These scapular muscles are the main stabilizers that hold the flimsy bone structure of the scapular region together. This article discusses each of these muscles in detail, about their attachments, innervation and action.
Subscapularis
Subscapularis is the muscle that occupies the subscapular fossa.
Attachments
The muscle originates from the medial 2/3rds of the subscapular fossa. Distally, it gets attached to the lesser tubercle of humerus.
Innervation
Subscapularis is innervated by the upper and lower subscapular nerves, which involve the nerve roots C5, C6 and C7.
Action
Its primary function is to medially rotate the arm at the shoulder joint. Subscapularis is one of the four rotator cuff muscles of the shoulder joint, which means that it helps in stabilizing the shoulder joint. It also functions as an adductor of the arm.
Teres Major
Teres major is a muscle that spans between the scapula and the humerus. Counterintuitively, This muscle is NOT a rotator cuff muscle; only teres minor is. And it is good to always keep in mind that when a muscle is named major, there is always a minor.
Attachments
Proximally, it originates from an elongated oval area on the posterior surface of the scapula, below the origin of the teres minor. Distally, it gets inserted to the medial lip of the intertubercular sulcus on the anterior surface of the humerus.
Innervation
Teres major is innervated by the lower subscapular nerve. This should be easier to remember, since the teres major arises from the lower part of the scapula. The nerve roots are C5, C6 and C7, the same as the subscapularis muscle.
Action
The Teres minor acts as a medial rotator and an extensor of the arm.
Teres minor
Teres minor is the smaller counterpart of teres major. It lies in between the Teres major inferiorly and the infraspinatus superiorly. The teres minor is a rotator cuff muscle.
Attachments
Teres Minor attaches to the lateral border of scapular, in its upper two-thirds. The attachment site is divided into two by the groove which occupies the circumflex scapular vessels. Therefore, you can say the teres minor has two heads. Distally, it attaches to the inferior facet of the greater tubercle of the humerus.
Innervation
The teres minor is innervated by the axillary nerve (C5,C6). It shares its nerve supply with the deltoid muscle. Paralysis of the axillary nerve causes loss of sensation in the regimental badge area.
Action
The primary function of teres minor is the external (lateral) rotation of the shoulder joint; a function it shares with the infraspinatus. The teres minor is also a stabilizer of the shoulder joint, being that it is a rotator cuff muscle. It assists in adduction and extension of the shoulder joint.
Supraspinatus
Supraspinatus is a rotator cuff muscle. As the name suggests, it occupies the supra spinous fossa of the posterior scapular region. It lies deep to the trapezius muscle. Supraspinatus tendon is the most common area to get tendinitis. Supraspinatus passes under the acromion process, A supraspinatus bursa is present to lubricate the contact of the tendon against the acromion process. Rupture of this bursa results in increased friction between the tendon and the acromion process, causing injury to the tendon.
Attachments
Proximally, the supraspinatus arises from the supraspinatus fossa. Distally, it gets inserted into the superior facet of the grater tubercle of the humerus.
Innervation
Supraspinatus muscle is innervated by the supra scapular nerve (C5, C6). Suprascapular nerve is a branch arising from the superior trunk of the brachial plexus.
Action
The supraspinatus muscle's action is to abduct the arm in the first 15 degrees of abduction. It has a higher mechanical advantage in abduction, than the deltoid muscle. Beyond 15 degrees, the deltoid muscle becomes the main abductor and supraspinatus looses its mechanical advantage. Therefore, paralysis of this muscle results in inability to initiate abduction of the arm at the shoulder joint.
Infraspinatus
Infraspinatus, as the name suggests, is the muscle that lies beneath the scapular spine. It occupies the infraspinous fossa.
Attachments
Attaches to the infaspinous fossa of scapula, proximally. Distally, attaches to the middle facet of the grater tubercle of humerus in between the insertions of teres minor and supraspinatus.
Innervation
The Infraspinatus is innervated by the suprascapular nerve, similar to the supraspinatus. The suprascapular nerve passes from the supraspinous fossa to the infraspinous fossa through the spinoglenoid notch at the lateral border of the scapular spine, to reach the infraspinous fossa to innervate the infraspinatus muscle.
Action
The Action of the Infraspinatus is somewhat similar to that of teres minor. It externally (laterally) rotates the arm at the shoulder joint. It is also a rotator cuff muscle, which mean stabilizing the shoulder joint is a part of its function.
Levator Scapulae
Direct branches from the anterior rami of C3 and C4 Spinal nerves and branches from the Dorsal Scapular nerve (C5) also innervate it.
Attachments
The Rhomboid Major arises from the spinous processes of the T2 to T5 vertebrae and the supraspinous ligaments between them. Furthermore, it inserts into the posterior surface of the medial border of the scapula, extending from the root of the spine of the scapula to the inferior angle.
Innervation
Direct branches from the anterior rami of C3 and C4 Spinal nerves and branches from the Dorsal Scapular nerve (C5) innervate it.
Action
Levator scapulae, as the name very obviously suggests, elevates the scapula. Apart from this, the levator scapulae can rotate the scapula downwards, to tilt the glenoid cavity inferiorly.
Rhomboid Major
Attachments
The Rhomboid Major arises from the spinous processes of the T2 to T5 vertebrae and the supraspinous ligaments between them. Additionally, it inserts into the posterior surface of the medial border of the scapula, extending from the root of the spine of the scapula to the inferior angle.
Innervation
The Rhomboid Major muscle is innervated by the dorsal scapular nerve (C4, C5).
Action
Elevates and retracts the scapula.
Rhomboid Minor
Attachments
The Rhomboid minor attaches to the lower end of the ligamentum nuchae and the spinous processes of C8 and T1 vertebrae, medially. Transitioning distally, it attaches to the posterior surface of the medial border of the scapula, at the root of the spine of the scapula.
Innervation
The Rhomboid Minor has innervation from the dorsal scapular nerve, same as the Rhomboid Major muscle. The nerve roots involved are C4 and C5.
Action
The Rhomboid Minor elevates and retracts the scapula.
Subclavius
The subclavius is a small muscle which hides itself under the clavicle, as the name suggests.
Attachments
It originates from the first rib at the junction between the rib and the costal cartilage. It inserts onto the groove on the inferior surface of the middle one-third of the clavicle.
Innervation
A dedicated nerve called the nerve to subclavius innervates it, and nerve roots C5 and C6 supply this nerve.
Action
The subclavius pulls the tip of the shoulder down and pulls the first rib up. Furthermore, it pulls the clavicle medially to stabilize the sternoclavicular joint during its movements, which is its main function
2 thoughts on “Deep muscles of the Scapular Region”