Latissimus Dorsi Tendon: Anatomy, Function, Clinical and Imaging

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Latissimus dorsi tendon

The latissimus dorsi tendon is the strong, flat terminal portion of the latissimus dorsi muscle, inserting into the humerus. It plays a vital role in shoulder adduction, extension, and internal rotation, and is crucial for powerful movements such as swimming, climbing, and rowing.

The tendon forms as the muscle fibers converge from a broad origin over the lower back and thorax into a narrowed fibrous band that twists before attaching to the floor of the intertubercular sulcus of the humerus. It lies close to the teres major and pectoralis major tendons, contributing to the posterior axillary fold.

Because of its strength and broad insertion, the latissimus dorsi tendon is often used in tendon transfer surgeries for shoulder reconstruction, especially in cases of massive rotator cuff tears.

Synonyms

Tendon of the latissimus dorsi
Humeral tendon of latissimus
Latissimus insertion tendon

Origin, Course, and Insertion

Origin (of muscle): Spinous processes of T7–T12 vertebrae, thoracolumbar fascia, iliac crest, and lower 3–4 ribs; sometimes from the inferior angle of the scapula.
Course: The muscle fibers ascend laterally and anteriorly, forming a flat tendon that spirals around the teres major tendon near the posterior axillary fold.
Insertion (of tendon): The floor of the intertubercular sulcus (bicipital groove) of the humerus, just medial to the tendon of the biceps brachii long head and posterior to the pectoralis major tendon.

Tendon Attachments

Proximal continuity: With the muscular belly of the latissimus dorsi.
Distal attachment: To the humeral shaft within the intertubercular groove.
Relations:
- Anterior: Pectoralis major tendon
- Posterior: Teres major tendon (often closely fused)
- Lateral: Biceps brachii long head tendon
- Medial: Humerus and joint capsule of the shoulder

Nerve Supply

Thoracodorsal nerve (C6–C8), a branch of the posterior cord of the brachial plexus.

Function

Shoulder adduction: Pulls the arm toward the body’s midline.
Shoulder extension: Draws the arm posteriorly from flexion.
Internal rotation: Rotates the humerus medially.
Forceful movements: Active during climbing, swimming, rowing, and pull-ups.
Postural support: Helps stabilize the scapula and trunk during movement.

Clinical Significance

Tendon tears or avulsions: May occur in athletes (e.g., baseball pitchers, gymnasts, weightlifters) due to sudden eccentric loading.
Symptoms: Pain in posterior axilla, weakness in adduction and internal rotation, or visible retraction of muscle belly.
Tendon transfer: Commonly used in reconstructive surgery for massive rotator cuff tears.
Post-surgical complications: Include tendon retraction, graft failure, and neural injury (thoracodorsal nerve).
Imaging relevance: MRI and CT help assess tendon integrity, repair status, and postsurgical anatomy.

MRI Appearance

T1-weighted images:
- Tendon: Low signal (dark linear structure).
- Muscle belly: Intermediate signal intensity.
- Marrow and fat planes: Bright.
- Normal attachment: Uniform low signal blending smoothly into the humerus.
- Tear or avulsion: Focal discontinuity, high-signal gap, or tendon retraction with surrounding edema.
T2-weighted images:
- Normal tendon: Low signal (dark).
- Muscle: Intermediate-to-dark signal, slightly darker than on T1.
- Tear or tendinopathy: Bright hyperintense signal within tendon or at insertion site.
- Fluid or edema: Bright hyperintensity surrounding the tendon sheath or humeral attachment.
STIR:
- Normal tendon and muscle: Intermediate-to-dark signal.
- Pathology: Bright hyperintense signal in cases of tendinitis, partial tear, or surrounding edema.
- Excellent for identifying soft-tissue inflammation or post-surgical changes.
Proton Density Fat-Saturated (PD FS):
- Normal tendon: Smooth, uniformly dark.
- Partial tear: Focal bright signal within tendon substance.
- Complete rupture: Bright fluid signal in tendon gap, often with retracted stump.
- Tendinopathy: Diffuse thickening and increased intratendinous signal.
T1 Fat-Sat Post-Contrast:
- Normal tendon: Minimal enhancement.
- Inflamed or repaired tendon: Focal or diffuse enhancement.
- Scar tissue: Peripheral rim enhancement with central low-signal fibrosis.
- Useful for assessing post-repair vascularization or chronic inflammation.

CT Appearance

Non-Contrast CT:

Tendon: Thin, soft-tissue density band attaching to the humeral shaft.
Muscle: Homogeneous soft-tissue density posterior to the thoracic wall and axilla.
Bone insertion: May show small cortical irregularity or sclerosis in chronic traction.
Pathology: Detects calcific tendinopathy, avulsion fractures, or post-surgical anchors.

Post-Contrast CT (standard):

Normal tendon: Minimal enhancement.
Inflamed tendon or postoperative changes: Focal enhancement around tendon or humeral insertion.
Utility: Excellent for evaluating calcifications, hardware positioning, and bony remodeling after surgery.

MRI images

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