The abductor pollicis longus (APL) is a muscle located in the deep compartment of the posterior forearm. Its tendon passes through the 1st extensor compartment at the wrist, where it contributes to the radial border of the anatomical snuffbox.
Attachment points include the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. The APL also attaches to the lateral aspect of the base of the first metacarpal.
Functionally, the APL is responsible for the abduction of the thumb, and is innervated by the radial nerve (posterior interosseous branch). Blood supply comes from the ulnar artery.
Figure 1 below shows the muscles in the deep layer of the posterior forearm.
The APL, FPL, EPL, and EPB all belong to the abductor pollicis group of muscles, which are responsible for moving and stabilizing the thumb. The pronator quadratus (PQu) is the muscle responsible for pronating the forearm, while the extensor indicis proprius (EIP) is responsible for extending the index finger.
The abduction of the thumb plays an important role in activities of daily living. It enables us to perform precise movements of the thumb, such as grasping and manipulating objects. The APL also works in synergy with other muscles in the forearm to stabilize the wrist and forearm during movements of the thumb.
The APL is also important for maintaining proper anatomical alignment of the thumb. Its contraction helps to maintain the thumb in the resting position, and also helps to center it between the index finger and the middle finger. This alignment helps to ensure that the muscles of the thumb, including the APL, work in harmony and without any undue strain.
So, the abductor pollicis longus is an important muscle in the posterior forearm, providing function and stability during daily activities, as well as contributing to the anatomical alignment of the thumb. Abduction of the thumb is necessary for grasping and manipulating objects, and proper alignment of the thumb is important for efficient and comfortable movement.
