What is the scapula?
The scapula, also known as the shoulder blade, is a thin, flat, roughly triangular-shaped bone that sits on either side of the upper back. This bone, along with theclavicleand the manubrium of the sternum, make up the shoulder girdle, connecting the upper limb of theappendicular skeletonin the directionaxial skeleton.
Where is the scapula located?
The scapula is located at the upper back of the ribcage, extending fromribs2-7. It is located between the arm bone,humerus, and clavicle or clavicle.
|how many are in the human body||2 (1 on each side)|
|articulates with||1.Humerus at the glenohumeral or shoulder joint|
2.Clavicle at the acromioclavicular joint
How does the scapula move?
The movement of this bone is coupled with that of the humerus, which means that every time you move your arm, your scapula moves as well. It can move in six different ways, towards (retract) and away (protract) the column, up and down (raise and lower) and also rotate up and down. There are 17 muscles attached to it that help produce these movements.
The scapula assists in various daily movements and smooth movements of the upper arm based on the movements mentioned above.
- Helps with forward and backward movement of theshoulder girdleand the chest muscles moving towards and away from the spine.
- During some movements, such as shoulder shrugs, the entire shoulder capsule moves up and down due to the elevation and depression of this bone.
- Stabilizes the shoulder capsule during excessive arm movement by pivoting up and down.
development and ossification
The scapula develops in the embryonic stage and ossifies from one primary center and seven secondary centers. The primary ossification center appears near the glenoid fossa during the eighth week of fetal development. Of the seven, the first secondary center appears in the middle of the coracoid process during the first year and merges at age 15.
Another ossification center, called the subcoracoid center, develops at the root of the coracoid process around age 10 and fuses between ages 16 and 18. Other centers, including one for the lower 2/3 of the glenoid rim, two for the acromion, one for the medial border, and one for the inferior angle, appear at puberty and fuse by age 25.
Anatomy - Parts of the Scapula
The body of the scapula consists of a flat blade of triangular shape, with a pointed apex below. Since it is triangular, it has three edges.
edges and angles
- upper edge:It is the shortest and thinnest edge.
- Must be medial:It is a thin border that runs parallel to the spine and is often called the vertebral border.
- Side edge:It is alternatively known as the axillary border, running towards the apex of the armpit. Of the three edges, it is the thickest and strongest. It also carries the glenoid cavity, which articulates with the rounded head of the humerus, forming the shoulder joint or glenohumeral joint.
It also has three angles:
- side angle:where the top edge meets the side edge.
- top angle:Where the superior border also meets the medial border.
- bottom angle:Where the medial and lateral borders meet.
1. Rib surface
It is the anterior surface of the scapula facing the rib cage orrib cage.
It has a large concave depression over most of its surface, called the subscapular fossa, from which the subscapularis muscle of the rotator cuff originates.
This region is marked by longitudinal grooves, of which a thick groove joins the lateral edge. This part of the bone acts as a lever for the action of the serratus anterior muscle, helping to move the arm away from the body.
A hook-shaped projection called the coracoid process arises from the superior border of the head of the scapula, projects forward, and curves laterally below the clavicle.
2. Lateral surfaces
This surface of the scapula faces the humerus.
Its important bony landmarks are:
fossa glenoidal -It is a shallow piriform cavity located at the lateral angle of the scapula. It articulates with the rounded head of the humerus, forming the glenohumeral (shoulder) joint.
supraglenoid tubercle -It is a small bumpy projection located just above the glenoid fossa near the base of the coracoid process.
infraglenoid tubercle -It is a gross impression located on the lateral aspect of the scapula, immediately below the glenoid fossa.
3. Back surface
This surface of the scapula faces outward. Most of the shoulder rotator cuff muscles arise from here. Its important anatomical landmarks are:
Coluna vertebral:It is a triangular bony plate located on the posterior surface, which crosses the scapula transversely and divides the dorsal surface of the scapula into supraspinatus and infraspinatus fossae. The two fossae remain connected by the spinoglenoid notch, located laterally to the root of the spine, attached by the spinoglenoid ligament. It has three edges and two surfaces. Its posterior border, the crest of the vertebral column, has the upper and lower lips.
supraspinatus fossa:It is the area above the spine of the scapula. It is concave, smooth and wider at its vertebra than at its humeral end. The supraspinatus muscle originates in the middle of this area. It is much smaller than the infraspinatus fossa and has the spinoglenoid fossa on its side. The fossa houses the suprascapular canal, which connects the suprascapular notch and the spinoglenoid notch, which carries the suprascapular nerve and vessels.
infraspinatus fossa:It is the area below the spine of the scapula. It is convex and much larger than the previous one. In its upper part, towards the vertebral margin, it presents a shallow concavity. In the center it is convex, while near the side edge it has a deep groove running from top to bottom.
acromion:It is a large bony projection on the upper end of the scapula. It arches over the shoulder joint and articulates with the clavicle at the acromioclavicular (AC) joint.
- glenohumeral joint:This is a spherical joint formed between the glenoid fossa of the scapula and the rounded head of the humerus.
- acromioclavicular joint:It is a sliding joint between the acromion of the scapula and the clavicle.
Muscles attached to the scapula
Since the scapula has a large surface area, a large number of muscles are attached to it. The 17 muscles attached here attach the scapula to the chest wall and allow it to move. Four muscles, namely subscapularis, infraspinatus, teres minor and supraspinatus, form the rotator cuff and cover the shoulder capsule.
These muscles are listed below and are classified according to their origin or insertion on the scapula.
originating from the scapula
- deltoid muscle:It originates from the lower edge of the crest of the spine to the lateral edge of the acromion. It helps to move the arm in and out of the body and also to rotate it at the shoulder joint.
- supraspinal muscle:It originates from the supraspinatus fossa. Send the arm away from the body.
- infraspinatus muscle:It originates from the infraspinatus fossa and involves lateral rotation at the shoulder joint.
- Triceps brachii muscle (long head):It originates from the infraglenoid tubercle. It is responsible for elbow extension.
- teres minor muscle:It arises from the lateral or axillary border of the posterior surface and rotates laterally at the shoulder joint.
- teres major muscle:It arises from the posterior surface of the inferior angle and the inferior part of the lateral border. This helps to bring the elbow towards the body and also to rotate it at the shoulder joint.
- The broad back muscle:Originating from the inferior angle, it performs various actions such as protraction and retraction of the arm and medial rotation at the shoulder joint.
- coracobrachialis muscle:It originates from the coracoid process. It is involved with retraction and depression in the shoulder joint.
- Biceps brachii muscle (long head and short head):The long head arises from the supraglenoid tubercle, while the short head arises from the coracoid process. It helps to bend the elbow.
- Subscapularis muscle:It originates from the subscapular fossa, performing depression and medial rotation on the shoulder joint.
- omo-hyoid muscle:It arises from the upper border (adjacent to the suprascapular notch) and causes depression of thehyoid bone.
insertion into the scapula
- trapezius muscle:It inserts superiorly along the vertebral column, process of the acromion and clavicle. Helps elevate and rotate the scapula during humeral protraction beyond 90 degrees.
- Levator scapula muscle:Insert at superior angle and medial border. They help elevate the scapula.
- rhomboid major muscle:It inserts on the medial border. Performs elevation and retraction of the scapula.
- Rhomboid minor muscle:Inserts above the scapular spine. Its actions include elevation and retraction of the scapula.
- Anterior serratile muscle:Insertion is along the medial border, from superior to inferior angle. Protracts, rotates and stabilizes the scapula.
- Pectoralis minor muscle:It inserts into the coracoid process. Assists in protraction and depression of the scapula.
Left and right scapula: how to identify
A quick way to identify whether the scapula comes from the right or left side of the body:
First, hold the bone at the bottom angle and orient it so that the convex back surface is facing you. In this position, the glenoid fossa faces outward and the vertebral column is clearly visible.
If the spine points to 2 o'clock, it's the right scapula. Alternatively, if it points to 10 o'clock, it's the one on the left.
Another way to identify the side is to look at which way the glenoid is facing. While holding the bone in the position mentioned above, if the glenoid is facing right as per your body then that is the right scapula and vice versa.
Q.1. Which muscles stabilize the scapula?
ResponderThe muscles that stabilize the scapula are the serratus anterior, rhomboids, levator scapulae, and trapezius muscles.
Q.2. Is the scapula part of the axial skeleton?
ResponderNo, the scapula is not part of the axial skeleton.
Q.3. Is the scapula part of the appendicular skeleton?
ResponderYes, the scapula is part of the appendicular skeleton.
Q.4. Is there a difference between the male and female scapula?
Responderaccording to ainvestigationperformed on Europeans of Hispanic descent, it was found that the female scapula is shorter than the male.