Anatomy of Rotator Cuff Muscle/The rotator cuff is a group of muscles in the shoulder that allow a wide range of movement while maintaining the stability of the glenohumeral joint. The rotator cuff includes the following musclesRotator cuff muscles can undergo independent evaluation when the patient presents with rotator cuff syndrome (explained ahead). [rx][rx][rx]
- Supraspinatus muscle – The evaluation of this muscle is with the Jobe’s test or commonly known as the “empty can” test. It is done with a 90 degrees abduction and internal rotation (thumb pointing to the floor) of the arm while pressing down on the arm. Positive, if painful or weak.
- Infraspinatus muscle – Evaluation of this muscle is via lateral rotation against resistance with the elbow flexed and the arm in neutral abduction/adduction position. Positive, if painful or weak.
- Teres minor muscle – This muscle’s evaluation is with the hornblower’s test, done with the arm at 90 degrees abduction, the elbow flexed (90 degrees), and doing a lateral rotation against resistance. Positive, if painful or weak.
- Subscapularis muscle – Evaluating this muscle uses the “lift-off” and the “bear hug” test. In the lift-off test, the patient brings the hands around the back to the lumbar region with the palms facing outward. The test is positive if the patient is unable to lift the hands away from the back. On the Bear hug test, the patient places the ipsilateral pal on the opposite deltoid and tries to resist the examiner pulling it away anteriorly. Positive, if painful or weak.
Blood Supply and Lymphatics of Rotator Cuff Muscle
The vascular supply to the rotator cuff muscles is mainly via the suprascapular artery, the subscapular artery, and the posterior circumflex humeral artery.
- The suprascapular artery is a branch of the thyrocervical trunk (a major branch of the subclavian artery) and originates at the base of the neck. It enters the posterior scapular region superior to the suprascapular foramen (the nerve passes through the foramen) and supplies the supraspinatus and infraspinatus muscles.
- The subscapular artery is the largest branch of the axillary artery. It originates from the third part of the axillary artery, follows the inferior margin of the subscapularis muscle, and then divides into the circumflex scapular artery and the thoracodorsal artery. It gives vascular supply to the subscapularis muscle.
- The posterior circumflex humeral artery originates from the third part of the axillary artery in the axilla. It enters the posterior scapular region through the quadrangular space (accompanied by the axillary nerve) and supplies the teres minor muscle.
All lymphatics from the upper limb drain into lymph nodes in the axilla.
Nerves Supply of Rotator Cuff Muscle
The subscapular nerve (upper and lower branches) innervates the subscapularis muscle.
- Originate from the posterior cord of the brachial plexus
- C5, C6, C7
The suprascapular nerve innervates the infraspinatus and supraspinatus
- Originates from the superior trunk of the brachial plexus
- Passes through the suprascapular foramen
- C5 and C6
The axillary nerve innervates teres minor
- Originates from the posterior cord of the brachial plexus
- Passes through the quadrangular space into the posterior scapula region
- C5 and C6
Muscles Attachment of Rotator Cuff Muscle
The subscapularis is the largest component of the posterior wall of the axilla. It prevents the anterior dislocation of the humerus during abduction and medially rotates the humerus. A large bursa separates the muscle from the neck of the scapula.[rx]
- Origin: subscapular fossa of the scapula
- Insertion: lesser tubercle of the humerus
The supraspinatus muscle is the only muscle of the rotator cuff that is not a rotator of the humerus.
- Origin: supraspinous fossa of the scapula
- Passes above the glenohumeral joint
- Insertion: greater tuberosity of the humerus
The infraspinatus is a powerful lateral rotator of the humerus. The tendon of this muscle is sometimes separated from the capsule of the glenohumeral joint by a bursa.
- Origin: infraspinous fossa of the scapula
- Insertion: greater tuberosity of the humerus, immediately below the supraspinatus.
The teres minor is a narrow and long muscle entirely covered by the deltoid, hardly differentiated from the infraspinatus.
- Origin: lateral border of the scapula (below the infraglenoid tubercle)
- Insertion: greater tuberosity of the humerus, below the infraspinatus tendon.
