Scapula

날짜:

 


Scapula

The scapula is a triangular, flat bone positioned in the upper posterior thorax. It features three distinct angles:
  1. Inferior Angle
  1. Superior Angle
  1. Lateral Angle
Each of these angles has specific anatomical significance. The inferior angle is particularly important clinically, as it serves as a key palpation point for assessing scapular movement during various arm motions.
Borders of the Scapula
The scapula has three primary borders, which define its structural integrity:
  • Medial Border (Vertebral Border): Runs parallel to the spine when the arms are placed at the sides in an anatomical position.
  • Lateral Border (Axillary Border): Extends diagonally upward from the inferior angle to the lateral angle.
  • Superior Border: Begins at the superior angle and extends laterally, terminating at the coracoid process.

Posterior Features of the Scapula

The scapular spine divides the posterior surface into two distinct fossae:
  1. Supraspinous Fossa – Houses the supraspinatus muscle, which is essential for arm abduction.
  1. Infraspinous Fossa – The attachment site for the infraspinatus muscle, which contributes to external rotation of the arm.
The scapular spine starts medially as the root of the spine, gradually widening and flattening as it extends laterally, eventually forming the acromion.
Acromion and Acromioclavicular Joint
The acromion is a flat, broad projection that extends laterally and anteriorly, creating a horizontal "roof" above the glenoid cavity. It contains the clavicular facet, which articulates with the clavicle to form the acromioclavicular (AC) joint.

Glenoid Fossa (Glenoid Cavity)

The glenoid fossa is a slightly concave surface that articulates with the humeral head to form the glenohumeral joint.
  • The term "glenoid" derives from the Greek words "glene" (socket) and "eidos" (resemblance).
  • It is angled upward by approximately 4°, but individual variation can range from -7° (downward tilt) to +16° (upward tilt).
The glenoid cavity is oriented approximately 35° anteriorly relative to the frontal plane, a position known as the scapular plane. The humerus and scapula tend to move within this plane during overhead arm motions.
Adjacent to the glenoid fossa, two important tubercles serve as muscle attachment sites:
  • Supraglenoid Tubercle – The attachment site for the long head of the biceps brachii.
  • Infraglenoid Tubercle – The attachment site for the long head of the triceps brachii.
The coracoid process extends anteriorly near the glenoid cavity and serves as a critical attachment site for several ligaments and muscles.

Anterior Surface of the Scapula

The subscapular fossa is located on the anterior aspect of the scapula and houses the subscapularis muscle, which plays a key role in internal rotation of the arm.

Osteological Features of the Scapula

  • Angles: Inferior, Superior, and Lateral – define the triangular shape.
  • Medial (Vertebral) Border: Runs parallel to the spine.
  • Lateral (Axillary) Border: Extends diagonally upward.
  • Superior Border: Forms the uppermost edge.
  • Supraspinous Fossa: Above the scapular spine, housing the supraspinatus muscle.
  • Infraspinous Fossa: Below the scapular spine, housing the infraspinatus muscle.
  • Scapular Spine: The bony ridge that divides the posterior surface.
  • Root of the Spine: Medial origin of the scapular spine.
  • Acromion: The lateral extension of the spine, forming the AC joint with the clavicle.
  • Clavicular Facet: Articulates with the clavicle.
  • Glenoid Fossa: The concave socket for the humeral head.
  • Supraglenoid & Infraglenoid Tubercles: Attachment points for biceps and triceps.
  • Coracoid Process: A forward-projecting structure for ligament and muscle attachment.
  • Subscapular Fossa: The anterior surface, where the subscapularis muscle resides.

Functional Significance

The scapula serves as a key structural component of the shoulder complex, providing:
  1. Stability – Forms the foundation for upper limb movement.
  1. Mobility – Facilitates dynamic shoulder motions through multiple articulations.
  1. Muscle Attachment – Anchors muscles that control the arm and shoulder girdle.
Understanding the scapular anatomy is essential for diagnosing and managing shoulder dysfunction, as its movement and positioning play a critical role in normal upper limb biomechanics.