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Shoulder Injuries Part 2 - Seventeen Muscles Are Involved

Updated: Dec 5, 2023

In Part 2 of "Shoulder Injuries," we will examine the various muscles and soft tissue structures connected to the shoulder and their influence on the kinetic chain during a shoulder injury.

Article Index:


Seventeen Muscles

The scapula (shoulder blade) serves as the foundation or base of support for the upper body's soft-tissue structures. With seventeen crucial muscles attached to the scapula, shoulder dysfunctions can arise from restrictions, injuries, or imbalances in any of these muscles.

The topic of shoulder injuries becomes increasingly complex when we take into account the interactions among all the structures connected to the scapulae. This complexity further intensifies as we consider each muscle's antagonists, synergists, fascial connections, and neurological innervation.

The seventeen muscles that attach directly to the scapulae include: (1)

  1. Biceps Brachii (long and short head)

  2. Coracobrachialis

  3. Deltoid

  4. Infraspinatus

  5. Latissimus Dorsi (sometimes absent)

  6. Levator Scapula

  7. Omohyoid Inferior Belly

  8. Pectoralis Minor

  9. Rhomboid Minor

  10. Rhomboid Major

  11. Serratus Anterior

  12. Subscapularis

  13. Supraspinatus

  14. Teres Major

  15. Teres Minor

  16. Trapezius

  17. Triceps Brachii (long head)


Scapular Dyskinesis

Dyskinesis (abnormal motion patterns) is one of the primary reasons we are now talking about all the muscles that attach to the scapulae. Research has shown that abnormal motion patterns of the shoulder blade (scapular dyskinesis) can result in considerable dysfunction. All it takes to cause an abnormal motion pattern is a problem with one these seventeen muscles.

Abnormal scapular motion can either cause, or exacerbate a shoulder injury. Clinically we often observe scapular dyskinesis (abnormal motion patterns) with rotator cuff injuries, nerve entrapment syndromes (Thoracic Outlet Syndrome – TOS), joint instability (glenohumeral joint) and cases where active range of motion and strength in the shoulder is diminished without any apparent injury. (2)

In the previous blog, we talked about the interplay of the five joints (three osseous and two physiological articulations) of the shoulder. These are the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, scapulothoracic joint and subacromial joint.

Equally as important as the synergy of shoulder girdle joints, an effective balance of myofascial (muscle and connective tissue) forces is needed to create a smooth scapulohumeral rhythm.

  • Scapulohumeral rhythm is the pattern of muscle contractions and motion that occurs between your scapula and your humerus (upper arm).

  • Good scapulohumeral rhythm is essential for optimal shoulder function. (3)

  • Without this smooth rhythm, a full resolution of shoulder injuries is often in question.


SICK Scapulae?

Issues arise when any of the 17 muscles connected to the scapulae (or their fascial links) become constrained, injured, or even exhausted. In a clinical setting, there's an acronym for injuries that stem from or are worsened by abnormal motion patterns. It's called "SICK" Scapula Syndrome. (4)

The acronym "SICK" stands for Scapular malposition, Inferior medial scapular border prominence, Coracoid pain and malposition, and DysKinesis of scapular movement. The most frequently observed symptoms of a "SICK" scapulae include:

  • Anterior shoulder pain (most common symptom).

  • Lateral arm pain (proximal pain).

  • Neck pain (scapular pain can radiate into the cervical paraspinal muscles).

  • Scapular pain (especially posterior superior scapular pain).

  • Shoulder pain (predominately superior shoulder pain).

  • Thoracic Outlet (TOS) symptoms (numbness or tingling in the arms or hands, pain in the neck, shoulder or hand, and even a weakened grip).

Note: Overhead athletes exhibit a higher prevalence of dyskinesis. (5)


Conclusion - Part 2

In conclusion, the 17 muscles that attach directly to the scapulae play a crucial role in maintaining the complex structure and function of the shoulder. These muscles, along with their fascial connections, contribute to the overall stability and mobility of the shoulder girdle. Understanding their individual roles and interrelationships is essential for addressing shoulder injuries and dysfunctions. By ensuring proper balance and functioning of these muscles, one can promote optimal shoulder health and effectively prevent or manage issues related to the "SICK" scapula syndrome.

In Part 3 of “Shoulder Injuries – The Big Seventeen” we will be discussing the Rotator Cuff and some the major factors to consider in shoulder injury diagnosis.



Dr. Abelson's approach in musculoskeletal health care reflects a deep commitment to evidence-based practices and continuous learning. In his work at Kinetic Health in Calgary, Alberta, he focuses on integrating the latest research with a compassionate understanding of each patient's unique needs. As the developer of the Motion Specific Release (MSR) Treatment Systems, he views his role as both a practitioner and an educator, dedicated to sharing knowledge and techniques that can benefit the wider healthcare community. His ongoing efforts in teaching and practice aim to contribute positively to the field of musculoskeletal health, with a constant emphasis on patient-centered care and the collective advancement of treatment methods.


Revolutionize Your Practice with Motion Specific Release (MSR)!

MSR, a cutting-edge treatment system, uniquely fuses varied therapeutic perspectives to resolve musculoskeletal conditions effectively.

Attend our courses to equip yourself with innovative soft-tissue and osseous techniques that seamlessly integrate into your clinical practice and empower your patients by relieving their pain and restoring function. Our curriculum marries medical science with creative therapeutic approaches and provides a comprehensive understanding of musculoskeletal diagnosis and treatment methods.

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References - Part 2

  1. Struyf, F., Scapular positioning and movement in unimpaired shoulders, shoulder impingement syndrome, and glenohumeral instability, Scandinavian Journal of Medicine and Science in sports, jrg20, nr3, 2011, p352.

  2. Cools AM, Witvrouw EE, Danneels LA, et al. Test-retest reproducibility of concentric strength values for shoulder girdle protraction and retraction using the Biodex isokinetic dynamometer. Isokinetics Exerc Sci 2002;10:129-136.

  3. Cools AM, Witvrouw EE, Declercq G, et al. Scapular muscle recruitment pattern: trapezius muscle latency in overhead athletes with and without impingement symptoms. Am J Sports Med 2003; 31:542-549.

  4. The disabled throwing shoulder: spectrum of pathology part III: the SICK scapula, scapular dyskinesis, the kinetic chain, and rehabilitationfckLRBurkhart, Stephen S et al.fckLRArthroscopy , Volume 19 , Issue 6 , 641 - 661

  5. Matthew B. Burn, Patrick C. McCulloch, David M. Lintner, Shari R. Liberman, and Joshua D. Harris Prevalence of Scapular Dyskinesis in Overhead and Nonoverhead Athletes: A Systematic Review Orthopaedic Journal of Sports Medicine February 2016 vol. 4 no. 2

  6. Neumann, D.A. (2017). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. St. Louis, MO: Elsevier.

  7. Kibler, W. B., & Sciascia, A. (2010). Current concepts: Scapular dyskinesis. British Journal of Sports Medicine, 44(5), 300-305.

  8. Ludewig, P. M., & Cook, T. M. (2000). Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement. Physical Therapy, 80(3), 276-291.

  9. Burkhart, S. S., Morgan, C. D., & Kibler, W. B. (2003). The disabled throwing shoulder: Spectrum of pathology Part I: Pathoanatomy and biomechanics. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 19(4), 404-420.

  10. McClure, P. W., Michener, L. A., & Karduna, A. R. (2006). Shoulder function and 3-dimensional scapular kinematics in people with and without shoulder impingement syndrome. Physical Therapy, 86(8), 1075-1090.

  11. Abelson, B., Abelson, K., & Mylonas, E. (2018, February). A Practitioner's Guide to Motion Specific Release, Functional, Successful, Easy to Implement Techniques for Musculoskeletal Injuries (1st edition). Rowan Tree Books.


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