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Make notes on scapula
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Here are comprehensive notes on the scapula, sourced from Gray's Anatomy for Students:
Scapula - Anatomy Notes
Overview
The scapula (shoulder blade) is a large, flat, triangular bone that forms the posterior part of the pectoral girdle. It lies on the posterolateral aspect of the thoracic wall, overlying ribs II-VII.
Basic Structure
The scapula has:
- 3 Angles: lateral, superior, inferior
- 3 Borders: superior, lateral (axillary), medial (vertebral)
- 2 Surfaces: costal (anterior) and posterior
- 3 Processes: acromion, spine, coracoid process
Borders
| Border | Description |
|---|---|
| Lateral (axillary) | Strong and thick - for muscle attachment |
| Medial (vertebral) | Thin and sharp |
| Superior | Thin; marked laterally by the suprascapular notch and the root of the coracoid process |
Angles
- Lateral angle - Marked by the glenoid cavity (shallow, comma-shaped), which articulates with the head of the humerus to form the glenohumeral joint
- Superior angle - At the junction of the medial and superior borders
- Inferior angle - Easily palpable; moves forward during arm elevation (used clinically to assess scapular rotation)
Surfaces
Posterior Surface
- Divided by the prominent spine of the scapula into:
- Supraspinous fossa (small, superior) - contains supraspinatus
- Infraspinous fossa (large, inferior) - contains infraspinatus
- The greater scapular notch (spinoglenoid notch) lies between the lateral angle and the attachment of the spine
Costal (Anterior) Surface
- Characterized by the large concave subscapular fossa
- Moves freely over the thoracic wall (on the subscapularis muscle)
Processes
Spine
- Prominent ridge on the posterior surface
- Projects laterally to become the acromion
- Both trapezius and deltoid attach to opposing surfaces of the spine
Acromion
- Anterolateral projection of the spine
- Arches over the glenohumeral joint
- Articulates with the clavicle via a small oval facet - forming the acromioclavicular (AC) joint
- Easily palpable
Coracoid Process
- Hook-like structure on the superior border
- Projects anterolaterally, lying directly inferior to the lateral part of the clavicle
- Site of attachment for:
- Pectoralis minor
- Short head of biceps brachii
- Coracobrachialis
Tubercles and Notches
| Feature | Location | Significance |
|---|---|---|
| Infraglenoid tubercle | Inferior to glenoid cavity | Attachment of long head of triceps brachii |
| Supraglenoid tubercle | Superior to glenoid cavity | Attachment of long head of biceps brachii |
| Suprascapular notch | Superior border, medial to coracoid | Suprascapular nerve passes through; suprascapular artery passes over the ligament |
Muscles Attached to the Scapula
Muscles Connecting Scapula to the Trunk
| Muscle | Origin | Insertion on Scapula | Action | Nerve |
|---|---|---|---|---|
| Trapezius | Occiput, nuchal line, spinous processes C7-T12 | Spine, acromion | Elevates, retracts, rotates scapula | Accessory (CN XI) |
| Serratus anterior | Lateral surfaces ribs 1-9 | Costal surface, medial border | Protracts, rotates scapula; keeps it against thorax | Long thoracic nerve (C5, C6, C7) |
| Levator scapulae | Transverse processes C1-C4 | Medial border, superior angle to root of spine | Elevates scapula | Dorsal scapular nerve + C3, C4 |
| Rhomboid minor | Lower ligamentum nuchae, spinous processes C7-T1 | Medial border at root of spine | Elevates and retracts scapula | Dorsal scapular nerve (C5) |
| Rhomboid major | Spinous processes T2-T5 | Medial border from spine to inferior angle | Elevates and retracts scapula | Dorsal scapular nerve (C4, C5) |
Muscles of the Posterior Scapular Region (Rotator Cuff + Others)
| Muscle | Origin (Scapula) | Insertion (Humerus) | Action | Nerve |
|---|---|---|---|---|
| Supraspinatus | Medial 2/3 supraspinous fossa | Superior facet of greater tubercle | Abduction + stabilization | Suprascapular nerve (C6) |
| Infraspinatus | Medial 2/3 infraspinous fossa | Middle facet of greater tubercle | Lateral rotation + stabilization | Suprascapular nerve (C6) |
| Teres minor | Upper 2/3, lateral border (posterior) | Inferior facet of greater tubercle | Lateral rotation + stabilization | Axillary nerve (C6, C7) |
| Teres major | Posterior surface of inferior angle | Medial lip of intertubercular sulcus | Medial rotation, adduction, extension | Lower subscapular nerve (C6, C7) |
| Subscapularis | Subscapular fossa | Lesser tubercle | Medial rotation + stabilization | Upper + lower subscapular nerves (C5, C6) |
Movements of the Scapula
| Movement | Prime Movers |
|---|---|
| Elevation | Trapezius (upper), levator scapulae, rhomboids |
| Depression | Trapezius (lower), serratus anterior (lower) |
| Protraction (forward) | Serratus anterior |
| Retraction | Rhomboids, trapezius (middle) |
| Upward rotation (glenoid tilts up) | Trapezius + serratus anterior |
| Downward rotation | Rhomboids, levator scapulae |
Scapulothoracic Joint
- Not a true synovial joint - it is a physiological joint (soft tissue articulation)
- The costal surface of the scapula glides over the thoracic wall on a "cushion" of serratus anterior and subscapularis
- Allows the wide range of scapular movements described above
Neurovascular Supply
| Structure | Detail |
|---|---|
| Suprascapular nerve | From upper trunk of brachial plexus (C5, C6); passes through suprascapular notch; supplies supraspinatus and infraspinatus |
| Suprascapular artery | Branch of thyrocervical trunk; passes over the transverse scapular ligament (not through the notch) |
| Dorsal scapular nerve | C5 root; supplies rhomboids and levator scapulae |
| Long thoracic nerve | C5, C6, C7; runs on the external surface of serratus anterior - very vulnerable to injury |
Clinical Correlates
Winged Scapula
- Caused by damage to the long thoracic nerve (e.g., during axillary surgery, mastectomy, or lateral thoracotomy)
- Results in paralysis of serratus anterior
- The medial border and inferior angle of the scapula lift away from the thorax posteriorly
- Winging is accentuated when the patient pushes against a wall or elevates the arm
- Normal arm elevation is no longer possible above horizontal
Suprascapular Nerve Entrapment
- Nerve can be compressed at the suprascapular notch
- Causes weakness and wasting of supraspinatus and infraspinatus
- Presents as shoulder pain and weakness of abduction and lateral rotation
Scapular Fractures
- Uncommon due to protective surrounding musculature
- When they do occur, they imply a significant force and associated injuries (neurovascular, thoracic) must be actively sought
Sources: Gray's Anatomy for Students, Chapter 7 (Upper Limb); pp. corresponding to scapula section and posterior scapular region.
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