Dominic Stone
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 can move in six directions, and each movement is produced by specific primary muscles. The serratus anterior, a fan-shaped muscle, is the prime mover in scapular protraction and scapular upward rotation. It is a key scapular stabilizer, keeping the shoulder blades against the rib cage at rest and during movement. Other muscles that aid in scapular movement include the upper and lower trapezius, the rhomboideus major, and the rhomboideus minor.
| Characteristics | Values |
|---|---|
| Common Name | Shoulder Blade |
| Bone Type | Flat, Triangular |
| Function | Connects Clavicle to Humerus |
| Movement | 6 Types: Protraction, Retraction, Elevation, Depression, Upward Rotation, Downward Rotation |
| Muscles | Rotator Cuff Muscles, Teres Major, Subscapularis, Teres Minor, Infraspinatus, Triceps, Biceps, Deltoid, Levator Scapulae, Trapezius, Rhomboids, Serratus Anterior |
| Primary Movement Muscles | Trapezius, Levator Scapulae, Rhomboid Major, Rhomboid Minor, Serratus Anterior |
| Protraction Muscles | Serratus Anterior, Pectoralis Major, Pectoralis Minor |
| Retraction Muscles | Trapezius, Rhomboids, Latissimus Dorsi |
| Elevation Muscles | Trapezius, Levator Scapulae, Rhomboid |
| Depression Muscles | Latissimus Dorsi, Serratus Anterior, Pectoralis Major, Pectoralis Minor, Trapezius |
| Upward Rotation Muscles | Trapezius, Serratus Anterior |
| Downward Rotation Muscles | Latissimus Dorsi, Levator Scapulae, Rhomboids, Pectoralis Major, Pectoralis Minor |
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Serratus Anterior
The Serratus Anterior (SA) is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs at the lateral wall of the thorax. It inserts along the superior angle, medial border, and inferior angle of the scapula. The main part of the serratus anterior lies deep under the scapula and the pectoral muscles. It is easily palpated between the pectoralis major and latissimus dorsi muscles.
The serratus anterior is a key scapular stabiliser, keeping the shoulder blades against the ribcage at rest and during movement. It is also known as the "big swing muscle" or "'boxer's muscle'" because it is largely responsible for the protraction of the scapula, or the pulling of the scapula forward and around the rib cage that occurs when someone throws a punch. The muscle is also responsible for scapular upward rotation.
The serratus anterior acts in concert with the upper and lower fibres of the trapezius muscle to sustain upward rotation of the scapula, allowing for overhead lifting. The lowest four digitations of the serratus anterior interdigitate with the fibres of the external oblique. The serratus anterior is divided into three parts: the serratus anterior superior, serratus anterior intermediate, and serratus anterior inferior. The serratus anterior superior and serratus anterior inferior work together to press the scapula against the thorax in conjunction with the rhomboids, creating a synergistic effect. The serratus anterior inferior is responsible for the anterolateral motion of the scapula, allowing for arm elevation.
When the shoulder girdle is fixed, all three parts of the serratus anterior muscle work together to lift the ribs, assisting with respiration. When the shoulder blade is in a fixed position, the serratus anterior, as one of the accessory inspiratory muscles, lifts the rib cage and supports breathing.
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Trapezius
The trapezius muscle is a large, paired muscle in the shape of a trapezium, or diamond-shaped quadrilateral. It is made up of long muscle fibres that span a large width of the upper back, running from the base of the neck down to the middle of the back. The trapezius muscle is one of the commonly affected muscles in facioscapulohumeral muscular dystrophy (FSHD).
The trapezius muscle has three sections: upper, middle, and lower. The upper section connects to the skull and neck (cervical spine), while the middle and lower sections attach to bones in the thoracic spine. The trapezius muscle is also connected to the lateral sides of the scapula (shoulder blade) and collarbone (clavicle).
The trapezius muscle helps to maintain posture and move the upper back, neck, and head. It is involved in various motions, including turning the head from side to side, adjusting posture (such as standing up straight or bending the upper back forward), twisting the torso, shrugging the shoulders, and moving the shoulders when lifting the arm or throwing something.
The trapezius muscle also plays a crucial role in scapular movement and stability. The upper fibres elevate the scapulae, the middle fibres retract the scapulae, and the lower fibres depress the scapulae. In addition, the trapezius induces scapular rotation, with the upper and lower fibres rotating the scapula around the sternoclavicular articulation. This movement allows for abduction of the shoulder above 90 degrees. The trapezius works in conjunction with other muscles, such as the rhomboids, levator scapulae, serratus anterior, and deltoid, to produce coordinated movements involving the scapula.
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Levator Scapulae
The levator scapulae is a posterior axio-appenducular muscle that connects the upper limb to the vertebral column. It is located in the posterior triangle of the neck and is covered by sternocleidomastoid and trapezius muscles. The levator scapulae originates on the posterior tubercle of the transverse process of cervical vertebrae 1 to 4. It inserts onto the vertebral margin of the scapula, between the superior angle and the root of the spine.
The levator scapulae is innervated by 2-3 branches of the 3rd and 4th cervical nerves and frequently by a branch from the dorsal scapular nerve. It is supplied by the dorsal scapular artery. The levator scapulae functions to elevate the scapula and tilt the glenoid cavity inferiorly by rotating the scapula downward. When the scapula is fixed, a contraction of the levator scapulae leads to the lateral flexion of the cervical vertebral column to the side and stabilizes the vertebral column during rotation.
The levator scapulae is one of the extrinsic muscles of the scapula, along with the triceps, biceps, and deltoid. These muscles are responsible for rotational movements and stabilization of the scapula. The scapula, or shoulder blade, is a sturdy, flat, triangular bone that connects the clavicle to the humerus. It forms the posterior of the shoulder girdle and provides attachment to several groups of muscles.
The levator scapulae is also implicated in certain medical procedures and pathologies. For example, in the Modified Eden-Lange procedure, the levator scapulae is attached to the spine of the scapula. Additionally, levator scapulae syndrome is a clinical manifestation characterized by tenderness over the upper medial angle of the scapula. This condition is often unrecognized, and effective treatment modalities include physical therapy and local corticosteroid injections.
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Rhomboid Major
The rhomboid major is a skeletal muscle of the back that connects the scapula with the vertebrae of the spinal column. It is a broad, quadrilateral muscle that arises from the spinous processes of the thoracic vertebrae T2–T5 and the supraspinous ligament. It inserts onto the lower portion of the medial border of the scapula, from about the level of the scapular spine to the scapula's inferior angle. The rhomboid major is the larger of the two rhomboid muscles, with "major" indicating its size relative to the other muscle, the rhomboid minor.
The rhomboid major acts together with the rhomboid minor to keep the scapula pressed against the thoracic wall and to retract the scapula toward the vertebral column. The main action of the rhomboid muscles is scapular retraction around the scapulothoracic joint, which involves a simultaneous sliding of the scapula superiorly and medially along the trunk. This superomedial movement of the scapula rotates the glenoid cavity inferiorly, dropping the shoulder girdle. By opposing excessive scapular protraction, the rhomboids help to maintain correct posture when sitting, standing, and walking.
The rhomboid major also works with the levator scapulae muscles to elevate the medial border of the scapula, downwardly rotating the scapula with respect to the glenohumeral joint. If the rhomboid major is torn, wasted, or unable to contract, scapular instability may result. This can lead to scapular winging during scapular protraction, excessive lateral rotation, and depression of the scapula.
The rhomboid major receives arterial blood from three sources: the dorsal scapular artery, the deep branch of the transverse cervical artery, and the dorsal branch of the upper five or six posterior intercostal arteries. These blood vessels stem from the thyrocervical trunk and the thoracic aorta.
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Rhomboid Minor
The rhomboid minor is a small skeletal muscle of the back. It is an extrinsic muscle of the shoulder, located deep to the trapezius and superior to the rhomboid major. The rhomboid minor originates from the nuchal ligament and the spinous processes of the seventh cervical (C7) and first thoracic (T1) vertebrae. The muscle extends obliquely in an inferolateral direction, inserting into the base of the medial end of the spine of the scapula.
The rhomboid minor is innervated by the dorsal scapular nerve, receiving arterial blood supply from the dorsal scapular artery. It acts to retract and rotate the scapula, also known as the shoulder blade. The scapula is a sturdy, flat, triangular bone that 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. These movements include protraction, retraction, elevation, depression, upward rotation, and downward rotation. The rhomboid minor is involved in retraction and elevation, working in conjunction with the rhomboid major and trapezius muscles.
The rhomboid minor also helps to stabilise the scapula, particularly when other shoulder muscles are active. It works in tandem with the levator scapulae and the rhomboid major to rotate the scapulae downward. Additionally, the rhomboid minor and major act together to keep the scapula pressed against the thoracic wall, contributing to the stability of the shoulder joint.
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Frequently asked questions
The scapula, or shoulder blade, is the bone that connects the clavicle to the humerus.
The scapula can move in six directions, each produced by specific primary muscles. The serratus anterior, trapezius, and rhomboids are the muscles responsible for scapular abduction.
Scapular abduction is the movement of the scapula away from the body's midline. This is a combination of motions, including protraction, retraction, elevation, depression, and rotation.
The serratus anterior is a fan-shaped muscle that originates on the superolateral surfaces of the first to eighth or ninth ribs. It acts as the prime mover in scapular protraction and upward rotation, and it is a key stabiliser, keeping the shoulder blades against the ribcage.
The extrinsic muscles of the scapula include the triceps, biceps, and deltoid. These muscles attach to the processes of the scapula and affect motion at the glenohumeral joint.
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