Logan Steele
The scapula, or shoulder blade, is a flat, triangular bone that connects the collarbone (clavicle) to the bone in the upper arm (humerus). It is a crucial bone as it provides a point of attachment for numerous muscles that make up the arm and shoulder. The scapula has 17 muscles attached to it, including the rotator cuff muscles, which are made up of four muscles: the supraspinatus, infraspinatus, subscapularis, and teres minor. These muscles form a musculotendinous cuff around the glenohumeral joint, providing stability and support. Other muscles that attach to the scapula include the deltoid, levator scapulae, trapezius, rhomboids, and serratus anterior. These muscles enable the scapula to perform various movements, such as protraction, retraction, elevation, and rotation, allowing for a wide range of motion in the upper limb.
| Characteristics | Values |
|---|---|
| Number of muscles attached | 17 |
| Function | The scapula provides a point of attachment for muscles that make up the arm and shoulder. |
| Bones connected | Humerus, Clavicle |
| Joints formed | Glenohumeral, Acromioclavicular |
| Muscle synergists for upward rotation | Upper and lower trapezius, serratus anterior |
| Intrinsic muscles | Rotator cuff muscles, teres major, subscapularis, teres minor, infraspinatus |
| Extrinsic muscles | Triceps, biceps, deltoid |
| Third group of muscles | Levator scapulae, trapezius, rhomboids, serratus anterior |
| Nerves | Dorsal scapular, upper and lower subscapular, suprascapular |
| Arteries | Suprascapular, subscapular, circumflex scapular, transverse cervical |
| Veins | Axillary, suprascapular |
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What You'll Learn
The supraspinatus muscle
The tendon of the supraspinatus muscle extends laterally, passing under the acromion process and over the head of the humerus. It inserts onto the superior facet of the greater tuberosity of the humerus. This insertion point is where the muscle attaches to the bone, ensuring stability and facilitating movement. The supraspinatus tendon is separated from the coracoacromial ligament, the acromion, and the deltoid muscle by the subacromial bursa, a fluid-filled sac that reduces friction.
In summary, the supraspinatus muscle is a vital component of the rotator cuff, providing stability and facilitating abduction and lateral rotation of the arm. Its innervation and blood supply contribute to its functional capabilities, making it an essential muscle for shoulder joint health and mobility.
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The infraspinatus muscle
The main function of the infraspinatus muscle is to externally rotate the humerus and stabilize the glenohumeral or shoulder joint. When the arm is abducted, the infraspinatus works together with the teres minor to oppose the upward pull of the deltoid muscle and stabilize the humeral head. This prevents the upward displacement of the humeral head and impingement on the coracoid process.
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The subscapularis muscle
The subscapularis tendon lies approximately 3 to 5 cm under the surface, which is relatively deep for ultrasonography. It is covered by a dense fascia that attaches to the scapula at the margins of its attachment (origin) on the scapula. The muscle fibres pass laterally from its origin before converging into a tendon of insertion. This tendon intermingles with the glenohumeral (shoulder) joint capsule. A bursa, a fluid-filled sac, intervenes between the tendon and a bare area at the lateral angle of the scapula/the neck of the scapula, reducing friction against the bone.
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The teres minor muscle
The teres minor is an intrinsic muscle of the shoulder region. It is one of the four muscles of the rotator cuff, along with the supraspinatus, infraspinatus, and subscapularis. The rotator cuff muscles act together to control the movements of the humeral head and stabilize it within the glenoid cavity of the shoulder joint, as the arm moves in various directions. The primary function of the teres minor is to modulate the action of the deltoid, preventing the humeral head from sliding upward as the arm is abducted. It also functions to externally rotate and adduct the arm.
The tendon of the teres minor passes across and is united with the posterior part of the capsule of the shoulder joint. The muscle is innervated by the axillary nerve, which forms a pseudoganglion. The axillary nerve and the posterior circumflex humeral artery provide blood supply to the teres minor.
Atrophy of the teres minor muscle is often a consequence of a rotator cuff tear. Selective atrophy of the teres minor muscle has been observed in cases of compression of the corresponding axillary nerve branch or posterior humeral circumflex artery. Ultrasonography can be used to detect fatty degenerative atrophy of the teres minor, while MR imaging helps to consolidate the diagnosis of neurogenic muscle atrophy.
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The deltoid muscle
The deltoid is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). The deltoid's fibres are pennate muscle, and studies have shown that there are seven neuromuscular segments to the deltoid muscle. Three of these lie in the anatomical anterior head of the deltoid, one in the anatomical middle head, and three in the anatomical posterior head of the deltoid.
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Frequently asked questions
The scapula, or shoulder blade, has 17 muscles attached to it. The four rotator cuff muscles (subscapularis, infraspinatus, teres minor, and supraspinatus) cover the shoulder capsule.
The rotator cuff muscles help raise and rotate the arms and provide structural support to the shoulder joint.
The scapula has several other important muscles, including the deltoid, levator scapulae, rhomboids, serratus anterior, and trapezius. These muscles help with movements like protraction, retraction, elevation, and rotation of the scapula.
Common conditions include adhesive capsulitis (frozen shoulder), bursitis, rotator cuff injuries, shoulder impingement syndrome, and strains.
