What are the attachments of the biceps muscle?

Biceps Muscle Attachments

The biceps brachii muscle has two distinct heads with specific attachments: the long head originates from the supraglenoid tubercle and superior labrum of the glenoid, while the short head attaches directly to the coracoid process with muscle fibers rather than a true tendon; both heads converge to insert distally onto the radial tuberosity with an additional aponeurotic extension called the lacertus fibrosus.

Proximal Attachments

• The long head of the biceps (LHB) has both intracapsular and extracapsular portions, originating from the supraglenoid tubercle and partly from the glenoid labrum 1
• The labral attachment of the LHB varies, with most cases (64.5%) inserting mainly on the posterosuperior part of the labrum, while some (19.4%) insert on both posterosuperior and posteroanterior labrum 2
• In a small percentage of cases (6.4%), the LHB inserts exclusively on the supraglenoid tubercle 2
• The short head of biceps does not attach via a true tendon as previously thought, but rather consists of muscle fibers attaching directly to the tip of the coracoid process with only a thin tendinous aponeurosis covering its anterior surface 3
• The short head typically has a common origin with the coracobrachialis muscle from the coracoid process 1

Distal Attachment

• The distal biceps tendon is bifurcated and generally inserts on the radial tuberosity, around which it rolls during pronation and supination movements 4
• An additional distal structure called the lacertus fibrosus (bicipital aponeurosis) branches off from the medial aspect of the tendon, crosses the median artery and median nerve, and inserts on the superficial aponeurosis of the flexor muscles 4

Anatomical Variations

• In rare cases, anatomical variations may occur, such as a split coracoid process or additional heads of the coracobrachialis muscle that may affect the origin of the short head of biceps 5
• Some variations include the LHB inserting on the intertubercular groove (3 cases in one study) 2
• The proximal portion of the LHB can have different shapes: flattened (84% of cases) or hemicylindrical (16% of cases) 2

Clinical Significance

• MRI is the most accurate imaging modality for diagnosing biceps tendon pathology, with an accuracy of 86.4% compared to ultrasound (45.5%) 6, 7
• The FABS (flexion-abduction-supination) view is recommended for optimal visualization of the biceps tendon on MRI 6, 7
• Lesions of the LHB pulley system are commonly associated with rotator cuff pathology, including supraspinatus and subscapularis tendon injuries 1
• Understanding the true nature of the short head attachment (muscle fibers rather than tendon) has important implications for surgical procedures that utilize this structure 3

Diagnostic Approach for Biceps Pathology

• Plain radiographs should be the first imaging study to rule out associated fractures or bony abnormalities 6, 7
• MRI without contrast is preferred for biceps tendon evaluation due to its superior accuracy compared to ultrasound 6, 7
• Ultrasound examination of the biceps should focus on nine zones of interest: glenoid insertion, extension to humeral head, rotator interval, reflection to upper bicipital groove, bicipital groove, upper and lower myotendinous junctions, distal tendon(s), and inferior enthesis 4