Shoulder Injuries Part 2 - Seventeen Muscles
Updated: Nov 19, 2020
Part 2: Scapular Attachments of the Shoulder
In Part 2 of "Shoulder Injuries - "The Big Seventeen" we are going to take a look at the various muscles and soft tissue structures that attach to the shoulder, and their impact on the kinetic chain of a shoulder injury.
The scapula (shoulder blade) is often considered to be the foundation (or base of support) for the soft-tissue structures of the upper body.
Seventeen important muscles attach to the scapula, and shoulder dysfunctions can occur whenever there are restrictions, injuries or imbalances in any of these muscles.
The subject of shoulder injuries can become very complex when you begin to consider the inter-actions between all the structures attached to the scapulae.
Add to this an ever increasing complexity when we consider each muscles antagonists, synergists, fascial connections, and neurological enervation.
The seventeen muscles that attach directly to the scapulae include: (1)
Biceps Brachii (long and short head)
Latissimus Dorsi (sometimes absent)
Omohyoid Inferior Belly
Triceps Brachii (long head)
Scapular Dyskinesis – Abnormal Motion Patterns
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 are 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 a shoulder injuries is often in question.
Problems occur when one of the 17 muscles that attach to the scapulae (or their fascial connections) become restricted, injured, or even fatigued. Clinically there is an anacronym for injuries that arise from or are exacerbated by, abnormal motion patterns. The acronym is “SICK” Scapula Syndrome. (4)
The acronym “SICK” refers to Scapular malposition, Inferior medial scapular border prominence, Coracoid pain and malposition, and DysKinesis of scapular movement. The most common symptoms of a “SICK” scapulae are:
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 have a prevalence of dyskinesis. (5)
CONCLUSION PART 2
The shoulder girdle is incredibly complex. Just the scapula itself has 17 muscles that attach to it. A restriction or injury to any of these structures will cause dyskinesis (abnormal motions) that could either cause or exacerbate an already existing injury. When treating any shoulder injury we must always consider the possible impact of abnormal motion patterns and the multiple structures that could be involved.
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.
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
DR. BRIAN ABELSON DC.
Dr. Abelson is the developer of Motion Specific Release (MSR) Treatment Systems. His clinical practice in is located in Calgary, Alberta (Kinetic Health). He has recently authored his 10th publication which will be available later this year.
Dr. Abelson believes in running what the World Federation of Chiropractic calls a EPIC clinical practice. The acronym EPIC stands for Evidence-based, Patient-centred, Inter-professional and Collaborative.
Kinetic Health strives to adhere to the best research evidence available, while combining clinical expertise with the specific values of each patient, in a inter-professional and collaborative care environment.
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