The puzzling Palmaris Longus

October 24, 2009 12:10 PM

The Palmaris Longus is a notorious muscle of the hand since some people don't have it at all. Wait, what!?

Yes, according to the Wikipedia, it is absent in about 14% of the population.

My anatomy book says this muscle does the flexion of the hand. My question is, are those 14% incapable of moving the hand that way? Do they miss something? Are they disabled in some way?

posted by jgwong to health & fitness (28 answers total)

This is really fascinating and I'd never heard of it before! New party trick? According to studies I Googled, some people are also only missing it in one of their hands! If you pinch your thumb and little finger together you can see the tendon pretty clearly.

In answer to your question, apparently it is also a useful muscle to harvest for reconstructive surgery, because (drumroll):

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.

(cite)
posted by rafter at 12:47 PM on October 24, 2009 [2 favorites]

Wikipedia says that "[t]he palmaris longus tendon is responsible for exposing the claws in lower vertebrates." Presumably, if people had claws, anyone without this muscle would be out of luck.
posted by booksandlibretti at 12:49 PM on October 24, 2009

I got nothing, either hand. The person standing next to me clearly has it in the right, but not left hand.
posted by R. Mutt at 12:52 PM on October 24, 2009

I seem not to have it either. This isn't the only weird thing about my hands, though.
posted by ocherdraco at 1:05 PM on October 24, 2009

From the article listed as a source in the wikipedia article:

"In vertebrates it is found only in mammals and is best developed those where the forelimb is used in ambulation. For example, the palmaris longus is always found in the orangutan but is variably absent in higher apes such as chimpanzees and gorillas. In humans the absence of the palmaris longus appears to hereditary[...]"

I just did the test, and I'm missing it on the right side, and I've got no dexterity problems (I'm right-handed, too). Luckily I don't use my arms to walk about, so I don't miss it. Unluckily, apparently I'm missing a tendon that would be really useful to harvest should I need it for reconstructive surgery (per the article, it's the first choice donor tendon for the hand due to its vestigiality).
posted by neda at 1:06 PM on October 24, 2009

I have it in my right hand, but not my left! I've never noticed any difference in the dexterity between them (I played piano and several other instruments, and didn't have trouble) - though I am right handed.
posted by Solon and Thanks at 1:09 PM on October 24, 2009

i have it in both hands. i feel like this is some sort of accomplishment.
posted by janepanic at 1:45 PM on October 24, 2009 [2 favorites]

apparently, right: yes, left: no. Mebbe I should start learning guitar Hendrix-style???
posted by mokuba at 1:52 PM on October 24, 2009

I have it in both hands too, but have never really noticed it before.
posted by sperose at 2:01 PM on October 24, 2009

rafter: I didn't know the pinching test, I have it on both hands, hah!

In conclusion, and as some of you personally attest, there is no disabling at all... or perhaps in a totally insignificant way. Solon playing the piano makes a strong case.

Thanks everyone for your answers!
posted by jgwong at 2:13 PM on October 24, 2009

Excerpt from Frank Zappa's autobiography:

When he was a young boy, his mother (who worked for the Probation Department) presented him with a copy of Gray's Anatomy. He read it dutifully and noted that in some of the illustrations of muscles it said, "such and such a muscle, when present --," and so it was that Jerry set out to develop the "when present" muscles of the human body. He invented 'exercise devices' for those 'special areas' that had not been inhabited by muscle tissue since the book was written.
posted by zippy at 2:16 PM on October 24, 2009 [1 favorite]

The wiki mentions that this muscle can be doubled. Indeed, I have two in my hand and one in my left.
posted by skintension at 2:19 PM on October 24, 2009

Two in my right hand, I meant to say.
posted by skintension at 2:21 PM on October 24, 2009

I have two in both hands, if it's what I think it is.
posted by you're a kitty! at 3:03 PM on October 24, 2009

This is such a cool question, which proves the adage that we learn something new everyday!

My husband and I both have it on both sides. His is much more prominent on the left, but we're both right-handed.

The palmaris longus tendon is responsible for exposing the claws in lower vertebrates. -- Does this mean we humans used to have retractable claws at some point in our evolutionary past?
posted by amyms at 3:48 PM on October 24, 2009

(WARNING: GORY PICTURES.) I had it in both hands, until this May, when I broke a vase at a wedding and accidentally severed both the palmaris longus and the flexor carpi radialis, which is the muscle that flexes the hand at the wrist (and the answer to your question). So I had an operation to have them reattached.
posted by nicwolff at 3:49 PM on October 24, 2009 [9 favorites]

Yeah, it's a weird one, the palmaris longus. Some people have it one wrist, but not the other. Mine have tendons that seem to run diagonally, which lets me do this nifty little party trick.
posted by greatgefilte at 4:02 PM on October 24, 2009 [1 favorite]

nicwolff: Oh wow, that's more than I ever wanted to know, haha.
posted by jgwong at 4:46 PM on October 24, 2009

Dang, I have it with my left but not my right hand. Interesting!
posted by St. Alia of the Bunnies at 5:19 PM on October 24, 2009

I love this AskMe! I have two on each hand, husband has one on each hand. If my daughter was home, I'd be asking her to check, too.
posted by Ruki at 5:52 PM on October 24, 2009

I don't have it in either hand. My son has it in both. I blame his father.
posted by onhazier at 6:03 PM on October 24, 2009

I have it doubled in both hands. This is classic I'm not a freak material so I've added it to the wiki.
posted by Mitheral at 6:50 PM on October 24, 2009

Oh wow, that's more than I ever wanted to know, haha.

Well there's more: I severed my radial artery too! Which is another amazing anatomical redundancy: we have two arteries serving the hand, the radial and the ulnar, which form a loop in the palm so that either can feed the whole hand. So, since my radial artery had stopped bleeding and retracted up my arm, they just tied it off and now I'm an ulnar-only guy on that side.

Yes, I bled like a fountain.
posted by nicwolff at 7:09 PM on October 24, 2009

Mitheral: That wiki page is cool!

nicwolff: Oh man, if I were you I would have passed out, haha.
posted by jgwong at 8:23 PM on October 24, 2009

I have it only on my right, not my left. I'm left handed but a quick google isn't bringing up any particularities of hand-dominance and presence/absense.

It is remarkable that the presence does seem to somewhat correlate to carpal tunnel - which I've only ever had in my right hand, and have blamed on poor mousing technique.
posted by Weighted Companion Cube at 11:26 PM on October 24, 2009

I seem to have two on each side, unless I'm doing it wrong. Mine get significantly more pronounced when I pinch thumb and -middle- finger, and splay the pinky way out to the side, though. Maybe I am doing it wrong.

I'm not sure if or how this would correlate with the fact that I spent much of my childhood galloping about on all fours (hands and feet, not hands and knees, mind you) and jumping over the couch.

Yes, I was as horse-crazy as they come.
posted by po at 1:45 AM on October 25, 2009

The palmaris longus tendon is the surgeon's favorite as a donor as it's easy to get to and doesn't really do anything functional. So if you have it, it makes a nice backup in case anything ever goes wrong with one of your more useful parts.
posted by monocyte at 2:09 PM on October 25, 2009

NOT EVERYONE HAS ONE? I am so freaked out to learn that. I have one in each arm. I will be looking at everyone's wrists as soon as I get to school tomorrow.
posted by motsque at 5:53 PM on October 25, 2009