The Subscapularis is the largest and strongest of the four Rotator Cuff muscles. Unlike the other three (Supraspinatus, Infraspinatus, Teres Minor) which are located on the back, the Subscapularis lies on the front (anterior) surface of the shoulder blade, sandwiched between the scapula and the rib cage.
[Image of Infraspinatus muscle anatomy]Quick Anatomy Snapshot
| Group | Rotator Cuff (The "S" in SITS). The only anterior cuff muscle. |
|---|---|
| Origin (Proximal) | Subscapular Fossa (the anterior surface of the Scapula). |
| Insertion (Distal) | Lesser Tubercle of the Humerus. |
| Nerve Supply | Upper and Lower Subscapular Nerves (C5, C6, C7). |
| Blood Supply | Subscapular Artery. |
| Primary Actions |
|
Deep Dive: The Anterior Wall
While the other cuff muscles act on the Greater Tubercle, the Subscapularis stands alone.
1. The Lesser Tubercle Attachment
It is the only rotator cuff muscle to insert onto the Lesser Tubercle. This attachment point allows it to act as a powerful lever for internal rotation. The tendon passes directly in front of the shoulder joint capsule, reinforcing it anteriorly.
2. The "Hugging" Muscle
Because it sits between the scapula and ribs, it is generally inaccessible to touch. However, it plays a vital role in movements like reaching into your back pocket or giving a hug (internal rotation).
Physio Corner: Clinical Relevance
Palpation
Palpating this muscle is uncomfortable but necessary.
Technique: With the patient supine, flex the shoulder slightly. Place your thumb or fingers deep into the Axilla (armpit), pressing posteriorly against the front face of the shoulder blade. Ask the patient to internally rotate gently to feel the contraction.
The Subscapularis is often the most restricted muscle in Frozen Shoulder. Fibrosis here severely limits external rotation (because a tight Subscapularis prevents the arm from turning out).
Manual Muscle Testing & Special Tests
Since the Pectoralis Major and Lats are also internal rotators, we use special tests to isolate the Subscapularis.
Special Tests
| Test Name | Procedure |
|---|---|
| Gerber's Lift-Off Test | Patient places the back of their hand against their lower back. Ask them to lift the hand away from the back. Inability to do so indicates Subscapularis tear/weakness. |
| Belly Press (Napoleon) Test | (Used if patient cannot reach behind back). Patient places hand on belly and presses in by bringing the elbow forward. If the elbow drops back (extension), the test is positive. |
Standard MMT (Internal Rotation)
Position: Prone, arm abducted 90°, elbow hanging off edge.
Action: Patient swings forearm backward/upward (Internal Rotation).
Resistance: Applied to the distal forearm pushing down.
Frequently Asked Questions
Why is it hard to stretch?
Because it is deep in the axilla. The best way to stretch it is via External Rotation (like the doorway stretch) with the arm at the side or abducted.
Does it adduct the arm?
Yes, it assists in adduction, especially when the arm is elevated. It also helps depress the humeral head during elevation.
What is the "Subscapularis Bursa"?
This is a bursa that lies between the muscle tendon and the neck of the scapula. It usually communicates with the shoulder joint cavity, helping to reduce friction.
Test Your Knowledge: Subscapularis Quiz
1. Which nerve supplies the Subscapularis?
2. Where does the Subscapularis insert?
3. What is the primary action of the Subscapularis?
4. Which test specifically assesses the Subscapularis?
5. The Subscapularis prevents which type of dislocation?
6. Where does the Subscapularis originate?
7. To palpate the Subscapularis, you must press into the:
8. The Subscapularis is the ________ of the rotator cuff muscles.
9. Which condition is characterized by a severe restriction of Subscapularis extensibility?
10. True or False: Subscapularis is the only rotator cuff muscle on the anterior side.
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.
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