The anconeus muscle is a small, yet significant, muscle in the arm. While often overshadowed by larger muscles, it plays a role in the intricate mechanics of the elbow joint. Understanding this muscle provides insight into the subtle contributions that smaller anatomical structures make to overall limb function.
Where It’s Located and Its Appearance
The anconeus muscle is found on the posterior, or back, aspect of the elbow joint. It has a small, triangular shape. This muscle forms a connection between the humerus, which is the upper arm bone, and the ulna, one of the two bones in the forearm. Specifically, it originates from the lateral epicondyle of the humerus and extends to insert onto the olecranon process and the superior part of the posterior surface of the ulna. Its position is close to the larger triceps brachii muscle, and some anatomical descriptions even consider it a continuation of the triceps, with their fibers occasionally blending together. Due to its superficial placement, the anconeus muscle can often be felt on the lateral side of the forearm near the elbow.
Its Main Action in Arm Movement
The primary role of the anconeus muscle is elbow extension, which is the straightening of the arm. It assists the triceps brachii muscle. Although it is considered a relatively weak elbow extensor compared to the triceps, it still contributes to the overall movement. The triceps brachii is the main muscle responsible for extending the elbow. It is particularly involved in fine, controlled arm movements and in maintaining full elbow extension. Research suggests that it plays a part when lower torque values are required for extension, and its activity contributes approximately 15% of the elbow extension moment during isometric contractions.
How It Supports the Elbow Joint
Beyond its role in extension, the anconeus muscle provides support to the elbow joint. It stabilizes the elbow during various arm movements, including the rotation of the forearm (pronation and supination). During pronation, the anconeus helps to abduct, or move away, the ulna, which is essential for stabilizing the bone and facilitating the forearm’s rotational motion. Another function of the anconeus is to prevent soft tissue impingement within the joint. As the elbow extends, the muscle pulls the joint capsule, a fibrous sac enclosing the joint, out of the way. This action helps to prevent the capsule from being pinched in the olecranon fossa, a depression on the humerus, during the straightening movement. The anconeus is also recognized as an active dynamic stabilizer of the humeroulnar joint, contributing to posterolateral elbow stability.