Question 1

Why are some people missing the palmaris longus muscle?

Accepted Answer

The palmaris longus is a vestigial muscle inherited from tree-climbing primate ancestors who used it to grip branches. Since humans no longer need it, it is drifting out of our anatomy, and roughly one in seven people are simply born without it, with no loss of hand function.

Question 2

How do I check if I have a palmaris longus muscle?

Accepted Answer

Press your thumb to your little finger and bend your wrist gently toward you, then look at the middle of your inner forearm. If a thin cord rises under the skin, you have the muscle. If nothing appears, you were born without it. This is called Schaeffer's test.

Question 3

What is the palmaris longus tendon used for in surgery?

Accepted Answer

Because losing the palmaris longus causes no functional loss, surgeons harvest its long tendon to repair torn tendons and ligaments elsewhere, including the thumb, hand, elbow, and eyelid. It is famously used in Tommy John elbow reconstruction surgery for baseball pitchers.

surgery

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