MSK Sonography

Refractile Shadowing

Bending of transmitted sound beam to an oblique path occurs often. • Seen as edge artifact Change in direction of sound beam results in hypoechoic band posterior to structure. Another cause of refractile shadowing is tissue impedance mismatch different than average speed of sound within soft tissue (1540 m/sec). • Seen at edge of round or oval ligament or as result of traumatic tear of a musculoskeletal structure

Sonography of Ligaments

Hyper to hypoechoic, depending on what structures are surrounding it Less echogenic than tendons Homogeneous appearance • 2-3 mm thick

Reverberation

Multiple delayed reflections from strong tissue boundaries, such as bone, result in linear artifact that decreases in intensity with depth. • Reflected sound is superimposed over primary signal, adding distracting information to image. Comet tail artifact: function of sound bouncing between two closely placed reflectors within imaged structure • Ringing occurs within metal object; each time sound returns to anterior border some of sound escapes

Descriptors of body movements - rotation - external - internal

Rotation - describes the motion of a body part turning along its axis External rotation - body part moves away from the body Internal rotation - body part moves toward the body

Ligaments

Short bands of tough fibers connect bones to other bones. • Structure similar to tendons but not as organized, making it difficult to image. • This type of connective tissue important in the knees, ankles, and shoulders for support and stabilization.

Common sites of MSK evaluation under Sonography

Shoulder • Rotator cuff Wrist • Carpal tunnel Heel • Achilles tendon Knee • Bakers Cyst

Muscle sono

Striated appearance, echogenic bands but not as much as subcutaneous fat Main muscle fibers appear hypoechoic with surrounding hyperechoic connective tissue Echogenic fascial layer in the middle (arrow) Comes to form a tendon

Tendon Tears - Intrasubstance

Tear entirely within the tendon substance and is not seen on either surface - in the middle - doesn't affect either side Bursal (anterior) OR Articular (bony attachment site)

Tendon Tears - Full Thickness

Tear goes through the tendon substance and is evident on both surfaces (bursal and articular sided)

Tendon Tears - Partial Thickness

Tear of only one margin of the tendon • Tear does not extend through the whole tendon

Synovium - biceps vs achilles

Tendons occur with or without synovial sheath Biceps tendon of shoulder is one example of tendon with synovial sheath Achilles tendon of ankle is an example of tendon without synovial sheath Contains viscous type fluid that helps with movement

Sonography of Tendinosis

Thickened and hypoechoic tendon without increased vascularity

Bursa sono

Thin structure with two hyperechoic layers with a thin hypoechoic space in between Thickness of sheath only couple of millimeters Some are so small and not seen on US unless filled with fluid 2 hyperechoic layers with thin fluid inbetween

Time of Flight Artifact

Time of flight, or speed of sound, artifacts occur when returning sound wave has passed between two tissues with markedly different speeds. • Misrepresentation of return time results from assumption that speed of sound is constant 1540 m/sec. If speed of sound less than average in tissue, artifact appears to be farther away from transducer. • Faster speed results in artifact being closer to transducer on image. Creation of this type of false information occurs most commonly when imaging obese patients at muscle-fat interface. Speed of sound artifact displaces image in anteroposterior (axial) plane. Speed artifact: coupled with refraction, structure displays with incorrect shape • Do not mistake very subtle artifact with transducer crystal malfunction. • Mechanical failure produces decrease in image information that begins at transducer face; time of flight artifact affects only image

Pennate - describes:

the number of attachments

Bursa - 2 types

1. Communicating - located adjacent to a joint and communicates with the synovial membrane • Ex. Bakers cyst in medial popliteal fossa 2. Noncommunicating - are near joints but don't directly connect to the joint - just provides lubrication • ex. Prepatellar bursa Categorization explains relationship of bursa to joint space.

Tendon Tears - 4 Classifications:

1. Partial thickness tear (PTT) - C 2. Full thickness tear (FTT) - D 3. Intra-substance tear - B 4. Complete tears - E

Three types of muscles within the human body: - voluntary or involuntary

1. Skeletal • muscles that attach to and move our bones and other structures • Movement is voluntary 2. Smooth • Muscle found in organs ex. bowel, bladder, uterus • Movement is involuntary 3. Cardiac • Heart muscle (myocardium) • Movement is involuntary

Ab vs Adduction

Abduction - moves the limb or part AWAY from the midline or body part • Ex. We abduct our arm to reach across the patient to scan the spleen Adduction - moves the limb or part TOWARDS the midline or body part • "add" it back - bring arm back to the body

Tendon Anatomy

Attach muscle to bone A collection of tough collagenous fibers

Sonographic Evaluation - technique

Begin with proper transducer selection, higher frequencies for superficial joints, but use lower frequencies for larger joints that need more penetration. Scan planes: • Labels are usually long axis (LAX) and short axis (SAX) Document: • symmetry • palpation • dynamic movements • vascularity • Proper annotation

Muscle Hematomas

Can vary in sonographic appearance New/acute hematoma - echogenic and pushes the muscle fibers apart • Often ill defined, area of enlargement within the muscle fibers or between muscles Aging hematoma - liquifies and becomes hypoechoic/anechoic eventually forming a seroma (fluid collection) • Once fluid is reabsorbed, hyperechoic scarring or calcification are typically present • Can mimics DVT in some areas such as the calf

Artifact Corrections - time of flight

Change angle of incidence

Bursa - major bursa of body

Major bursa of body is subacromial-subdeltoid bursa found in shoulder covering deep surface of deltoid muscle.

Muscle scanning - contraction - compression

Check to see if the muscle is actually a muscle and working normally • Have the patient flex/extend Muscle contraction will make the muscle become thicker • Athletes and patients sustaining contraction will actually make the muscle appear slightly less echogenic. This is normal. Compression of the muscle will increase the echogenicity slightly. • Think about it-you're pushing the muscle fibers together) You can always scan the contralateral muscle for comparison

Nerves - Collagenous epineurium:

Collagenous epineurium: outer layer of nerve; appears as hyperechoic layer

Bursa

Collapsed saclike structure surrounding two moving surfaces, usually tendon and bone • Lined with minute amount of synovium Thin tissue layer made of viscous fluid that lines joint capsules, bursae and tendon sheaths to reduce friction and facilitates movement of two musculoskeletal structures Sliver - normal Large fluid amount - abnormal

Artifact Corrections - refractile shadow

Compound imaging or tissue harmonics help reduce or eliminate artifact

Sonography of Muscle

Connective tissue surrounding the fiber bundles create echogenic bands Striated appearance Main portions of muscle fibers are hypoechoic and radiate toward a central tendon Echogenic connective tissue surrounding the muscle- not as echogenic as subcutaneous fat, but more echogenic than the muscle fibers - Sonographic appearance of muscle can be deceiving in some areas, such as hand, because of similar echotexture to mass or tenosynovitis. - Careful scanning and transducer rotation help image pinnate structure of muscle, aiding in identification of possible normal muscle variant. - Transverse scanning does not always help- it looks disorganized with punctate echoes.

Fascicle - covers - wrapped by

Covers the muscle fibers and is wrapped by perimysium

Digit Pollex Hallux

Digit - describes fingers or toes Pollex - the thumb Hallux - big toe

Muscle Tears

Discontinuity or disruption of the muscle fibers with resulting hematoma • Important to document if hematoma is intramuscular (within muscle fibers) or intermuscular (between muscles) Most common pathologic condition of muscles of limbs.

Descriptors of body movements - dorsiflexion - plantar flexion - radial deviation - ulnar deviation - valgus - varus

Dorsiflexion - motion that pulls toes up toward head Plantar flexion - motion that points toes down Radial deviation - motion of wrist towards the radial side Ulnar deviation - motion of wrist towards ulnar side Valgus - outward movement or position of the distal part of the body • When foot is more lateral than the knee Varus - inward movement or position of the distal part of the body • When foot is more medial than the knee

Sonography of Normal Tendons

Echogenic fibular pattern as a result of parallel fibers Numerous interfaces of collagen fascicles running in parallel path provide strong linear reflector that images well Familiarity with normal sonographic appearance important because injury to area of tendon results in thickening of insertion site. IMPORTANT TO KNOW NORMAL IN ORDER TO RECOGNIZE ABNORMAL

Tendon anatomy - enthesis - myotendinous junction - aponeurosis

Enthesis - site of attachment to the bone (yellow arrow in bottom image) Myotendinous junction - other end of tendon that gradually merges with the muscle Aponeuroses - flat sheet or cordlike attachment of tendons - type of attachment that thins out and fans over bone

Descriptors of body movements - flexion - extension - hyperextension

Flexion - decreases the angle between the bones, bends the joint • Ex - bending the knee Extension - increases the angle of the joint, straightens • Ex - straightening the knee Hyperextension - extension of joint beyond its normal range of motion

Sonographic features of tendinitis

Focal or diffuse: - decrease in echogenicity in the tendon fibers - enlargement of tendon • Loss of fibrillar pattern • Hyperemia or increased Doppler signal • Thickness discrepancy of greater than 1.5 cm is indicative of focal inflammation • Bursitis or synovial fluid • Occasionally will see tears and or calcifications (chronic) • Areas can be very subtle, utilize the contralateral side • Tends to be more of an acute process

Muscles -

Groups of fibers/tissues that make voluntarily or involuntarily movements

Artifact Corrections - anisotropy

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

Tendinitis - clinical symptoms

Inflammation of tendon due to age-related elasticity loss, rheumatoid arthritis, overuse, or acute trauma • Occurs in any tendon, more often in shoulder, wrist, heel, elbow. Clinical symptoms: • Pain at tendinous insertion onto bone • Palpable mass in area of pain • Decreased ROM Image: thickened tendon with slight fluid

Strain

Injury to a tendon or muscle Damage can range from minor overstretching to a complete tear Causes pain, swelling and muscle weakness

Tendon Tears - Complete

Involves the entire thickness of the tendon The torn ends will then retract • Yellow arrow is retracted tendon • Blue arrow is fluid/hematoma filling space where tendon should be

Joint/articulation - Fascia -

Joint/articulation - point where two or more bones come together (or cartilage and bone meet) Fascia - connective tissue found throughout body providing support and separation of organs and tissues

Muscle sono - long vs short axis

Long Axis (LAX) Fine linear echo pattern Short Axis (SAX) Speckled appearance

Sonography of Nerves

Longitudinal plane reveals fibrillar pattern with parallel inner linear echoes, similar to tendons. In transverse imaging nerve fibers appear hypoechoic, with hyperechoic perineurium surrounding each fiber. "Honeycomb" appearance

Most common pathologic condition of muscles of limbs

Muscle tears

Nerves - with movement - anisotropy - power doppler

Nerve will remain stable within muscle tissue with dynamic movement Anisotropy not as evident on nerve as on tendon; nerves imaged best with transducer of 10 MHz or higher. Power Doppler especially helpful because vessels accompany

Normal nerves appear ____ when compared with muscle, but _____ compared with tendons

Normal nerves appear hyperechoic when compared with muscle, but hypoechoic compared with tendons

Tendinosis

Not a true inflammatory condition Chronic process causing a degeneration of the tendon fibers - happens over time

Sprain

Occurs when a ligament is stretched beyond it's normal length Usually a result of inversion or eversion injury Causes pain and swelling

Origin Insertion

Origin- proximal portion of the muscle Insertion- distal end

Skeletal Muscle Anatomy - most attached to ___ by ___ - fibers that run:

Our focus in MSK sono • Most skeletal muscles are attached to bone by tendons • Typically, the motion that a muscle and its tendon produce are part of the muscle name Have fibers that run parallel to bone in a fan shape or pennate pattern Featherlike muscle patterns that run oblique to long axis of muscle • Categorized as bi, uni, multi or circumpennate

Body movements - pronation - supination - inversion - eversion

Pronation - face down • Turning palm of hand down Supination - face up • Turns palm of hand up Inversion - motion that turns the sole of the foot toward the midline Eversion - motion that turns the sole of the foot away from the midline

Sonography of Normal Tendons - anisotropy

Prone to anisotropy • Artifact related to angle of insonation - need to be exactly 90 degrees or else it can look like a tear or tendonitis Real-time imaging shows tendons that move when corresponding joint or muscle contracts/relaxes

Pennate - uni - bi - multi - circum

Unipennate: fascicles attach in one side of tendon Bipennate: fascicles insert into the tendon on opposite sides and the muscle resembles a tendon Multipennate: looks like many feathers side by side all inserting into on large tendon Circumpennate: AKA cylindrical, muscle fibers converge into the central tendon from all sides. (Think sphincters)

Artifact Corrections - reverb

Use of a standoff pad or changing angle of incidence

Anisotropy

When the sound beam misses the transducer on the return trip because of the curve of the structure being imaged Structures will appear anechoic or hypoechoic • Depends on angle of incidence. • Sound beam misses the transducer on the return because of the curve of the structure.

Critical components to ligament identification

• equipment parameter adjustment • Too much gain with either overall gain or time gain compensation (TGC) results in loss of detail. Longitudinal imaging of ligament - only method used to image injuries. - Transverse planes: little help when imaging ligament