Supraspinatus Tendon: Anatomy, Function, Clinical Significance, MRI & CT Imaging

Topic

Supraspinatus tendon

The supraspinatus tendon is the tendinous extension of the supraspinatus muscle, one of the four rotator cuff tendons of the shoulder. It passes laterally beneath the acromion and coracoacromial arch to insert onto the superior facet of the greater tubercle of the humerus.

This tendon plays a critical role in shoulder abduction and stabilization of the glenohumeral joint by maintaining the humeral head within the glenoid fossa. Because of its anatomical position beneath the acromion, it is highly susceptible to degenerative changes, impingement, and tears, making it the most frequently injured rotator cuff tendon.

Synonyms

Tendon of supraspinatus muscle
Superior rotator cuff tendon
Upper rotator cuff insertion

Origin, Course, and Insertion

Origin (muscle): Supraspinous fossa of the scapula and overlying fascia.
Course: The tendon forms at the lateral border of the supraspinous fossa and passes under the acromion and coracoacromial ligament within the subacromial space. It courses laterally and slightly anteriorly over the humeral head, merging with the capsule of the shoulder joint.
Insertion: Superior facet of the greater tubercle of the humerus.
The tendon fibers interdigitate with those of the infraspinatus posteriorly and subscapularis anteriorly near the humeral insertion, forming a continuous rotator cuff.

Tendon Attachments

Primary attachment: Superior facet of the greater tubercle of the humerus.
Secondary attachments: Joint capsule of the glenohumeral joint and the subacromial bursa (superficial surface).
Bursal side: Faces the subacromial-subdeltoid bursa.
Articular side: Faces the humeral head and glenohumeral joint cavity.

Relations

Superiorly: Subacromial-subdeltoid bursa and deltoid muscle.
Inferiorly: Humeral head and joint capsule.
Anteriorly: Coracoacromial ligament and subscapularis tendon.
Posteriorly: Infraspinatus tendon.
Laterally: Greater tubercle of the humerus.

Nerve Supply

Suprascapular nerve (C5–C6) — motor branch to the supraspinatus muscle.
Sensory innervation to the tendon and capsule via branches of the suprascapular and axillary nerves.

Function

Abduction: Initiates the first 15° of shoulder abduction before deltoid activation.
Joint stabilization: Holds the humeral head within the glenoid cavity during motion.
Force coupling: Works with infraspinatus, subscapularis, and teres minor to balance shoulder movements.
Smooth gliding: Facilitates frictionless movement beneath the acromion through the subacromial bursa.

Clinical Significance

Tendinopathy: Chronic overuse or impingement leads to degenerative tendinopathy and partial tears.
Tears: Most common site of rotator cuff tears (articular-sided > bursal-sided > full-thickness).
Impingement syndrome: Compression between humeral head and acromion causes pain and inflammation.
Calcific tendinitis: Calcium deposition within the tendon leads to acute pain and limited motion.
Tendon retraction: Chronic full-thickness tears result in muscle atrophy and fatty degeneration.
Surgical relevance: Key structure in arthroscopic rotator cuff repair and subacromial decompression.

MRI Appearance

T1-weighted images:
- Normal tendon: Low signal (dark), homogeneous and sharply defined.
- Muscle belly: Intermediate signal; normal fatty marrow in humeral head is bright.
- Tendinopathy: Mild thickening with intermediate signal intensity.
- Tear: Focal or linear high-signal cleft interrupting low-signal fibers.
- Retraction: Gap between tendon end and greater tuberosity, with interposed fluid or fat.
T2-weighted images:
- Normal tendon: Uniform low signal (dark).
- Tendinitis or partial tear: Bright hyperintense signal within tendon or at attachment site.
- Full-thickness tear: Bright fluid-filled gap extending from articular to bursal surface.
- Muscle atrophy or fatty infiltration: Increased signal intensity within supraspinatus muscle belly.
- Bursal fluid: Hyperintense signal overlying tendon in subacromial-subdeltoid bursa.
STIR:
- Normal tendon: Dark, low signal.
- Pathology: Bright hyperintense signal representing edema, inflammation, or tear-related fluid.
- Excellent for identifying subtle peritendinous inflammation or subacromial bursitis.
Proton Density Fat-Saturated (PD FS):
- Normal: Low signal (dark) tendon with smooth margins.
- Partial tears: Bright hyperintense linear zones in tendon substance or on articular/bursal surface.
- Full-thickness tears: Bright gap from articular to bursal surface with fluid signal intensity.
- Peritendinitis: Surrounding bright signal in subacromial or subdeltoid region.
T1 Fat-Sat Post-Contrast:
- Normal tendon: Minimal to no enhancement.
- Tendinopathy or inflammation: Focal or diffuse enhancement at tendon insertion.
- Postoperative scar tissue: Enhances, whereas recurrent tear shows non-enhancing gap.
- Calcific tendinitis: Peripheral enhancement around hypointense calcific focus.

CT Appearance

Non-Contrast CT:

Tendon: Seen as a fine, low-density structure overlying the greater tubercle.
Calcific tendinitis: Appears as dense, well-circumscribed calcifications within the tendon.
Chronic tears: May show irregular cortical changes or sclerosis at humeral insertion.
Associated findings: Subacromial spurs, humeral head sclerosis, or cystic changes.

Post-Contrast CT (standard):

Tendon itself: Does not enhance.
Inflamed or thickened peritendinous tissues: Show subtle enhancement.
Useful for:
- Identifying calcific deposits and bony erosions.
- Evaluating osseous remodeling and postoperative anchor placement in repaired tendons.