SHOULDER GIRDLE
The shoulder girdle, also known as the pectoral girdle or shoulder complex, is a complex of bones and joints that attach the upper limb to the axial skeleton. It consists of the clavicle, scapula, and humerus bones, as well as the muscles, ligaments, and tendons that connect them.
Clavicle:
The clavicle, also known as the collarbone, is a long bone that connects the sternum to the scapula. It is located at the base of the neck and serves as an important bony landmark for the shoulder girdle and upper limb. In this article, we will discuss the anatomy of the clavicle in detail.
The clavicle is an S-shaped bone that is divided into three parts: the medial end, the shaft, and the lateral end. The medial end is located close to the sternum and is thicker and more rounded than the lateral end. It articulates with the sternum at the sternoclavicular joint. The shaft of the clavicle is long and cylindrical, and it curves gently outward and backward. The lateral end of the clavicle is flattened and broad and articulates with the acromion process of the scapula at the acromioclavicular joint.
The clavicle has two surfaces, two borders, and two ends. The anterior surface of the clavicle is convex and smooth, while the posterior surface is concave and rough. The superior border of the clavicle is smooth and rounded, while the inferior border is rough and gives attachment to several ligaments and muscles.
The clavicle also has several important bony landmarks. The sternal end of the clavicle has a facet that articulates with the sternum at the sternoclavicular joint. The acromial end of the clavicle has a facet that articulates with the acromion process of the scapula at the acromioclavicular joint. The conoid tubercle is a bony projection located on the inferior surface of the lateral end of the clavicle. It serves as an attachment site for the conoid ligament, which is an important stabilizer of the acromioclavicular joint.
The clavicle is surrounded by several muscles and ligaments that provide stability and mobility to the shoulder girdle and upper limb. The clavicular head of the sternocleidomastoid muscle attaches to the medial end of the clavicle and is responsible for flexing and rotating the neck. The pectoralis major muscle attaches to the clavicle and is responsible for flexing, adducting, and medially rotating the arm. The trapezius muscle attaches to the lateral third of the clavicle and is responsible for elevating and retracting the scapula. The coracoclavicular ligament attaches to the clavicle and the coracoid process of the scapula and is responsible for stabilizing the acromioclavicular joint.
In summary, the clavicle is an important bone that connects the sternum to the scapula and serves as a bony landmark for the shoulder girdle and upper limb. It is a long, S-shaped bone that is divided into three parts and has several important bony landmarks and attachments for muscles and ligaments. Understanding the anatomy of the clavicle is important for healthcare professionals, athletes, and individuals who use their upper limbs extensively in their daily activities.
Scapula:
The scapula, commonly known as the shoulder blade, is a large flat bone that connects the upper arm bone (humerus) with the clavicle. It is located at the posterior (back) aspect of the thorax, between the levels of the second and seventh ribs. In this article, we will discuss the anatomy of the scapula in detail.
The scapula has three borders: the superior border, the medial (vertebral) border, and the lateral (axillary) border. The superior border is the shortest border and runs from the superior angle to the coracoid process. The medial (vertebral) border is the longest border and runs from the superior angle to the inferior angle. The lateral (axillary) border runs from the inferior angle to the glenoid cavity.
The scapula also has three angles: the superior angle, the inferior angle, and the lateral angle. The superior angle is the highest point of the scapula and is located at the junction of the superior and medial borders. The inferior angle is the lowest point of the scapula and is located at the junction of the medial and lateral borders. The lateral angle is the point where the lateral and superior borders meet.
The scapula has several processes, including the spine, the acromion, and the coracoid process. The spine of the scapula is a bony ridge that runs from the medial border to the lateral border and separates the supraspinous and infraspinous fossae. The acromion is a flat bony projection that arises from the superior border of the scapula and articulates with the clavicle to form the acromioclavicular joint. The coracoid process is a hook-shaped projection that arises from the superior aspect of the scapula and serves as an attachment site for several muscles and ligaments.
The scapula also has two fossae: the supraspinous fossa and the infraspinous fossa. The supraspinous fossa is located above the spine of the scapula and is the attachment site for the supraspinatus muscle. The infraspinous fossa is located below the spine of the scapula and is the attachment site for the infraspinatus and teres minor muscles.
The glenoid cavity is a shallow depression on the lateral aspect of the scapula that articulates with the head of the humerus to form the glenohumeral joint. It is located at the lateral angle of the scapula and is surrounded by the labrum, a fibrocartilaginous ring that deepens the socket and provides stability to the joint.
The scapula is surrounded by several muscles and ligaments that provide stability and mobility to the shoulder girdle and upper limb. The supraspinatus, infraspinatus, and teres minor muscles attach to the scapula and are responsible for the external rotation of the humerus. The subscapularis muscle attaches to the anterior surface of the scapula and is responsible for the internal rotation of the humerus. The biceps brachii muscle attaches to the coracoid process and is responsible for flexing the elbow joint.
In summary, the scapula is a large flat bone that connects the upper arm bone (humerus) with the clavicle. It has three borders, three angles, and several processes, including the spine, acromion, and coracoid process. The scapula has two fossae, the supraspinous fossa and the infraspinous fossa, and a glenoid cavity that articulates with the head of the humerus to form the glenohumeral joint.
Humerus:
The humerus is the long bone of the upper arm, extending from the shoulder to the elbow joint. It plays a vital role in the shoulder girdle as it forms the major bone articulating with the scapula to create the shoulder joint.
Here is an in-depth description of the anatomy of the humerus:
Head:
The head of the humerus is a rounded, ball-like structure located at the proximal end of the bone. It articulates with the glenoid cavity of the scapula to form the shoulder joint.
Greater Tubercle:
The greater tubercle is a prominent, lateral projection located just below the head of the humerus. It provides attachment to several muscles of the rotator cuff, which are responsible for stabilizing and rotating the shoulder joint.
Lesser Tubercle:
The lesser tubercle is a smaller, medial projection located below the greater tubercle. It also provides attachment to muscles of the rotator cuff.
Intertubercular Groove:
This groove is located between the greater and lesser tubercles and serves as a passage for the tendon of the biceps brachii muscle.
Deltoid Tuberosity:
The deltoid tuberosity is a roughened, V-shaped area located on the lateral surface of the midshaft of the humerus. It serves as the attachment site for the deltoid muscle, which is responsible for shoulder abduction.
Shaft:
The shaft of the humerus extends from the tuberosities to the distal end of the bone. It is cylindrical in shape and has several muscle attachments, including the triceps brachii muscle.
Medial Epicondyle:
The medial epicondyle is a bony projection located on the medial side of the distal end of the humerus. It serves as the attachment site for several muscles of the forearm.
Lateral Epicondyle:
The lateral epicondyle is a bony projection located on the lateral side of the distal end of the humerus. It serves as the attachment site for several muscles of the forearm.
Capitulum:
The capitulum is a rounded, knob-like structure located on the lateral side of the distal end of the humerus. It articulates with the head of the radius bone to form the elbow joint.
Trochlea:
The trochlea is a spool-like structure located on the medial side of the distal end of the humerus. It articulates with the ulna bone to form the elbow joint.
Overall, the humerus is a complex bone that plays a critical role in the shoulder girdle. Its various projections and attachments provide a framework for numerous muscles to attach, which together allow for the wide range of motion seen in the shoulder joint.
Muscles:
The shoulder girdle is supported and moved by a complex arrangement of muscles that originate from the axial skeleton and insert into the bones of the shoulder girdle. These muscles work together to stabilize and move the shoulder joint in a wide range of motions. Here is an in-depth description of the anatomy of the muscles of the shoulder girdle:
Trapezius Muscle:
The trapezius muscle is a large muscle that spans the upper back and neck. It attaches to the occipital bone, spinous processes of the cervical and thoracic vertebrae, and the scapula. The trapezius muscle is responsible for scapular elevation, depression, retraction, and upward rotation.
Levator Scapulae Muscle:
The levator scapulae muscle is a thin, strap-like muscle that attaches to the transverse processes of the cervical vertebrae and the superior angle of the scapula. It is responsible for scapular elevation and downward rotation.
Rhomboid Major and Minor Muscles:
The rhomboid major and minor muscles are located in the upper back and attach to the spinous processes of the thoracic vertebrae and the medial border of the scapula. They are responsible for scapular retraction and downward rotation.
Serratus Anterior Muscle:
The serratus anterior muscle is a broad muscle that attaches to the upper eight or nine ribs and the medial border of the scapula. It is responsible for scapular protraction and upward rotation.
Pectoralis Minor Muscle:
The pectoralis minor muscle is a small, triangular muscle located in the upper chest. It attaches to the third, fourth, and fifth ribs and the coracoid process of the scapula. The pectoralis minor muscle is responsible for scapular protraction and downward rotation.
Deltoid Muscle:
The deltoid muscle is a large muscle that covers the shoulder joint. It has three portions: anterior, middle, and posterior. The anterior portion is responsible for shoulder flexion, the middle portion is responsible for shoulder abduction, and the posterior portion is responsible for shoulder extension.
Rotator Cuff Muscles:
The rotator cuff muscles consist of four muscles: supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate from the scapula and attach to the humerus. They work together to stabilize the shoulder joint and allow for rotation and elevation of the arm.
Overall, the muscles of the shoulder girdle play a vital role in the stability and movement of the shoulder joint. Their various attachments and functions allow for a wide range of movements in the upper limb, including abduction, adduction, flexion, extension, and rotation.
Ligaments and tendons:
The shoulder girdle is also supported by a network of ligaments and tendons that connect the bones of the shoulder girdle to each other and to the axial skeleton. In the shoulder girdle, the ligaments and tendons work together to provide stability and movement to the joint. Here is an in-depth description of the anatomy of the ligaments and tendons of the shoulder girdle:
Glenohumeral Ligaments:
The glenohumeral ligaments are three ligaments that attach the humerus to the glenoid fossa of the scapula. They provide stability to the shoulder joint and limit excessive movement. The three glenohumeral ligaments are:
• Superior Glenohumeral Ligament:
It attaches the superior aspect of the humerus to the glenoid fossa of the scapula.
• Middle Glenohumeral Ligament:
It attaches the anterior humerus to the glenoid fossa of the scapula.
• Inferior Glenohumeral Ligament:
It attaches the inferior humerus to the glenoid fossa of the scapula and is divided into three bands: anterior, posterior, and axillary.
Coracoclavicular Ligament:
The coracoclavicular ligament connects the clavicle to the coracoid process of the scapula. It is made up of two parts: the conoid ligament and the trapezoid ligament. The coracoclavicular ligament provides stability to the acromioclavicular joint and prevents upward displacement of the clavicle.
Coracoacromial Ligament:
The coracoacromial ligament is a thick, triangular-shaped ligament that runs from the coracoid process to the acromion process of the scapula. It forms the roof of the shoulder joint and helps to prevent superior dislocation of the humerus.
Rotator Cuff Tendons:
The rotator cuff tendons are a group of four tendons that attach the muscles of the rotator cuff to the humerus. The four tendons are:
Supraspinatus Tendon:
It attaches the supraspinatus muscle to the greater tubercle of the humerus.
Infraspinatus Tendon:
It attaches the infraspinatus muscle to the greater tubercle of the humerus.
Teres Minor Tendon:
It attaches the teres minor muscle to the greater tubercle of the humerus.
Subscapularis Tendon:
It attaches the subscapularis muscle to the lesser tubercle of the humerus.
Biceps Tendon:
The biceps tendon attaches the biceps muscle to the radial tuberosity of the radius bone. It runs through the intertubercular groove of the humerus and provides stability to the shoulder joint.
Overall, the ligaments and tendons of the shoulder girdle work together to provide stability and movement to the joint. They allow for a wide range of movements in the upper limb, including abduction, adduction, flexion, extension, and rotation.
In conclusion, the anatomy of the shoulder girdle is complex and involves the interaction of bones, muscles, ligaments, and tendons. The shoulder girdle is essential for the stability and mobility of the upper limb, and any injury or dysfunction in this region can have a significant impact on the overall function of the upper limb. Understanding the anatomy of the shoulder girdle is essential for healthcare professionals, athletes, and individuals who use their upper limbs extensively in their daily activities.
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