A tendon is a strong, flexible band of connective tissue that links a muscle to a bone to transmit force. The elbow joint is a complex hinge connecting the humerus (upper arm bone) with the radius and ulna (forearm bones). This arrangement allows for bending, straightening, and rotating the forearm. The movement and stability of this joint rely on specialized tendons that originate and insert near the elbow.
Tendons for Bending the Arm
Bending the arm, or flexion, is driven by muscles on the anterior (front) side of the upper arm. The Biceps Brachii muscle is the most recognizable, ending in a prominent tendon that crosses the elbow joint to attach to the radius bone in the forearm. Contraction of this muscle pulls the radius toward the humerus, effectively bending the arm. The Biceps tendon also has a dual function: its attachment point allows it to assist with supination, the rotating motion that turns the palm upward.
The Brachialis is the other major flexor, lying deeper beneath the biceps muscle. The Brachialis tendon inserts onto the ulna, making it a pure and powerful flexor of the elbow. Unlike the biceps, the Brachialis is considered the workhorse for flexion because its action is unaffected by the rotation of the forearm. This muscle provides the majority of the force whenever the arm is bent.
Tendons for Straightening the Arm
The opposite motion, straightening the arm or extension, is controlled by a large muscle group located on the posterior (back) side of the upper arm. The Triceps Brachii muscle is the sole major extensor of the elbow joint. This muscle is composed of three separate heads that merge to form a single, thick Triceps tendon. This collective tendon crosses the back of the elbow to firmly anchor onto the olecranon process, the bony tip of the ulna.
When the Triceps Brachii muscle contracts, the force transmitted through this tendon pulls the ulna back, extending the forearm. The Triceps tendon is significantly wider than many other tendons in the upper limb due to the high forces required for pushing and straightening movements. This robust anchor point is engineered to withstand the load generated when extending the arm against resistance.
Tendons Controlling Forearm and Wrist Motion
A large collection of tendons crosses the elbow joint, originating from the upper arm but primarily governing the movements of the wrist and fingers. These tendons are grouped based on their attachment sites at the two bony bumps above the elbow, known as the epicondyles. This arrangement creates two distinct groups: the common flexor tendon group and the common extensor tendon group.
The common flexor tendon attaches to the medial epicondyle (the inside bump) and originates from muscles responsible for bending the wrist and fingers. While their main function is in the forearm, their origin at the elbow provides a secondary role as a dynamic stabilizer of the joint. On the opposite side, the common extensor tendon attaches to the lateral epicondyle (the outside bump) and is the origin for muscles that straighten the wrist and fingers. The common extensors are also important dynamic stabilizers, particularly against forces that try to push the elbow outward.
Overuse or repetitive strain on these common tendons is a frequent source of pain. This strain results in conditions commonly known as “golfer’s elbow” for the flexor group and “tennis elbow” for the extensor group.