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The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the posterior of the shoulder girdle. The scapula has a large surface area, allowing for a large number of muscles to attach to it (17 in total). These muscles fix the scapula to the thoracic wall and enable it to move in six directions. The intrinsic muscles of the scapula include the rotator cuff muscles, while the extrinsic muscles include the triceps, biceps, and deltoid. The third group of muscles, responsible for rotational movements and stabilization of the scapula, includes the levator scapulae, trapezius, rhomboids, and serratus anterior.
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What You'll Learn
The rotator cuff muscles
The rotator cuff is a group of four distinct muscles and their tendons that provide strength and stability to the shoulder complex. The four muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis, collectively referred to as the SITS muscle, referencing the first letter of each muscle's name. These muscles arise from the scapula (or shoulder blade) and connect to the head of the humerus, forming a cuff around the glenohumeral (GH) joint. The rotator cuff muscles are responsible for stabilising the glenohumeral joint by compressing the humeral head against the glenoid, preventing the sliding of the head of the humerus during arm movements. This allows for a full range of motion and provides stability to the shoulder joint.
Injuries to the rotator cuff muscles are common and can occur at any age. They can be caused by trauma or overuse due to overhead activities. Dysfunction of the rotator cuff muscles can lead to shoulder pain, impaired functional capacities, and a reduced quality of life. Diagnosing rotator cuff injuries can be done through clinical tests, with MRI being the best imaging method for visibility of soft tissue and detecting tears and inflammation.
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The extrinsic muscles
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that connects the clavicle to the humerus. There are 17 muscles attached to the scapula, which fix it to the thoracic wall and allow it to move. The extrinsic muscles of the scapula attach to the processes of the scapula and affect motion at the glenohumeral joint. These include the triceps, biceps, and deltoid. The deltoid muscle is responsible for flexion and medial rotation (anterior fibres), abduction (middle fibres), extension and lateral rotation (posterior fibres) at the shoulder joint. The biceps and triceps are also associated with scapular winging, a condition where the scapula protrudes posteriorly when a posterior force is applied to the extended upper extremity.
The supraspinatus muscle is another extrinsic muscle of the scapula. It originates from the supraspinous fossa and is responsible for abduction at the shoulder joint. The lower fibres of the extrinsic muscles pull the scapula inferiorly, and their origin is the skull, nuchal ligament, and the spinous processes of C7 to T12.
The third group of scapular muscles, including the levator scapulae, trapezius, rhomboids, and serratus anterior, are responsible for rotational movements and stabilization of the scapula. Protraction is accomplished by the actions of the serratus anterior, pectoralis major, and pectoralis minor muscles. Retraction is accomplished by the actions of the trapezius, rhomboids, and latissimus dorsi muscles. The elevation is accomplished by the trapezius, levator scapulae, and rhomboid muscles.
The scapula moves in six directions, and each movement is produced by specific muscles. The scapula must upwardly rotate, posteriorly tilt and externally rotate to achieve full elevation of the arm. The muscle synergists for upward rotation are the upper and lower trapezius and the serratus anterior. Downward rotation is accomplished by the force of gravity, along with the latissimus dorsi, levator scapulae, rhomboids, and the pectoralis major and minor muscles.
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The scapulothoracic joint
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the posterior of the shoulder girdle. The scapula is not directly attached to the axial skeleton, but it is held in place and connected to the thorax and vertebral column by muscles, allowing it to move freely across the posterior thoracic wall. This creates the scapulothoracic joint, which is not a true anatomical joint as it lacks the typical joint characteristics of fibrous, cartilaginous, or synovial tissues. Instead, it is considered a unit that combines the sternoclavicular and
The scapulothoracic junction can be described in terms of three degrees of freedom: elevation-depression, protraction-retraction, and external rotation-internal rotation. During these movements, the scapula is stabilised by the muscles attached to it and the ligaments of the AC joint. For example, the protraction and retraction of the scapula occur around a vertical axis passing through the lateral end of the clavicle, while elevation and depression occur around a sagittal axis passing through the centre of the AC joint.
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Protraction, retraction, elevation, depression, and rotation
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus and forms the posterior of the shoulder girdle. The scapula is an important bone as it provides a point of attachment for a number of muscles that make up the arm and shoulder.
The scapula can move in six directions: protraction, retraction, elevation, depression, upward rotation, and downward rotation. These movements are produced by specific, primary muscles.
Protraction is accomplished by the actions of the serratus anterior, pectoralis major, and pectoralis minor muscles. Retraction is accomplished by the actions of the trapezius, rhomboids, and latissimus dorsi muscles. The elevation is accomplished by the trapezius, levator scapulae, and rhomboid muscles.
Depression is accomplished through the force of gravity and the actions of the latissimus dorsi, serratus anterior, pectoralis major and minor, and the trapezius muscles. Upward rotation is accomplished by the trapezius and serratus anterior muscles. Downward rotation is accomplished by the force of gravity as well as the latissimus dorsi, levator scapulae, rhomboids, and the pectoralis major and minor muscles.
These six motions enable the full function of the shoulder joint, one of the most mobile and versatile joints in the human body.
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Winging of the scapula
The scapula, or shoulder blade, is a sturdy, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the posterior of the shoulder girdle. The scapula can move in six directions, each produced by specific primary muscles.
The most common causes of scapular winging are injuries to the nerves or muscles that support the shoulder blade. These injuries damage the nerves that control the muscles, disrupting the natural balance of tension in the shoulder. This prevents the muscles from holding the scapula flat against the rib cage. Sports injuries, repetitive strain injuries, dislocated shoulders, and traumas like car accidents or falls are common causes of scapular winging. People who play sports that stress the shoulders, do physically demanding work, or have a slumped posture are at a higher risk of developing the condition.
Medial scapular winging results from weakness in the serratus anterior muscle, caused by injury to the long thoracic nerve. Lateral winging arises from dysfunction of the trapezius or rhomboid muscles, associated with spinal accessory or dorsal scapular nerve impairment. Fascioscapulohumeral dystrophy, an autosomal dominant condition affecting several muscles related to the scapula, can also cause winging.
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Frequently asked questions
The scapula, commonly referred to as the shoulder blade, is the bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the glenohumeral (shoulder) joint.
There are 17 muscles attached to the scapula, which fix it to the thoracic wall and allow it to move.
The muscles that move the scapula include the serratus anterior, pectoralis major, pectoralis minor, trapezius, rhomboids, latissimus dorsi, levator scapulae, triceps, biceps, deltoid, supraspinatus, subscapularis, infraspinatus, teres major, teres minor, and the rotator cuff muscles.
