Teres Minor: Origin, Insertion, Nerve, Action & Rotator Cuff Function

The Teres Minor is a narrow, elongated muscle of the rotator cuff. Located on the posterior aspect of the scapula, it sits immediately superior to the Teres Major and inferior to the Infraspinatus. It works primarily to rotate the arm outward and stabilize the ball-and-socket joint of the shoulder.

[Image of Infraspinatus muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	Upper two-thirds of the Lateral Border of the Scapula.
Insertion (Distal)	Inferior Facet of the Greater Tubercle of the Humerus.
Nerve Supply	Axillary Nerve (C5, C6).
Blood Supply	Circumflex Scapular Artery and Posterior Circumflex Humeral Artery.
Primary Actions	External Rotation: Rotates the arm laterally. Adduction: Weakly assists in bringing the arm to the side. Stabilization: Holds the humeral head in the glenoid.

Deep Dive: The "T" in SITS

The Teres Minor is often indistinguishable from the Infraspinatus in function, but it has distinct anatomical relationships.

1. The Quadrangular Space

The Teres Minor creates the Superior Border of the Quadrangular Space (a gap in the armpit muscles).
The Boundaries:
• Superior: Teres Minor
• Inferior: Teres Major
• Medial: Triceps Long Head
• Lateral: Humerus
The Axillary Nerve and Posterior Circumflex Humeral Artery pass through this space.

2. The Facet insertion

On the Greater Tubercle of the Humerus, the rotator cuff muscles insert in a "SIT" order from top to bottom:
• Supraspinatus (Top)
• Infraspinatus (Middle)
• Teres Minor (Bottom/Inferior facet)

Physio Corner: Clinical Relevance

💪 Functional Fact: The Teres Minor provides roughly 45% of the external rotation strength of the shoulder. It is particularly important for stabilizing the shoulder when the arm is abducted (raised to the side), preventing the head of the humerus from sliding upward.

Palpation

Locate the lateral border of the scapula. Palpate about halfway up the border, just above the bulk of the Teres Major and below the Infraspinatus. Ask the patient to externally rotate the arm against resistance. The Teres Minor is the thin muscle strip that tenses right on the edge of the shoulder blade.

⚠️ Clinical Pathology: Hornblower's Sign
This test specifically assesses the Teres Minor. The patient's arm is abducted to 90° and elbow flexed to 90°. The patient attempts to externally rotate against resistance. If they cannot, or if the hand drops in front of the mouth (like holding a horn), it indicates Teres Minor pathology or Axillary nerve damage.

Manual Muscle Testing (MMT)

To differentiate Teres Minor from Infraspinatus, we change the arm position.

Testing Tip: The Teres Minor is more active when testing external rotation with the shoulder Abducted (at 90°). The Infraspinatus is more active when the arm is at the side (0° abduction).

Step-by-Step Procedure (Oxford Scale)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Prone. Arm abducted to 90°, elbow flexed 90° hanging off the table. Action: Patient lifts the back of the hand toward the ceiling (External Rotation). Resistance: Applied just above the wrist, pushing down into internal rotation. Grade 3: Completes range. Grade 4/5: Holds against resistance.
Grade 2 (Gravity Eliminated)	Position: Sitting or Prone with arm hanging freely. Action: Patient rotates arm outward. Result: Visible rotation of the humerus.
Grade 0, 1 (Palpation)	Action: Palpate lateral scapular border (upper half). Cue: "Try to turn your arm out."

Frequently Asked Questions

How is it different from Teres Major?

Teres Minor: Rotator Cuff muscle, Axillary Nerve, External Rotation.
Teres Major: NOT Rotator Cuff, Subscapular Nerve, Internal Rotation (Action matches Latissimus Dorsi).

Why is it supplied by the Axillary nerve?

The Teres Minor and the Deltoid are the two muscles supplied by the Axillary nerve. This is clinically important because an anterior shoulder dislocation or fracture of the surgical neck can damage this nerve, weakening both muscles.

What is Quadrangular Space Syndrome?

Compression of the Axillary nerve and Posterior Circumflex Humeral artery within the quadrangular space. This can cause vague shoulder pain and atrophy of the Teres Minor and Deltoid.

Test Your Knowledge: Teres Minor Quiz

1. Which nerve supplies the Teres Minor?

2. Where does Teres Minor insert?

3. What is the primary action of Teres Minor?

4. Hornblower's Sign assesses weakness in:

5. The Teres Minor forms which border of the Quadrangular Space?

6. Where does Teres Minor originate?

7. Which muscle is the direct antagonist to Teres Minor?

8. The Long Head of the Triceps passes _______ to the Teres Minor.

9. Does Teres Minor assist in Adduction?

10. Is Teres Minor part of the Rotator Cuff?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Magee, D. J. (2014). Orthopedic Physical Assessment. 6th ed. Elsevier.