The palmaris longus is a small muscle located in the wrist, although it is not found in around 14 percent of humans as there is some muscle variation with regards to ethnicity. Even though the muscle is associated with flexing the wrist there aren’t thought to be any negative side effects to not having a palmaris longus. The muscle is located between the flexor carpi ulnaris and flexor carpi radialis. As well as flexing the wrist, the muscle is also helps to tense certain muscles.
The origin of the palmaris longus is on the humerus. It originates from the common flexor tendon. The insertion of the muscle is at the palmar aponeurosis and finishes with a thin and flat tendon. Innervation of the muscle is via the median nerve.
Aside from the fact that the muscle is not present in some humans there is also some variation in how the muscle is presented. For example, some people may have a muscle that is tendon-like above and more muscular below. Some people may have a variation where the muscle is in the center while the tendon is found above and below. It is thought that none of the variations have any effect on grip strength.
One of the benefits of the palmaris longus being relatively unimportant is that it can be used for tendon grafts. A common wrist injury involves one of the tendons becoming ruptured. When this happens, the palmaris longus can sometimes be used to graft the tendon back together. The palmaris longus is also commonly used for this purpose due to its shape and size.
If the muscle and tendon are not present in a person who requires a tendon graft in the wrist then the tissue has to be taken from elsewhere in the body. If this is not possible then a tendon from a separate body must be used although this can cause problems due to a foreign substance being introduced into the body.
For example, in some animals the tendon is used to expose claws. It’s usually straightforward to discover whether a particular person has a palmaris longus muscle by flexing the wrist while pressing down on the base of the outer two fingers. If the muscle and tendon is present then it will be immediately visible through the skin. Although the muscle is not essential for humans, it is much more important for other animals.
