what is serratus anterior?

Serratus Anterior Muscle: Anatomy, Function, Assessment, Exercises, and Clinical Relevance

Introduction

The serratus anterior is a unique and often overlooked muscle that plays a pivotal role in upper limb function, particularly in scapular movement and stabilization. Sometimes called the "boxer’s muscle" due to its role in punching movements, it wraps around the rib cage and connects the shoulder blade (scapula) to the thorax.

This muscle is essential not only for upper extremity motion but also for postural support and shoulder joint integrity. Dysfunction in the serratus anterior can contribute to conditions such as scapular winging, shoulder impingement, and poor upper-body biomechanics. As such, understanding its anatomy, function, and clinical importance is key for physiotherapists, sports rehab specialists, and healthcare professionals involved in musculoskeletal care.

Anatomy of the Serratus Anterior Muscle

The serratus anterior is a fan-shaped, flat muscle that lies on the lateral wall of the thorax. It is largely hidden beneath the scapula and pectoral muscles, but its activation is essential for proper scapular control.

[Origin]

• Arises from the outer surfaces of the upper 8 or 9 ribs (ribs 1–8 or 1–9), near their costal cartilages.

[Insertion]

• Inserts onto the anterior (costal) surface of the medial border of the scapula.
  This means the muscle wraps around the thorax and connects deep under the scapula.

[Nerve Supply]

• Supplied by the long thoracic nerve (roots C5, C6, and C7).
  This nerve runs superficially along the thoracic wall, making it vulnerable to injury.

[Blood Supply]

• Receives blood from the lateral thoracic artery and branches of the thoracodorsal artery.

Function

The serratus anterior plays a vital role in scapulothoracic rhythm, a key component of overhead and upper limb movements.

Its primary actions include

• Protraction of the scapula (pulling the shoulder blade forward and around the ribcage).

• Upward rotation of the scapula, especially during arm elevation (e.g., raising the arm overhead).

• Anchoring the scapula against the thoracic wall, preventing winging.

These functions are essential for any pushing, punching, or reaching movements, as well as for proper shoulder joint mechanics.

Clinical Assessment

Assessing the serratus anterior helps identify weakness, nerve injury, or scapular dysfunction. Common findings include scapular winging and poor shoulder control.

[Palpation]
Due to its deep position, palpation of the serratus anterior is limited.

• Patient position: Sitting or supine.

• Procedure: Ask the patient to punch forward or push against resistance (like a wall or therapist’s hand). Palpation can be attempted over the lateral thoracic wall between ribs 5–8, beneath the axilla.

[Muscle Power Testing]
The most common functional test is the Wall Push Test.

• Patient position: Standing, hands against a wall at shoulder height.

• Procedure: Ask the patient to perform a wall push-up slowly.

• Observation: Watch for scapular winging, especially on one side. Prominence of the medial border of the scapula indicates serratus anterior weakness or long thoracic nerve palsy.

[Length Testing]
There is no formal "length test" for the serratus anterior due to its functional nature, but tightness is rarely an issue. Instead, inhibition or weakness is the more common clinical problem.

Exercises for Strength and Rehabilitation

Rehabilitating the serratus anterior is essential in treating shoulder instability, winging, and impingement syndromes. Strengthening this muscle restores normal scapular motion.

[Wall Slides]

• Position: Standing with forearms on a wall.

• Procedure: Slide arms up the wall while maintaining light pressure through the forearms. Emphasize upward rotation and protraction of the scapula.

• Reps: 10–15 reps × 2–3 sets.

[Push-Up Plus]

• Position: Standard push-up or on knees (modified).

• Procedure: After the push-up movement, push the body further upward by protracting the scapulae (rounding the shoulders forward), then return to the starting position.

• Reps: 12–15 reps × 2 sets.

[Dynamic Hug] (Resistance Band)

• Position: Standing, band anchored behind.

• Procedure: Hold the band in both hands and move arms forward and inward, simulating a hugging motion, focusing on scapular protraction.

• Reps: 10–15 reps × 3 sets.

[Serratus Wall Punch]

• Position: Standing with fist on the wall, elbow slightly bent.

• Procedure: Gently punch forward into the wall, activating the serratus anterior.

• Can also be performed supine with a weight held vertically.

Trigger Points

The serratus anterior can harbor trigger points that refer pain in a misleading pattern.

[Common Trigger Point Locations]

• Mid-axillary line near ribs 5–8.

[Referred Pain Pattern]

• Lateral thorax

• Side of the rib cage

• Occasionally the medial arm or scapula

[Management]

• Myofascial release

• Trigger point therapy (manual or dry needling)

• Stretching and postural retraining

• Breathing exercises may help due to the rib origin

Related Injuries and Clinical Conditions

[Long Thoracic Nerve Palsy]
Damage to the long thoracic nerve leads to serratus anterior paralysis, causing scapular winging. This is commonly seen in athletes or after surgical procedures like lymph node removal.

[Scapular Winging]
One of the hallmark signs of serratus anterior dysfunction. The scapula lifts off from the thoracic wall, especially when pushing against resistance.

[Shoulder Impingement]
Poor scapular control due to serratus anterior weakness can cause the scapula to fail to rotate properly, leading to impingement of rotator cuff tendons.

[Shoulder Instability]
Inadequate activation of the serratus anterior may result in poor scapular rhythm, leading to excessive strain on the glenohumeral joint.

Frequently Asked Questions (FAQs)

1. What is the main role of the serratus anterior?
The serratus anterior protracts and rotates the scapula upward, keeping it stabilized against the rib cage during arm movements.

2. What happens when the serratus anterior is weak?
Weakness can cause scapular winging, resulting in shoulder pain, limited arm elevation, and reduced upper limb strength.

3. How do I strengthen my serratus anterior?
Exercises like push-up plus, wall slides, and dynamic hugs target and strengthen the serratus anterior effectively.

4. Can serratus anterior cause rib or chest pain?
Yes, trigger points in this muscle can refer pain to the side of the chest or ribs and mimic cardiac or respiratory symptoms.

5. What nerve supplies the serratus anterior?
The long thoracic nerve (C5–C7), which runs along the lateral chest wall, innervates the serratus anterior.

6. Is serratus anterior tightness common?
No, this muscle is more often inhibited or weak, especially in shoulder dysfunction. Tightness is rarely a clinical concern.

Here are AdSense-friendly references for your article on the Serratus Anterior muscle. These sources are trusted, medically accurate, and publicly accessible, making them ideal for educational and health-related content:

References

1. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2013). Clinically Oriented Anatomy (7th Edition). Wolters Kluwer.
   https://shop.lww.com/Clinically-Oriented-Anatomy/p/9781451119459
   (Comprehensive textbook widely used in medical education for muscle origin, insertion, and nerve supply.)

2. Travell, J. G., & Simons, D. G. (1999). Myofascial Pain and Dysfunction: The Trigger Point Manual, Volume 1. Lippincott Williams & Wilkins.
   https://www.wolterskluwer.com/en/solutions/ovid/myofascial-pain-and-dysfunction-the-trigger-point-manual-vol-1-1498
   (Trusted source for understanding trigger points and referred pain patterns.)

3. Magee, D. J. (2014). Orthopedic Physical Assessment (6th Edition). Elsevier.
   https://www.elsevier.com/books/orthopedic-physical-assessment/magee/978-1-4557-0973-5
   (Covers clinical testing, including palpation, power, and length assessment.)

4. National Library of Medicine (PubMed). Serratus Anterior Muscle Overview.
   https://pubmed.ncbi.nlm.nih.gov/* (Search: “Serratus Anterior”)
   (Access peer-reviewed journals and research articles related to the muscle’s function and clinical relevance.)

5. Physiopedia. Serratus Anterior Muscle.
   https://www.physio-pedia.com/Serratus_Anterior
   (An open-access platform for evidence-based physiotherapy education.)

6. TeachMeAnatomy. Serratus Anterior Muscle.
   https://teachmeanatomy.info/thorax/muscles/serratus-anterior/
   (Illustrated, easy-to-read content for anatomy learners.)

7. Kenhub. Serratus Anterior: Anatomy, Function & Clinical Notes.
   https://www.kenhub.com/en/start/serratus-anterior
   (Great for visual learners; includes anatomy diagrams and narrated videos.)

8. AAOS—American Academy of Orthopaedic Surgeons. Shoulder Injuries and Muscle Function.
   https://orthoinfo.aaos.org/* (Search: “Serratus Anterior”)
   (Credible source for injury-related information.)