Supraspinatus

The supraspinatus is one of the four muscles that form the rotator cuff. It is the most superiorly located rotator cuff muscle and plays a crucial role in initiating shoulder abduction and stabilizing the glenohumeral joint⁴.

Anatomy

The supraspinatus muscle originates from the medial two-thirds of the supraspinous fossa of the scapula, a concave depression superior to the spine of the scapula. The muscle is covered by the supraspinous fascia and extends laterally beneath the acromion and coracoacromial ligament².

The muscle fibers converge laterally to form a strong tendon that passes through the subacromial space and inserts onto the superior facet of the greater tuberosity of the humerus. The tendon blends with the shoulder joint capsule, reinforcing it superiorly¹.

The supraspinatus has two distinct muscle bellies: an anterior belly with a larger cross-sectional area (140 ± 43 mm²) and a posterior belly (62 ± 25 mm²). The anterior belly is responsible for the majority of contractile force generation⁵.

The muscle is innervated by the suprascapular nerve, which arises from the upper trunk of the brachial plexus (C5-C6)¹⁶.

Function

The primary function of the supraspinatus is to initiate arm abduction at the glenohumeral joint. It begins the first 10-15 degrees of abduction, after which the deltoid takes over to continue the movement¹⁴.

In addition to abduction, the supraspinatus depresses the humeral head during arm elevation, keeping it centered on the glenoid cavity. This function allows the deltoid to maintain its mechanical advantage during abduction. Without this depression, the humeral head would migrate superiorly, causing impingement under the acromion³.

The supraspinatus also contributes weakly to external rotation of the humerus and works synergistically with the other rotator cuff muscles—infraspinatus, teres minor, and subscapularis—to stabilize the glenohumeral joint⁵⁶.

Clinical Significance

Supraspinatus Tendinopathy

The supraspinatus tendon is particularly susceptible to degeneration and injury due to its position in the confined subacromial space beneath the acromion. Supraspinatus tendinopathy is on the spectrum of rotator cuff syndrome and is a common cause of shoulder pain³.

Supraspinatus Tears

The supraspinatus is the most frequently torn of the rotator cuff tendons. Tears can be partial-thickness or full-thickness. A partial-thickness tear involves only one surface (joint or bursal), while a full-thickness tear creates a hole that allows communication between the glenohumeral joint and the subacromial bursa¹.

The footprint of the supraspinatus tendon is triangular, measuring approximately 12.7 mm medial-to-lateral and 6.9 mm anterior-to-posterior. The point of maximal susceptibility is along the tendon insertion nearest the greater tuberosity, underneath the acromion³.

Clinical Examination

The supraspinatus is tested using the Jobe test, also known as the empty can test. The patient holds the arm in 90 degrees of abduction, 30 degrees of forward flexion, and maximally internally rotates. The examiner applies downward pressure, and weakness or pain indicates supraspinatus pathology³⁶.

Surgical Considerations

When repairing the supraspinatus tendon, the anterior fibers must be incorporated whenever possible. These fibers are responsible for the primary functions of abduction and humeral head depression, and failing to repair them may result in functional deficits post-surgery⁴.

Biomechanics

The moment arm of the supraspinatus for abduction measures approximately 2.5 cm in neutral rotation. With the arm in internal rotation, the moment arm decreases to 2.2 cm. With external rotation, it increases to 2.8 cm. This variation affects the muscle's mechanical advantage during different arm positions⁵.

The supraspinatus tendon has been shown to have an aponeurotic expansion adjacent to the bicipital groove in approximately 50% of individuals. This structure runs parallel to the long head of the biceps tendon and may have clinical significance in surgical repairs⁴.

References

1. Supraspinatus Tendon and Muscle: Function and Common Pathology(accessed Apr 18, 2026)
2. Supraspinatus Muscle - Anatomy, Function, Clinical Relevance(accessed Apr 18, 2026)
3. Supraspinatus Tendonitis(accessed Apr 18, 2026)
4. Anatomy, Shoulder and Upper Limb, Arm Supraspinatus Muscle(accessed Apr 18, 2026)
5. Supraspinatus - Anatomy and Biomechanics(accessed Apr 18, 2026)
6. Supraspinatus Muscle(accessed Apr 18, 2026)