Infraspinatus and Teres Minor

Infraspinatus and Teres Minor

OVERVIEW
Muscle Test Group: Infraspinatus and teres minor.
 
Key Points:
• Lateral rotators of the shoulder include the infraspinatus and teres minor. There is a contribution by the posterior deltoid.
• Infraspinatus and teres minor are tested together as a group.
• Examination can be confusing because the infraspinatus and teres minor are innervated by different nerves: infraspinatus (suprascapular nerve) and teres minor (axillary nerve).
EXAMINATION
Muscle Function of Infraspinatus: Externally rotates the shoulder joint. Stabilizes the head of humerus in the glenoid cavity during movements of the joint.
 
Palpation of Infraspinatus: The posterior surface inferior to the spine of the scapula.
 
Muscle Function of Teres Minor: Externally rotates the shoulder joint. Stabilizes the head of humerus in the glenoid cavity during movements of the joint.
 
Palpation of Teres Minor: The posterior lateral surface inferior and adjacent to the infraspinatus muscle.
 
Strength Testing: 
Gravity-lessened Test: Position ““ the subject in supine position with the shoulder at 90º of abduction and elbow at 90º of flexion. Place a small support under the humerus to bring the elbow into the plane of the scapula. Stabilize ““ the humerus and the forearm. Resist ““ against external rotation of the shoulder with slight pressure given to the forearm.
 
Anti-gravity Test: Position ““ the subject in prone with the shoulder at 90º of abduction and elbow at 90º of flexion. Place a small support under the humerus to bring the elbow into the plane of the scapula. Stabilize ““ the humerus and the forearm. Resist ““ against external rotation of the shoulder with slight pressure given to the forearm. Subject can be asked to actively raise the hand and rotate the glenohumeral joint laterally.
 
Possible Substitutions: This includes the posterior deltoid and wrist extensor muscles. To monitor the posterior deltoid, be sure the subject avoids humeral horizontal abduction or shoulder extension. Wrist extensors may appear to be giving lateral rotation and palpation will distinguish this substitution.
 
Relevant Anatomy:
Infraspinatus
Innervation:
• Roots: C(4), C5, C6.
• Nerve: Suprascapular nerve.
• Innervation Route: C(4), C5, C6 → suprascapular nerve → infraspinatus.
Origin: Medial â…” of infraspinous fossa of scapula.
 
Insertion: Middle facet of greater tubercle of humerus and shoulder joint capsule.
 
Teres Minor
Innervation:
• Roots: C5, C6.
• Nerve: Axillary nerve.
• Innervation Route: C5, C6 → axillary nerve → teres minor branch.
Origin: Superior â…” of lateral border of scapula dorsally. 
 
Insertion: Inferior facet of greater tubercle of humerus. 

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Infraspinatus and Teres Minor

OVERVIEW
Muscle Test Group: Infraspinatus and teres minor.
 
Key Points:
• Lateral rotators of the shoulder include the infraspinatus and teres minor. There is a contribution by the posterior deltoid.
• Infraspinatus and teres minor are tested together as a group.
• Examination can be confusing because the infraspinatus and teres minor are innervated by different nerves: infraspinatus (suprascapular nerve) and teres minor (axillary nerve).
EXAMINATION
Muscle Function of Infraspinatus: Externally rotates the shoulder joint. Stabilizes the head of humerus in the glenoid cavity during movements of the joint.
 
Palpation of Infraspinatus: The posterior surface inferior to the spine of the scapula.
 
Muscle Function of Teres Minor: Externally rotates the shoulder joint. Stabilizes the head of humerus in the glenoid cavity during movements of the joint.
 
Palpation of Teres Minor: The posterior lateral surface inferior and adjacent to the infraspinatus muscle.
 
Strength Testing: 
Gravity-lessened Test: Position ““ the subject in supine position with the shoulder at 90º of abduction and elbow at 90º of flexion. Place a small support under the humerus to bring the elbow into the plane of the scapula. Stabilize ““ the humerus and the forearm. Resist ““ against external rotation of the shoulder with slight pressure given to the forearm.
 
Anti-gravity Test: Position ““ the subject in prone with the shoulder at 90º of abduction and elbow at 90º of flexion. Place a small support under the humerus to bring the elbow into the plane of the scapula. Stabilize ““ the humerus and the forearm. Resist ““ against external rotation of the shoulder with slight pressure given to the forearm. Subject can be asked to actively raise the hand and rotate the glenohumeral joint laterally.
 
Possible Substitutions: This includes the posterior deltoid and wrist extensor muscles. To monitor the posterior deltoid, be sure the subject avoids humeral horizontal abduction or shoulder extension. Wrist extensors may appear to be giving lateral rotation and palpation will distinguish this substitution.
 
Relevant Anatomy:
Infraspinatus
Innervation:
• Roots: C(4), C5, C6.
• Nerve: Suprascapular nerve.
• Innervation Route: C(4), C5, C6 → suprascapular nerve → infraspinatus.
Origin: Medial â…” of infraspinous fossa of scapula.
 
Insertion: Middle facet of greater tubercle of humerus and shoulder joint capsule.
 
Teres Minor
Innervation:
• Roots: C5, C6.
• Nerve: Axillary nerve.
• Innervation Route: C5, C6 → axillary nerve → teres minor branch.
Origin: Superior â…” of lateral border of scapula dorsally. 
 
Insertion: Inferior facet of greater tubercle of humerus. 

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