Topic Overview

Scapula

General Features

• Flat, triangular bone forming the posterior part of the shoulder girdle.

• Lies on the posterolateral aspect of thorax between 2nd and 7th ribs.

• Provides large surface area for muscle attachment and contributes to the shoulder joint.

Parts of Scapula

1. Angles

   • Superior angle → level of T2 vertebra.

   • Inferior angle → level of T7 vertebra.

   • Lateral angle → thick, bears glenoid cavity.

2. Borders

   • Superior → short, with suprascapular notch.

   • Medial (vertebral) → parallel to vertebral column.

   • Lateral (axillary) → thick, bears infraglenoid tubercle.

3. Surfaces

   • Costal surface → concave, forms subscapular fossa.

   • Dorsal surface → divided by spine into supraspinous and infraspinous fossae.

4. Processes

   • Spine → prominent ridge, ends laterally as acromion.

   • Acromion → articulates with clavicle.

   • Coracoid process → hook-like projection, muscle attachment.

5. Glenoid Cavity

   • Shallow, pear-shaped cavity.

   • Articulates with head of humerus → forms shoulder joint.

   • Supraglenoid tubercle (long head of biceps).

   • Infraglenoid tubercle (long head of triceps).

Attachments (Summary)

• Muscles attached:

  • Medial border → serratus anterior, levator scapulae, rhomboids.

  • Lateral border → teres minor, teres major.

  • Coracoid process → pectoralis minor, short head of biceps, coracobrachialis.

  • Spine → trapezius (upper), deltoid (lower).

  • Subscapular fossa → subscapularis.

  • Supraspinous fossa → supraspinatus.

  • Infraspinous fossa → infraspinatus.

Ossification of Scapula

• Begins: 8th week intrauterine life.

• Primary center: appears near the glenoid cavity → expands to form body.

• Secondary centers:

  • 2 for coracoid process.

  • 2 for acromion.

  • 1 for medial border of scapula.

  • 1 for inferior angle.

  • 1 for glenoid cavity.

• Fusion of secondary centers completed around 20–25 years.

• Thus, scapula has 1 primary + 7 secondary centers.

Clinical Anatomy

• Fractures:

  • Rare due to protection by muscles and chest wall.

  • When occur, usually associated with rib fractures.

• Winged scapula:

  • Paralysis of serratus anterior (injury to long thoracic nerve).

  • Medial border of scapula protrudes backward when pushing against resistance.

• Dislocation of acromioclavicular joint:

  • Common in contact sports.

  • Results in prominent acromion (step deformity).

• Scapular dyskinesis:

  • Abnormal scapular movements due to muscle imbalance.

• Ossification centers: important in forensic age estimation.