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Biceps brachii tendon (distal)

The distal tendon of the biceps brachii is the strong fibrous continuation of the biceps muscle, attaching the muscle to the radial tuberosity on the proximal radius. It is a critical structure for forearm supination and elbow flexion, transmitting force generated by the muscle belly.

The tendon forms from the convergence of the long and short heads of the biceps muscle in the lower arm and descends through the cubital fossa, anterior to the brachialis. Before its insertion, it is accompanied medially by a broad fibrous expansion known as the bicipital aponeurosis (lacertus fibrosus), which blends with the fascia of the forearm flexors and provides additional stabilization.

Because of its twisting insertion and tension during supination, the distal tendon is susceptible to partial or complete ruptures, particularly in middle-aged men during sudden eccentric loading.

Synonyms

  • Biceps tendon (distal)

  • Bicipital tendon

  • Tendon of insertion of the biceps brachii

Origin, Course, and Insertion

  • Origin: Formed by the union of the long and short heads of the biceps brachii approximately 5–7 cm above the elbow joint.

  • Course: Descends through the anterior compartment of the arm, lying anterior to the brachialis muscle; passes anterior to the elbow joint, then turns laterally and posteriorly to reach the radial tuberosity. The tendon twists upon itself so that the long head fibers lie posterior to the short head fibers at the insertion.

  • Insertion: Posterior rough portion of the radial tuberosity and to the deep fascia of the forearm via the bicipital aponeurosis.

Tendon Attachments

  • Primary attachment: Posterior part of the radial tuberosity (bony insertion).

  • Secondary attachment: Bicipital aponeurosis extends medially into forearm fascia, reducing strain on the tendon and protecting underlying neurovascular structures.

  • Fibrous sheath: Surrounded by a thin paratenon and bursal tissue to reduce friction during forearm rotation.

Relations

  • Anteriorly: Skin, superficial fascia, median cubital vein, and bicipital aponeurosis.

  • Posteriorly: Brachialis muscle and elbow joint capsule.

  • Medially: Median nerve and brachial artery (protected by aponeurosis).

  • Laterally: Brachioradialis and supinator muscles.

Arterial Supply

  • Supplied mainly by branches of the brachial artery and radial recurrent artery.

Function

  • Elbow flexion: Powerful flexor of the elbow joint.

  • Forearm supination: The most effective supinator when the elbow is flexed.

  • Force transmission: Transfers contractile force from the biceps muscle to the radius for forearm movement.

  • Stabilization: Assists in maintaining elbow joint stability during active motion.

Clinical Significance

  • Distal biceps tendon rupture: Common in middle-aged men during forceful eccentric contraction; may result in “Popeye deformity.”

  • Partial tear: Presents with pain and weakness without visible deformity; best detected on MRI.

  • Bicipitoradial bursitis: Inflammation of the bursa deep to the tendon due to repetitive pronation-supination.

  • Tendinopathy: Degenerative changes from overuse, often seen in athletes and manual laborers.

  • Surgical relevance: Tendon repair or reconstruction is indicated for complete ruptures to restore supination strength.

MRI Appearance

T1-weighted images:

  • Normal tendon: low signal (dark linear structure) extending to the radial tuberosity.

  • Muscle belly: intermediate signal intensity.

  • Fat planes: bright, delineating tendon borders.

  • Complete tear: gap with retracted tendon and interposed bright fat signal.

  • Partial tear: focal intermediate or bright signal within the tendon.

T2-weighted images:

  • Normal tendon: low signal, slightly darker than on T1 due to flow artifact suppression.

  • Fluid or edema: bright hyperintense signal surrounding tendon sheath.

  • Partial tear: bright intratendinous streaks without full-thickness gap.

  • Complete rupture: discontinuity with surrounding fluid collection at insertion site.

  • Bicipitoradial bursa: may appear as a small bright fluid pocket anterior to the radial tuberosity.

STIR:

  • Normal tendon: dark flow void appearance.

  • Pathology: bright hyperintense signal in tendon, muscle, or peritendinous tissue indicating edema, inflammation, or tear.

  • Useful for early detection of tendinopathy and reactive soft-tissue changes.

Proton Density Fat-Saturated (PD FS):

  • Normal tendon: dark, well-defined structure.

  • Partial tear or tendinitis: focal bright hyperintensity within tendon fibers or insertion.

  • Peritendinous fluid and subtle edema best visualized on this sequence.

T1 Fat-Sat Post-Contrast:

  • Normal tendon: minimal enhancement.

  • Tendinitis or post-surgical change: peritendinous enhancement.

  • Tear with granulation tissue: focal or nodular enhancement within defect.

  • Bicipitoradial bursitis: enhancing fluid collection adjacent to tendon.

CT Appearance

Non-Contrast CT:

  • Tendon: soft-tissue density structure inserting on the radial tuberosity.

  • Radial tuberosity: well-defined cortical margin with subtle concavity for tendon insertion.

  • Calcific tendinopathy: punctate or linear calcifications along tendon path.

  • Chronic tears: cortical irregularity or ossification near insertion site.

Post-Contrast CT (standard):

  • Tendon and muscle: mild homogeneous enhancement.

  • Inflammation or granulation tissue: enhanced along tendon sheath.

  • Fluid collections or bursitis: appear as low-attenuation areas around tendon.

  • Excellent for visualizing enthesophytes, avulsion fractures, or post-repair integrity.

MRI image

Biceps brachii tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

MRI image

Biceps brachii tendon axial cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000_00001

MRI image

Biceps brachii tendon sag cross sectional anatomy 3T MRI AI enhanced radiology image -img-00000-00000

CT images

Biceps brachii tendon CT SAG image