In this four-part series on shoulder complexities, we'll delve into the shoulder's intricate design, embracing its five joint structures, the pivotal role of the rotator cuff, the diagnostic challenges it presents, and the impressive seventeen muscles that connect to it. We aim to offer a holistic view, highlighting both manual therapy and exercise treatment recommendations. The shoulder's design ensures a balance between mobility and stability. When this balance is disrupted, susceptibility to injuries heightens."
Article Index:
Introduction
5 Joints
Conclusion & References
Introduction
The shoulder complex, an intricate and sophisticated anatomical system, comprises the glenohumeral joint along with 4 other osseous components, muscular attachments, tendinous insertions, ligamentous support, fascial elements, and neurovascular constituents.
The scapula, a key component in this assembly, boasts connections to an astounding seventeen distinct muscular structures. In concert, the osseous, muscular, and soft tissue elements of the shoulder work synergistically to establish a delicate equilibrium of forces, ensuring both mobility and stability. However, when this finely tuned homeostasis is perturbed, the shoulder becomes increasingly predisposed to injuries and functional impairments.
Understanding the Unique Nature of Your Shoulders
Our shoulders are ingeniously designed to offer a remarkable range of motion, albeit at the expense of stability. In comparison to other joints in the body, the shoulder girdle is relatively unstable. This inherent instability can have immediate repercussions on various other anatomical structures when shoulder injuries occur.
In order to effectively address a shoulder injury, it is crucial to comprehend the interconnections, relative movements, and kinetic chain associations among the shoulder's various soft-tissue and osseous structures. To begin, let's explore the shoulder joints.
Note that we have an abundance of information to share on this intricate subject. In this initial segment, we will concentrate on the shoulder joints. Future articles in this series will delve into other affected structures, diagnostic approaches, and potential solutions. Stay tuned, or feel free to skip ahead to the section that piques your interest!
Anatomy and Biomechanics of Shoulder Joints
Contrary to popular belief, the shoulder is not composed of just one joint. Instead, it encompasses five distinct joints that work together to facilitate movement.
The shoulder girdle comprises five crucial joints, including three traditional joints and two physiological joints:
Glenohumeral Joint.
Acromioclavicular Joint.
Sternoclavicular Joint.
Scapulothoracic Joint (physiological joint).
Subacromial Joint (physiological joint).
Appreciating the interconnections among the components of these five joints is crucial for effectively addressing shoulder injuries.
Bear in mind that joints do not function independently; a limitation or dysfunction in one region invariably leads to compensatory adjustments elsewhere in the body. To fully resolve a shoulder injury, it is often necessary to address these compensatory mechanisms along the joint's kinetic chain.
Glenohumeral (GH) Joint
The glenohumeral joint, also known as the shoulder joint, is a ball-and-socket joint filled with synovial fluid. This fluid aids in reducing friction between the articular cartilage during movement in synovial joints. The glenohumeral joint facilitates flexion, extension, adduction, abduction, and internal and external rotation of the arm.
Glenohumeral Instability
During shoulder joint examinations and translation tests, practitioners frequently encounter glenohumeral instability. Studies indicate that prolonged periods of shoulder instability, specifically glenohumeral instability, can initiate a cycle of micro-trauma. This, in turn, may lead to secondary impingement syndromes that often result in persistent shoulder pain.
Anterior shoulder instability, characterized by laxity of the anterior capsule, is often associated with issues in the posterior shoulder capsule, significantly impacting the shoulder's kinetic chain.
When the posterior shoulder capsule tightens, it influences the function of the Inferior Glenohumeral Ligament (IGHL). The IGHL plays a vital role in maintaining the shoulder's position within the joint, acting as a supportive hammock or sling for the humerus (humeral head). If the IGHL is not functioning properly, the position of the arm shifts, potentially leading to a range of impingement issues (1, 2).
The glenohumeral joint showcases intriguing fascial connections. For instance, the subscapular fascia is continuous with the rhomboid fascia, which subsequently inserts into the glenohumeral joint. Any constraints or forces produced along this fascial line have the potential to impact the functionality of the glenohumeral joint (1).
Acromioclavicular (AC) Joint
The acromioclavicular (AC) joint is situated between the acromion process of the scapula and the lateral end of the clavicle. The AC joint is classified as a 'gliding' or 'plane type' synovial joint.
The scapula's acromion rotates on the clavicle's acromial end. Although the AC joint is a gliding joint, it functions as a pivot point to enhance scapular motion, which subsequently increases arm rotation. The AC joint's motion is often described as scapular movement relative to the clavicle.
The AC joint is highly susceptible to both trauma and degenerative changes (3).
Sternoclavicular (SC) Joint
The sternoclavicular joint is situated between the manubrium of the sternum and the first costal cartilage.
The SC joint represents the sole attachment point of the upper limb to the axial skeleton. This joint enables clavicle movement across three planes, with the majority of the movement taking place in the anteroposterior and vertical planes.
Instabilities due to injuries and osteoarthritic changes are the most prevalent issues associated with the SC joint. The sternoclavicular joint is is classified as a saddle-type synovial joint.
Scapulothoracic (Scapulocostal) Joint
The scapulothoracic joint is a 'physiological joint', which is musculo-tendinous in nature. It forms through the articulation of the anterior scapula and the posterior thoracic rib cage. The trapezius, rhomboids, and serratus anterior muscles primarily constitute the scapulothoracic joint.
The scapulothoracic joint facilitates gliding movements such as elevation, depression, retraction, protraction, and superior and inferior rotation of the scapula. The joint's movement generally results from a combination of SC and AC joint motion. The scapulothoracic joint enhances arm elevation while offering a stable foundation for the controlled motions between the humeral head and glenoid fossa (4).
The most frequently encountered issues with the scapulothoracic joint are due to abnormal motion patterns. Abnormal shoulder blade motion patterns (scapular dyskinesis) can lead to significant dysfunction. We will explore this topic further in part two of "Shoulder Injuries".
Subacromial (Suprahumeral) Joint
The subacromial joint is a 'physiological joint' formed by the articulation of the coracoacromial ligament and the humerus head.
This joint arises from the space between the humerus and the acromion process of the scapula. The subacromial joint is primarily occupied by the subacromial bursa and the supraspinatus tendon.
Subacromial Impingement Syndrome (SIS) manifests as anterior-lateral shoulder pain during arm elevation. This syndrome is characterized by symptomatic irritation of the subacromial structures, situated between the coraco-acromial arch and the humeral head, during the arm's elevation.
Anatomy of the Shoulder
Interested in delving deeper into shoulder joint anatomy and biomechanics?
Take a look at our shoulder anatomy video. In this presentation, we discuss the bones (osseous structures) that comprise the shoulder girdle.
RECOMMENDED REFERENCE BOOKS
Netter Atlas of Human Anatomy https://amzn.to/3SQYWgx
Functional Atlas of the Human Fascial System - Carla Stecco https://amzn.to/3TE1EqP Functional Anatomy: Anatomy, Kinesiology, and Palpation https://amzn.to/3f49Xgn
Anatomy Trains: Myofascial Meridians for Manual Therapists https://amzn.to/3SCkhtZ
Conclusion
In conclusion, the shoulder girdle, with its five joints, is a complex and sophisticated structure crucial for our daily activities. Dysfunctions within any of these joints can result in compensations and abnormal motion throughout the entire shoulder complex. Understanding the interrelationships and biomechanics of these joints is essential for effectively addressing shoulder injuries and dysfunction.
As we proceed to Part 2 of "Shoulder Injuries," we will explore the soft tissue structures connected directly to the shoulder blades (scapulae) and examine how restrictions in any of these structures can easily cascade, leading to the development of abnormal motion patterns (dyskinesis), impingement syndromes, and various other issues. By increasing our knowledge of the shoulder's anatomy and the implications of dysfunction, we can better identify potential problems, prevent injuries, and facilitate rehabilitation when needed.
DR. BRIAN ABELSON DC. - The Author
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.
Our system offers a blend of orthopedic and neurological assessments, myofascial interventions, osseous manipulations, acupressure techniques, kinetic chain explorations, and functional exercise plans.
With MSR, your practice will flourish, achieve remarkable clinical outcomes, and see patient referrals skyrocket. Step into the future of treatment with MSR courses and membership!
References - Part 1
Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology: Part I: pathoa-natomy and biomechanics. Arthroscopy 2003;19:404-420
Shuenke, Micheal (2010). Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. New York: Everbest Printing Ltd. ISBN 978-1-60406-286-1.
Levangie PK, Norkin CC. Joint Structure and Function : A Comprehensive Analysis. 4th ed. India: JAYPEE; 2006.
Levangie, P.K. and Norkin, C.C. (2005). Joint structure and function: A comprehensive analysis (4th ed.). Philadelphia: The F.A. Davis Company.
Stecco, Carla; Stecco, Carla. Functional Atlas of the Human Fasical System. Elsevier Health Sciences.
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.
Magee, D.J. (2014). Orthopedic Physical Assessment. St. Louis, MO: Elsevier.
Palastanga, N., Field, D., & Soames, R. (2012). Anatomy and Human Movement: Structure and Function. Edinburgh: Elsevier.
Wilk, K.E., Reinold, M.M., & Andrews, J.R. (2009). The Athlete's Shoulder. Philadelphia, PA: Churchill Livingstone/Elsevier.
Ludewig, P.M., & Braman, J.P. (2011). Shoulder impingement: Biomechanical considerations in rehabilitation. Manual Therapy, 16(1), 33-39.
Lewis, J.S. (2011). Rotator cuff tendinopathy: A model for the continuum of pathology and related management. British Journal of Sports Medicine, 45(13), 918-923.
Ellenbecker, T.S., & Cools, A. (2010). Rehabilitation of shoulder impingement syndrome and rotator cuff injuries: An evidence-based review. British Journal of Sports Medicine, 44(5), 319-327.
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