Muscles Attached To The Scapula

The scapula, or shoulder blade, is a triangular flat bone located on the posterior side of the rib cage. It plays a vital role in the mobility and stability of the shoulder joint. The scapula serves as an anchor point for several muscles that contribute to the movement of the upper limb, stabilization of the shoulder, and overall posture. 

1.0Introduction

The muscles that attach to the scapula allow it to perform six movements:

• Elevation: The upper trapezius and levator scapulae raise the scapula.
• Depression: The lower trapezius brings down the scapula.
• Upward rotation: The upper and middle trapezius rotate the scapula during upper extremity abduction.
• Downward rotation: The rhomboids rotate the scapula when reaching behind the back and downward.
• Retraction (adduction): The rhomboids and middle trapezius separate the scapula from the thoracic wall, active when performing rowing motions.
• Protraction (abduction): The serratus anterior brings the scapula against the thoracic wall, active when reaching forward.

2.0Types of Muscles Attach to Scapula

Supraspinatus

• Function: Initiation of arm abduction (first 15 degrees), stabilize glenohumeral joint
• Origin: Supraspinous fossa
• Insertion: Top of the greater tubercle
• Innervation: Suprascapular nerve (C5, C6)

Infraspinatus

• Function: Lateral rotation of the arm, stabilize glenohumeral joint
• Origin: Infraspinous fossa
• Insertion: Greater tubercle of humerus, between the supraspinatus and teres minor insertion
• Innervation: Suprascapular nerve (C5, C6)

Teres Minor

• Function: Lateral rotation of the arm, stabilize glenohumeral joint
• Origin: Lateral/axillary border and adjacent posterior aspect of the scapula
• Insertion: Inferior aspect of the greater tubercle on the humerus
• Innervation: Axillary nerve (C5, C6)

Subscapularis

• Function: Adduction and medial rotation of the arm, stabilize glenohumeral joint
• Origin: Subscapular fossa
• Insertion: Lesser tubercle of humerus
• Innervation: Subscapular nerves (C5, C6, C7)

The extrinsic muscles of the scapula attach to the processes of the scapula and affect motion at the glenohumeral joint: These include:

Biceps brachii

• Function: Resists dislocation of the shoulder, major flexor of the forearm, supination of the forearm
• Origin:

Short head: Coracoid process

Long head: Supraglenoid tubercle

• Insertion: Radial tuberosity and forearm fascia (as bicipital aponeurosis)
• Innervation: Musculocutaneous nerve (C5, C6)

Triceps brachii

• Function : Resists dislocation of the shoulder, major extensor of the forearm

Origin:

• Lateral head: Above the radial groove,
• Medial head: Below the radial groove
• Long head: Infraglenoid tubercle of scapula
• Insertion: Olecranon process of ulna and fascia of the forearm
• Innervation: Radial nerve (C6, C7, C8)

Deltoid 

• Function
• • Anterior aspect is responsible for flexion and medial rotation of the arm
  • Middle aspect is responsible for abduction of the arm (up to 90 degrees)
  • The posterior aspect is responsible for extension and lateral rotation of the arm
• Origin: Lateral clavicle, acromion and scapular spine
• Insertion: Deltoid tuberosity
• Innervation: Axillary nerve (C5, C6)
• Stabilizing muscles of the scapula include:

Trapezius

• Function:
• Upper fibers elevate the scapula and rotate it during abduction of the arm (90 to 180 degrees)
• Middle fibers retract the scapula
• Lower fibers pull the scapula inferiorly.
• Origin: Skull, nuchal ligament and the spinous processes of C7 to T12
• Insertion: Clavicle, acromion and the scapular spine
• Innervation: Accessory nerve (Cranial nerve XI)

Levator scapulae

• Function: Elevates the scapula
• Origin: Transverse processes of the C1 to C4 vertebrae
• Insertion: Medial border of the scapula
• Innervation: C3, C4, and the Dorsal scapular nerve (C5)

Serratus anterior

• Function: Fixes the scapula into the thoracic wall, and aids in rotation and abduction of the arm (90 to 180 degrees)
• Origin: Surface of the upper eight ribs at the side of the chest
• Insertion: Along the entire anterior length of the medial border of the scapula
• Innervation: Long thoracic nerve (C5, C6, C7)

Rhomboid Major

• Function: Retracts and rotates the scapula
• Origin: Spinous processes of T2 to T5 vertebrae
• Insertion: Inferomedial border of the scapula
• Innervation: Dorsal scapular nerve (C5)

Rhomboid Minor

• Function: Retracts and rotates the scapula
• Origin: Spinous processes of C7 to T1 vertebrae
• Insertion: Medial border of the scapula
• Innervation: Dorsal scapular nerve (C5)

Other muscles attached to the scapula include:

Latissimus Dorsi

• Function: Extends, adducts and medially rotates the upper limb
• Origin: Spinous processes of T6 to T12, iliac crest, thoracolumbar fascia, the inferior three ribs, and the inferior angle of the scapula
• Insertion: Intertubercular sulcus of the humerus
• Innervation: Thoracodorsal nerve (C6, C7, C8)

Teres Major

• Function: Adduction and medial rotation of the arm
• Origin: Posterior surface of the scapula at its inferior angle 
• Insertion: Intertubercular groove on its medial aspect
• Innervation: Lower scapular nerve (C5, C6)

Pectoralis Minor

• Function: Depression of the shoulder, protraction of the scapula
• Origin: Third, fourth, fifth ribs close to their respective costal cartilages
• Insertion: Coracoid process
• Innervation: Medial pectoral nerve (C8, T1)

Coracobrachialis

• Function: Flexion and adduction of the arm
• Origin: Coracoid process
• Insertion: Middle of the humerus, on its medial aspect
• Innervation: Musculocutaneous nerve (C5, C6, C7)

Omohyoid

• Function: Pulls hyoid bone down, active while talking and swallowing
• Origin: Superior border of scapula
• Insertion: Inferior edge of the hyoid
• Innervation: Ansa cervicalis (C1, C2, C3)

3.0Clinical Significance

Scapular Winging

• Injury causing denervation of the long thoracic nerve leads to paralysis of the serratus anterior, the primary muscle involved in protracting and pulling the scapula toward the rib cage. 
• This weakened protraction allows the rhomboid muscles and the trapezius to work unopposed, leading to retraction of the medial scapula and elevation of the entire scapula. 
• The result is medial winging of the scapula and limitation of functionality of the upper extremity.