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The scapula, or shoulder blade, is a flat, triangular bone that forms the posterior portion of the shoulder girdle. It is located in the upper thoracic region on the dorsal surface of the rib cage. The scapula provides attachment points for muscles, including the rotator cuff muscles, and is involved in 6 types of motion, allowing for a full range of motion in the upper extremity. These motions include protraction, retraction, elevation, depression, upward rotation, and downward rotation. The scapula also plays a crucial role in the scapulohumeral rhythm, which is a combination of motions that results in the full elevation of the arm. This complex joint movement involves the scapula, clavicle, and humerus working together in a precise ratio.
| Characteristics | Values |
|---|---|
| Number of muscles attached to the scapula | 17 (or 18, if counting the long and short head of the biceps brachii separately) |
| Muscle names | Biceps brachii, Coracobrachialis, Deltoid, Infraspinatus, Latissimus dorsi, Levator scapulae, Omohyoid (inferior belly), Pectoralis minor, Rhomboid major, Rhomboid minor, Serratus anterior, Subscapularis, Supraspinatus, Teres major, Teres minor, Trapezius, Triceps brachii (long head) |
| Muscle groups | Intrinsic, extrinsic, and a third group including levator scapulae, trapezius, rhomboids, and serratus anterior |
| Nerves | Dorsal scapular, upper and lower subscapular, and suprascapular nerves |
| Arteries | Suprascapular, posterior circumflex humeral, circumflex scapular, transverse cervical |
| Bones connected to the scapula | Clavicle, Humerus |
| Joints | Glenohumeral, Acromioclavicular, Scapulothoracic, Sternoclavicular |
| Functions | Abduction, external and internal rotation of the glenohumeral joint, rotational movements, stabilization of the scapula, elevation, depression, upward rotation, downward rotation, retraction (adduction), protraction (abduction) |
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What You'll Learn
- The supraspinatus muscle attaches to the posterior surface of the scapula
- The infraspinatus muscle attaches to the posterior surface of the scapula
- The subscapularis muscle attaches to the anterior surface of the scapula
- The serratus anterior muscle attaches to the medial margin of the scapula
- The rhomboids major and minor muscles attach to the medial border of the scapula
The supraspinatus muscle attaches to the posterior surface of the scapula
The scapula, also known as the shoulder blade, is a flat triangular bone located at the back of the trunk. It sits over the posterior surface of ribs two to seven. The scapula forms the posterior of the shoulder girdle and is an important bone in the function of the shoulder joint. The scapula provides attachment to several groups of muscles, including the supraspinatus muscle.
The supraspinatus muscle is supplied by the suprascapular nerve (C5 and C6), which arises from the superior trunk of the brachial plexus. The nerve passes laterally through the posterior triangle of the neck and through the scapular notch on the superior border of the scapula. After supplying fibres to the supraspinatus muscle, the nerve supplies articular branches to the capsule of the shoulder joint.
The supraspinatus muscle plays an important role in shoulder joint stability by keeping the head of the humerus firmly pressed medially against the glenoid fossa of the scapula. It is also involved in shoulder flexion, as it is consistently recruited prior to movement of the limb at all loads. The supraspinatus tendon is commonly ruptured in sports involving sudden forceful movements of the upper limb and can become inflamed, leading to supraspinatus tendinitis.
In summary, the supraspinatus muscle attaches to the posterior surface of the scapula at the supraspinous fossa. It is one of the rotator cuff muscles and plays a crucial role in shoulder joint stability and movement. The supraspinatus muscle is supplied by the suprascapular nerve and is vulnerable to injury, especially during sudden and forceful movements.
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The infraspinatus muscle attaches to the posterior surface of the scapula
The scapula, or shoulder blade, is a flat triangular bone located at the back of the trunk. It provides attachment points for several groups of muscles, including the intrinsic muscles, extrinsic muscles, and a third group of muscles that includes the levator scapulae, trapezius, rhomboids, and serratus anterior.
The infraspinatus is one of the intrinsic muscles of the scapula, also known as the rotator cuff muscles. These muscles attach directly to the surface of the bone and include the subscapularis, teres minor, and supraspinatus. The infraspinatus originates from the infraspinous fossa, found on the posterior scapula, and connects to the proximal humerus. It occupies the majority of the dorsal surface of the scapula and is considered a powerful lateral rotator of the humerus.
The infraspinatus muscle fibres course towards the shoulder joint, almost parallel to the teres minor and major muscles. They are separated from these muscles by a thick fascia. The infraspinatus is supplied arterially by the suprascapular and circumflex scapular arteries, which provide a source of collateral circulation.
The infraspinatus muscle can be tested by laterally rotating the arm at the glenohumeral joint against resistance, with the forearm held in a flexed position and the arm in the adducted position. This muscle is essential for the full function of the shoulder joint, allowing for movements such as hitting overhead.
The infraspinatus also works together with the teres minor muscle to stabilise the glenohumeral joint and prevent the upward displacement of the humeral head, which is crucial for the full elevation of the arm.
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The subscapularis muscle attaches to the anterior surface of the scapula
The scapula, or shoulder blade, is a flat, sturdy, triangular bone that forms the posterior of the shoulder girdle. It connects the clavicle to the humerus and provides attachment points for several groups of muscles. These include the intrinsic muscles, which attach directly to the scapular surface, and the extrinsic muscles, which attach to the processes of the scapula.
The subscapularis is a large, powerful, triangular shoulder muscle that fills the subscapular fossa of the scapula. It is one of the four rotator cuff muscles, along with the supraspinatus, infraspinatus, and teres minor. The subscapularis muscle attaches to the anterior surface of the scapula, also known as the subscapular fossa. Specifically, it originates from the medial and lower two-thirds of the groove on the lateral border of the scapula.
The subscapularis muscle fibres pass laterally from their origin, narrowing towards a round tendon that courses towards the proximal humerus. This tendon intermingles with the glenohumeral (shoulder) joint capsule. The subscapularis tendon separates from the scapula by a bursa, which communicates with the cavity of the shoulder joint via an aperture in the joint capsule. The subscapularis bursa separates the subscapularis from the serratus anterior, which covers the superolateral part of the subscapularis.
The subscapularis muscle is the only medial (internal) rotator of the rotator cuff muscles. It medially rotates the humeral head within the glenoid fossa, contributing to the creation of concavity compression, which stabilizes the shoulder joint. The subscapularis also adducts the arm, drawing the humerus forward and downward when the arm is raised. This sequence of movements is seen when walking with a swinging arm motion.
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The serratus anterior muscle attaches to the medial margin of the scapula
The scapula, or shoulder blade, is a flat, triangular bone located at the back of the trunk. It sits over the posterior surface of ribs two to seven. The scapula is a crucial bone as it provides an attachment point for numerous muscles that form the arm and shoulder.
The serratus anterior is a fan-shaped muscle that originates from the upper eight or nine ribs at the lateral wall of the thorax. It is a key scapular stabiliser, keeping the shoulder blades against the rib cage during rest and movement. The serratus anterior is also referred to as the "boxer's muscle" because it is responsible for scapular protraction, or the pulling of the scapula forward and around the rib cage when throwing a punch.
The serratus anterior attaches to the medial margin of the scapula, or the medial border, between the superior and inferior angles. The muscle wraps around the rib cage, passing beneath the scapula to attach to the underside of the scapula on its medial border. The serratus anterior is divided into three parts: the upper/superior, middle/intermedius, and lower/inferior. The lower/inferior part is the most prominent and powerful section of the muscle.
The serratus anterior acts in conjunction with the upper and lower fibres of the trapezius muscle to enable upward rotation of the scapula, allowing for overhead lifting. It also assists in respiration by lifting the ribs when the shoulder girdle is fixed.
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The rhomboids major and minor muscles attach to the medial border of the scapula
The rhomboid muscles consist of two separate muscles: the rhomboid major and the rhomboid minor. These muscles are found deep to the trapezius. The rhomboid minor is a cylindrical muscle that originates at the ligamentum nuchae and C7 and T1 vertebra. It inserts at the medial border of the scapula, near the base of the spine of the scapula. The rhomboid major is a quadrangular muscle located inferior to the rhomboid minor. It originates from the spinous processes of the T2-T5 vertebra and inserts on the medial border of the scapula, just inferior to the rhomboid minor.
The rhomboid major and minor muscles play an important role in shoulder function and stability. They work together to keep the scapula pressed against the thoracic wall and to retract the scapula toward the vertebral column. Additionally, they help to elevate and rotate the scapula, contributing to the full range of motion of the shoulder joint.
The motor function of the rhomboid muscles is controlled by the dorsal scapular nerve (DSN), which originates from the ventral ramus of the spinal nerve root C5. The DSN innervates the rhomboid muscles at their anterior border. Along with other muscles such as the trapezius, pectoralis muscles, and levator scapulae, the rhomboid major and minor form the shoulder girdle. This group of muscles is crucial for the movement and stabilization of the shoulder.
The rhomboid muscles are susceptible to injuries such as tears or weakness, which can lead to scapular instability and a condition known as scapular winging. In some cases, surgical intervention may be required, such as using rhomboid muscle flaps in the treatment of head and neck cancers or reconstructive procedures. However, the treatment for rhomboid-related issues is usually conservative, focusing on physical therapy, muscle relaxants, and, in extreme cases, surgery.
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