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| Biceps brachii | |
|---|---|
| Name | Biceps brachii |
| Latin | musculus biceps brachii |
| Caption | Anterior view of the arm showing the biceps brachii |
| Origin | Scapula (short head: coracoid process; long head: supraglenoid tubercle) |
| Insertion | Radial tuberosity and bicipital aponeurosis |
| Action | Elbow flexion, forearm supination, shoulder flexion (minor) |
| Blood supply | Brachial artery |
| Nerve | Musculocutaneous nerve |
Biceps brachii is a two-headed superficial muscle of the anterior compartment of the upper arm, important for forearm supination and elbow flexion. The muscle spans the Glenohumeral joint, crosses the Elbow joint, and contributes to movements involving the Scapula, radius, and Ulna. Clinically and anatomically, the biceps brachii is discussed alongside structures such as the Brachialis muscle, Brachioradialis, and neurovascular elements like the Median nerve, Radial nerve, and Musculocutaneous nerve.
The biceps brachii has two proximal heads: the long head originates from the supraglenoid tubercle of the Scapula and traverses the Glenohumeral joint through the Intertubercular groove, while the short head arises from the coracoid process of the Scapula, which it shares with the Coracobrachialis muscle. Distally, fibers converge into a common tendon inserting on the radial tuberosity of the radius and into the bicipital aponeurosis that fans medially toward the Ulna. Innervation is typically from the Musculocutaneous nerve, with vascular supply from branches of the Brachial artery and perforating branches from the Profunda brachii artery. The musculotendinous junction and the long head tendon are anatomically adjacent to the Glenohumeral ligaments and the synovial lining of the shoulder joint, and relate anteriorly to the Biceps aponeurosis and the Cubital fossa.
The biceps brachii acts primarily as a powerful supinator of the forearm and a flexor at the elbow, with secondary roles in shoulder flexion and stabilization of the Glenohumeral joint. During resisted supination, the muscle exerts torque on the radius via the distal tendon; during elbow flexion it acts with the Brachialis muscle and the Brachioradialis. Biomechanical studies performed at institutions such as Johns Hopkins University, Massachusetts Institute of Technology, and University of Oxford have characterized its moment arms, fiber-type composition, and recruitment patterns during activities like rowing, throwing, and weightlifting.
Injury patterns include proximal long head tendinopathy, distal biceps tendon rupture, and musculocutaneous nerve entrapment; these are managed by clinicians at centers like Mayo Clinic, Cleveland Clinic, and Charité – Universitätsmedizin Berlin. Distal ruptures typically present with a sudden pop, ecchymosis, and the Popeye deformity, often treated surgically with reattachment techniques developed and refined in studies from Harvard Medical School and Stanford University School of Medicine. Proximal long head pathology often coexists with rotator cuff disease and is evaluated in settings referencing protocols from American Academy of Orthopaedic Surgeons and National Institute for Health and Care Excellence. Electromyography protocols used by laboratories at University of California, San Francisco and Karolinska Institutet help localize denervation or neuropathy.
Anatomic variations include accessory heads, absence of the short head, bifurcated distal insertions, and anomalous connections with the Coracobrachialis muscle or with fascial structures of the Forearm. These variants have been documented in cadaveric surveys from University of São Paulo, University of Tokyo, and University College London and can alter surgical approaches advocated by institutions like Guy's and St Thomas' NHS Foundation Trust. Variant innervation patterns—such as contributions from the Radial nerve or communicating branches with the Median nerve—are described in comparative anatomy texts and affect decisions in regional anesthesia practiced at centers including Massachusetts General Hospital.
Embryologically, the biceps brachii arises from mesenchymal condensations of the paraxial mesoderm in the lateral plate region that form the upper limb bud, under patterning control of signaling centers and transcription factors studied at National Institutes of Health, European Molecular Biology Laboratory, and Salk Institute for Biological Studies. Genes and pathways implicated include members of the HOX gene family, TBX5, and FGF signaling, with morphogen gradients directing segmentation and muscle splitting events that produce two distinct heads. Developmental anomalies, influenced by perturbations documented in model organisms at The Jackson Laboratory and Max Planck Institute for Molecular Genetics, can yield the anatomical variations observed in adults.
Evaluation employs ultrasound, MRI, and CT protocols established in musculoskeletal radiology departments at Radiology Department, Johns Hopkins Hospital, Mayo Clinic, and Memorial Sloan Kettering Cancer Center. Ultrasound provides dynamic assessment of distal tendon integrity and guides percutaneous repair techniques proven in trials reported from Cleveland Clinic and Vanderbilt University Medical Center, while MRI sequences characterize tendon tears, tendinopathy, and associated labral or rotator cuff lesions as described in literature from University of Toronto and University of Sydney. CT arthrography and conventional radiography assist when bony avulsion or calcific tendinopathy is suspected, with imaging interpretation standards propagated by bodies such as the Radiological Society of North America and European Society of Musculoskeletal Radiology.
Category:Upper limb muscles