What Is Scapula ?
The scapula is a triangular, thin bone placed on the posterolateral aspect of the thoracic cage and overlapping second to seventh ribs. It is also called shoulder blade. It articulates with the acromial extremity of the clavicle and the head of the humerus. The scapula has two surfaces, three borders, three angles, and three processes .
Side Determination Of Scapula.
1. The lateral or glenoid angle is large and bears the glenoid cavity.
2. The dorsal surface is convex and is divided by the triangular spine into the supraspinous and infraspinous fossae. The costal surface is occupied by the concave subscapular fossa to fit on the convex chest wall .
3. The thickest lateral border runs from the glenoid cavity above to the inferior angle below.
Surfaces Of Scapula
There are two surface of scapula.
1. The costal surface or subscapular fossa
2. The dorsal surface
1. The costal surface or subscapular fossa:- The costal surface or subscapular fossa is concave and is directed medially and forwards. It is marked by three longitudinal ridges. Another thick ridge adjoins the lateral border. This part of the bone is almost rod-like. It acts as a lever for the action of the serratus anterior in overhead abduction of the arm.
2. The dorsal surface:- The dorsal surface gives attachment to the spine of the scapula which divides the surface into a smaller supraspinous fossa and a larger infraspinous fossa. The two fossae are connected by the spinoglenoid notch, situated lateral to the root of the spine.
Borders Of Scapula
There are three boarder of scapula.
1. The superior border
2. The lateral border
3. The medial border
1. The superior border:- The superior border is shortest. Near the root of the coracoid process, it presents the suprascapular notch.
2. The lateral border:- The lateral border is thick. At the upper end, it presents the infraglenoid tubercle.
3. The medial border:- The medial border is thin. It extends from the superior angle to the inferior angle.
Angles Of Scapula
There are three angles of scapula.
1. The superior angle
2. The inferior angle
3. The lateral or glenoid angle
1. The superior angle:- The superior angle is covered by the trapezius.
2. The inferior angle:- The inferior angle is covered by the latissimus dorsi. It moves forwards round the chest when the arm is abducted.
3. The lateral or glenoid angle:- . The lateral or glenoid angle is broad and bears the glenoid cavity or fossa, which is directed forwards, laterally and slightly upwards. A supraglenoid tubercle is present above the glenoid cavity.
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Processes Of Scapula.
There are three processes of scapula.
1. The spine or spinous process
2. The acromion process
3. . The coracoid process
1.The spine or spinous process:- The spine or spinous process is a triangular plate of bone with three borders and two surfaces. It divides the dorsal surface of the scapula into the supraspinous and infraspinous fossae. Its posterior border is called the crest of the spine. The crest has upper and lower lips.
2.The acromion process:- The acromion process has two borders, medial and lateral; two surfaces, superior and inferior; and a facet for the clavicle.
3.The coracoid process:- is directed forwards and slightly laterally. It is bent and finger-like. It is an atavistic type of epiphysis.
Muscle Of Scapula.
The intrinsic muscles of the scapula attach directly to the surface of the bone. These muscles are the four members of the rotator cuff and act to stabilize the glenohumeral joint. These include:
1.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)
2. 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)
3. 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)
4. 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)
5. 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)
6. 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)
7. 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)
8. 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)
9. 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)
10. 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)
11. 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)
12.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)
13. Latissmus 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)
14. 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)
15.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)
16. 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)
17.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)
# Ligament Of Scapula.
Nerves
The nerves to the scapula include the dorsal scapular, upper and lower subscapular, and suprascapular nerves, which arise from the brachial plexus at the anterior ramus C5 root, the posterior cord, and the superior trunk respectively. See “Muscles” section below for more details regarding specific muscle innervations.
OSSIFICATION
• The scapula ossifies from one primary centre and seven secondary centres.
• The primary centre appears near the glenoid cavity during the eighth week of development.
• The first secondary centre appears in the middle of the coracoid process during the first year and fuses by the 15th year. The subcoracoid centre appears in the root of the coracoid process during the 10th year and fuses by the 16th to 18th years.
• The other centres, including two for the acromion process, one for the lower two-thirds of the margin of the glenoid cavity, one for the medial border and one for the inferior angle, appear at puberty and fuse by the 25th year.
• The fact of practical importance is concerned with the acromion process. If the two centres appearing for acromion process fail to unite, it may be interpreted as a fracture on radiological examination. In such cases, a radiograph of the opposite acromion process will mostly reveal similar failure of union.
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