Metaphoric Signs in msk Sonography – Physiology

This post is dedicated to article called Mnemonics and Metaphorical Videos for Teaching/Learning Musculoskeletal Sonoanatomy. The article was published in American Journal of Physical Medicine and Rehabilitation in December 2022.

In this article, the authors describe a new approach to teaching musculoskeletal ultrasonography. The authors have created a collection of images, drawings, and multimedia videos that use mnemonic aids, pictures, and characteristic sounds to help novice sonographers understand and remember the topographic anatomy of the musculoskeletal system. This approach, called “entertainment education,” combines text and video to provide a clear and engaging explanation of procedures in musculoskeletal medicine.

PHYSIOLOGY

I. General
1. Muscle – Starry sky
  2. Muscle – Feather
  3. Tendon – Spaghetti
  4. Nerve – Honeycomb
  5. Vessels – Mickey Mouse
II. Specific
  1. Rotator cuff (longitudinal) – Bird beak
  2. Rotator cuff (transversal) – Tire
  3. Pronator teres + brachialis + median nerve – Hamburger
  4. Flexor carpi ulnaris + ulna – Moon over a house
  5. Flexor pollicis longus tendon – Full moon
  6. Greater trochanter – Pyramid
  7. Greater trochanter – Matterhorn
  8. Sciatic nerve + tendons – Windmill
  9. Sciatic nerve + tendons – Mercedes
  10. Short head of biceps femoris – Railway
  11. Semimembranosus + semitendinosus – Cherry on the cake
  12. Gastrocnemius – Sunglasses
  13. Tibialis posterior – Seal with a ball
  14. Calcaneofibular ligament – Hammock
  15. Plantar muscles and tendons – Pac-Man
  16. Nerve roots C5, C6 nd C7 – Traffic lights
  17. Brachial plexus – Grapes
  18. Cervical spine facet joints – Saw teeth
  19. Lubmar spine – transverse processes – Trident
  20. Lumbar spine facet joints – Camel humps
21. Lumbar spine laminae – Horse heads
  22. Lumbar vertebra – Bat
  23. Lumbar paraspinal muscles – Butterfly
  24. Cornua sacralia – Frog eyes

General

Muscle – Starry sky – video link

Muscles have a specific internal structure made up of hypoechoic fascicles (dark areas) and hyperechoic perimysium (bright areas). When examining muscles using transverse scans, these two compartments can be observed alternating with one another. The hypoechoic fascicles resemble the dark sky, while the hyperechoic perimysium resembles stars. The appearance of this “relaxing starry sky” pattern is often used as a way to identify muscle tissue during diagnostic examinations. The presence or absence of this pattern can help determine if a muscle is normal or abnormal.

Muscle – Feather – video link

Muscle fascicles are long, thin fibers that run either parallel to the length of the muscle (in fusiform muscles) or at an angle to the aponeurosis (in pennate muscles). When examining a bipennate muscle using a longitudinal scan, the hypoechoic muscular tissue can be seen to contain branches of hyperechoic fibroadipose tissue. This pattern is similar to the structure of a feather, with a central beam and multiple peripheral branches. Recognizing this pattern can be helpful in accurately measuring the architecture of the muscle.

Tendon – Spaghetti – video link

Tendons are highly organized structures made of overlapping collagen fascicles and septa planes. Longitudinal scan of a tendon shows the (physiological) fibrillar pattern, that is, regularly aligned multiple hyperechoic lines. Multiple collagen fibers arranged parallel to each other look like a bunch of spaghetti—savory with the right sauce. Its recognition might facilitate the distinction from other tubular structures. In addition, because of fibrous or fibrocartilaginous tissue, their attachment sites (entheses) can also appear in the shape of free spaghetti ends giving anisotropy.

Nerve – Honeycomb – video link

Peripheral nerves are made up of multiple nerve fibers that are organized into bundles called fascicles. When a nerve is examined using ultrasound, the scan shows several small, hypoechoic “bubbles” within the larger, hyperechoic epineurium. These bubbles represent the fascicles and have a honeycomb-like structure. It is important to be able to recognize this organized structure in order to distinguish it from a tendon, which has a fibrillar structure rather than fascicles.

Vessels – Mickey Mouse – video link

Neurovascular structures, such as arteries and veins, are often found together. When examining a vascular bundle using a transverse scan, it is possible to see three anechoic “bubbles” that resemble the face and ears of Mickey Mouse. To differentiate between the artery and veins, it may be helpful to gently compress the “venous ears” with the probe to collapse them, or to use Doppler imaging to visualize the different flow patterns of steady and pulsatile blood flow. Recognizing the Mickey Mouse pattern can help avoid injury during neuromusculoskeletal interventions.

Specific

Rotator cuff (longitudinal) – Bird beak – video link

The supraspinatus tendon is a long, thin structure that runs from the top of the shoulder blade, under the acromioclavicular joint, and attaches to the upper arm bone. When examining the supraspinatus tendon using a longitudinal scan with the shoulder in a neutral position, it may resemble the beak of a bird, with the acromion corresponding to the head of the bird. This strong “beak” helps to prevent the humeral head from sliding upward and becoming dislocated from the acromion (a condition known as cranial subluxation). The appearance of a normal supraspinatus tendon, as seen through this “beak” pattern, may indicate the presence of a healthy tendon in the critical zone.

Rotator cuff (transversal) – Tire – video link

The modified crass position is a technique used to get a better view of the top and back parts of the supraspinatus tendon. To do this, the patient is asked to place the palm of their hand on their hip on the same side as the shoulder being examined. An anterior transverse scan can then be performed, which may show the rotator cuff as a tire. When the rotator cuff is “inflated” (i.e., fully covering the humeral head), it helps to absorb shocks and prevent subluxation of the shoulder joint. Examining the rotator cuff in this way can provide important information about the width and thickness of any possible tears in the tendon.

Pronator teres + brachialis + median nerve – Hamburger – video link

At the elbow, the median nerve runs between the pronator teres and brachialis muscles. When examining this area using a transverse-oblique plane, the median nerve may resemble a cucumber, while the brachial vessels may resemble another cucumber. The intermuscular fascia may resemble cheese. This pattern, which resembles a hamburger, can be useful when administering botulinum toxin injections to target spastic muscles in this region.

Flexor carpi ulnaris + ulna – Moon over a house – video link

The interosseous transverse septum is a structure that divides the muscles in the forearm into superficial and deep layers. The muscles in the superficial layer include the flexor digitorum superficialis, pronator teres, palmaris longus, flexor carpi radialis, and flexor carpi ulnaris (which is the most medial muscle in this group). When examining the forearm using transverse sonotracking, the ulna (one of the bones in the forearm) may resemble a quadrangular “house,” with the flexor carpi ulnaris muscle located superficially, like a “moon” illuminating the house. Recognizing this pattern can be helpful when targeting specific muscles in the forearm.

Flexor pollicis longus tendon – Full moon – video link

The flexor pollicis longus tendon is a thin, strong structure that runs between the superficial and deep layers of the flexor pollicis brevis muscle in the thumb. When examining this area using a transverse oblique scan on the palm side of the thenar eminence (the fleshy pad at the base of the thumb), it is possible to see a round, hyperechoic structure that represents the flexor pollicis longus tendon. Among the surrounding hypoechoic muscles, the tendon may resemble a “full moon.” Examining the tendon in this way, particularly by testing its anisotropy (the degree to which it differs in properties depending on the direction in which it is measured), can be useful for assessing the tendon’s morphology and vascularity (blood supply).

Greater trochanter – Pyramid – video link

The greater trochanter is a bony prominence on the outside of the hip that can be important for evaluating the lateral hip region. When examining this area using a transverse scan, the greater trochanter may resemble a triangular, hyperechoic shape similar to an ancient Egyptian pyramid. Recognizing this shape can be helpful for identifying the different facets of the greater trochanter and for distinguishing it from the rounder shape of the femoral shaft.

Greater trochanter – Matterhorn

The greater trochanter is a bony prominence on the outside of the hip that can be important for evaluating the lateral hip region. When examining this area using a transverse scan, the greater trochanter may resemble a triangular, hyperechoic shape similar to Mtterhorn. Recognizing this shape can be helpful for identifying the different facets of the greater trochanter and for distinguishing it from the rounder shape of the femoral shaft.

Sciatic nerve + tendons – Windmill – video link

When examining the top third of the back of the thigh using a transverse scan, it is possible to see a “windmill” pattern formed by the conjoined tendon of the semitendinosus and biceps femoris muscles, the sciatic nerve, and the adductor magnus muscle. These anatomical structures, which metaphorically resemble the blades of a windmill, play a crucial role in providing the “energy” for lower limb movements. Recognizing this pattern can help physicians accurately locate the sciatic nerve and avoid injury. This pattern has also been referred to as the “Mercedes-Benz sign” in the literature, but in the future it may be more commonly referred to as the “windmill” pattern.

Sciatic nerve + tendons – Mercedes

Short head of biceps femoris – Railway – video link

The biceps femoris is a long muscle located in the back of the thigh that is also known as the lateral hamstring muscle. As its name suggests, it has two heads, one of which extends deeper into the thigh. When examining the lower back of the thigh using a transverse scan, the short head of the biceps femoris muscle may resemble a railway track located between the long head of the biceps femoris muscle and the vastus lateralis muscle. Recognizing this pattern can be helpful for guiding electromyography (a test that measures the electrical activity of muscles) or other interventions in this area.

Semimembranosus + semitendinosus – Cherry on the cake – video link

The semimembranosus and semitendinosus muscles are located in the back of the thigh, on the inner side of the leg. When examining the lower third of the back of the thigh using a transverse scan, it is possible to see the semitendinosus tendon gradually shifting over the semimembranosus muscle, similar to a cherry on top of a cake. Recognizing these structures can be helpful for better orientation in this region.

Gastrocnemius – Sunglasses – video link

The gastrocnemius is a muscle located in the calf that has two heads (medial and lateral) that are separated from the thigh bone (femur). When examining the upper part of the calf using a transverse scan, the two heads of the gastrocnemius may resemble a pair of fashionable sunglasses. Recognizing this pattern can be important for various diagnostic and interventional procedures, such as the evaluation of conditions like tennis leg or spasticity.

Tibialis posterior – Seal with a ball – video link

The tibialis posterior muscle is a deep muscle located on the back and inner side of the leg. It is covered by the flexor hallucis longus and flexor digitorum longus muscles. When examining this area using a transverse scan, it is possible to see the tibialis posterior muscle, the posterior tibial artery, and the tibial nerve, which together may resemble a sweet seal with a ball. Identifying these structures is important in order to accurately target the right muscle and avoid the nerve and artery when administering botulinum toxin injections or other interventions in this region.

Calcaneofibular ligament – Hammock – video link

The calcaneofibular ligament is a band of tissue that is part of the lateral ligament complex in the ankle. It runs from the lateral malleolus (the bony bump on the outside of the ankle) to the tubercle on the outer side of the heel bone (calcaneus). To visualize the calcaneofibular ligament, it may be helpful to perform a longitudinal (oblique) scan. The ligament may appear like a comfortable hammock on which the fibularis brevis and longus tendons (two muscles in the lower leg) swing.

Plantar muscles and tendons – Pac-Man – video link

The plantar intrinsic muscles of the foot are located near the tendons of the extrinsic muscles of the foot. When examining the sole of the foot using a transverse scan, it is possible to see the plantar intrinsic muscles resembling a hungry Pac-Man, with the flexor digitorum longus and flexor hallucis longus tendons nearby. If these tendons are traced proximally (toward the body), their point of crossing, known as the “knot of Henry,” can be easily visualized. Identifying this knot can be important during the examination of plantar intersection syndrome, a condition that affects the tendons and muscles in the foot.

Nerve roots C5, C6 nd C7 – Traffic lights – video link

After leaving the neural foramina (small openings in the bones of the spine), the cervical nerve roots run between the scalene muscles in the neck. When examining the side of the neck from top to bottom using a transverse scan, it is possible to see the C5, C6, and C7 nerve roots positioned between the anterior and middle scalene muscles, resembling a set of traffic lights. Recognizing the location of these nerve roots can be crucial for a variety of neck interventions.

Brachial plexus – Grapes – video link

In the suprascapular region (the area above the shoulder blade), the cervical nerve roots come together to form trunks, which are then divided into upper and lower divisions. When examining the side of the neck using a transverse scan, it is possible to see the brachial plexus (a network of nerves that supplies the upper limb) running between the anterior and middle scalene muscles. This pattern may resemble a bunch of grapes. Recognizing the location of the brachial plexus is important for various neck procedures.

Cervical spine facet joints – Saw teeth – video link

Facet joints are small joints located between the bones of the spine. At the upper part of the neck, these joints are angled at about 45 degrees, while in the lower part of the neck they are more vertical. When examining the bones of the spine from the back using a posterior parasagittal scan, it is possible to see the regularly aligned facet joints, which may resemble saw teeth. Recognizing the appearance of these joints can be helpful for accurately targeting them or the surrounding structures (such as the medial branches) during procedures or interventions.

Lubmar spine – transverse processes – Trident – video link

When examining the lower back using a longitudinal paramedian scan, it is possible to see the three transverse processes (small bony projections from the sides of the vertebrae) that may create sharp shadowings. Recognizing this pattern, which may resemble a trident, can help ensure that the imaging provides a far lateral view of the spine. This can be useful for targeting the lumbar roots (the nerves that emerge from the lower back) during interventional procedures.

Lumbar spine facet joints – Camel humps – video link

Each lumbar vertebra (a bone in the lower back) consists of a body, arch (made up of two laminae and two pedicles), and two transverse processes and one spinous process (bony projections from the back of the vertebra). When examining the lower back using longitudinal paramedian scans, it is possible to see the facet joints and the laminae, which may resemble camel humps and horse heads, respectively. These structures are often targeted during relevant interventions.

Lumbar spine laminae – Horse heads – video link

Lumbar vertebra – Bat – video link

When examining the lumbar vertebrae using a transverse scan, it is possible to see the deep bony lining and the erector spinae muscles. These structures may resemble a bat and a butterfly, respectively. The bony structures serve as important landmarks during relevant interventions, and imaging the erector spinae muscles may also be useful during exercise therapy when using “sono-feedback” (a technique that involves using ultrasound images to provide visual feedback to guide muscle training).

Lumbar paraspinal muscles – Butterfly – video link

Cornua sacralia – Frog eyes – video link

The sacrum is a bone formed by the fusion of the sacral vertebrae and is the continuation of the vertebral canal. The 5th sacral laminae do not fuse, resulting in a bony defect known as the sacral hiatus. The lateral walls of the sacral hiatus are made up of the tubercles of the inferior articular processes of the 5th sacral vertebrae, known as the sacral cornua. When examining this area using a transverse scan, it is possible to see the sacral cornua, which may resemble frog eyes. Identifying the hyperechoic band between these “eyes,” which is known as the sacrococcygeal ligament, can be important when planning ultrasound-guided procedures in this region.

References

1. Jačisko J, Mezian K, Güvener O, Ricci V, Kobesová A, Özçakar L. Mnemonics and Metaphorical Videos for Teaching/Learning Musculoskeletal Sonoanatomy. Am J Phys Med Rehabil. 2022 Dec 1;101(12):e189-e193. doi: 10.1097/PHM.0000000000002084. Epub 2022 Aug 9. PMID: 35944076.

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