Shoulder Injuries Part 2 - Seventeen Muscles Are Involved
- Dr. Brian Abelson DC
- Apr 11, 2023
- 6 min read
Updated: Jun 14, 2024
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 Shoulder Muscles
The scapula (shoulder blade) is 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 consider the interactions among all the structures connected to the scapulae. This complexity 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)
Biceps Brachii (long and short head)
Coracobrachialis
Deltoid
Infraspinatus
Latissimus Dorsi (sometimes absent)
Levator Scapula
Omohyoid Inferior Belly
Pectoralis Minor
Rhomboid Minor
Rhomboid Major
Serratus Anterior
Subscapularis
Supraspinatus
Teres Major
Teres Minor
Trapezius
Triceps Brachii (long head)
Scapular Dyskinesis
Dyskinesis (abnormal motion patterns) is one of the primary reasons we are now talking about all the muscles attached 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 of 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 the active range of motion and strength in the shoulder is diminished without any apparent injury. (2)
In the previous article, we discussed the interplay of the shoulder's five joints (three osseous and two physiological articulations). These are the glenohumeral joint, acromioclavicular joint, sternoclavicular joint, scapulothoracic joint and subacromial joint.
Equally important as the synergy of shoulder girdle joints, an effective balance of myofascial (muscle and connective tissue) forces are needed to create a smooth scapulohumeral rhythm.
Scapulohumeral rhythm is the pattern of muscle contractions and motion between your scapula and your humerus (upper arm).
Good scapulohumeral rhythm is essential for optimal shoulder function. (3)
A full resolution of shoulder injuries is often questioned without this smooth rhythm.
SICK Scapulae
Issues arise when the 17 muscles connected to the scapulae (or their fascial links) become constrained, injured, or 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).
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 roles and interrelationships is essential for addressing shoulder injuries and dysfunctions. Ensuring proper balance and functioning of these muscles 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 discuss the Rotator Cuff and some of the major factors to consider in shoulder injury diagnosis.
References - Part 2
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.
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.
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.
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
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
Neumann, D.A. (2017). Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. St. Louis, MO: Elsevier.
Kibler, W. B., & Sciascia, A. (2010). Current concepts: Scapular dyskinesis. British Journal of Sports Medicine, 44(5), 300-305.
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.
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.
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.
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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DR. BRIAN ABELSON DC. - The Author
Dr. Abelson is dedicated to using evidence-based practices to improve musculoskeletal health. At Kinetic Health in Calgary, Alberta, he combines the latest research with a compassionate, patient-focused approach. As the creator of the Motion Specific Release (MSR) Treatment Systems, he aims to educate and share techniques to benefit the broader healthcare community. His work continually emphasizes patient-centred care and advancing treatment methods.
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