Shoulder Injuries, Part 2: Muscles, Scapular Movement and Coordination
In Part 1, we explored the joints and functional articulations that make up the shoulder complex. In Part 2, we turn our attention to the muscles that produce and coordinate movement of the scapula, shoulder, neck, and upper extremity.
The scapula provides attachment for 17 muscles, creating an important link between the arm, shoulder, neck, and trunk. These muscles do much more than move the shoulder blade in a single direction. Their coordinated activity continually changes according to the movement being performed, the load being handled, and the speed and demands of the task.
Understanding these relationships can help us interpret shoulder function, but variations in muscle activity or scapular movement do not automatically indicate dysfunction. In this article, we will examine the major muscular connections of the scapula, how they contribute to shoulder movement and control, and what changes in scapular movement may mean when assessing shoulder pain and injury.
Article Index:
Seventeen Muscles Shoulder Muscles
The scapula provides attachment for a remarkable number of muscles that connect the shoulder blade with the arm, chest, neck, and upper back. Together, these muscles contribute to movement and control of both the scapula and the upper extremity.
Seventeen muscles are commonly described as having an attachment to the scapula.
Some act directly on the scapula, while others primarily move the humerus, stabilize the glenohumeral joint, or contribute to movements of the neck and upper extremity. Their activity changes continuously depending on the position of the arm, the load being handled, and the demands of the task.
This interconnected anatomy helps explain why shoulder function cannot be understood by examining a single muscle in isolation. Strength, endurance, mobility, neurological control, previous injury, and coordination between muscle groups can all influence how the shoulder performs. However, finding weakness, tightness, or altered activation in an individual muscle does not necessarily mean that it is the cause of a person's shoulder pain.
The seventeen muscles that attach directly to the scapulae include: (1)
Biceps Brachii (long and short head)
Coracobrachialis
Deltoid
Infraspinatus
Latissimus Dorsi (variable scapular attachment)
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
Scapular dyskinesis describes an alteration or variation in the position or movement of the scapula during arm motion. It is commonly observed during clinical examination, particularly in people with shoulder symptoms, but it is not a diagnosis by itself.
Scapular movement can change for many reasons, including pain, fatigue, muscle weakness, altered motor control, previous injury, joint mobility, neurological involvement, and the demands of a particular activity. It is therefore rarely useful to attribute an altered movement pattern to a single muscle.
Scapular dyskinesis is frequently observed in association with conditions such as rotator cuff-related shoulder pain, instability, and other shoulder disorders. However, altered scapular movement is also common in people without shoulder pain. This means that its presence does not automatically identify the source of a patient's symptoms or establish that the movement pattern caused the injury.
The more useful clinical question is whether the observed scapular movement appears to be relevant to the individual's symptoms or function. This can be explored as part of a broader examination that considers shoulder mobility, strength, endurance, neurological function, symptom response, and the physical demands placed on the shoulder.
Scapulohumeral Rhythm
As discussed in Part 1, shoulder elevation involves coordinated movement between the glenohumeral joint and the scapula, together with movement through the acromioclavicular and sternoclavicular joints. The scapula does not simply rotate upward as the arm rises. It moves in three dimensions, continually adjusting its position as the humerus moves.
This coordinated interaction between the scapula and humerus is commonly referred to as scapulohumeral rhythm. Rather than representing one ideal or fixed movement pattern, scapulohumeral rhythm varies between individuals and changes according to the task, load, speed, fatigue, and range of motion.
Effective shoulder function therefore depends less on reproducing a theoretically perfect scapular position and more on having sufficient mobility, strength, endurance, and motor control to meet the demands placed on the shoulder.
Why Scapular Movement Matters
When scapular movement appears to contribute to a patient's symptoms or functional limitations, rehabilitation may include exercises directed toward scapular control, strength, endurance, and integration with movements of the arm and trunk. The goal is not necessarily to make the scapula move according to a single predetermined pattern, but to improve the shoulder's ability to coordinate movement and tolerate progressively greater loads. Contemporary clinical literature similarly emphasizes motor control and integrated rehabilitation rather than simply strengthening an isolated "weak" scapular muscle.
The SICK Scapulae Concept
The term SICK scapula was introduced by Burkhart, Morgan and Kibler in 2003 as part of their work on shoulder dysfunction in overhead throwing athletes. The acronym describes a group of clinical findings that may accompany altered scapular position and movement.
SICK stands for:
Scapular malposition
Inferior medial border prominence
Coracoid pain and malposition
Kinesis abnormalities of scapular movement
The original model described changes in scapular position and movement associated with shoulder pain and impaired function in throwing athletes. It helped draw greater clinical attention to the role of the scapula within the shoulder complex rather than focusing exclusively on the glenohumeral joint.
How We View the SICK Scapula Today
The SICK scapula remains a useful historical framework, but our understanding of scapular movement has evolved. Scapular asymmetry, prominence of the medial border, or altered movement does not necessarily indicate pathology. These findings need to be interpreted in relation to the individual's symptoms, strength, mobility, neurological function, activity demands, and overall shoulder examination.
Scapular dyskinesis can accompany shoulder conditions, including rotator cuff-related shoulder pain, instability and acromioclavicular joint disorders, but it should not automatically be assumed to be the cause of those conditions. For example, scapular dyskinesis and SICK scapula findings have been documented following chronic AC joint dislocation, illustrating that altered scapular movement can also occur as part of another shoulder disorder rather than necessarily initiating it.
For clinicians, the important question is therefore not simply, “Does this patient have a SICK scapula?” Instead, we need to determine whether the observed scapular movement is relevant to the patient's pain, function, and ability to perform the activities that matter to them.
Conclusion - Part 2
The 17 muscles that attach to the scapula illustrate just how interconnected the shoulder complex is. Together, they contribute to movement and control of the scapula, glenohumeral joint, neck, and upper extremity, continually adapting their activity to the position of the arm, the load being handled, and the demands of the task.
Scapular movement is equally complex. Variations in scapular position or motion do not automatically represent dysfunction, and there is no single ideal movement pattern that applies to everyone. Findings such as scapular dyskinesis or features historically described as a SICK scapula become clinically meaningful when they are considered alongside a person's symptoms, strength, mobility, neurological function, activity demands, and overall shoulder examination.
For rehabilitation, the goal is not simply to correct an individual muscle or restore the scapula to a predetermined position. Instead, treatment should focus on the factors that are relevant to the individual, progressively developing the mobility, strength, endurance, coordination, and load tolerance needed for the activities they want to perform.
In Part 3: Rotator Cuff, Examination and Diagnosis, we will examine the rotator cuff in greater detail and explore how clinical examination, special tests, neurological assessment, and diagnostic imaging can be integrated when evaluating shoulder pain and injury.
References - Part 2
Sciascia A, Kibler WB. Current views of scapular dyskinesis and its possible clinical relevance. Int J Sports Phys Ther. 2022;17(2):117–130.
Salamh PA, Hanney WJ, Boles T, Holmes D, McMillan A, Wagner A, Kolber MJ. Is it time to normalize scapular dyskinesis? The incidence of scapular dyskinesis in those with and without symptoms: A systematic review of the literature. Int J Sports Phys Ther. 2023;18(3):558–576.
Hogan C, Corbett JA, Ashton S, Perraton L, Frame R, Dakic J. Scapular dyskinesis is not an isolated risk factor for shoulder injury in athletes: A systematic review and meta-analysis. Am J Sports Med. 2021;49(10):2843–2853.
Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: Spectrum of pathology Part III: The SICK scapula, scapular dyskinesis, the kinetic chain, and rehabilitation. Arthroscopy. 2003;19(6):641–661.
Kibler WB, Sciascia A. Current concepts: Scapular dyskinesis. Br J Sports Med. 2010;44(5):300–305.
Burn MB, McCulloch PC, Lintner DM, Liberman SR, Harris JD. Prevalence of scapular dyskinesis in overhead and nonoverhead athletes: A systematic review. Orthop J Sports Med. 2016;4(2):2325967115627608.
Ludewig PM, Cook TM. Alterations in shoulder kinematics and associated muscle activity in people with symptoms of shoulder impingement. Phys Ther. 2000;80(3):276–291.
McClure PW, Michener LA, Karduna AR. Shoulder function and 3-dimensional scapular kinematics in people with and without shoulder impingement syndrome. Phys Ther. 2006;86(8):1075–1090.
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DR. BRIAN ABELSON DC. - The Author
Dr. Brian Abelson is a chiropractor, author, and educator with more than 30 years of clinical experience in musculoskeletal care, rehabilitation, and sports performance. His educational work focuses on musculoskeletal conditions, human movement, sports biomechanics, and evidence-informed approaches to treatment and rehabilitation.
He is the developer of Motion Specific Release (MSR) and Clinical Director of Kinetic Health in Calgary, Alberta, Canada.
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