The subscapularis muscle is the largest and most powerful muscle of the rotator cuff, which stabilizes the shoulder joint. Its location on the anterior surface of the scapula makes it challenging to access directly through palpation. Learning to palpate this muscle is necessary for a thorough assessment of shoulder health and function. This guide provides the step-by-step procedure for safely and accurately locating the subscapularis.
Location and Primary Function
The subscapularis is a broad, triangular muscle that originates from the subscapular fossa, the large concave area on the front side of the scapula. The muscle fibers converge into a tendon that inserts onto the lesser tubercle of the humerus, a prominent bony landmark on the upper arm bone.
The primary action of the subscapularis is the internal rotation of the shoulder joint. It is responsible for approximately 50% of the total rotator cuff strength and acts as a dynamic stabilizer, keeping the head of the humerus centered within the shoulder socket. Because it lies between the scapula and the rib cage, a specific axillary (armpit) approach is required for palpation.
Essential Safety and Patient Positioning
Before beginning any physical assessment, obtain explicit consent, clearly explaining the procedure, especially since it involves the sensitive axillary region. A gentle and cautious approach is mandatory because the axilla contains neurovascular structures, including the brachial plexus and the axillary artery. Contraindications such as recent shoulder surgery, severe localized pain, or skin integrity issues in the armpit area must be confirmed and respected.
The person should be positioned lying on their back (supine position) with their arm slightly abducted and externally rotated. This positioning maximizes relaxation of the surrounding muscles, helping to draw the scapula laterally and lift soft tissues like the pectoralis and latissimus dorsi, making the subscapular fossa more accessible.
Detailed Steps for Palpation
The palpation process begins by locating the coracoid process, a hook-like bony projection on the anterior scapula that serves as an important landmark. This process is situated inferior to the clavicle and medial to the shoulder joint, guiding the path toward the subscapular fossa.
The next step involves guiding two or three fingertips gently but firmly into the axilla, posterior and lateral to the pectoralis muscles. The fingertips should aim to sink toward the anterior surface of the scapula, targeting the area deep to the shoulder joint. The individual should be instructed to take a slow, deep breath. On the exhale, the examiner should attempt to sink the fingers slightly deeper, using the relaxation of the surrounding chest and back muscles to facilitate access.
As the fingers move past the soft tissues of the axilla, they will gently hook onto the anterior surface of the scapula, where the muscle belly lies. The pressure should be broad and slow, not sharp, to prevent a ticklish or painful reaction common in this sensitive area. Once contact is made with the bony surface, the fingertips are resting on the subscapularis muscle within the subscapular fossa. The muscle tissue may feel ropey or lumpy as it is compressed against the bone. It is important to differentiate the subscapularis from the more lateral teres major muscle, which is usually contacted less deeply. Maintaining gentle contact, the fingers can be slowly maneuvered to follow the muscle fibers toward the lesser tubercle insertion point on the humerus.
Confirming Palpation Through Muscle Engagement
Once contact is established with the muscle belly, confirmation through muscle activation is necessary. The individual should be asked to perform a slight resisted internal rotation of the arm, which directly engages the subscapularis, its primary function. The resistance applied must be minimal to prevent the powerful pectoralis major and latissimus dorsi muscles from taking over the movement. A common method is to have the person gently push their palm against their abdomen or the examiner’s forearm while the fingertips remain in the subscapular fossa. The confirmation is a distinct tightening or contracting sensation felt under the palpating fingers as the muscle fibers shorten. If the muscle is correctly located, the contraction will push back against the fingertips, verifying the precise anatomical placement.