Applied Anatomy – Humerus
1. Definition Table
| Category | Explanation |
|---|---|
| What is it? | – Long bone of the upper arm – Extends from the shoulder to the elbow |
| Most unique feature | – Connects shoulder girdle to forearm – Involved in both fine and powerful upper limb movements |
| Structurally characterized by | – Proximal head articulating with glenoid fossa (shoulder joint) – Shaft forming the arm – Distal end articulating with radius and ulna (elbow joint) |
| Functionally characterized by | – Supports upper limb mobility – Transmits mechanical force from the hand to the trunk – Provides attachment points for many muscles |
| Composed of | – Proximal end: Head, anatomical neck, surgical neck, greater and lesser tubercles, intertubercular (bicipital) groove – Shaft: Cylindrical in upper part, triangular in lower part – Distal end: Capitulum, trochlea, medial and lateral epicondyles |
| Common diseases | – Proximal humeral fractures – Humeral shaft fractures – Distal humerus fractures – Biceps tendon rupture – Pathologic fractures (e.g., metastases) |
| Diagnosis – Clinical | – Pain, swelling, and deformity after trauma – Limited range of motion – Radial nerve injury signs (wrist drop) in shaft fractures |
| Diagnosis – Imaging | – X-ray: Primary tool for fractures – CT: Complex or intra-articular fractures – MRI: Soft tissue injury (e.g., biceps tendon, rotator cuff involvement) |
| Diagnosis – Labs | – CBC and inflammatory markers if infection suspected – Biopsy if suspicious lesion for malignancy |
| Treatment (Rx) | – Conservative management with sling or casting for non-displaced fractures – Open reduction and internal fixation (ORIF) for displaced fractures – Rehabilitation for restoring range of motion and strength |
2. Parts Table
| Part | Description |
|---|---|
| Head | – Articulates with glenoid fossa of scapula – Forms the ball of the ball-and-socket shoulder joint |
| Anatomical neck | – Slight constriction just distal to the head – Attachment site for joint capsule |
| Surgical neck | – Below the tubercles – Common site for fractures |
| Greater tubercle | – Lateral prominence – Attachment for supraspinatus, infraspinatus, teres minor |
| Lesser tubercle | – Anterior prominence – Attachment for subscapularis |
| Intertubercular (bicipital) groove | – Groove between tubercles – Houses long head of biceps tendon |
| Shaft | – Long, cylindrical mid-portion – Site for muscle attachment (deltoid, brachialis) |
| Distal end | – Capitulum articulates with radius – Trochlea articulates with ulna – Epicondyles provide muscle attachment sites |
3. Historical Note
| Era | Highlights |
|---|---|
| Ancient Times | – Evidence of humeral fractures and primitive splinting seen in mummies – Early records of bony injuries involving the arm |
| Classical Era | – Hippocrates described humeral dislocations and reduction techniques – Galen emphasized muscle and tendon attachments |
| Modern Era | – Advances in orthopedic surgery, including internal fixation – Modern imaging refined the understanding of complex fractures – Development of prosthetic humeral replacements in severe injuries |
4. MCQs
🧠 Basic Science
Q1: Which structure separates the greater and lesser tubercles of the humerus?
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A. Anatomical neck
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B. Intertubercular groove
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C. Surgical neck
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D. Deltoid tuberosity
Answer: B. Intertubercular groove
Explanation:
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Intertubercular groove (Correct): Groove where the long head of the biceps tendon lies between the tubercles.
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Anatomical neck (Incorrect): Surrounds the humeral head, not between the tubercles.
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Surgical neck (Incorrect): Below tubercles, frequent fracture site.
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Deltoid tuberosity (Incorrect): Mid-shaft prominence for deltoid attachment.
Q2: The head of the humerus articulates with which structure?
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A. Acromion
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B. Coracoid process
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C. Glenoid fossa
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D. Capitulum
Answer: C. Glenoid fossa
Explanation:
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Glenoid fossa (Correct): Part of the scapula that receives the humeral head.
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Acromion (Incorrect): Roof of shoulder joint, not articulation point.
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Coracoid process (Incorrect): Muscle attachment site, not articulation.
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Capitulum (Incorrect): Distal humerus articulation with radius.
🩺 Clinical
Q3: Injury to the radial nerve is most commonly associated with fractures of which part of the humerus?
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A. Head
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B. Anatomical neck
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C. Shaft
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D. Distal epiphysis
Answer: C. Shaft
Explanation:
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Shaft (Correct): Radial nerve wraps around the humeral shaft in the radial groove.
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Head (Incorrect): Fracture more likely to affect the axillary nerve.
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Anatomical neck (Incorrect): Rare injury site for nerves.
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Distal epiphysis (Incorrect): More associated with ulnar nerve injury.
Q4: A patient falls directly onto their shoulder and is unable to lift their arm. X-ray shows a fracture just below the tubercles. This is most likely a fracture of the:
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A. Anatomical neck
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B. Greater tubercle
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C. Surgical neck
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D. Deltoid tuberosity
Answer: C. Surgical neck
Explanation:
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Surgical neck (Correct): Common fracture site after falls, particularly in elderly.
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Anatomical neck (Incorrect): Rarely fractures; usually related to dislocations.
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Greater tubercle (Incorrect): May fracture but usually associated with rotator cuff tears.
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Deltoid tuberosity (Incorrect): Midshaft injury, not near shoulder.
🖼️ Imaging
Q5: What imaging modality is best for initial evaluation of a suspected humeral shaft fracture?
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A. MRI
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B. CT
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C. Ultrasound
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D. X-ray
Answer: D. X-ray
Explanation:
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X-ray (Correct): First-line imaging for fractures, easily shows shaft injuries.
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MRI (Incorrect): Reserved for soft tissue injuries.
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CT (Incorrect): Used for complex or intra-articular fractures.
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Ultrasound (Incorrect): Limited value for bone fracture.
Q6: Which imaging modality is most sensitive for detecting a subtle biceps tendon tear?
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A. X-ray
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B. CT
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C. MRI
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D. Bone scan
Answer: C. MRI
Explanation:
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MRI (Correct): Best soft tissue imaging, excellent for tendon injuries.
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X-ray (Incorrect): No soft tissue visualization.
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CT (Incorrect): Mainly for bone evaluation.
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Bone scan (Incorrect): Detects metabolic activity, not tendon tears.
5. Memory Image Idea 💡
| Concept | Components |
|---|---|
| The Arm’s Keystone | – Visualize the humerus as a strong bridge beam connecting the mobile shoulder crane to the precision machinery of the forearm – Head = rounded ball fitting into a shallow socket (glenoid) – Shaft = strong supportive column with muscular cables attached (deltoid, brachialis) – Distal end = dual articulation points (capitulum for radius, trochlea for ulna) – Radial nerve winds like a control wire around the shaft – Title: “The Arm’s Keystone – TheCommonVein.com“ |