallel series of collagen fibers are

hyperechoic, separated by darker/hypoechoic surrounding connective tissues.

◦The fibres will be continuous/intact.◦ Interruptions in tendon fibres are

visualised as anechoic /black areas within the tendon.

Anisotropy The physical characteristic of muscle, tendons

and nerves to vary in their ultrasound appearances depending upon the angle of insonation of the incident sound beam. Produced when the probe is not perpendicular with the structure being evaluated.

The apparent change in echogenicity within the structure may mimic the appearance of fluid or lead to loss of visulisation of the structure.

Thus angulation of probe is important for beam to insonates at 90 degree

Most common artifact in MS US

Anisotropy artifact. Transverse sonograms of the extensor surface of the wrist show the extensor digitorum (ED) and extensor pollicis longus (EPL) tendons, clearly and without artifact on the image obtained with the probe held exactly perpendicular to the tendons

but with a significant loss of echogenicity on the image obtained with the probe held at an oblique angle to the tendons

Tendon pathology◦Tendonitis: acute ◦Tendinoses/tendinosis : chronic, may

have ischemia in critical zones followed by myxoid degeneration Caused by degenerative process,

overuse, steriod injection, systemic disease etc…

Ligaments◦Bright echogenic linear structure.◦Have more compact fibrillar

echotexture.◦Individual strands/fibers of the

ligaments are 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.

ATFL- lat malleolus with talus

CFL- lat malleoulus with calcaneous

Ultrasound grading of ligt injury◦Grade I: mild stretching-normal◦Grade II: partial tear-thickened

hypoechoic◦Grade III: complete tear-complete

disruption

I II III

Bursae◦Thin black/anechoic line no more

than 2 mm thick. ◦Will fill with fluid due to irritation or

infection and become distend and enlarge.

◦Internal brightness echoes are inflammatory debris.

Longitudinal sonogram shows 30-year-old man with knee pain. Fluid is visible in deep infrapatellar bursa (solid arrow), indicating deep infrapatellar bursitis. Patellar tendon is normal (open arrow), but overlying soft tissues appear swollen (arrowhead).

Peripheral Nerves◦Appear a parallel hyperechoic lines

with hypoechoic separations between them.

◦Longitudinal view: appearance similar to tendons but less bright/echogenic.

◦Transverse view: the peripheral nerve individual fibers and fibrous matrix, present with multiple punctate echogenicities( bright dots) within an ovid well defined nerve sheath.

Longitudinal sonogram of the median nerve shows parallel hypoechoic groups of nerve fascicles and the median nerve, which lies deep to the flexor digitorum superficialis (FDS) muscle in the distal forearm.

Sequel…

References Introduction to Musculoskeletal Ultrasound

Imaging Randy E Moore DC RDMSwww.mskmasters.com John Lin at el, “ An illustrated Tutorial of

Musculoskeletal sonography” AJR:175, Sept 2000

www.essr.org/Real Time Ultrasound in Physiotherapy

Practice AIU