Long head of biceps brachii

Origin

• The long head of biceps brachii originates from the supraglenoid tubercle of the scapula and, in many cases, from the superior glenoid labrum.

Tendon structure and pathway

• The tendon of the long head of biceps brachii passes intra-articularly through the glenohumeral joint cavity. It is surrounded by a synovial sheath, which is an extension of the synovial membrane of the glenohumeral joint. This sheath provides lubrication and reduces friction, preventing the tendon from adhering to the fibrous joint capsule or underlying bones during its intra-articular course..

• As the tendon arches over the shoulder joint, it contributes to joint stability, specifically by preventing superior dislocation of the humeral head.

• After exiting the joint capsule, the tendon descends through the intertubercular groove (bicipital groove) of the humerus. It remains partially ensheathed by the synovial membrane and is secured in the groove by the transverse humeral ligament and a fibrous extension from the pectoralis major tendon.

Insertion

The muscle belly of the long head lies lateral to the short head in the upper arm. It is more slender and has a longer proximal tendon compared to the short head. Distally, it merges with the short head to form a common tendon that inserts on the radial tuberosity.

Function

• Stabilizes the humeral head within the glenoid cavity.

• Assists in elbow flexion and forearm pronation, particularly effective when the forearm is already supinated.

• Acts as a weak flexor of the shoulder joint.

Innervation and blood supply

• Innervation is by the musculocutaneous nerve, and blood supply comes from the branches of the brachial artery.