Why is the Subscapularis Called a Forgotten Muscle? Uncovering Its Critical Role

Despite being the largest and strongest muscle in the rotator cuff, the subscapularis was historically nicknamed the “forgotten tendon,” with tears often described as “hidden lesions”. This article explores why is subscapularis called a forgotten muscle and details its critical function in overall shoulder health.

Quick Summary

This article examines the historical reasons the subscapularis was overlooked, its vital function within the rotator cuff, the evolution of its diagnosis, and methods for modern treatment.

Key Points

• Hidden Anatomy: The subscapularis lies on the front of the shoulder blade, making it inaccessible for observation and diagnosis in historical medical practice.

• Diagnostic Advances: Older imaging techniques and open surgery made subscapularis tears easy to miss, but modern MRI, arthroscopy, and specific physical tests have drastically improved detection.

• Largest of the Rotator Cuff: Despite being overlooked, the subscapularis is the largest and most powerful of the four rotator cuff muscles.

• Crucial for Shoulder Stability: It provides key anterior stability and performs internal rotation, which is vital for many daily and athletic movements.

• Specific Tests Exist: Diagnosing subscapularis injuries requires specific physical tests, such as the belly-press, lift-off, and bear hug tests.

• Targeted Rehabilitation is Key: Treatment involves targeted strengthening and stretching exercises, and sometimes surgery, followed by a specific rehabilitation program.

The Anatomy of the 'Hidden' Rotator Cuff Muscle

The rotator cuff is a group of four muscles—the supraspinatus, infraspinatus, teres minor, and subscapularis—that work together to stabilize and move the shoulder joint. The subscapularis, however, holds a unique anatomical position. Unlike the other three muscles, which are located on the posterior (back) side of the shoulder blade, the subscapularis is situated on the anterior (front) side, filling the entire subscapular fossa. Its tendon then runs under the coracoid process to insert onto the lesser tubercle of the humerus. This deep, anterior location means it is completely hidden from view and palpation from the posterior perspective, making it far less accessible during physical examination or traditional surgical approaches.

The Historical Reasons for the 'Forgotten' Label

For decades, the subscapularis was largely overlooked by clinicians and researchers for a variety of reasons. The primary attention was often given to the supraspinatus tendon, whose tears are more common and easier to identify. Additionally, older medical technologies made it challenging to properly diagnose subscapularis injuries.

Challenges Leading to Missed Diagnosis

• Difficult Access: The muscle's location deep beneath other structures, like the deltoid and coracoid process, made it difficult to inspect during open surgical procedures.
• Limitations of Early Imaging: Standard magnetic resonance imaging (MRI) in the past often failed to capture the nuances of subscapularis injuries, especially partial-thickness tears. As one study noted, over half of these injuries were not identified pre-surgery.
• “Hidden Lesions”: Many subscapularis tears, particularly those starting on the articular (joint-side) surface, were described as “hidden lesions” that could be missed during routine cuff repair surgery.
• Asymptomatic Injuries: Smaller tears or injuries were sometimes compensated for by the surrounding, larger shoulder muscles. This could mask symptoms and lead to misdiagnosis or non-diagnosis.

Advances Bringing the Subscapularis to Light

• Improved Imaging: Modern, high-resolution MRI and the use of MR arthrography have significantly improved the ability to detect subscapularis tears.
• Widespread Arthroscopy: The adoption of arthroscopic surgical techniques allows surgeons to get an internal, detailed view of the joint, leading to a much higher rate of subscapularis tear diagnoses and repairs.
• Specialized Physical Exams: Specific physical examination tests, including the belly-press, lift-off, and bear hug tests, were developed and refined to isolate and assess subscapularis function.
• Increased Awareness: A greater understanding of the complex biomechanics of the shoulder has highlighted the crucial role of the subscapularis in overall shoulder function and stability.

The Crucial Role in Shoulder Function

The subscapularis is more than just another rotator cuff muscle; it's the largest and most powerful of the group, representing a majority of the rotator cuff muscle mass. Its functions are essential for proper shoulder mechanics:

• Internal Rotation: It is the primary internal rotator of the arm, allowing movements like reaching behind your back or fastening a bra.
• Humeral Head Depression: It helps depress the humeral head during overhead movements, preventing impingement against the acromion.
• Dynamic Stabilization: As a key dynamic stabilizer, it provides anterior stability to the glenohumeral joint, especially when the arm is abducted and externally rotated. This is particularly important for athletes who perform repetitive overhead motions, like baseball pitchers.

Diagnosis and Assessment

Unlike the more common supraspinatus tears, subscapularis injuries are often the result of a traumatic event, such as a fall on an outstretched arm or a forceful external rotation injury. Diagnosing an injury requires a thorough evaluation, often involving a combination of specific clinical tests and advanced imaging.

Common Symptoms:

• Pain in the front of the shoulder, especially with overhead movements.
• Weakness with internal rotation.
• Difficulty lifting objects or performing push-ups.
• Anterior clicking or popping sensation in the shoulder.

Specific Physical Exam Tests:

• Belly-Press Test: The patient presses their hand into their abdomen, and the clinician looks for a compensatory motion of the elbow moving backward, indicating weakness.
• Lift-Off Test: The patient places the back of their hand on their lower back and is asked to lift it off. An inability to do so is a positive sign.
• Bear Hug Test: The patient holds their hand against their opposite shoulder, and the clinician attempts to pull the hand away. The inability to resist is a positive test.

Subscapularis vs. Other Rotator Cuff Muscles

Feature	Subscapularis	Supraspinatus	Infraspinatus & Teres Minor
Primary Function	Internal Rotation and Anterior Stability	Abduction (first 15°)	External Rotation
Location	Anterior side of the scapula	Superior side of the scapula	Posterior side of the scapula
Commonality of Tear	Less common than supraspinatus tear, often traumatic	Most common rotator cuff tear	Less common than supraspinatus, sometimes chronic
Diagnostic Challenge	Historically difficult due to location, improved with modern imaging	Generally more accessible and easier to diagnose	Easier to test with targeted motions

Rehabilitation and Treatment Strategies

Treatment for subscapularis injuries varies depending on the severity. Partial tears are often managed conservatively, while full-thickness tears may require surgical repair. A comprehensive physical therapy program is a crucial component of recovery, whether or not surgery is performed.

Key Rehabilitation Exercises

• Internal Rotation with Resistance Band: Standing with the elbow bent at 90 degrees and tucked at the side, pull a resistance band across the body.
• Doorway Stretch: Stand in a doorway and place the forearm of the affected side against the frame. Gently lean forward to stretch the chest and anterior shoulder.
• Isometric Push: Stand near a wall and place the palm against it. Press into the wall gently, holding the contraction for several seconds to strengthen the muscle without movement.
• Shoulder External Rotation: This exercise uses a resistance band to strengthen the opposing muscles (infraspinatus and teres minor) to ensure balanced shoulder stability.

For more information on the evolving understanding and treatment of this muscle, see the article Subscapularis tears: hidden and forgotten no more.

Conclusion

The narrative of the subscapularis as a “forgotten muscle” is a testament to the evolution of medical understanding and technology. What was once a challenging and frequently missed diagnosis has become a recognized and treatable condition. By shedding light on its hidden location and vital stabilizing function, modern medicine has ensured that the subscapularis is no longer overlooked. Paying attention to this crucial component of the rotator cuff is essential for proper shoulder health and functional movement, enabling better diagnostic accuracy and more effective treatment for those with shoulder pain.

Frequently Asked Questions

What is the primary function of the subscapularis muscle?

The primary function of the subscapularis muscle is to facilitate the internal, or medial, rotation of the arm and provide dynamic stability to the front of the shoulder joint.

Why were subscapularis injuries often misdiagnosed in the past?

Historically, subscapularis injuries were often misdiagnosed because the muscle is deeply hidden on the front of the shoulder blade, making diagnosis difficult with older imaging and surgical techniques.

What are the common symptoms of a subscapularis injury or tear?

Symptoms can include anterior shoulder pain, weakness with internal rotation, difficulty lifting objects, a clicking or popping sensation in the shoulder, and problems reaching behind the back.

How can doctors diagnose a subscapularis tear today?

Modern diagnosis relies on advanced imaging techniques like high-resolution MRI, sometimes with arthrography, combined with specific physical exam tests such as the belly-press, lift-off, and bear hug tests.

Are subscapularis tears more or less common than other rotator cuff tears?

Tears of the subscapularis tendon are less common than supraspinatus tendon tears and often occur from a traumatic event, like a fall.

What are some effective exercises for strengthening the subscapularis?

Effective exercises include internal rotation with a resistance band, isometric presses against a wall, and movements designed to balance the strength of the opposing external rotators.

When is surgery necessary for a subscapularis tear?

Surgery may be recommended for severe, full-thickness tears, particularly in younger or more active individuals. Smaller partial tears are often managed with conservative treatment and physical therapy.

Does poor subscapularis function affect other parts of the shoulder?

Yes, weakness or injury in the subscapularis can cause muscle imbalances in the shoulder, potentially leading to conditions like shoulder impingement syndrome.