APB is the most superficial thenar muscle and the primary palmar thumb abductor. Its unique insertion onto the extensor expansion assists IP extension during opposition.
| Origin | Flexor retinaculum, scaphoid tubercle, and trapezium |
|---|---|
| Insertion | Radial base of thumb proximal phalanx and lateral extensor expansion |
| Nerve Supply | Recurrent (thenar) branch of median nerve (C8, T1) |
| Blood Supply | Superficial palmar branch of radial artery |
| Actions | Abducts the thumb in the palmar plane (perpendicular to palm); Contributes to thumb opposition via extensor expansion insertion |
|---|
APB denervation is pathognomonic for median nerve compression at the carpal tunnel. The CMAP amplitude from APB is the electrodiagnostic gold standard for CTS severity. Weakness produces inability to hold the thumb perpendicular to the palm against resistance.
Palpable as the superficial radial thenar bulk beneath the thumb MCP joint during palmar abduction.
Reduced APB CMAP amplitude indicating axonal loss, requiring urgent surgical decompression.
This website uses cookies to enhance your experience. Some are essential for site functionality, while others help us analyze and improve your usage experience. Please review your options and make your choice.
If you are under 16 years old, please ensure that you have received consent from your parent or guardian for any non-essential cookies.
Your privacy is important to us. You can adjust your cookie settings at any time. For more information about how we use data, please read our privacy policy. You may change your preferences at any time by clicking on the settings button below.
Note that if you choose to disable some types of cookies, it may impact your experience of the site and the services we are able to offer.
Some required resources have been blocked, which can affect third-party services and may cause the site to not function properly.
This website uses cookies to enhance your browsing experience and ensure the site functions properly. By continuing to use this site, you acknowledge and accept our use of cookies.
