Subscapularis Muscle is Involved with Internal Rotation of the Shoulder

The subscapularis muscle is the primary muscle responsible for internal rotation of the shoulder. 1, 2

Anatomy and Function of the Subscapularis

The subscapularis is the largest and strongest muscle of the rotator cuff, with more bulk mass than all three other rotator cuff muscles combined 3
It functions as the primary internal rotator of the shoulder, with its tendon inserting onto the superior portion of the lesser tuberosity 3
The subscapularis is located anteriorly in the rotator cuff complex, while the supraspinatus is superior, and the infraspinatus and teres minor are positioned posteriorly 1
The subscapularis plays an essential role in both shoulder stability and function 4

When examining a patient with limited internal rotation, the subscapularis tendon should be the primary focus of assessment 2, 4
The Hawkins' test (forcible internal rotation with the patient's arm passively flexed forward at 90 degrees) is highly sensitive (92%) but not specific (25%) for impingement involving the subscapularis 1, 2
Specific tests for subscapularis function include the lift-off, belly-press, and bear-hug tests 4
Pain during internal rotation is often located anteriorly in the shoulder when the subscapularis is involved 2, 4

The subscapularis provides crucial anterior stabilization of the glenohumeral joint 5
Without proper subscapularis function, anterior translation and potential dislocation of the humeral head can occur during arm movement 5
In throwing athletes, the subscapularis experiences significant stress during the deceleration phase of throwing as it works eccentrically to control internal rotation 2
The integrity of the subscapularis is essential for maintaining proper humeral head positioning within the glenoid fossa 2, 5

Subscapularis tears were historically underdiagnosed but are now recognized as more common than previously thought 3, 6
MRI and ultrasound are effective imaging modalities for evaluating subscapularis integrity 6, 4
Subscapularis tears can be isolated but more commonly occur in conjunction with other rotator cuff pathology, particularly supraspinatus tears 6
Subscapularis dysfunction can lead to biceps pulley instability, SLAP tears, and anterosuperior impingement 6

Proper identification of subscapularis involvement is crucial for treatment planning in rotator cuff injuries 4
Rehabilitation for subscapularis injuries should focus on strengthening internal rotation and anterior shoulder stabilization 2
Surgical outcomes for latissimus dorsi transfers (a treatment for irreparable rotator cuff tears) are significantly worse when the subscapularis is also damaged 7, 5
An intact and functioning subscapularis is considered mandatory for successful outcomes in certain rotator cuff reconstruction procedures 7, 5