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Deltoid and Supraspinatus

OVERVIEW
Muscle Test Group:
Middle deltoid and supraspinatus.

Key Points:

• Deltoid muscle is divided into three sections: anterior, middle, and posterior fibers.
• Middle deltoid is tested as a muscle group with the supraspinatus.
• Examination can be confusing because the deltoid and supraspinatus are innervated by different nerves: deltoid (axillary nerve) and supraspinatus (suprascapular nerve).

EXAMINATION
DELTOID
Muscle Function: Abduction of the shoulder joint, which is performed mainly by the middle fibers with the stabilization by the anterior and posterior fibers. The anterior fibers flex the shoulder joint and in the supine position, internally rotate the shoulder joint. The posterior fibers extend the shoulder joint and in prone position, externally rotate the shoulder joint.
 
ANTERIOR DELTOID
Palpation: Inferior on the lateral ⅓ of the clavicle, between the clavicle and the coracoids process.
 
Strength Testing:
Anti-gravity Test: Position – the subject in sitting with the shoulder in slight lateral rotation with the elbow flexed. Stabilize – the arm. Resist – the subject is asked to abduct and flexion the shoulder to 90º with slight humeral lateral rotation to increase the effect of gravity on the anterior fibers, which medially rotate the humerus. If subject is able to abduct the shoulder in slight flexion fully to 90º, pressure is applied to the anterior and medial surface of the arm in the direction of adduction with slight extension.
 
Possible Substitutions: Pectoralis major can substitute by flexing the humerus. The long head of biceps brachii can assist in humeral flexion and elevation of the shoulder girdle, which gives the appearance of humeral flexion.
 
MIDDLE DELTOID AND SUPRASPINATUS
Palpation: Middle deltoid can be palpated just inferior to the acromion process on the lateral humerus. Supraspinatus can be palpated superior to the spine of the scapula.
 
Strength Testing:
Gravity-lessened Test: Position – the subject in supine with the humerus in neutral and the elbow flexed to 90º. Stabilize – the arm. Resist – against shoulder abduction.
 
Anti-gravity Test: Position – the subject in sitting with the humerus in neutral and the elbow flexed to 90º. Stabilize – the arm. Resist – against shoulder abduction.
 
Possible Substitutions: Substitutions include the long head of biceps brachii, which may help when the arm is in some lateral rotation. The anterior and posterior deltoid when acting together may also produce abduction. Elevation of the shoulder girdle is often a substitution pattern used when humeral abduction is unable to be performed. Trunk flexion to the opposite side may substitute.
 
POSTERIOR DELTOID
Palpation: Inferior to the later border of the spine of the scapula.
 
Strength Testing:
Gravity-lessened Test: Position – the subject in sitting with the elbow flexed. Stabilize – the arm supported by the examiner. Resist – against horizontal abduction of the shoulder with the elbow flexed to 90º.
 
Anti-gravity Test: Position – the subject in sitting with the humerus in slight medial rotation and the elbow flexed. Stabilize – the scapula if the scapular stabilizers are weak and may need to give counter pressure anterior to the shoulder girdle when giving resistance. Resist – against shoulder abduction with slight extension and the humerus in slight medial rotation to increase the effect of gravity on the posterior fibers. Resistance is given to the distal humerus towards adduction and slight flexion while stabilizing the shoulder.
 
Possible Substitutions: Substitutions include the long head of triceps brachii, which tends to assist in extension when the arm is in 45º of abduction. Addition substitutions include the shoulder rotators, muscles involved with upper trunk movement, latissimus dorsi, and scapular adductors.
 
Relevant Anatomy:
Deltoid

Innervation: 
• Roots: C5, C6.
• Nerve: Axillary nerve.
• Innervation Route: C5, C6 → axillary nerve → deltoid branches.
Origins of Anterior Fibers: Anterior border, superior surface, and lateral ⅓ of clavicle.
 
Origins of Middle Fibers: Lateral margin and superior surface of acromion.
 
Origin of Posterior Fibers: Inferior lip of posterior border of spine of scapular.
 
Insertion: Deltoid tuberosity of humerus. 
 
Supraspinatus
Innervation: 
• Roots: C5, C6.
• Nerve: Suprascapular nerve
• Innervation Route: C5, C6 → suprascapular nerve → supraspinatus.
Origin: Medial ⅔ of supraspinatus fossa of scapula.
 
Insertion: Superior facet of greater tubercle of humerus.