The palmaris longus is a small muscle located in the wrist, although it is not found in about 14% of humans as there is some muscle variation with respect to ethnicity. Although the muscle is associated with wrist flexion, it is not believed that there are any negative side effects to not having a palmaris longus. The muscle is located between the ulnar flexor of the carpus and the radial flexor of the carpus. In addition to flexing the wrist, the muscle also helps contract certain muscles.
The origin of the palmaris longus is on the humerus. It comes from the common flexor tendon. The insertion of the muscle occurs at the palmar aponeurosis and ends in a thin, flat tendon. Innervation of the muscle is through 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 tendon-like muscle on top and more muscle on the bottom. Some people may have a variation where the muscle is in the middle while the tendon is on top and below. None of the variations are thought to have any effect on grip strength.
One of the advantages of palmaris longus is relatively minor is that it can be used for tendon grafts. A common wrist injury involves the rupture of one of the tendons. When this happens, the palmaris longus can sometimes be used to re-graft the tendon. The palmaris longus is also commonly used for this purpose because of its shape and size.
If muscle and tendon are not present in a person who requires a tendon graft in the wrist, tissue must be harvested from other parts of the body. If this is not possible, a tendon from a separate body should be used, although this may cause problems because of the introduction of a foreign substance into the body.
For example, in some animals the tendon is used to expose the claws. It is usually easy to find out if a particular person has a palmaris longus muscle by flexing the wrist while pressing down on the base of the two outer fingers. If the muscle and tendon is present, it will be immediately visible through the skin. Although the muscle is not essential for humans, it is much more important for other animals.
- ALSHAHAM, A., MULAR, P., JAWAD, K.. Anomalous V-shape Palmaris Longus Tendon: Two Cases. Journal of Medical Cases, North America, 1, Oct. 2010. Available at: <https://www.journalmc.org/index.php/JMC/article/view/67/50>. Date accessed: 22 Feb. 2022.