Surfaces and Articulations of the Scapula Explained
What is a Scapula?
The flat bone that is in a trilateral shape is known as the Scapula. It is observed positioned at the back of the trunk. The scapula performs a significant role in supporting the other bones connected to the shoulder motion rhythm. The blood supply to the scapula is usually impaired in neurological conditions such as strokes, cerebrovascular accidents, and other brain hemorrhages.
In the pectoral girdle, a pair of scapula bones are present. It forms the posterior part of the shoulder girdle and is situated over the ribs posteriorly, covering the second to seventh ribs.
The scapula location is on the outer edge of your ribcage, between ribs 2 and 7. It's one of the bones that make up the pectoral girdle, including the clavicle or collarbone. The Scapula structure consists of a spine, a coracoid, an acromion process, and a glenoid cavity.
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Scapula Function
The Scapula is liable for various motions essential to everyday movement and sleek upper extremity motion. The scapula moves forward and back with the pectoral girdle as a result of protraction and retraction.
Protraction occurs when the whole pectoral girdle moves backwards as the arm is raised from below shoulder level, while retraction occurs as the arm descends from above shoulder level. It supports the shoulder capsule throughout extreme arm movement by revolving upwards and downwards.
The scapula region is on the higher posterior surface of the trunk and is circumscribed by the muscles that connect to the Scapula (shoulder blade). These scapula muscles can be divided into :
Extrinsic scapula muscles - It joins the appendicular skeleton to the axial ( levator scapulae, latissimus dorsi, trapezius, rhomboid minor, and rhomboid major)
Intrinsic scapula muscles - These muscles join the Scapula to the humerus (deltoid, supraspinatus, infraspinatus, teres minor, teres major, and subscapularis).
Stabilization and Rotation of the Scapula - This consists of the serratus anterior, trapezius, levator scapulae, and rhomboid muscles and is attached to the superior, medial and inferior borders of the Scapula.
Scapula Bone Anatomy - Parts of Scapula
Borders
Superior border: It is the thinnest and the shortest border.
Medial border: It is a tiny border moving parallel to the vertebral column and is usually ascribed to as the vertebral border.
Lateral border: It is alternatively identified as the axillary border, operating towards the axilla apex. Among the 3 borders, it is the strongest and the thickest. It also sustains the glenoid cavity, which connects with the rounded head of the humerus, creating the shoulder joint or glenohumeral joint.
Angles
The superior border meets with the lateral border, creating the lateral angle.
The superior border also coincides with the medial border to create the superior angle.
The third angle, named the inferior angle, is developed where the lateral and medial borders meet.
Scapula Surfaces
1. Costal Surface - It is the anterior surface of the Scapula covering the thoracic cage or ribcage. It has a large depression oriented toward the back, called the subscapular fossa, from which the subscapularis muscle emerges. A projection hook-like, termed the coracoid method, starts from the superior border of the head of the Scapula, projecting forward and curving laterally, lying under the clavicle.
2. Lateral Surface - This covering of the Scapula faces the humerus. Its major bony landmarks are:
Glenoid fossa – It is a shoal pyriform cavity found at the lateral angle of the Scapula. It connects with the rounded head of the humerus, creating the glenohumeral (shoulder) joint.
Supraglenoid tubercle – A tiny projection on the scapula's glenoid fossa, at the base of the coracoid process.
Infraglenoid tubercle – It is a rugged impression located on the side part of the Scapula, directly under the glenoid fossa.
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3. Posterior Surface - This Scapula faces outwards. Most of the rotator cuff tissues of the shoulder start from here. Its critical anatomical landmarks are:
Spine: It is a long, thin piece of bone located on the back of the Scapula. It divides the back of the Scapula into two parts: the supraspinous and infraspinous fossa. The spinoglenoid notch connects the two fossae. This notch, situated next to the spine, is bridged by the spinoglenoid ligament.
Supraspinous fossa: It is the area over the spine of the Scapula. It is smooth, concave, and wider at its vertebral than at its humeral point. The supraspinatus muscle begins from the heart of this area. It is smaller than the infraspinous fossa, owning the spinoglenoid fossa on its side.
Infraspinous fossa: It is the area under the scapula spine. It is convex and significantly bigger than the preceding one. At its higher part, towards the vertebral margin, it displays a shallow concavity. In the core, it is convex, while near the lateral border, it possesses a deep groove flowing from the upper to the lower part.
Acromion: It is a big bony projection on the uppermost end of the Scapula. It extends over the shoulder joint, articulating with the clavicle at the acromioclavicular (AC) joint.
Articulations of Scapula
The joint between two bones or cartilages is called articulation. Articulation in the scapula refers to the sliding joint that hosts the head of the humerus and connects the glenoid cavity. The scapula forms important articulations with other bones in the body. It connects to two bones at the top of the arm: the humerus, which leads to the elbow and the forearm, and the clavicle, or collarbone, which leads to the shoulder.
FAQs on Scapula: Anatomy, Functions & Clinical Significance
1. What is the scapula, and what are its main anatomical parts?
The scapula, commonly known as the shoulder blade, is a large, flat, triangular bone located in the upper back that connects the humerus (upper arm bone) with the clavicle (collarbone). Its main anatomical parts include three borders (superior, medial, and lateral), three angles (superior, inferior, and lateral), and prominent processes like the acromion, spine, and coracoid process. It also has key surfaces like the subscapular fossa (anterior) and the supraspinous and infraspinous fossae (posterior).
2. How does the scapula articulate with the clavicle and humerus to form the shoulder complex?
The scapula forms two critical joints in the shoulder complex. Firstly, the acromion process of the scapula articulates with the lateral end of the clavicle, forming the acromioclavicular (AC) joint. Secondly, the glenoid cavity, a shallow socket on the lateral angle of the scapula, articulates with the head of the humerus to form the glenohumeral joint, which is the primary shoulder joint responsible for the arm's wide range of motion.
3. What are the six primary movements of the scapula and why are they important?
The scapula's movements are crucial for achieving full arm motion and stability. The six primary movements are:
- Elevation: Shrugging the shoulders upwards.
- Depression: Lowering the shoulders downwards.
- Protraction (Abduction): Moving the scapula forward and away from the spine, like when reaching for something.
- Retraction (Adduction): Pulling the scapula back towards the spine.
- Upward Rotation: The bottom tip of the scapula moves out and up, allowing the arm to be raised overhead.
- Downward Rotation: The return movement from upward rotation.
These movements, known as scapulohumeral rhythm, ensure the shoulder joint remains stable and functional throughout its entire range.
4. Which key muscles attach to the scapula and what are their functions?
Seventeen different muscles attach to the scapula, facilitating its movement and stability. Key examples include:
- The rotator cuff muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) which originate from the scapula and are vital for shoulder rotation and stability.
- The serratus anterior, which is responsible for protraction and upward rotation.
- The trapezius and rhomboids, which control elevation, depression, and retraction.
- The deltoid, which originates in part from the scapular spine and acromion, and is the prime mover for arm abduction.
5. What is the clinical significance of the scapula in overall shoulder health?
The scapula's clinical significance is immense because its position and movement directly impact shoulder function. Improper movement patterns, known as scapular dyskinesis, can lead to a range of problems like shoulder impingement, rotator cuff tears, and instability. Because it serves as a stable base for the rotator cuff muscles, any fracture or muscular imbalance affecting the scapula can severely compromise the strength and mobility of the entire upper limb.
6. What is a 'winged scapula' and what typically causes this condition?
A 'winged scapula' is a condition where the medial border of the shoulder blade protrudes from the back, resembling a wing. This occurs when the muscles holding the scapula against the rib cage are weak or paralysed. The most common cause is damage to the long thoracic nerve, which innervates the serratus anterior muscle. When this muscle fails to function, it can no longer hold the scapula flat, leading to pain, limited arm movement (especially lifting objects or raising the arm), and the visible 'winging' deformity.
7. How does the process of ossification in the scapula occur from birth to adulthood?
The scapula's main body begins to ossify (turn from cartilage to bone) in the fetal stage. However, at birth, several key parts, including the acromion, coracoid process, and glenoid cavity, are still largely cartilaginous. Separate ossification centres appear in these areas during childhood and adolescence. These separate bone pieces gradually fuse with the main body of the scapula, a process that typically completes between the ages of 15 and 25, resulting in the single, solid bone seen in adults.
8. Why is the scapula often described as a 'floating bone', and what are the functional implications?
The scapula is described as a 'floating bone' because its only direct bony connection to the axial skeleton (the trunk) is through the clavicle at the acromioclavicular joint. It is not fixed in a rigid joint but is instead suspended and controlled by a complex network of muscles. This arrangement has a significant functional implication: it allows for an incredible range of motion. Instead of being a fixed pivot point, the scapula can glide and rotate across the rib cage, repositioning the entire shoulder joint to grant the arm its extensive mobility.
