The article Shoulder Joints Anatomy: Shoulder Joints and Their Movements provides complete information about shoulder joints and their movement. The article includes the following:
Introduction to the Shoulder Joint
The article Shoulder joints anatomy: shoulder joints and their movements explores the intricate anatomy of shoulder joints and delves into the dynamic range of movements they enable in the human body. The shoulder joint is complex and versatile in the human body. It allows a wide range of motion for the upper extremities. It plays a crucial role in our daily activities, such as → reaching, lifting, and throwing.
Let’s discuss the functions of the shoulder joint.
The Function of the Shoulder Joint
The shoulder joint enables a wide range of motions. It includes → flexion, extension, abduction, adduction, internal rotation, and external rotation. Its versatility allows us to perform various activities, such as → throwing a ball, lifting objects, and combing our hair. The coordinated actions of → muscles, tendons, and ligaments, contribute to the stability and smooth functioning of the joint. We will discuss movements later in this article.
In the upcoming section, we will discuss the anatomy of the shoulder joint, which includes → Arterial surfaces, Ligaments, Innervation, and Blood supply.
Anatomy of the Shoulder Joints
The shoulder joint (glenohumeral joint) is complex and highly mobile It connects the upper extremity to the axial skeleton (the central bony framework of the human body). Understanding its anatomy is crucial for healthcare professionals, athletes, and anyone interested in shoulder health.
It is divided into various categories:
Articular Surfaces
They are found in joints, where two or more bones come together. Articular surfaces are covered with a layer of smooth, specialized connective tissue known as articular cartilage. This cartilage reduces friction between the bones, provides shock absorption, and enables smooth movement within the joint. These surfaces are divided into several types:
1. Glenoid Fossa of the Scapula (Glenoid Cavity)
It is a shallow concave surface located on the lateral aspect of the scapula (shoulder blade). It forms the articulating surface for the head of the humerus (long bone of the upper arm), creating the glenohumeral joint, which is the main joint of the shoulder. The glenoid fossa is lined with cartilage. It helps reduce friction and allows for smooth movement of the humerus.
2. Head of the Humerus
The head of the humerus is the rounded, ball-like structure located at the proximal end (upper part) of the humerus bone in the upper arm. It is the articulating surface that connects with the glenoid fossa of the scapula to form the glenohumeral joint. The head of the humerus is covered with articular cartilage, which provides cushioning and allows for smooth movement within the joint.
3. Glenoid Labrum
Glenoid Labrum is a fibrocartilaginous structure. It surrounds the outer surface of the glenoid fossa. It deepens the socket of the glenoid fossa, providing stability and enhancing the uniformity of the glenohumeral joint. The glenoid labrum helps to stabilize the head of the humerus and provides attachment sites for ligaments and tendons involved in shoulder movement. It acts as a seal to keep the head of the humerus in place and prevent dislocation.
Ligaments
The shoulder joint is reinforced by several ligaments that play a crucial role in stabilizing the joint and preventing excessive movements. Here are the main ligaments of the shoulder joint:
- Glenohumeral Ligaments: These ligaments are a group of three thickened bands that strengthen the anterior aspect of the joint capsule. They are named according to their locations: superior, middle, and inferior. The glenohumeral ligaments restrict excessive external rotation and anterior translation (forward movement) of the humeral head.
- Coracohumeral Ligament: This ligament arises from the base of the coracoid process (a bony projection serving as an attachment site) of the scapula and attaches to the greater tubercle of the humerus. It reinforces the upper part of the joint capsule and assists in stabilizing the shoulder joint.
- Transverse Humeral Ligament: This ligament spans across the intertubercular groove (a shallow groove located on the anterior surface) of the humerus, holding the long head of the biceps tendon in place.
Innervation
The shoulder joint receives innervation (nerve impulses) from several nerves that supply both sensory and motor fibers The key nerves involved in the innervation of the shoulder joint include:
A. Subscapular Nerve (Joint): It arises from the posterior cord of the brachial plexus (a network of nerves). This nerve innervates the subscapularis muscle. And this muscle is one of the rotator cuff muscles that help stabilize the shoulder joint.
B. Suprascapular Nerve: This nerve originates from the superior trunk of the brachial plexus. It provides motor innervation to the supraspinatus and infraspinatus muscles (rotator cuff muscles). Where both of these muscles are important for shoulder movement and stability.
C. Axillary Nerve: The axillary nerve arises from the posterior cord of the brachial plexus and innervates the deltoid muscle (a triangular-shaped muscle) and teres minor muscle. It plays a vital role in shoulder abduction and external rotation.
Lateral Pectoral Nerve (Joint Capsule): This nerve arises from the lateral cord of the brachial plexus and provides sensory innervation to the joint capsule of the shoulder.
Blood Supply
Adequate blood supply is crucial for maintaining the health and vitality of the shoulder joint. The blood supply to the shoulder joint comes from the following arteries:
- Anterior and Posterior Circumflex Humeral Arteries: These arteries branch off the axillary artery. And it provides the main blood supply to the shoulder joint. They form a vascular network around the surgical neck of the humerus and contribute to the blood supply of the humeral head.
- Circumflex Scapular and Suprascapular Arteries: These arteries arise from the subscapular artery and provide additional vascular support to the shoulder joint and surrounding structures.
In the next part, we will talk about the movements shown by the shoulder joint, which include → flexion, extension, abduction, and other movements.
Movements in the Shoulder Joint
The shoulder joint is a highly mobile joint that allows for a wide range of movements. It consists of → the humerus (upper arm bone), scapula (shoulder blade), and clavicle (collarbone). The movements in the shoulder joint are crucial for performing everyday activities and sports-related tasks. These movements are:
Flexion
It refers to the movement of bringing the arm forward, towards the anterior side of the body. In the shoulder joint, this movement involves → the anterior deltoid (located at the front of the shoulder), pectoralis major (large chest muscle), and coracobrachialis muscles (a muscle located in the upper arm). Flexion allows us to perform actions like raising the arm in front of the body or lifting objects.
Extension
The extension is the opposite of flexion and involves moving the arm backward away from the body’s anterior side. The main muscles responsible for the extension of the shoulder joint include → the posterior deltoid (located at the back of the shoulder) and the latissimus dorsi (a large, flat muscle that spans the lower back). This movement is utilized when reaching behind the body or during activities like swimming.
Abduction
It is the movement of the arm away from the midline of the body. It involves the lateral deltoid muscle. When we raise our arms to the side, such as during a jumping jack exercise, it demonstrates shoulder abduction. Abduction helps to provide a wide range of motion and contributes to movements like throwing a ball.
Adduction
It is the opposite of abduction and involves bringing the arm back toward the midline of the body. This type of movement is created by the action of → the pectoralis major and latissimus dorsi muscles. Adduction is essential for movements like hugging someone or crossing the arms in front of the chest.
Internal Rotation
It refers to rotating the arm inward towards the body. This type of movement involves the subscapularis muscle along with → the pectoralis major and latissimus dorsi muscles. Internal rotation is commonly utilized when reaching for the back pocket or during activities like throwing a ball with an underhand motion.
External Rotation
It is the opposite of internal rotation and involves rotating the arm outward away from the body. It primarily involves the infraspinatus and teres minor muscles. External rotation is important for actions like reaching for a seatbelt or throwing a ball with an overhand motion.
Circumduction
It is a complex movement that involves a combination of flexion, extension, abduction, and adduction. It creates a circular motion with the arm as if drawing a circle in the air. Circumduction allows for a wide range of motion and is often seen in activities like swimming or pitching in baseball.
In the next section, we will learn about the muscles involved in the shoulder joint. And the rotator cuff is the most-known muscle in the region.
Muscles involved in Shoulder Joint Movements
The shoulder joint is a highly mobile joint that allows for a wide range of movements. It is stabilized by a complex system of muscles and tendons.
And those muscles are:
Rotator Cuff Muscles
The rotator cuff is composed of a group of four muscles that work together to stabilize and move the shoulder joint. These muscles include:
- Supraspinatus: It initiates shoulder abduction, which is the movement of raising the arm away from the body.
- Infraspinatus: It aids in the external rotation of the shoulder, allowing the arm to rotate outward.
- Teres Minor: It also contributes to external rotation and helps with arm adduction (movement towards the body).
- Subscapularis: It facilitates internal rotation of the shoulder joint, enabling the arm to rotate inward.
Deltoid Muscle
The deltoid muscle is a large, triangular muscle that covers the shoulder joint. It is responsible for several movements of the shoulder, including:
- Shoulder Abduction: Raising the arm away from the body.
- Shoulder Flexion: Moving the arm forward and upward.
- Shoulder Extension: Moving the arm backward.
- Shoulder Adduction: Bringing the arm back towards the body.
Trapezius Muscle
The Trapezius Muscle is large and extends from the base of the skull down to the middle of the back. It contributes to shoulder movements in the following ways:
- Upper Trapezius: It helps elevate the shoulder girdle, allowing shrugging of the shoulders.
- Middle Trapezius: It helps retract the scapula, pulling them towards the spine.
- Lower Trapezius: It aids in depressing the shoulder girdle, which is the downward movement of the shoulders.
Latissimus Dorsi Muscle
Latissimus Dorsi muscle is commonly referred to as the “lats”. It is a broad muscle located on the back. It plays a role in several shoulder movements, including:
- Shoulder Extension: Moving the arm backward.
- Shoulder Adduction: Bringing the arm back towards the body.
- Medial Rotation: Rotating the arm inward towards the body.
Pectoralis Major Muscle
Pectoralis Major is a large muscle that covers the front of the chest. It contributes to the following shoulder movements:
- Shoulder Flexion: Moving the arm forward and upward.
- Shoulder Adduction: Bringing the arm back towards the body.
- Medial Rotation: Rotating the arm inward towards the body.
Biceps Brachii Muscle
Although primarily considered an elbow flexor, the biceps brachii muscle also assists in certain shoulder movements, such as:
- Shoulder Flexion: Moving the arm forward and upward.
- Shoulder Adduction: Bringing the arm back towards the body.
Triceps Brachii Muscle
The triceps brachii muscle is located at the back of the upper arm and has an indirect influence on shoulder movements. It aids in shoulder extension by straightening the arm backward.
In the next section, we will figure out the common injuries in the shoulder joints, which include → Rotator Cuff Tear, Shoulder Impingement Syndrome, Shoulder Dislocation, and Frozen Shoulder.
Common Shoulder Joint Injuries
The shoulder joint is a complex structure that allows a wide range of motion, but it is also prone to various injuries. And those injuries are:
Rotator Cuff Tear
It is a group of muscles and tendons. It surrounds the shoulder joint, providing stability and facilitating movement. A rotator cuff tear occurs when one or more of these tendons become damaged or torn. This injury often results from repetitive overhead motions or acute trauma.
Symptoms
- Persistent shoulder pain, particularly when lifting or reaching.
- Weakness and limited range of motion.
- Audible popping or clicking sounds.
- Gradual onset of symptoms in chronic cases.
Treatment
- Resting the affected shoulder and avoiding activities that reduce the pain.
- Physical therapy to strengthen the muscles and improve flexibility.
- Non-steroidal anti-inflammatory drugs (NSAIDs) work as an antidote to → pain and inflammation.
- In severe cases, surgical intervention may be necessary to repair the torn tendon.
Shoulder Impingement Syndrome
Shoulder impingement syndrome occurs when the tendons of the rotator cuff and the bursa (a fluid-filled sac that cushions the tendons) become compressed or irritated. This condition often results from repetitive overhead activities or poor shoulder mechanics.
Symptoms
- Pain and tenderness in the front or side of the shoulder.
- Pain worsens with overhead movements.
- Weakness and difficulty reaching behind the back.
- Gradual onset of symptoms.
Treatment
- Resting the affected shoulder and avoiding activities that provoke pain.
- Physical therapy to strengthen the surrounding muscles and correct posture.
- Anti-inflammatory medications and corticosteroid injections help in reducing → pain and inflammation.
- In severe cases, arthroscopic surgery may be recommended to remove impinging structures.
Shoulder Dislocation
A shoulder dislocation occurs when the upper arm bone (humerus) pops out of the shoulder socket. This injury often results from traumatic events such as → falls, sports-related collisions, or accidents.
Symptoms
- Intense pain and swelling in the shoulder area.
- Visible deformity or an abnormal bulge (a little similar to swelling) in the shoulder.
- Limited range of motion and inability to move the arm.
Treatment
- Seeking immediate medical attention to relocate the shoulder joint (shoulder reduction).
- Wearing a sling or immobilizer to support the shoulder during the healing process.
- Physical therapy to regain strength, stability, and range of motion.
- In some cases, surgery can be done. In order, to repair damaged ligaments or tendons.
Frozen Shoulder (Adhesive Capsulitis)
It is a condition characterized by stiffness and pain in the shoulder joint. It typically develops gradually and progresses through three stages: freezing, frozen, and thawing (melting).
Symptoms
- Pain and stiffness that worsens over time.
- Limited range of motion, especially in external rotation.
- Difficulty with activities such as → reaching, dressing, or sleeping on the affected side.
Treatment
- Physical therapy exercises to improve range of motion and decrease pain.
- Pain-relieving medications and corticosteroid injections (to reduce pain).
- Heat therapy and gentle stretching exercises.
- In some cases, manipulation under anesthesia or arthroscopic surgery (minimally invasive surgical procedure) may be recommended.
Conclusion
In conclusion, understanding the Shoulder joints anatomy: shoulder joints and their movements is essential for maintaining optimal function and preventing injuries in the upper body. the shoulder joint is a complex structure. It allows for a wide range of movements. Its anatomy, including → the articular surfaces, ligaments, innervation, and blood supply, which provides the foundation for their function.
Understanding the movements of the shoulder joint and the muscles involved is essential for → maintaining shoulder health and preventing injuries. Common injuries such as → rotator cuff tears, shoulder impingement syndrome, shoulder dislocation, and frozen shoulder. They can significantly impact the shoulder joint’s functionality, but with proper treatment and rehabilitation, individuals can regain → strength, stability, and range of motion in their shoulder joint.
Further Reading
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For more reading, check on the other sources such as:
- Wikipedia: https://en.wikipedia.org/wiki/Shoulder_joint
- Wikipedia: https://en.wikipedia.org/wiki/Shoulder_problem
- Wikipedia: https://en.wikipedia.org/wiki/Deltoid_muscle
- Wikipedia: https://en.wikipedia.org/wiki/Rotator_cuff
- NCBI: https://www.ncbi.nlm.nih.gov/books/NBK536933/
Attribution
- Images used in this article are Designed by Freepik: www.freepik.com
- OpenStax College, CC BY 3.0, via Wikimedia Commons
- InjuryMap, CC BY-SA 4.0, via Wikimedia Commons
- Mikael Häggström, M.D. Author info – Reusing images- Conflicts of interest: NoneMikael Häggström, M.D.Consent note: Written informed consent was obtained from the individual, including online publication., CC0, via Wikimedia Commons
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