Fundamentals of Musculoskeletal Ultrasound

Comprehensive vocabulary flashcards covering principles, physics, scanning technique, sonographic appearances, artifacts, and regional musculoskeletal ultrasound pathology.

Piezoelectric Effect

The property of an ultrasound transducer crystal that allows an electrical signal to be converted into ultrasonic energy (sound waves) and vice versa.

Acoustic Anisotropy

An artifact occurring when an ultrasound beam insonates a fibrillar structure (such as a tendon or ligament) at an angle oblique to its long axis by as little as $2\text{ to }3^\text{ degrees}$, causing the structure to lose its normal hyperechoic appearance and appear artifactually hypoechoic.

Heel-Toe Maneuver

A transducer manipulation technique in which the probe is rocked or angled along its long axis without changing its position on the skin surface, used to bring a structure perpendicular to the ultrasound beam to eliminate anisotropy.

Toggle Maneuver

A transducer manipulation technique where the probe is angled from side to side along its short axis without changing position on the skin surface, commonly used to eliminate anisotropy when viewing structures in short axis.

Posterior Acoustic Enhancement (Increased Through-Transmission)

An artifact where sound waves passing through a weakly attenuating medium (such as fluid or certain cellular solid tumors) result in tissues deep to the structure appearing artifactually brighter or hyperechoic relative to adjacent tissues.

Ring-Down Artifact

A form of posterior reverberation artifact produced when sound waves bounce repeatedly between the transducer and a smooth, flat metallic surface, generating a series of continuous, closely spaced linear reflective echoes extending deep to the object.

Comet-Tail Artifact

A reverberation artifact characterized by a short, triangular, tapering band of bright posterior echoes that narrows with distance from its origin, commonly produced by small soft-tissue gas bubbles or foreign bodies.

Spatial Compound Sonography

An ultrasound imaging technique that transmits sound beams from multiple steering angles and combines the data into a single composite frame, improving tissue boundary definition while smoothing artifacts at the expense of potential motion blur.

Tissue Harmonic Imaging

An imaging technique that uses harmonic frequencies generated by non-linear sound propagation through tissues rather than the transmitted fundamental frequency, thereby improving deep tissue penetration and boundary delineation while reducing near-field clutter.

Power Doppler

A Doppler imaging modality that maps the total integrated amplitude of the Doppler signal rather than frequency shift, providing high sensitivity to slow or low-volume blood flow without displaying directional information.

Delayed Onset Muscle Soreness (DOMS)

A condition resulting from intense or unaccustomed physical activity that sonographically demonstrates diffuse or focal hyperechoic muscle edema and mild muscle enlargement without discrete fiber disruption.

Morel-Lavallée Lesion

A post-traumatic, closed degloving injury characterized by a hemolymphatic fluid collection that shears the subcutaneous fat from the underlying deep muscular fascia, most commonly involving the proximal thigh and lateral hip.

Myositis Ossificans

A benign, non-neoplastic condition of heterotopic bone formation within damaged muscle characterized sonographically by early hyperechoic mineralization within a hypoechoic hematoma, typically progressing to a peripheral rim of calcification.

Tendinosis

A chronic, non-inflammatory tendon degeneration characterized histologically by mucoid, fibrillar, and eosinophilic changes, appearing sonographically as focal or diffuse hypoechoic tendon thickening without discrete fiber tearing.

Double Contour Sign

A sonographic finding pathognomonic for gout characterized by a hyperechoic, irregular band of monosodium urate crystal deposition layering directly on the outer surface of anechoic/hypoechoic hyaline articular cartilage.

Gouty Tophus

A soft-tissue collection of monosodium urate crystals appearing sonographically as a heterogeneous, predominantly hyperechoic amorphous mass with internal punctate echoes, surrounded by a hypoechoic inflammatory halo.

Diabetic Muscle Infarction

A non-infectious, ischemic complication seen in patients with longstanding diabetes, manifesting sonographically as painful, hypoechoic swelling of a muscle belly (most often the vastus intermedius or thigh/calf musculature) with preservation of internal hyperechoic fibroadipose septa.

Schwannoma (Neurilemmoma)

A benign peripheral nerve sheath tumor characteristically appearing as a well-defined, hypoechoic, eccentric mass in direct continuity with a peripheral nerve, often exhibiting increased through-transmission and internal vascularity.

Target Sign (Neurofibroma)

A sonographic appearance of a localized neurofibroma showing a hyperechoic fibrocollagenous center surrounded by a peripheral hypoechoic myxoid rim in cross-section.

Rotator Interval

An anatomic space between the anterior margin of the supraspinatus tendon and the superior margin of the subscapularis tendon, through which the intra-articular portion of the biceps brachii long head tendon and the coracohumeral and superior glenohumeral ligaments pass.

Biceps Reflection Pulley

A stabilizing capsuloligamentous sling in the rotator interval composed of the superior glenohumeral ligament and the coracohumeral ligament that prevents medial dislocation of the intra-articular long head of the biceps brachii tendon.

Modified Crass Position

A shoulder ultrasound positioning technique in which the patient places the palm on the ipsilateral hip with the elbow directed posteriorly, rotating the greater tuberosity anteriorly to allow long- and short-axis assessment of the distal supraspinatus tendon and rotator interval.

Rotator Cable

A curved, thick, fibrous transverse bundle within the deep articular aspect of the rotator cuff that courses perpendicular to supraspinatus fibers and spans between the anterior and posterior greater tuberosity facets, enclosing the rotator crescent.

PASTA Lesion (Rim-Rent Tear)

A partial articular-side supraspinatus tendon avulsion characterized by an anechoic or hypoechoic cleft disrupting the deepest tendon fibers at their direct footprint insertion onto the greater tuberosity.

Cartilage Interface Sign

An accentuated, prominent hyperechoic line seen at the interface between the superficial aspect of hypoechoic hyaline articular cartilage and an overlying anechoic fluid-filled tendon tear or hypoechoic fluid collection.

Subacromial Impingement Syndrome

Mechanical compression of the supraspinatus tendon and subacromial-subdeltoid bursa beneath the coracoacromial arch, demonstrated dynamically on ultrasound by pooling or bunching of bursal fluid or tissue against the lateral acromion during arm abduction.

Adhesive Capsulitis (Frozen Shoulder)

A condition characterized by shoulder stiffness and restricted range of motion, displaying limitation of subacromial supraspinatus sliding during dynamic abduction and thickening or stiffness of the coracohumeral ligament.

Calcific Tendinitis (Resorptive Phase)

The symptomatic phase of calcium hydroxyapatite deposition disease characterized by soft, amorphous, or globular hyperechoic intratendinous deposits that exhibit little or no acoustic shadowing and are surrounded by hyperemic neovascular flow.

Geyser Sign

The superior decompression of glenohumeral joint fluid through a massive chronic full-thickness rotator cuff tear across a disrupted acromioclavicular joint capsule, producing a prominent subcutaneous fluid collection or cyst above the acromioclavicular joint.

Elastofibroma Dorsi

A benign pseudotumor composed of fibroelastic tissue and fat located characteristically at the inferior angle of the scapula deep to the serratus anterior and latissimus dorsi muscles, displaying alternating curvilinear hypoechoic and hyperechoic bands.

Slipping Rib Syndrome

A condition of excessive costal cartilage hypermobility affecting the false ribs, demonstrated dynamically with ultrasound as a lower cartilaginous rib end snapping or subluxating over an adjacent rib or the xiphoid process.

Cubital Tunnel Syndrome

An entrapment neuropathy of the ulnar nerve at the medial elbow characterized by hypoechoic nerve enlargement proximal to the Osborne fascia/arcuate ligament with a cross-sectional area greater than $9\text{ mm}^2$ or an enlargement ratio greater than $2.8$.

Snapping Triceps Syndrome

A dynamic condition wherein both the ulnar nerve and the medial head of the triceps brachii muscle subluxate or dislocate anteriorly over the apex of the medial epicondyle during elbow flexion, creating two distinct palpable snaps.

Anconeus Epitrochlearis

An accessory muscular variant at the medial elbow present in up to $23\%$ of the population that bridges the olecranon process and medial epicondyle in place of Osborne fascia, serving as a potential cause of ulnar nerve compression.

Bicipitoradial Bursitis (Cubital Bursitis)

Inflammation or distention of the non-communicating, U-shaped bursa surrounding the distal biceps brachii tendon at its insertion on the radial tuberosity, which can mimic a soft-tissue mass or compress the adjacent radial nerve.

Tennis Elbow (Lateral Epicondylitis)

A degenerative overuse tendinopathy and microtearing primarily affecting the extensor carpi radialis brevis component of the common extensor tendon origin at the lateral epicondyle, appearing as hypoechoic thickening greater than $4.2\text{ mm}$ with cortical irregularity.

Posterior Interosseous Nerve Syndrome

Compression of the motor deep branch of the radial nerve between the superficial and deep heads of the supinator muscle at the arcade of Fröhse, manifesting clinically as finger and thumb extension weakness without wrist drop or sensory deficits.

Saturday Night Palsy

Compressive neuropathy of the radial nerve within the spiral groove of the posterior humerus, typically resulting in hypoechoic swelling and wrist drop with preserved triceps function.

Carpal Tunnel Syndrome

The most common upper extremity entrapment neuropathy characterized by compression of the median nerve within the carpal tunnel, diagnosed sonographically by hypoechoic nerve swelling with a cross-sectional area greater than $12\text{ mm}^2$ at the wrist crease or a proximal-to-distal cross-sectional area difference greater than $2\text{ mm}^2$.

Notch Sign

A sagittal ultrasound appearance of the median nerve in carpal tunnel syndrome showing an abrupt contour indentation and caliber reduction at the proximal edge of the transverse carpal ligament.

Persistent Median Artery

A congenital vascular variant seen in up to $15\%$ of individuals where an embryonic vessel persists in the carpal tunnel, coursing between the two trunks of a bifid median nerve.

Fibrolipomatous Hamartoma

A rare benign lesion of the median nerve characterized sonographically by diffuse infiltration of mature fibrofatty tissue that separates and surrounds enlarged, coaxial, hypoechoic nerve fascicles.

Hypothenar Hammer Syndrome

Post-traumatic vascular insufficiency and aneurysm or thrombosis of the ulnar artery as it passes over the hook of the hamate in Guyon canal, secondary to repetitive blunt trauma to the hypothenar eminence.

Wartenberg Syndrome

Entrapment neuropathy of the superficial sensory branch of the radial nerve as it exits beneath the brachioradialis in the distal forearm, presenting with pain and paresthesias over the dorsoradial hand.

Stener Lesion

A complication of a complete distal ulnar collateral ligament tear of the first metacarpophalangeal joint in which the retracted, balled-up ligament stump becomes caught superficial to the adductor pollicis aponeurosis, creating a characteristic 'yo-yo on a string' sonographic appearance.

De Quervain Disease

Stenosing tenosynovitis of the first dorsal extensor compartment of the wrist, presenting sonographically with hypoechoic thickening of the extensor retinaculum and synovial sheath surrounding the abductor pollicis longus and extensor pollicis brevis tendons.

Intersection Syndrome

An overuse peritendinitis and tenosynovitis located approximately $4\text{ to }8\text{ cm}$ proximal to Lister tubercle, where the abductor pollicis longus and extensor pollicis brevis of the first compartment cross superficial to the extensor carpi radialis longus and brevis tendons.

Boxer Knuckle

Traumatic disruption of the sagittal bands of the extensor hood over the metacarpophalangeal joint, resulting in dynamic subluxation or dislocation of the extensor digitorum tendon into the intermetacarpal groove during digit flexion.

Trigger Finger

Stenosing flexor tenosynovitis at the digit base caused by hypoechoic thickening and stiffness of the A1 annular pulley, preventing smooth gliding and producing locking or snapping of the flexor digitorum tendons.

Bowstringing (Finger)

Abnormal volar displacement of the flexor digitorum tendons away from the phalanges during resisted active finger flexion, exceeding $3\text{ mm}$ at the distal A2 pulley or $5\text{ mm}$ for combined A2 and A3 ruptures.

Giant Cell Tumor of the Tendon Sheath

A benign, localized synovial proliferative solid tumor (nodular tenosynovitis) in intimate contact with a tendon sheath, appearing sonographically as a non-compressible, hypoechoic mass with internal Doppler flow that does not translate during tendon movement.

Dupuytren Contracture (Palmar Fibromatosis)

A benign fibrosing disorder of the hand characterized by nodular, hypoechoic, mass-like thickening of the palmar aponeurosis located superficial to the flexor tendons that causes progressive flexion deformities of the digits.

Glomus Tumor

A benign neuro-myo-arterial mesenchymal neoplasm typically found in the subungual space of the distal phalanx, appearing as a focal, well-defined, highly vascular hypoechoic nodule that often induces underlying bony remodeling.

Knuckle Pads

Benign hypoechoic subcutaneous fibrous plaques developing over the dorsal extensor surfaces of the proximal interphalangeal or metacarpophalangeal joints, frequently associated with Dupuytren contracture.

Hesselbach Triangle

An anatomic space in the lower abdominal wall bounded medially by the rectus abdominis, laterally by the inferior epigastric artery, and inferiorly by the inguinal ligament; direct inguinal hernias originate through this area.

Indirect Inguinal Hernia

A groin hernia originating lateral to the inferior epigastric artery through the deep inguinal ring that traverses the inguinal canal parallel to the skin surface toward the superficial ring and scrotum or labium majus.

Direct Inguinal Hernia

A groin hernia originating medial to the inferior epigastric vessels through a weakened abdominal wall in the Hesselbach triangle, protruding directly anteriorly toward the transducer during Valsalva maneuver.

Femoral Hernia

A hernia passing inferior to the inguinal ligament through the femoral canal, situated immediately medial to the common femoral vein and causing compression of the vein during a Valsalva maneuver.

Spigelian Hernia

A ventral abdominal wall defect occurring along the Spigelian aponeurosis at the lateral border of the rectus abdominis muscle, through which peritoneal fat or bowel herniates anteriorly.

Internal Snapping Hip (Coxa Saltans)

An extra-articular snapping syndrome produced when the psoas major tendon of the iliopsoas complex abruptly flips over the medial fibers of the iliacus muscle and superior pubic ramus during extension from a flexed, abducted, and externally rotated position.

External Snapping Hip

An extra-articular snapping syndrome produced when a thickened posterior border of the iliotibial tract or anterior border of the gluteus maximus abruptly translates over the bony prominence of the greater trochanter during hip flexion and extension.

Athletic Pubalgia

A chronic sports-related groin pain syndrome characterized by injury, tendinosis, or tearing involving the common aponeurosis formed by the distal rectus abdominis and proximal adductor longus tendons at the pubic symphysis.

Thigh Splints (Adductor Insertion Avulsion Syndrome)

A chronic stress injury characterized by periostitis and potential cortical irregularity along the posteromedial femoral diaphysis at the insertion site of the adductor musculature, presenting with focal transducer point tenderness.

Pseudohypertrophy of Tensor Fasciae Latae

A soft-tissue pseudomass appearance resulting from denervation-induced fatty replacement and enlargement of the tensor fasciae latae muscle, commonly secondary to chronic lumbar radiculopathy.

Alpha Angle (Graf Hip Ultrasound)

The angle formed between the vertical baseline of the lateral ilium and the acetabular roof line on a coronal infant hip ultrasound, where an angle of $> 60^\text{ degrees}$ is considered normal and $< 50^\text{ degrees}$ indicates acetabular dysplasia.

Baker Cyst (Popliteal Cyst)

A fluid distention of the gastrocnemio-semimembranosus bursa characterized by a pathognomonic neck or communicating channel that passes between the semimembranosus tendon and the medial head of the gastrocnemius tendon to connect with the posterior knee joint.

Jumper’s Knee (Patellar Tendinosis)

An overuse tendinopathy affecting the proximal attachment of the patellar tendon at the inferior patellar pole, characterized sonographically by hypoechoic thickening, loss of fibrillar pattern, and hyperemic neovascularity.

Osgood-Schlatter Disease

A traction apophysitis of the tibial tuberosity in adolescents characterized sonographically by distal patellar tendon hypoechoic thickening, unossified cartilage swelling, and fragmentation of the tibial tuberosity.

Sinding-Larsen-Johansson Disease

A chronic traction apophysitis affecting the proximal patellar tendon origin at the inferior pole of the patella in adolescents, displaying tendon hypoechogenicity and adjacent patellar cortical fragmentation.

Patellar Clunk Syndrome

A complication of posterior-stabilized total knee arthroplasty in which a fibrous, hypoechoic synovial nodule at the suprapatellar junction catches within the intercondylar box of the femoral component and abruptly snaps free during terminal extension.

Pellegrini-Stieda Lesion

Post-traumatic calcification or ossification occurring at the femoral attachment of the medial collateral ligament following a remote grade 2 or 3 sprain or avulsion tear.

Intraneural Ganglion Cyst (Peroneal Nerve)

A mucinous, multilocular cyst tracking within the epineurium of the common peroneal nerve, originating from the proximal tibiofibular joint via the articular nerve branch and capable of proximal propagation into the sciatic nerve.

Tennis Leg

An acute rupture or tear of the distal myotendinous junction and aponeurosis of the medial head of the gastrocnemius muscle where it tapers over the soleus muscle, presenting with fluid and hematoma between the two muscle bellies.

Plantar Fasciopathy

Degenerative thickening of the proximal central cord of the plantar aponeurosis greater than $4\text{ mm}$ at its calcaneal insertion, associated with loss of normal fibrillar architecture and subjacent hypoechogenicity.

Plantar Fibromatosis (Ledderhose Disease)

A benign fibroblastic proliferative disorder of the central and medial bands of the plantar aponeurosis, appearing sonographically as single or multiple fusiform, hypoechoic-to-isoechoic nodular thickenings within the superficial plantar arch.

Maisonneuve Fracture

A proximal fibular neck fracture caused by an external rotation injury that tears the anterior inferior tibiofibular ligament, disrupts the interosseous membrane throughout the leg, and exits through the proximal fibula.

Morton Neuroma

A non-neoplastic, hypoechoic perineural fibrosis and entrapment mass of a common plantar digital nerve located in the intermetatarsal space (most commonly the second or third web space), typically measuring greater than $5\text{ mm}$ in diameter.

Sonographic Mulder Sign

A dynamic ultrasound maneuver in which medial-lateral compression of the metatarsal heads forces a Morton neuroma to displace in a plantar direction between the metatarsal heads, often accompanied by a palpable or audible click and pain reproduction.

Tarsal Tunnel Syndrome

An entrapment neuropathy involving the tibial nerve or its terminal branches within the fibro-osseous tarsal tunnel beneath the flexor retinaculum, commonly caused by space-occupying lesions such as ganglion cysts or venous varicosities.

Haglund Syndrome

A clinical and imaging triad characterized by Achilles tendinosis, retrocalcaneal bursitis, and retro-Achilles bursitis, associated with a prominent, posterosuperior bony calcaneal tuberosity (Haglund deformity).

Freiberg Disease

Osteonecrosis and subchondral collapse of a metatarsal head (most commonly the second metatarsal) resulting from repetitive microtrauma, demonstrating cortical flattening and irregularity with surrounding synovitis on ultrasound.

In-Plane Needle Technique

An ultrasound-guided interventional method in which the needle is directed along the long axis of the transducer face and sound beam, allowing continuous, real-time visualization of the entire needle shaft and needle tip throughout the procedure.

Out-of-Plane Needle Technique

An ultrasound-guided interventional method where the needle is advanced perpendicular to the sound beam, imaging the needle as a single hyperechoic cross-sectional point with reverberation artifact, commonly used for superficial joints of the hands and feet.

Tendon Fenestration (Dry Needling)

An ultrasound-guided percutaneous procedure wherein a 20- or 22-gauge needle is repeatedly passed ($20\text{ to }30\text{ times}$) through a region of tendinosis to disrupt degenerate tissue, induce bleeding, and release intrinsic growth factors to stimulate tendon healing.