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M01.03.013 Humerus
The humerus is a long bone in the upper limb, extending from the shoulder to the elbow. It serves as a crucial component for movement, muscle attachment, and articulation at both its proximal and distal ends.
Key Features
| Aspect | Articulations | Significance |
|---|---|---|
| Proximal End | Articulates with the glenoid fossa of the scapula to form the glenohumeral (shoulder) joint | Provides sites for rotator cuff muscle attachments |
| Shaft | No direct articulations | Serves as an anchor for muscles involved in arm movement |
| Distal End | Articulates with the radius and ulna at the elbow joint | Contains structures for elbow flexion and extension |
Proximal Landmarks
- Head:
- Faces medially, upward, and backward.
- Separated from the tuberosities by the anatomical neck.
- Greater Tuberosity:
- Located laterally.
- Serves as the attachment site for:
- Supraspinatus (superior facet)
- Infraspinatus (middle facet)
- Teres minor (inferior facet)
- Lesser Tuberosity:
- Found medially, with a single anterior surface.
- Site of attachment for subscapularis.
- Intertubercular Sulcus:
- A deep groove between tuberosities.
- Passage for the long head of biceps brachii.
- Muscle insertions:
- Pectoralis major (lateral lip)
- Latissimus dorsi (floor)
- Teres major (medial lip)
- Surgical Neck:
- A common fracture site.
- Clinical concern: proximity to the axillary nerve and circumflex humeral vessels.
Shaft of the Humerus
| Features | Details |
|---|---|
| Deltoid Tuberosity | Lateral roughened surface where the deltoid muscle attaches. |
| Radial Groove | Runs obliquely along the posterior surface, housing the radial nerve and profunda brachii artery. |
Muscle Attachments
| Region | Muscles |
|---|---|
| Anterior | Coracobrachialis, deltoid, brachialis, brachioradialis. |
| Posterior | Medial and lateral heads of the triceps (marked by the spiral groove). |
Distal Landmarks
- Medial and Lateral Supraepicondylar Ridges:
- Medial: Larger, extends further distally.
- Lateral: Roughened for attachment of forearm extensor muscles.
- Epicondyles:
- Medial Epicondyle:
- Site for the ulnar nerve (palpable in the posterior groove).
- Lateral Epicondyle:
- Attachment for muscles of the forearm.
- Medial Epicondyle:
- Trochlea and Capitulum:
- Trochlea: Medial, articulates with the ulna.
- Capitulum: Lateral, articulates with the radius.
- Fossae:
- Coronoid, radial, and olecranon fossae accommodate forearm bones during elbow movement.
Clinical Relevance
1. Surgical Neck Fractures
- Mechanism: Direct blow or fall on an outstretched hand.
- At risk: Axillary nerve and posterior circumflex artery.
- Signs:
- Motor: Deltoid and teres minor paralysis (difficulty with arm abduction).
- Sensory: Loss over the deltoid region (“regimental badge area”).
2. Mid-Shaft Fractures
- Mechanism: Trauma to the humeral shaft.
- At risk: Radial nerve and profunda brachii artery.
- Signs:
- Motor: Wrist extensor paralysis → wrist drop.
- Sensory: Loss over dorsal hand and lateral 3½ fingers.
3. Supracondylar Fractures
- Mechanism: Falling on an outstretched hand (common in children).
- At risk: Brachial artery, anterior interosseous nerve, and ulnar nerve.
- Complications:
- Ischaemia → Volkmann’s contracture.
- Test: Weakness in making an “okay” sign (anterior interosseous nerve injury).
- Classification: Gartland types 1-3.
Key Points for Students
- Mnemonic for Intertubercular Sulcus: “A lady between two majors”
- Latissimus dorsi (between teres major and pectoralis major).
- Remember Nerves at Risk:
- Axillary nerve (surgical neck fractures).
- Radial nerve (mid-shaft fractures).
- Ulnar nerve (distal humerus).
- Always correlate fractures with nearby neurovascular structures!