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The scapula, or shoulder blade, is a large, flat, triangular bone that sits above the rib cage in the upper back. It connects the clavicle to the humerus, forming the glenohumeral (shoulder) joint. The scapula has a large surface area, providing attachment points for 17 muscles that make up the arm and shoulder. These muscles enable the scapula to move in six directions, including protraction, retraction, elevation, depression, upward rotation, and downward rotation. The intrinsic muscles of the scapula include the rotator cuff muscles (supraspinatus, infraspinatus, subscapularis, and teres minor), while the extrinsic muscles include the triceps, biceps, and deltoid.
| Characteristics | Values |
|---|---|
| Bones | Shoulder blade, sits above the rib cage in the upper back |
| Joint | Glenohumeral (shoulder) joint, acromioclavicular joint, scapulothoracic joint |
| Movements | Six directions: protraction, retraction, elevation, depression, upward rotation, downward rotation |
| Muscles | Rotator cuff muscles (supraspinatus, infraspinatus, subscapularis, teres minor), teres major, subscapularis, triceps, biceps, deltoid, levator scapulae, trapezius, rhomboids, serratus anterior, latissimus dorsi, pectoralis major, pectoralis minor |
| Nerves | Dorsal scapular, upper and lower subscapular, suprascapular, thoracodorsal |
| Conditions | Winged scapula, shoulder impingement syndrome, snapping scapula syndrome, scapular dysplasia |
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What You'll Learn
The four rotator cuff muscles
The rotator cuff is a group of four muscles that arise from the scapula, or shoulder blade, and insert into the humerus. These muscles include the supraspinatus, infraspinatus, subscapularis, and teres minor. These four muscles work together to stabilize the glenohumeral joint, which is a ball-and-socket joint formed by the head of the humerus and the glenoid cavity of the scapula. This joint is highly mobile but inherently unstable, so the rotator cuff muscles play a crucial role in providing stability and allowing a wide range of motion in the shoulder.
The rotator cuff muscles have a primary biomechanical role in stabilizing the glenohumeral joint by compressing the humeral head against the glenoid cavity. They form a musculotendinous collar that surrounds the posterior, superior, and anterior aspects of the joint, leaving the inferior aspect unprotected. This arrangement is important because most shoulder dislocations occur when the humerus slides out through the unprotected inferior aspect of the joint. During arm movements, the rotator cuff muscles contract and prevent the sliding of the humeral head, allowing a full range of motion while maintaining joint stability.
The rotator cuff muscles are essential for various upper extremity movements, including flexion, abduction, internal rotation, and external rotation. They provide the "fine-tuning" movements of the head of the humerus within the glenoid fossa, enlarging the range of motion in the glenohumeral joint and avoiding mechanical obstruction. Balanced strength and flexibility in each of the four muscles are vital to maintain the functioning of the entire shoulder girdle.
Injuries to the rotator cuff muscles are common and can occur at any age. Younger individuals may experience rotator cuff tears due to trauma or overuse in overhead activities such as volleyball, tennis, or pitching. With age, the risk of injuries increases due to muscle degeneration, impingement, and tearing. Rotator cuff tendinitis, tendinopathy, and tears are common pathologies associated with these muscles. Pain and weakness are often presenting symptoms, and MRI is the most effective imaging method for diagnosis.
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The extrinsic muscles
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 provides attachment points for several groups of muscles, including the extrinsic muscles.
The scapula can move in six directions, and each movement is produced by specific muscles. The extrinsic muscles play a crucial role in these movements, ensuring the smooth gliding of the scapula over the chest wall, known as the scapulothoracic joint. This allows for a wide range of motion and mobility in the upper limbs.
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The third group of muscles
The scapula, or shoulder blade, connects the clavicle to the humerus, forming the posterior of the shoulder girdle. The scapula provides attachment points for several groups of muscles. The third group of muscles includes the levator scapulae, trapezius, rhomboids, and serratus anterior.
The levator scapulae muscle is inserted along the dorsal aspect of the medial border of the scapula, from the superior angle up to the root of the spine. It is responsible for elevation and downward rotation of the scapula.
The trapezius muscle is inserted into the upper border of the crest of the spine and into the medial border of the acromion. It is responsible for retraction, elevation, and upward rotation of the scapula.
The rhomboids consist of the rhomboideus minor and rhomboideus major muscles. The rhomboideus minor is inserted into the medial border of the scapula (dorsal aspect) opposite to the root of the spine, while the rhomboideus major is inserted into the medial border (dorsal aspect) between the root of the spine and the inferior angle. The rhomboids are responsible for retraction and downward rotation of the scapula.
The serratus anterior is inserted along the medial border of the costal surface of the scapula, with one digitation from the superior angle to the root of the spine, two digitations to the medial border, and five digitations to the inferior angle. It is responsible for protraction, elevation, and upward rotation of the scapula.
These muscles in the third group are crucial for the rotational movements and stabilization of the scapula, allowing for the full function of the shoulder 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 allows for multiple types of motion, including protraction, retraction, elevation, depression, upward rotation, and downward rotation. These motions enable a full range of motion in the shoulder joint.
Protraction
Protraction is accomplished by the actions of the serratus anterior, pectoralis major, and pectoralis minor muscles. Scapular protraction exercises can help improve scapular health and stability.
Retraction
Retraction is accomplished by the actions of the trapezius, rhomboids, and latissimus dorsi muscles. The scapular retraction test allows a physician to examine the integrity of the rotator cuff.
Elevation
Elevation is accomplished by the trapezius, levator scapulae, and rhomboid muscles. The upper trapezius and lower trapezius act as scapular elevators, while the middle trapezius and serratus anterior act as scapular depressors.
Depression
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.
Rotation
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. The scapula's rotational movements are also stabilized by the levator scapulae, trapezius, rhomboids, and serratus anterior muscles.
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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 forms the posterior of the shoulder girdle and connects the clavicle to the humerus. The scapula has several groups of muscles attached to it, including the intrinsic and extrinsic muscles. The intrinsic muscles include the rotator cuff muscles, while the extrinsic muscles include the triceps, biceps, and deltoid.
The most common causes of scapular winging are injuries to the nerves or muscles that support the shoulder blade. These injuries can include sports injuries, repetitive strain, dislocated shoulders, traumas such as car accidents or falls, and surgical side effects. People who have had surgery on their chest, particularly mastectomies, are at a higher risk of developing this condition. Certain sports, physically demanding work, wearing a heavy backpack, and having a slumped posture can also increase the risk of scapular winging.
The symptoms of scapular winging include pain, stiffness, reduced range of motion, grinding or snapping sensations when moving the shoulder, and straining on one side of the neck when raising the arm. During a physical examination, a healthcare provider may observe the patient's back and ask them to perform specific movements to assess the range of motion and level of pain.
Treatment for scapular winging depends on the severity of the condition. Most cases can be treated with non-surgical methods such as pain control and physical therapy. However, severe cases may require surgical intervention, such as grafting nerve or muscle tissue to a different part of the body or attaching the scapula to the ribs or vertebrae.
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Frequently asked questions
The scapula, or shoulder blade, has a large surface area that allows for the attachment of many muscles. These include the rotator cuff muscles (teres major, subscapularis, teres minor, infraspinatus, and supraspinatus), the extrinsic muscles (triceps, biceps, and deltoid), and the levator scapulae, trapezius, rhomboids, and serratus anterior.
The muscles attached to the scapula enable a wide range of movements. Protraction is accomplished by the serratus anterior, pectoralis major, and pectoralis minor muscles. Retraction is accomplished by the trapezius, rhomboids, and latissimus dorsi muscles. Elevation is made possible by the trapezius, levator scapulae, and rhomboid muscles, while depression is caused by gravity and the actions of the latissimus dorsi, serratus anterior, pectoralis major and minor, and trapezius muscles.
The scapula forms the posterior of the shoulder girdle and connects the clavicle to the humerus. It provides a wide range of movement and mobility for the upper limb, allowing the arm to achieve a full 180 degrees of elevation.
