SUBSCAPULARIS MUSCLE . Everything You Need To Know - Dr. Nabil Ebraheim

Описание: Dr. Ebraheim’s educational animated video describes the anatomical and surgical considerations of the subscapularis muscle.
Subscapularis Muscle: Anatomy, Function, Injury, and Surgical Considerations

By Nabil Ebraheim

The subscapularis is a large triangular muscle that originates from the subscapular fossa on the anterior surface of the scapula and lies in front of the shoulder joint. The muscle fibers pass laterally beneath the coracoid process and the arch formed by the tendinous origins of the coracobrachialis and the short head of the biceps brachii to insert into the lesser tuberosity of the humerus. Among the four rotator cuff muscles, the subscapularis is the largest and provides approximately 50% of the total rotator cuff strength.

Innervation and Blood Supply

The subscapularis muscle receives innervation from the upper and lower subscapular nerves, both of which arise from the posterior cord of the brachial plexus.
Its blood supply comes mainly from the subscapular artery, the largest branch of the axillary artery.

Anatomical Relations

The nerve branches from the posterior cord pass over the anterior surface of the subscapularis and then course posteriorly beneath the muscle and the shoulder capsule to enter the quadrangular space together with the posterior circumflex humeral artery.

Function

The subscapularis acts as a powerful internal rotator of the shoulder and a dynamic stabilizer of the humeral head. It assists in adduction and in moving the arm across the chest. Its main function is to internally rotate and stabilize the humeral head within the glenoid cavity.

Anatomical Note on the Biceps Groove

At the insertion of the subscapularis tendon into the lesser tuberosity lies the transverse humeral ligament, which stabilizes the long head of the biceps tendon within the bicipital groove. In cases of complete subscapularis tendon rupture, the transverse humeral ligament may also be torn, resulting in medial dislocation of the biceps tendon from the groove. Therefore, medial subluxation of the biceps tendon is a clinical indicator of a subscapularis tear.

Mechanism of Injury

The mechanism of subscapularis tendon rupture is usually acute, occurring in younger patients following a fall onto an outstretched arm in hyperabduction and external rotation. The condition can also develop following anterior shoulder dislocation, or as a complication of shoulder surgery involving anterior approaches.
Tears may be isolated or associated with other rotator cuff injuries. Studies show that 88% of patients with medial biceps tendon subluxation have a concurrent subscapularis tendon tear.

Clinical Presentation

Patients typically present with anterior shoulder pain, swelling, and weakness of internal rotation. Passive external rotation of the shoulder is increased compared to the opposite side. Range of motion is often decreased, and the condition may cause significant functional limitation.
Subscapularis tears may be acute, partial, or complete, and can become chronic if not diagnosed and treated early.

Clinical Examination

Several manual tests assess the integrity of the subscapularis muscle and tendon. These tests demonstrate weakness in internal rotation:

Lift-Off Test:
The patient places the hand behind the back at the lumbar level and attempts to lift it away. Inability to lift indicates a tear. The examiner can assess strength by resisting this motion and comparing both sides.

Lift-Off Lag Test:
The examiner holds the patient’s hand away from the back and releases it. Inability to maintain the position indicates subscapularis tendon rupture.

Belly-Press Test:
The patient presses the palm against the abdomen with the wrist in a neutral position. If the patient compensates by flexing the wrist or allowing the elbow to drift posteriorly, the test is positive—indicating a tear, particularly of the upper portion of the tendon.

Bear Hug Test:
The patient places the palm on the opposite shoulder with the elbow anterior to the body. The examiner tries to externally rotate the arm while the patient resists. Weakness compared with the other side indicates a positive test and a subscapularis tear.

All of these tests assess internal rotation strength and stability of the subscapularis.

Radiologic Evaluation

Diagnosis is confirmed by MRI or ultrasound.

MRI shows detachment of the subscapularis tendon from the lesser tuberosity and can demonstrate muscle atrophy in chronic cases.

In patients with a shoulder prosthesis or when radiographs appear normal, ultrasound is particularly useful.
The ultrasound probe is placed transversely over the bicipital groove to identify the biceps tendon while the arm is in a neutral position, and then externally rotated to visualize the subscapularis tendon.

Treatment

Treatment depends on the severity and chronicity of the tear:

Complete tears require surgical repair, which may be performed open or arthroscopically.