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It’s also perfectly normal to have it one arm but not the other. “This palmaris longus muscle can weakly help flex the wrist,” says Bennion in the video. This muscle is usually visible through the skin when we make gripping motions and according to Bennion, isn’t really necessary for everyday activities.The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; however, this number can vary in African, Asian, and Native American populations.Variations of PL muscle are not uncommon. It has been estimated that in about 11% of cases, they are found to be absent (2, 3). However, a study conducted by Mangala et al reported the agenesis of this muscle in 26% of individuals (4).

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About 15% of humans don’t have a muscle in their forearms called the Palmaris Longus. As a muscle, it’s pretty useless. But still, why do some people have it while others don’t?
What mechanism is behind the whole thing? In this video, I explain why there’s still variation among different bodies and why this obsolete muscle exists still.
☠️NONE OF THE INFORMATION IN THIS VIDEO SHOULD BE USED AS MEDICAL ADVICE OR OPINION. IT IS FOR GENERAL EDUCATION AND ENTERTAINMENT☠️
🔗 L I N K S 🔗
📱Instagram: https://www.instagram.com/patkellyteaches/
🐦Twitter: https://twitter.com/PatKellyTeaches
💰Patreon: https://www.patreon.com/corporis
📽 O T H E R V I D E O S 📽
⚰️Medical History playlist: https://www.youtube.com/playlist?list=PL2rpvfNeooNGcIesiheCNuPvuQyRlRavb
🔬Anatomy Basics playlist: https://www.youtube.com/playlist?list=PL2rpvfNeooNE5E4jKX9JOrXITW-kIfZCc
💪Kinesiology and Biomechanics playlist: https://www.youtube.com/playlist?list=PL2rpvfNeooNGkKlDT2ctqTpPtJgAPOpjx
📜 S O U R C E S 📜
Grip Strength Unaffected By PL Removal (2005)
http://journals.sagepub.com/doi/10.1016/J.JHSB.2005.03.011
Heredity of PL (2013)
http://jms.org.br/PDF/v30n4a08.pdf
Palmaris Longus comparison (2014)
https://www.hindawi.com/journals/bmri/2014/178906/#B21
The changing upper extremity (2014)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4059683/#!po=3.33333
Percentages of PL (2016)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4596262/?report=reader#!po=23.3333
https://www.flickr.com/photos/internetarchivebookimages/20351083601
Lemur Hand By Alex Dunkel (Maky) – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=12468465
Chimpanzee By © Hans Hillewaert /, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=16267899
https://en.wikipedia.org/wiki/Ring-tailed_lemur#/media/File:Ring_tail_lemur_leaping.JPG
https://en.wikipedia.org/wiki/Ring-tailed_lemur#/media/File:Lemur_catta_1.jpg
https://www.youtube.com/watch?v=oZXwD9i0bcQ
💊A B O U T 💊
Hi, I’m Patrick. I’m a freelance science writer based in the San Francisco Bay Area. I hold a bachelor’s degree in Athletic Training and a master’s in clinical exercise physiology. I used to work in the clinical setting as a certified athletic trainer, physical therapy aide, and a certified strength and conditioning specialist. After working in the clinical setting, I went back to school and became a teacher. The goal of my content is to help normal people, not just pre-med students, learn about the human body. That might mean explaining a topic from an anatomy class or exploring a topic from medical history.
💻 C O N T A C T 💻
If you’d like to sponsor a video or have other business inquiries:
patkellyteaches [at] gmail.com
#corporis #anatomy #medicalhistory

See more information on the topic Can you have palmaris longus in one arm here:

Why does only my right arm have a palmaris longus muscle?

Palmaris longus is a muscle that can be found partly in the forearm, wrist, and hand. It has two functions. A minor function is t… This answer reserved by the …

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Source: www.quora.com

Date Published: 2/6/2022

View: 6217

Here’s Proof of Evolution You Can Find on Your Own Body

Scientists have found that, while palmaris longus is present in many species of mammals today, it’s most developed in those that use their forearms to move …

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Source: www.sciencealert.com

Date Published: 5/22/2021

View: 9597

Palmaris longus muscle – Wikipedia

The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always …

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Source: en.wikipedia.org

Date Published: 2/24/2022

View: 9715

Some bodies contain mysterious variations – The Conversation

One of the easiest to observe (or observe its absence) is a muscle called palmaris longus. The best way to see if you have this muscle is to …

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Source: theconversation.com

Date Published: 6/13/2022

View: 744

Today I discovered that I am missing my palmaris longus …

You got me to look at my arm and realize I have no clue what I am looking for. Thank you.

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Source: www.reddit.com

Date Published: 4/21/2021

View: 3884

The Variation in the Absence of the Palmaris Longus in a …

Here, we corroborate the previous Asian studies by showing that our Asian population does, in fact, have a much lower prevalence of absent PL (2.9%). Clinically …

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Source: www.hindawi.com

Date Published: 1/8/2022

View: 1134

Palmaris Longus – Physiopedia

However, it has been accepted as a vestigial muscle since studies have shown that almost 30% of the population could be lacking this muscle either in one …

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Source: www.physio-pedia.com

Date Published: 3/11/2021

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How rare is it to have a palmaris longus?

The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; however, this number can vary in African, Asian, and Native American populations.

Are two palmaris longus rare?

Variations of PL muscle are not uncommon. It has been estimated that in about 11% of cases, they are found to be absent (2, 3). However, a study conducted by Mangala et al reported the agenesis of this muscle in 26% of individuals (4).

How do you know if you have a palmaris longus?

The palmaris longus (PL) tendon can be assessed with clinical tests whose reliability varies. Herewith, two new tests are described – the ‘Bunched Finger’ test and ‘Hooked Finger test’ that are simple and visualise the PL tendon easily and prominently.

What percentage of people have no palmaris longus?

The prevalence of the palmaris longus (PL) muscle varies more than any other muscle in the human body. Its absence across the world ranges between 1.5% and 63.9%.

Can you have palmaris longus in one arm and not the other?

It’s also perfectly normal to have it one arm but not the other. “This palmaris longus muscle can weakly help flex the wrist,” says Bennion in the video. This muscle is usually visible through the skin when we make gripping motions and according to Bennion, isn’t really necessary for everyday activities.

Does palmaris longus make you stronger?

No statistically significant difference was seen in the grip or pinch strength measurements between subjects who had a palmaris longus tendon and those who did not. This study demonstrates that absence of the palmaris longus is not associated with a decrease of grip or pinch strength.

Can you have 3 palmaris longus?

Rarely is the palmaris longus muscle double, whereas the three-headed reversed palmaris longus muscle is mentioned only once in the literature as a surgical finding, in a patient who suffered from edema and pain in the wrist [Yildiz, M., Sener, M., Aynaci, O., 2000.

Does everyone have a palmaris brevis?

Even though it is located in this region, palmaris brevis doesn’t belong to the hypothenar muscle group, but rather, it is classified on its own as an outstanding superficial muscle of this region.

Palmaris brevis muscle.
Origin Palmar aponeurosis, flexor retinaculum
Blood supply Superficial palmar arch
11 thg 5, 2020

Does the palmaris longus do anything?

Function. Palmaris longus synergistically works with the long flexors of the forearm to bring about flexion at the wrist joint and small joints of the hand. Apart from this, the muscle also helps in tightening and tensing up the palmar aponeurosis.

What ethnicity has palmaris longus?

The prevalence of this absence of the palmaris longus is reported as 22.4 % in Caucasian, 4.8 % in Asian, 3.0 % in Black, 7.1 % in Native American, 26.6 % in Turkish, and 17.2 % in Indian population (8 % bilateral and 9.2 % unilateral) [5, 6, 11].

How do you train a palmaris longus?

Begin by keeping your wrists straight in line with the rest of your forearms. Slowly bend your wrists back as far as you can comfortably allow it. Then, slowly bring the weight back up and past the starting point, giving it a little contraction. Continue doing ten repetitions for three sets.

Why is palmaris longus absent in some people?

Palmaris longus (PL) is one of the most variable and most superficial flexor muscles of the forearm. It is well known that there is a wide variation in the reported prevalence of PL absence in different ethnic groups. Its absence appears to be hereditary but genetic transmission is not clear.

Are Your Missing the Palmaris Longus? Try This Arm Test to See

There’s a sign of human evolution hidden right inside your body, and one little test could help you see it.

Jonathan Bennion, M.P.A, the co-founder and director of the Institute of Human Anatomy in Salt Lake City, Utah reveals in a video a muscle in our wrist that we often don’t notice, which could be because a good number of people don’t have it.

Bennion explains that most people have 20 muscles in our forearm (or antebrachium)—and all of these muscles help us twist our arms, move our wrists, wave our hands, and so much more. However, some people only have 19 muscles there, missing one that might disappear from humans forever as we evolve: the palmaris longus tendon.

Reportedly 14 percent of the human population is missing this muscle, though this may vary in Asian, Black and Native American populations.

Here’s the test to see if you have the muscle or not. Gently flex your wrist and touch your pinky finger to your thumb. If the tendon over the top of the inside of your wrist is visible, you have it. If not, you likely don’t. It’s also perfectly normal to have it one arm but not the other.

“This palmaris longus muscle can weakly help flex the wrist,” says Bennion in the video. This muscle is usually visible through the skin when we make gripping motions and according to Bennion, isn’t really necessary for everyday activities. “If you don’t have this muscle, you can still do all the hand and wrist movements that you would need to do without the palmaris longus.”

Whether you’re equipped with the muscle or not, it’s good to know you’re not missing out on much either way.

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Palmaris longus muscle

Muscle of the upper limb

The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; however, this number can vary in African, Asian, and Native American populations.[1] Absence of the palmaris longus does not have an effect on grip strength.[2] However, the lack of palmaris longus muscle results in decreased pinch strength in fourth and fifth fingers. The absence of palmaris longus muscle is more prevalent in females than males.[3]

The palmaris longus muscle can be seen by touching the pads of the fourth finger and thumb and flexing the wrist. The tendon, if present, will be visible in the midline of the anterior wrist.

Structure [ edit ]

Palmaris longus is a slender, elongated, spindle shaped muscle, lying on the medial side of the flexor carpi radialis. It is widest in the middle, and narrowest at the proximal and distal attachments.[4]

It arises mainly from the medial epicondyle of the humerus via the common flexor tendon. It also takes origin from the adjacent intermuscular septa and from the antebrachial fascia.[4]

It ends in a slender, flattened tendon, which passes over the upper part of the flexor retinaculum and inserts onto the central part of the flexor retinaculum and lower part of the palmar aponeurosis. Frequently, it sends a tendinous slip to the short muscles of the thumb.[4]

Nerve supply [ edit ]

The palmaris longus is innervated by the median nerve.[5]

Variation [ edit ]

Palmaris Longus: misplaced or absent

The fleshy belly occasionally migrates distally and comes to lie close above the wrist, as here.

Palmaris Longus was absent in 98 of 716 dissected limbs (i.e., in 13.7% of 358 paired limbs, 26 times in both limbs, 26 in the right only, and 20 in the left only. (R. K. George).[6] The fleshy belly occasionally migrates distally and comes to lie close above the wrist, as here.Palmaris Longus was absent in 98 of 716 dissected limbs (i.e., in 13.7% of 358 paired limbs, 26 times in both limbs, 26 in the right only, and 20 in the left only.

The palmaris longus muscle is a variable muscle. The most common variation is its absence. Several in vivo and in vitro studies have documented the prevalence or absence of the PL tendon in different ethnic groups. Between 5.5 and 24% of Caucasian populations (European and North American) and 4.6 to 26.6% of Asian populations (Chinese, Japanese, Indian, Turkish, Malaysian) have been reported to lack the PL tendon.[7]

There are also variations related to its form. It may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may be double, or missing entirely. Slips of origin from the coronoid process or from the radius have been seen. Partial or complete insertion into the fascia of the forearm, into the tendon of the flexor carpi ulnaris and pisiform bone, into the scaphoid, and into the muscles of the little finger have been observed.

Clinical significance [ edit ]

Use in tendon grafts [ edit ]

Cross-section through the middle of the forearm

The palmaris longus muscle is the most popular for use in tendon grafts for the wrist due to the length and diameter of the palmaris longus tendon, and the fact that it can be used without producing any functional deformities. When a tendon becomes ruptured in the wrist, the palmaris longus tendon may be removed from the flexor retinaculum and grafted to take the place of the ruptured tendon. The tendons most commonly replaced or supplemented by the palmaris longus tendon when ruptured are the long flexors of the fingers and the flexor pollicis longus tendon.[8]

The palmaris longus muscle itself is a weak flexor, and provides no substantial flexing force that would inhibit movement in the wrist if its tendon were cut and moved elsewhere. The palmaris longus may contribute and assist in thumb abduction movements; an action necessary to open the hand.[9][10] If the palmaris longus muscle is not available for harvesting in an individual, the anatomically homologous plantaris muscle in the leg may be taken instead.[11] Using the patient’s own tendon is advantageous, as it does not introduce foreign material into the body.

Carpal tunnel syndrome and palmaris longus variants [ edit ]

Of the known anatomical variants of the palmaris longus, the reverse belly of the palmaris longus may be localized within the carpal tunnel producing symptoms of carpal tunnel syndrome. Knowledge of this variation is important to prevent unnecessary carpal tunnel release surgery, in which the median nerve compression may remain unresolved due to the presence of this palmaris longus variant.[12]

Other animals [ edit ]

Evolution [ edit ]

The evolutionary interpretation of the muscle’s absence is that humans inherited the muscle through common descent, and numerous animals that humans share a common ancestor with (such as the orangutan) still actively employ the muscle.[13] Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability.[14] The common descent principle suggests that at some stage our ancestors employed the muscle actively. The thumb apparatus (and particularly the thenar muscle group) then started developing in the hominin branch, and consequently the Palmaris longus became vestigial. As there is no apparent evolutionary pressure (positive or negative) concerning the muscle, it has remained largely unaffected by evolutionary processes.[15]

See also [ edit ]

This article uses anatomical terminology

References [ edit ]

This article incorporates text in the public domain from page 446 of the 20th edition of Gray’s Anatomy (1918)

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Your access to the NCBI website at www.ncbi.nlm.nih.gov has been temporarily blocked due to a possible misuse/abuse situation involving your site. This is not an indication of a security issue such as a virus or attack. It could be something as simple as a run away script or learning how to better use E-utilities, http://www.ncbi.nlm.nih.gov/books/NBK25497/, for more efficient work such that your work does not impact the ability of other researchers to also use our site. To restore access and understand how to better interact with our site to avoid this in the future, please have your system administrator contact [email protected]

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Access Denied

Your access to the NCBI website at www.ncbi.nlm.nih.gov has been temporarily blocked due to a possible misuse/abuse situation involving your site. This is not an indication of a security issue such as a virus or attack. It could be something as simple as a run away script or learning how to better use E-utilities, http://www.ncbi.nlm.nih.gov/books/NBK25497/, for more efficient work such that your work does not impact the ability of other researchers to also use our site. To restore access and understand how to better interact with our site to avoid this in the future, please have your system administrator contact [email protected]

Here’s Proof of Evolution You Can Find on Your Own Body

It might sound a little offensive, but your body is a museum, full of ancient relics no one really needs anymore. From your wisdom teeth to that weird way some of us can wiggle our ears, so much of how we ended up as humans reflects what our animal ancestors needed for survival.

As this video by Vox explains, these strange remnants, that stuck around only because they’re not ‘costly’ enough to have disappeared across many millennia, only make sense within the framework of evolution by natural selection.

Here’s one you can see for yourself right now: if you hold your arm out, and touch your thumb to your pinky, you’ll probably see a raised tendon in the middle of your wrist.

Right? If you don’t have that, lucky you – you’re among the 10-15 percent of humans on Earth who were born without this prominent feature in one or both of their arms.

This tendon connects to the palmaris longus, a muscle that most of us have, but there seems to be no real reason for it being there. As the video explains, research has found that the presence of this muscle in our forearms does not give us any more discernible arm or grip strength than people born without the muscle.

In fact, it’s so inconsequential, surgeons often remove it and use it for reconstructive or plastic surgery procedures elsewhere on the body.

So why did we end up with such a useless piece of tissue? Scientists have found that, while palmaris longus is present in many species of mammals today, it’s most developed in those that use their forearms to move around – such as lemurs and monkeys.

Here’s another one: have you figured out how to manipulate the three muscles around the base of your ear so you can wriggle it ever-so-slightly?

Good job – you’re demonstrating how another evolutionary remnant has transitioned from an essential piece of equipment for our animal ancestors to a party trick no one cares about in humans.

Just like many nocturnal animals today – such as rabbits, gazelles, and cats – rely on the wide range of angles their ears can turn and face to better locate the origin of a sound, the creatures we’ve evolved from would have used the same trick millions of years ago.

And we haven’t completely lost all of the ‘equipment’ they would have used.

As Vox points out, not only did humans retain three of the muscles involved in ear movement, studies have shown that these muscles still respond to sound. They don’t respond strongly enough to make our ears move anymore, but they appear to give it their best shot.

From goosebumps and tailbones, to that adorable thing babies do when they grasp whatever you put in front of their tiny fingers, there are plenty of other examples of weird things our bodies have that hint at the abilities of our ancient ancestors.

I’ll let the Vox video above explain those to you, but let’s just say there’s a good reason for why you always get chills when you listen to Adele.

Palmaris longus muscle

Muscle of the upper limb

The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; however, this number can vary in African, Asian, and Native American populations.[1] Absence of the palmaris longus does not have an effect on grip strength.[2] However, the lack of palmaris longus muscle results in decreased pinch strength in fourth and fifth fingers. The absence of palmaris longus muscle is more prevalent in females than males.[3]

The palmaris longus muscle can be seen by touching the pads of the fourth finger and thumb and flexing the wrist. The tendon, if present, will be visible in the midline of the anterior wrist.

Structure [ edit ]

Palmaris longus is a slender, elongated, spindle shaped muscle, lying on the medial side of the flexor carpi radialis. It is widest in the middle, and narrowest at the proximal and distal attachments.[4]

It arises mainly from the medial epicondyle of the humerus via the common flexor tendon. It also takes origin from the adjacent intermuscular septa and from the antebrachial fascia.[4]

It ends in a slender, flattened tendon, which passes over the upper part of the flexor retinaculum and inserts onto the central part of the flexor retinaculum and lower part of the palmar aponeurosis. Frequently, it sends a tendinous slip to the short muscles of the thumb.[4]

Nerve supply [ edit ]

The palmaris longus is innervated by the median nerve.[5]

Variation [ edit ]

Palmaris Longus: misplaced or absent

The fleshy belly occasionally migrates distally and comes to lie close above the wrist, as here.

Palmaris Longus was absent in 98 of 716 dissected limbs (i.e., in 13.7% of 358 paired limbs, 26 times in both limbs, 26 in the right only, and 20 in the left only. (R. K. George).[6] The fleshy belly occasionally migrates distally and comes to lie close above the wrist, as here.Palmaris Longus was absent in 98 of 716 dissected limbs (i.e., in 13.7% of 358 paired limbs, 26 times in both limbs, 26 in the right only, and 20 in the left only.

The palmaris longus muscle is a variable muscle. The most common variation is its absence. Several in vivo and in vitro studies have documented the prevalence or absence of the PL tendon in different ethnic groups. Between 5.5 and 24% of Caucasian populations (European and North American) and 4.6 to 26.6% of Asian populations (Chinese, Japanese, Indian, Turkish, Malaysian) have been reported to lack the PL tendon.[7]

There are also variations related to its form. It may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may be double, or missing entirely. Slips of origin from the coronoid process or from the radius have been seen. Partial or complete insertion into the fascia of the forearm, into the tendon of the flexor carpi ulnaris and pisiform bone, into the scaphoid, and into the muscles of the little finger have been observed.

Clinical significance [ edit ]

Use in tendon grafts [ edit ]

Cross-section through the middle of the forearm

The palmaris longus muscle is the most popular for use in tendon grafts for the wrist due to the length and diameter of the palmaris longus tendon, and the fact that it can be used without producing any functional deformities. When a tendon becomes ruptured in the wrist, the palmaris longus tendon may be removed from the flexor retinaculum and grafted to take the place of the ruptured tendon. The tendons most commonly replaced or supplemented by the palmaris longus tendon when ruptured are the long flexors of the fingers and the flexor pollicis longus tendon.[8]

The palmaris longus muscle itself is a weak flexor, and provides no substantial flexing force that would inhibit movement in the wrist if its tendon were cut and moved elsewhere. The palmaris longus may contribute and assist in thumb abduction movements; an action necessary to open the hand.[9][10] If the palmaris longus muscle is not available for harvesting in an individual, the anatomically homologous plantaris muscle in the leg may be taken instead.[11] Using the patient’s own tendon is advantageous, as it does not introduce foreign material into the body.

Carpal tunnel syndrome and palmaris longus variants [ edit ]

Of the known anatomical variants of the palmaris longus, the reverse belly of the palmaris longus may be localized within the carpal tunnel producing symptoms of carpal tunnel syndrome. Knowledge of this variation is important to prevent unnecessary carpal tunnel release surgery, in which the median nerve compression may remain unresolved due to the presence of this palmaris longus variant.[12]

Other animals [ edit ]

Evolution [ edit ]

The evolutionary interpretation of the muscle’s absence is that humans inherited the muscle through common descent, and numerous animals that humans share a common ancestor with (such as the orangutan) still actively employ the muscle.[13] Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability.[14] The common descent principle suggests that at some stage our ancestors employed the muscle actively. The thumb apparatus (and particularly the thenar muscle group) then started developing in the hominin branch, and consequently the Palmaris longus became vestigial. As there is no apparent evolutionary pressure (positive or negative) concerning the muscle, it has remained largely unaffected by evolutionary processes.[15]

See also [ edit ]

This article uses anatomical terminology

References [ edit ]

This article incorporates text in the public domain from page 446 of the 20th edition of Gray’s Anatomy (1918)

Some bodies contain mysterious variations – here are some examples

Scientists in the UK recently reported that a bone that was thought to be lost to evolution is making a comeback. The little bone, known as the fabella (little bean), is found at the back of the knee – if it is found at all. The scientists discovered that people were nearly three-and-a-half times more likely to have the bone in 2000 than in 1900. Its exact purpose, however, remains a mystery.

The fabella is not the only variation in human anatomy. Variants occur as a result of genetics, environmental factors, mistimings in embryological development, or simply a failure of structures to disappear as part of normal development. Most variations are benign and don’t cause disease. Here are some of those that are well known to us anatomists…

Teeth

People have 20 primary teeth (“milk teeth”), which are lost and replaced by 32 permanent teeth. But up to 2% of people have extra teeth. Most of these people have one or two extra (supernumerary) teeth, but there are medical reports of people with many more extra teeth, with one female having 19 supernumerary teeth.

Nipples

Males and females have nipples because, early on in development, before the sex of the foetus has been determined, two ridges of tissue form, running from the front of the armpits to the groin. These ridges are known as mammary ridges.

Over time, both disappear to leave a single area where the mammary gland and nipple develop. It is possible for people to have supernumerary nipples, known as polythelia, along these lines, not in the middle of the chest between the existing nipples, as depicted in some TV and film shows. There are reports of people with seven nipples.

Digits

Most people have ten fingers and ten toes, but many people are born with extra digits. They are most commonly seen on the hands and are usually associated with disorders, such as Down syndrome.

Some ethnic groups are more likely to have extra digits than others. African-Americans have a much higher presence of an ulnar polydactyly – a digit on the little finger side of the hand. Caucasians have a higher presence of an additional digit on the radial (thumb) side of the hand, known as radial polydactyly. But this is less common.

While most people with extra digits have one or two, there are reports of people with 31 and even 34 digits.

Muscles

Muscles can also vary from one person to another. One of the easiest to observe (or observe its absence) is a muscle called palmaris longus. The best way to see if you have this muscle is to put your thumb and ring finger together and then bend your hand towards you. If you have this muscle, you should see a tendon pop up out of the wrist, running from the forearm and into the hand.

This muscle can be in one or both arms. In some people, it is absent in both. It is absent in both arms in about 10% of Caucasians and absent in one arm in 16%.

There are suggestions of an evolutionary loss of this muscle, with mammals such as orangutans, who use their arms for walking, having this muscle, but higher apes, such as gorillas and chimpanzees, showing an absence.

The good news for those of us who don’t have it is that it doesn’t make our grip strength weaker compared with those who have it. Although those who do have it may find it useful if surgeons ever need to repair a tendon, as the palmaris tendon is easily accessible and can be harvested for grafting.

There is a similar muscle in the lower leg called plantaris. It is believed to be absent in 7-20% of limbs. This muscle cannot be seen without using imaging, such as ultrasound, as it lies deep in the calf region of the leg. But like its variably present compatriot in the arm, it can be used for tendon grafting if needed.

Uterus

Some variations only come to light as people age, such as men born with a uterus. This developmental anomaly may only become manifest during puberty, with blood appearing in the urine. This is actually the menstrual cycle exiting through the urinary system.

All of this goes to show that human anatomy is not as clear-cut as school textbooks might suggest. We’re as variable as snowflakes. Something to be celebrated, surely.

The Variation in the Absence of the Palmaris Longus in a Multiethnic Population of the United States: An Epidemiological Study

Abstract

The absence of the palmaris longus (PL) has been shown to vary based on body side, gender, and ethnicity. In prior studies, homogenous ethnic populations have been shown to have differences in rates of absence. However, no study thus far has analyzed the differences in palmaris longus prevalence in a multiethnic population. We prospectively collected data on 516 patients visiting the outpatient hand clinics at LAC+USC Medical Center and Keck Medical Center. Analysis of the data was then performed for variables including ethnicity, laterality, and gender. There were no differences in the absence of the PL based on laterality or gender. Ethnically, there was no difference between white (non-Hispanic) and white (Hispanic) patients, with prevalence of 14.9% and 13.1%, respectively. However, African American (4.5%) and Asian (2.9%) patients had significantly fewer absences of the PL than the Caucasian, Hispanic reference group ( and , resp.). African Americans and Asians have a decreased prevalence of an absent PL. The Caucasian population has a relatively greater prevalence of an absence of the PL. This epidemiological study demonstrates the anatomic variation in this tendon and may be taken into account when planning an operation using tendon grafts.

1. Introduction

The palmaris longus (PL) muscle is a slender, superficial flexor muscle of the forearm whose presence is anatomically highly variable and in many cases absent, either unilaterally or bilaterally. The presence of the PL can be determined through noninvasive and standard physical examination of the volar wrist [1, 2]. Several exams have been described which test for the PL, the standard being Schaeffer’s test in which the patient joins the thumb to little finger while flexing the wrist [3]. It has been suggested that the palmaris longus contributes to the strength of thumb abduction and may provide an advantage to sports that require hand grip [4, 5]; however, most studies have shown that absence of the PL is not associated with any significant physical or functional deficits, and therefore, the PL is frequently harvested for use in many different hand, reconstructive, and orthopedic surgeries [3, 6–10]. The PL has a characteristically short belly and long tendon, making it an ideal donor for tendon grafts for secondary tendon reconstruction, tendon transfers, and other reconstructive efforts [11].

The absence of the PL has been shown to vary based on body side, gender, and ethnicity in prior studies [1, 12–14]. Interestingly, Erić et al. in 2011 reported on the differential absence of the PL in comparison to hand dominance [1]. They concluded that the PL was more likely to be absent on the nondominant hand [1]. Hereditary variables have been examined in specific racial populations, specifically Nigerian, Caucasian, and Chinese [3, 6, 15–17]. In a Caucasian population, unilateral absence was 16% and bilateral absence was 9%, with males being more affected [2]. In contrast, unilateral and bilateral PL absence is far less common among the Chinese, with 3% and 1%, respectively. All prior anatomical variation studies of the PL have been conducted in separate homogenous populations, such as the Chinese study previously cited. No studies to date have examined the anatomical variation of this tendon in a multiethnic population such as in the United States. Additionally, some studies have shown correlations between PL absence and certain anatomical anomalies, such as an anomalous superficial palmar arch [18].

Taking into account the large variability in the PL absence, 2.8 to 24%, our goal was to examine the prevalence of the PL absence in the multiethnic population of the Los Angeles County + University of Southern California Medical Center (LAC + USC) and the Keck Medical Center of the University of Southern California (USC), reflecting the demographics of Los Angeles [19]. The demographic predictive data could then be used by surgeons worldwide to provide information on possible absence of this valuable tendon preoperatively.

2. Methods

Patients were prospectively followed and evaluated in the hand surgery clinics at the Los Angeles County + University of Southern California Medical Center (LAC + USC) and Keck Medical Center of the University of Southern California (USC). Our objective was to evaluate the extent to which PL is unilaterally and bilaterally absent with regard to age, gender, race, ethnicity, and laterality (right or left). Institutional Review Board (IRB) approval was granted through the University of Southern California (USC) prior to conducting the study. The study size of 500 patients was determined by our statistician to be of sufficient power to prove significance prior to our beginning of the data collection phase of the study. In total, 516 patients were evaluated in this multiethnic population, and statistical data was collected and recorded. Demographic data was provided by an informational sheet, including age, sex, race, and ethnicity. After verifying the self-reported data, the presence or absence of the PL tendon was identified by using the Schaeffer’s test and recorded. This examination was performed first by our trained research staff and confirmed by an attending hand surgeon. An example examination is demonstrated in Figures 1 and 2. Ultrasound was available in cases of morbid obesity or difficult diagnosis but was not used in our series of patients in this study. Patients were placed into specific race and ethnic groups based on the United States Census designations. Analysis of the data was then performed for variables including ethnicity, laterality, and gender. Patients with mixed ethnicity or other than Asian, African American, or White were excluded only from the ethnicity portion of the statistical analysis. Statistical analysis of the data using the chi squared test was then performed using Prism version 5 (GraphPad Software, La Jolla, CA) and verified by our statistician (LS Chan).

3. Results

The study population included 516 patients in total, including 415 Caucasian, 55 African American, and 35 Asian subjects, and 11 patients of other/mixed origin. Their ages ranged from 12 to 94 years of age, with an average of 42.2 years. There were 288 male patients (55.8%) and 228 female patients (44.2%) evaluated in the hand clinics. There were no differences in the absence of the PL based on laterality. The right side was absent in 11.8% and left 12.0% of the time (see Table 1). Further, there were no differences in the absence of the PL based on gender, value 0.369 (see Table 2). Ethnically, there was no difference in the absence of the PL between White (non-Hispanic) and White (Hispanic) patients, with prevalence of 14.9% and 13.1%, respectively. However, African American (4.5%) and Asian (2.9%) patients had significantly fewer absences of the PL than the Hispanic reference group ( and , resp.), please see Table 3 for details.

Hand affected Absent PL Right ( ) 61 (11.8%) 0.924a Left ( ) 62 (12.0%) aChi-squared ( , df = 1).

Gender Bilaterally absent PL Unilaterally absent PL No absence of PL Male ( ) 19 (6.6%) 22 (7.6%) 247 (85.8%) 0.369a Female ( ) 20 (8.8%) 23 (10.1%) 185 (81.1%) Total ( ) 39 (7.6%) 45 (8.7%) 432 (83.7%) aChi-squared ( , df = 2).

PL: palmaris longus.

Ethnicity Absent PL

Odds ratio

95% CI

White Hispanic ( ) 87 (13.1%) 1.00 Reference group — Non-Hispanic ( ) 25 (14.9%) 1.16 0.71–1.87 0.530 African American ( ) 5 (4.5%) 0.31 0.12–0.79 0.005 Asian ( ) 2 (2.9%) 0.19 0.05–0.81 0.008 Total ( ) 119 (11.8%) Chi-squared ( , df = 3, ).

PL: palmaris longus; CI: confidence interval.

4. Discussion

The palmaris longus has a highly variable prevalence in different ethnic populations. This has been demonstrated priorly in published reports from countries such as Northern Ireland, India, China, Malaysia, and Turkey. These countries have a fairly homogenous ethnic population, in contrast to the United States. Our study population reflects the current multiethnic population of the county of Los Angeles, and hence, is a novel study demonstrating the ethnic variability in the presence of the absent PL. Here, we corroborate the previous Asian studies by showing that our Asian population does, in fact, have a much lower prevalence of absent PL (2.9%). Clinically, for the surgeon, it is a valuable fact that one can be fairly certain for a patient of Asian background that the PL will be highly likely to be present. This is information that should be taken into account preoperatively when planning surgical algorithms in treating tendon injuries or palsy. The PL is one such option as a tendon transfer for opponensplasty in restoring intrinsic function in cases of recurrent median nerve injury. If the PL is absent on the affected side, it is important to know preoperatively to plan using another donor muscle such as the extensor indicis proprius. In our study, the African American population had a statistically significantly lower rate of absent PL (4.5%), which is radically different than previously published reports from Nigeria, where the absence rates were much higher (31%). This could be due to the ethnic heterogeneity of the African American population of the United States compared to the Nigerian population. Nevertheless, the PL is present in high likelihood in this particular ethnic group which bodes well for using the PL in a surgical scenario. The PL is used quite frequently in cases of secondary tendon reconstruction, and it is useful for the surgeon to be aware of that issue preoperatively for surgical safety and efficiency in harvesting the tendon graft. The patient needs to be aware of the location of possible surgical incisions for tendon harvesting. Further, the surgeon should examine all possible tendon donors preoperatively, and one’s suspicion might be heightened by knowing the patient’s ethnicity. This is particularly important for the White population which in our study had the highest rates of absence, in both the Hispanic and non-Hispanic subsets. The surgeon must be aware in these patients that it is more likely that the PL might be absent. Thus, in Caucasian patients, it is particularly important to have a thorough examination of possible tendon donor sites. However, we did not come to the same conclusion in our study, as the right and left sides were absent in 11.8% and 12.0% of patients, respectively.Our study was limited by the ethnic demographics of the patients visiting the affiliated hand clinics of USC, and the population samples were not evenly distributed between the four groups. The distribution of patients included a majority of Hispanics and a relative scarcity of Asians and African Americans, which could be a source of sampling error due to the low sample size. Nevertheless, statistical significance was confirmed and the data set stayed within the predetermined power guideline. Thus, this epidemiological study demonstrates the ethnically based anatomic variation in this tendon, which has practical clinical application.

Palmaris Longus

Palmaris Longus muscle in the Flexor compartment of the forearm

The Palmaris longus (PL) muscle is a long, slender muscle which is usually present in the superficial volar compartment of the forearm, interposed between the Flexor Carpi Ulnaris and the Flexor Carpi Radialis muscles.

However, it has been accepted as a vestigial muscle since studies have shown that almost 30% of the population could be lacking this muscle either in one forearm (unilateral) or both the forearms (bilateral) but the percentage can always vary. The peculiarity associated with this muscle is not merely its presence or absence, but it’s a high degree of anatomical variations even when present. The absence of the palmaris longus does not have an effect on grip strength.[1]

Apart from its anatomical anomalies, there are other categories of variations of the Palmaris Longus muscle in terms of its prevalence amongst different ethnicities and it’s absence being more common in women than men. Also, the prevalence of the muscle is higher bilaterally but if present unilaterally, it is usually in the left upper limb [2].It is classified as a phylogenetically retrogressive muscle i.e. muscles having a short belly with a long tendon.[3]

Medial epicondyle of the Humerus via the common flexor tendon[4]

Palmar Aponeurosis and Flexor Retinaculum at the wrist joint[4]

Nerve supply [ edit | edit source ]

It is innervated through the Median Nerve with root value C8 via the medial as well as lateral cords of the brachial plexus[4]

Arterial supply [ edit | edit source ]

Ulnar Artery[5]

Palmaris longus synergistically works with the long flexors of the forearm to bring about flexion at the wrist joint and small joints of the hand.

Apart from this, the muscle also helps in tightening and tensing up the palmar aponeurosis.

Its main function appears to be as an anchor for the skin and fascia of the hand in resisting horizontal shearing forces in distal direction.

Clinical tests to determine the presence of the muscle [ edit | edit source ]

Over the years, several clinical tests have been developed by practitioners from around the world to accurately detect the Palmaris Longus muscle. These tests merely rely upon certain positions of the wrist and hand in order to put the muscle in a state of tension so that it’s tendon is both visible and palpable. The validity and reliability of the tests, however, show variations amongst each other[6].

1. Standard Test – Schaeffer’s Test [ edit | edit source ]

The first test developed in 1909

Involves maintaining the forearm at 90 degrees first followed by moving the thumb in opposition towards the little finger with the wrist partially flexed.[6] [7]

Maneuver involves first making a fist with the testing hand, followed by wrist flexion against the resistance with the thumb flexed over the other digits.[6] [8]

Involves passive hyperextension of the Metacarpophalangeal Joints along with mild active wrist flexion.[6]

The initial testing position is the thumb in abduction. The subject is then asked to resist both thumb abduction and wrist flexion.[6]

5. “Two Finger Sign” – Pushpakumar’s Test [ edit | edit source ]

The subjects are made to completely extend the 2nd and 3rd digits, flex the 4th and 5th digits with the first digit fully opposed and flexed.[6]

Combines forced anteduction and pronation of the thumb at the first MCP with full extension of the second to fifth digits.[6]

Clinical Significance [ edit | edit source ]

Compression neuropathies at the wrist are commonly encountered conditions in the clinical practice which involve either the Median nerve or the Ulnar nerve. In case of median nerve neuropathies, most of the documented cases have no external cause to be attributed but there have been cases where the etiological factor has been the presence of hypertrophied/anomalous muscles. There are three muscles which have been documented: the Palmaris Longus, the first (or second) Lumbrical and the Superficial Flexor of the 1st digit. In case of ulnar nerve neuropathies, idiopathic ulnar tunnel syndrome is rare and extrinsic causes have been identified. Anomalous muscles include Palmaris Longus, Abductor Digits Minimi and Flexor Carpi Ulnaris. In both Median and Ulnar nerve neuropathies, Palmaris longus is seen to be a common contributor to the pathological process[9].

The Palmaris Longus tendon is of great importance for surgeons in particular, as it is widely utilized as a tendon graft for upper limb tendon repair and tendon transfer surgeries. Since this muscle is an accessory muscle and no functional loss in grip and pinch strength have been noted in its absence, this makes it ideal for use in surgical procedures[10].

Palmaris longus tendon has been used for correction of claw-finger deformities because it is long enough (12-15cms.) & its tendon fibres are parallel & loosely held, Palmaris longus tendon was constantly used for correction of hand deformities in leprosy Palmaris longus tendon has been used in opponensplasty and radial palsy, the Palmaris longus muscle has been found to be of adequate strength to substitute for paralyzed lumbricals.

The attributes that make the Palmaris longus suitable for the above said procedures are:

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