The Musculoskeletal System Chap 24

Normal Sonographic Appearance of Nerves

Hyperechoic compared to muscle but hypoechoic compared to tendons Parallel inner linear echoes in sagittal Fibers appear hypoechoc in transverse (can mimic a vein), become more echogenic with applied pressure

3 msk structures we will scan

Rotator cuff Carpal tunnel Achilles tendon

Bursa

Sac-like structure surrounding joints and some tendons Contain synovial fluid Reduces friction between points that may rub against each other

Indications for Shoulder Sonography

Shoulder pain or swelling Pain with joint rotation Weakness with arm elevation Trauma Decreased range of motion Evaluation of soft tissue masses

Muscles

Skeletal muscle composed of long organized units of muscle fibers Bundles of muscle fibers separated by fibrous sheaths Muscle fibers may run parallel to bone, obliquely in a feather-like pattern (pennate) or fan out

Refractile Shadowing

"Edge" artifact Sound beam bends to an oblique path Can also occur at mismatches in impedance Appears as a hypoechoic band posterior to the lateral borders of the structure Seen at edges of cysts and torn tendons

Biceps Tendon

3-5 mm thick Echogenic oval structure within the bicipital groove of the humerus Normal to see a small amount of fluid surrounding tendon (< 1.5 mm)

Artifacts in Musculoskeletal Imaging

Anisotropy Reverberation Refractile shadowing Time of flight artifact

correction of time of flight

Change angle of incidence - *so we aren't going though two different tissue types, find a new window

Infraspinatus Tendon

Come from a posterior approach Sits lateral and inferior to scapular spine Located anterior to echogenic triangular posterior glenoid labrum

correction of refractile

Compound imaging or tissue harmonics help reduce or eliminate artifact

Nerves

Connection between central nervous system and muscles *makes muscles contract Arranged in bundles of fibers surrounded by dense sheaths of myelin and connective tissue Follow the fibrous partitions between muscles

Rotator Cuff

Frequencies of 7-10 MHz should be used Deeper structures may require lower frequency (5 MHz) Begin anteriorly with arm in neutral position Comparison to contralateral side helpful

Subscapularis Tendon

Have patient externally rotate arm Located anteromedial from the biceps tendon at the humeral head Runs horizontally, so transverse transducer orientation = long axis of subscapularis

correction of anisotropy

Heel-to-toe rocking of transducer creates perpendicular angle of incidence to remove anisotropy.

Normal Sonographic Appearance of Ligaments

Hyperechoic strap-like structures (except cruciate ligament in knee, which appears hypoechoic) Dense and less regular pattern to fibers than tendons Usually 2-3 mm thick Only evaluated in sagittal plane

Normal Sonographic Appearance of Bursa

Hypoechoic halo usually seen between tendon and bone surfaces Difficult to see as they blend with surrounding tissues Normal measurements should not exceed 2 mm thick

Supraspinatus Tendon

Located posterolateral from the biceps tendon 3-7 mm thick Most likely site for injury is "critical zone" located 1cm posterolateral to the biceps tendon Locate biceps tendon and rotate transducer until acromion comes into view Should be imaged with arm in neutral position and internally rotated

Reverberation

Multiple delayed reflections from very strong boundaries, such as bone Linear artifact that decreases in intensity with depth Comet-tail: type of reverberation resulting from sound bouncing between two closely spaced reflectors, widens with depth Adds unnecessary information and can obscure useful information Can be minimized with use of a standoff pad

Components of MSK

Muscles Tendons Ligaments Nerves Bursa

Normal Sonographic Appearance of Tendons

Numerous parallel echogenic interfaces Synovial sheath appears as a hypoechoic halo of mucoid material around tendon Tendons without synovial sheaths blend in with surrounding connective tissue (paratenon)

Time of Flight Artifact*step-down

Occurs when the sound beam passes through tissue with markedly different speeds than the soft tissue average Tissues with slower speeds result in structures being displayed deeper than they really are, faster speeds more shallow More prevalent in obese patients with increased fat layer adjacent to muscle

Ligaments

Provide attachment of bones to other bones Give strength and support to joints Essential in knees, ankles and shoulders

Tendons

Provide attachment of muscle to bone May either be cords *like gastrocnemius, as seen with parallel or pennate muscles, or flat sheets (aponeuroses) as seen with flat muscles *like the trapezius Lack vascularity, resulting in poor healing capability May or may not have surrounding synovial sheath

Normal Sonographic Appearance of Muscles

Relatively hypoechoic to adjacent tissues In sagittal shows multiple fine, parallel echoes In transverse shows multiple fine, punctate echoes Fiber bundles surrounded by echogenic bands Fibers radiate towards central tendon or aponeurosis Real-time imaging can visualize muscle contraction

correction reverb

Use of a standoff pad or changing angle of incidence

Anisotropy

Varying sonographic appearance of the same structure from different approaches Results from loss of returning sound waves due to incidence upon a curved surface Lose definition and intensity at edges of image Most pronounced in tendons *at curve Requires heel-toe motion to adjust angle of incidence of sound beam to prevent diseased appearance

Minimum Shoulder Views of the Rotator Cuff

View 1/2: Biceps tendon (front upper arm) longitudinal and transverse View 3/4: Subscapularis (front clavical) longitudinal and transverse View 5/6/7/8: Supraspinatus in neutral and internal rotation View 9/10: Infraspinatus/posterior glenoid labrum View 11: Teres minor