Subscapularis

Original Editor - Wendy Walker

Lead Editors - Andeela Hafeez, Kim Jackson, Lilian Ashraf, Wendy Walker, Pacifique Dusabeyezu, 127.0.0.1, Tony Lowe, Naomi O'Reilly, George Prudden, Kai A. Sigel, WikiSysop, Candace Goh, Joao Costa, Daphne Xuan and Aya Alhindi

Description

The subscapularis muscle is a large triangular shaped muscle that originates from the subscapular fossa. The term "subscapularis" means under (sub) the scapula (wingbone).

It is the largest, strongest part of the four rotator cuff muscles, the other three are the supraspinatus, infraspinatus and teres minor muscles. The subscapularis is the largest and strongest muscle of the rotator cuff.

Origin

Medial two-thirds of the subscapular fossa (anterior surface of the scapula).

Insertion

The fibers form a tendon that inserts into the lesser tubercle of the humerus and the front of the shoulder joint capsule.

Nerve Supply

Subscapularis is innervated by both the upper and lower subscapular nerves (C5-C6) which come from the posterior cord of the brachial plexus.

• The upper subscapular nerve supplies the upper part of the subscapularis.
• The lower subscapular nerve branches into two, with one branch supplying the lower part of subscapularis.

Blood Supply

The primary blood supply to the subscapularis muscle is subscapular artery, a branch of the axillary artery.

Lymphatic Supply

Lymph drains into the axillary lymph nodes.

Action

The primary function is the internal rotation of the humerus. It helps in shoulder adduction and extension in certain positions. 

Arm position has a marked effect on the actions caused by this muscle:

• When the arm is raised, subscapularis pulls the humerus forward and downward.
• When the humerus is in a fixed position, the insertion of the subscapularis can act as an origin, producing abduction of the inferior border of the scapula.

Function

As part of the rotator cuff, Subscapularis plays an important role in the stabilisation of the shoulder.

Pathologies

• Subscapularis may include up to three trigger points, with the two most common occurring near the outside edge of the muscle. Luckily, the trigger point on the inside edge of the muscle is much less common, because it is nearly impossible to contact by palpation and release manually. Referred pain from trigger points in the subscapularis muscle concentrates in the posterior shoulder region, with spillover into the shoulder blade region and down the back of the upper arm. A unique “band” of referred pain around the wrist may occur as well. Typically the client is aware of this wrist pain but does not think it is related to their shoulder pain.
• It is often injured by throwers. Tenderness and pain will be felt when pressing in on the tendon insertion on the inside of the upper arm. Subscapularis tendonitis symptoms include pain when moving the shoulder especially when the arm is raised above the shoulders.
• An overworked subscapularis muscle may make you feel like you are not able to lift your arm. It may be even responsible for your frozen shoulder.
  

Tests For Subscapularis

Lift-Off Test

The lift-off test was originally described by Gerber and Krushell (199l) and is sometimes referred to as 'Gerber's Test'.

The patient is examined in standing and is asked to place their hand behind their back with the dorsum of the hand resting in the region of the mid-lumbar spine. The dorsum of the hand is raised off the back by maintaining or increasing internal rotation of the humerus and extension at the shoulder.
The ability to actively lift the dorsum of the hand off the back constitutes a normal lift-off test. Inability to move the dorsum off the back constitutes an abnormal lift-off test and indicates subscapularis rupture or dysfunction.

Lift-off test video provided by Clinically Relevant

Bear Hug Test

To perform the Bear Hug Test, the patient is asked to place the palm of their affected arm on their opposite shoulder, with their elbow anterior to the body in maximum anterior translation position.  The patient is instructed to maintain the starting position, while the physician applies an externally rotating force to the patient’s forearm.

The test is positive if the patient can’t maintain his arm position or showed internal rotation weakness compared to the opposite side, indicating subscapularis muscle tear or dysfunction.

Belly Press Test

To perform the Belly Press Test the affected arm is placed at the side, with the shoulder flexed 90 degrees and the palm of the hand resting on the patient’s belly. The patient is instructed to press the palm of his hand against his belly in an internal rotation movement.The test is positive if the patient showed internal rotation weakness compared to the opposite side or pressed on his belly my elbow or shoulder extension instead of internal rotation.

Treatment

Subscapularis tendonitis and tendinopathy is managed conservatively through rest, activity modification, analgesia, ice and physical therapy. Applying ice initially helps reduce pain and inflammation.

For massaging the subscapularis muscle use thumb technique, feel it contracting, then release the tension and start to massage it. Make sure you only massage the muscle and not your nerves. Otherwise you are likely to end up with some pain for quite a few days because you stressed the nerves in your armpit instead of the muscle.