Shoulder Anatomy

The parts that make up the shoulder form a biomechanical relationship between different elements, which allow flexion, extension and abduction movements, among others. This leads to permanent injuries to the shoulder system, which can be treated in different ways. Read on to find out what biomechanical movements are all about.

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Parts and anatomy of the shoulder

Bones and joints

• The glenohumeral joint, which carries out the movements of the shoulder. That is, between the glenoid socket of the scapula and the head of the humerus is the hyaline cartilage, which cushions the movements of this part of the body.
• Another important joint is the subdeltoid joint: This articular body with the one mentioned in the previous point and connects the rotator cuff with the deltoid muscle.
• The non-anatomical scapulothoracic joint is involved in the movements of the thorax with the scapula at the top.
• While the acromioclavicular joint is responsible for moving the end of the clavicle with the acromion. This joint body is seated in a synovial bursa and surrounded by a ligament of the same name.
• Finally, the sternoclavicular joint joins the sternum to the clavicle on the inside. This allows adduction and abduction movements.

Muscles

• Supraspinatus: This muscle, together with the tendon of the same name, forms the rotator cuff of the shoulder. This muscle runs from the supraspinatus fossa of the scapula to the tip of the humerus. Its function is to stabilise the humerus bone and raise the arm.
• Subscapularis: It also covers the subscapular fossa and inserts on the lesser humeral tubercle. It is located in the anterior area of the scapula and is responsible for adducting the arm, maintaining shoulder stability and rotating the humerus.
• Roundus teres minor: It also has a rounded shape like the anterior muscle and its origin is similar to that of the roundus teres major, but the difference lies in its insertion, as it ends its course in the greater tubercle of the humerus. Lateral rotation of the arm is the main action of this tissue.
• Roundus major: It is possible to find this muscle on the back of the shoulder, as its job is to rotate and extend the arm. It has its origin in the scapula, in the inferior region, and is inserted in the number, precisely in the intertubercular groove.
• Deltoid: This shoulder muscle arises from the scapula, in the lower region of the crest, and inserts on the clavicle, on the edge of the acromion and on the spine of the scapula. They in turn converge on the humerus, inserting into the deltoid impression. Flexion, extension and abduction of the arm are its main biomechanical actions.
• Infraspinatus: This muscle extends from the infraspinous fossa to the epiphysis of the humerus or trochlea. Lateral rotation of the upper limbs is the main work of this soft tissue.
• Coracobrachialis: This muscle acts when the biomechanical movements of extension and flexion of the shoulder occur. The coracoid process is responsible for giving birth to this tissue, while the humeral diaphysis is the insertion zone.
• Pectoralis minor: This thin muscle has its insertion in the coracoid process and can therefore be considered an integral part of the muscular anatomy of the shoulder. Its task is to elevate the ribs during breathing.
• Trapezius: Although it is a muscle that can be considered as a muscle of the neck and trunk, its long course allows it to be mentioned as an integral part of the muscular tissues of the shoulder. Its action is to coordinate the movements of the scapula with the spine.

Ligaments

• Coracoacromial: It is responsible for joining the clavicle to the coracoid process and its function is to limit the abduction movement of the shoulder. It can be divided into two sections, one called the conoid and the other called the trapezoid.
• Conoid: It is the first part of the anterior ligament, the acromion, at the medial part of its medial border, with the clavicle. It is related to the deltoid, trapezius and subclavian muscle.
• Trapezoid: As mentioned, this tissue is the second section of the coracoacromial ligament. It is up to 5 millimetres thick and runs from the coracoid process of the scapula to the underside of the clavicle.
• Acromioclavicular: Its route allows the clavicle to be joined to the acromion to maintain the work of the joint of the same name.
• Superior transverse of the scapula: This tissue joins the coracoid process with the medial end of the scapula. Its action, among other things, is to protect the suprascapular nerve.
• Glenohumeral: It can be divided into three sections, called superior, middle and inferior. This ligament joins the edges of the glenoid cavity to the medial bony protuberance of the humerus.
• Transverse humeral: The lesser and greater tubercles of the humerus are connected to the notch of the scapula by this ligament. Also known as coracohumeral.
• Coracoglenoid: This ligament extends from the coracoid process of the scapula to the glenoid socket, opposite the medial border of the scapula.

Biomechanics of the shoulder

• Flexion: This action occurs when the hand is raised forward, fully extending the arm. In this way the pectoralis major and deltoid muscles allow a 180° opening.
• Extension: By means of the teres major, latissimus dorsi and pectoralis major it is possible to bring the arm backwards with an amplitude of 50°.
• Adduction: It is possible to turn the arm 90° to the side of the body. In this way the upper limb joins the trunk at the hip. The latissimus dorsi, pectoralis major and subscapularis are the main muscles involved in this biomechanical movement.
• Abduction: This biomechanical act is the opposite of adduction. It consists of detaching the arm from the trunk until it reaches a maximum amplitude of 90°.
• Rotation: If the hand is moved outwards from the line of the elbow, an internal rotation of 90° is produced. On the other hand, if the hand flexes inward from the elbow to an opening not exceeding 90°, this movement is considered a biomechanical external rotation of the shoulder.