• Anatomy - bones, muscles, nerves, vessels, organ systems
• Physiology - how body systems function (cardiac, respiratory, renal, neuro, etc.)
• Biochemistry - metabolism, enzymes, molecular biology, genetics
• Histology - tissue types and microscopic anatomy
• Embryology - developmental biology
• Clinical correlations - connecting basic science to real diseases

• Clear headings/points
• Key facts and definitions
• Diagrams described where relevant
• Concise but complete coverage

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Acid-Base Balance Disorders

Normal Acid-Base Status

• Normal arterial pH = 7.35 - 7.45
• Regulated by the Henderson-Hasselbalch equation:
  • pH = 6.1 + log([HCO3-] / 0.03 × PaCO2)
• Normal values: HCO3- = 24 mEq/L, PaCO2 = 40 mmHg

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Classification of Acid-Base Disorders

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1. Metabolic Acidosis

• Cause: Excessive acid production (e.g., diabetic ketoacidosis, lactic acidosis), loss of bicarbonate (diarrhea), or renal failure
• Features: Low pH, low HCO3-, compensatory hyperventilation (Kussmaul breathing)

2. Metabolic Alkalosis

• Cause: Vomiting (loss of HCl), excess alkali intake, diuretic use
• Features: High pH, high HCO3-, compensatory hypoventilation

3. Respiratory Acidosis

• Cause: Hypoventilation - COPD, respiratory failure, sedative overdose
• Features: Low pH, high PaCO2; kidneys retain HCO3- to compensate

4. Respiratory Alkalosis

• Cause: Hyperventilation - anxiety, fever, pulmonary embolism, high altitude
• Features: High pH, low PaCO2; kidneys excrete HCO3- to compensate

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Key Points for Compensation

• Metabolic disorders → compensated by the lungs (change in CO2)
• Respiratory disorders → compensated by the kidneys (change in HCO3-)
• Compensation never fully corrects the pH - it only minimizes the change
• If compensation is excessive or insufficient, a mixed disorder is present

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Mixed Disorders

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Sources: Medical Physiology (Boron & Boulpaep); ROSEN's Emergency Medicine; Quick Compendium of Clinical Pathology

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Diagram 1 - Simple Acid-Base Disorder (Decision Tree)

• pH ↓ + PaCO2 ↓ = Metabolic acidosis
• pH ↓ + PaCO2 ↑ = Respiratory acidosis
• pH ↑ + PaCO2 ↓ = Respiratory alkalosis
• pH ↑ + PaCO2 ↑ = Metabolic alkalosis

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Diagram 2 - Acid-Base Nomogram (90% Confidence Bands)

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Shoulder Joint (Glenohumeral Joint)

1. Type and Articulation

• Type: Ball-and-socket synovial joint - the most mobile joint in the body
• Articulation: Between the head of humerus (ball) and the glenoid cavity of scapula (socket)
• The glenoid cavity is shallow and small (covers only 1/3 of humeral head) - this allows wide movement but sacrifices stability
• The glenoid labrum (fibrocartilaginous rim) deepens the socket and improves congruity

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2. Articular Capsule

• The fibrous capsule is loose and redundant - especially inferiorly, allowing wide movement
• Attaches to the glenoid labrum medially and anatomical neck of humerus laterally
• Weak point: The inferior wall is the thinnest - site of most dislocations
• Two openings in the capsule:
  1. For the tendon of long head of biceps (superiorly)
  2. Communication with subscapular bursa (anteriorly)

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3. Ligaments

The inferior glenohumeral ligament (with its anterior band, posterior band, and axillary recess) forms a hammock during abduction and is the primary restraint to anterior dislocation.

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4. Rotator Cuff Muscles (Dynamic Stabilizers)

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5. Movements and Muscles

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6. Nerve Supply and Blood Supply

• Nerve: Axillary nerve (C5, C6) and suprascapular nerve
• Blood supply: Anterior and posterior circumflex humeral arteries (branches of axillary artery)

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7. Clinical Correlations

• Anterior dislocation (95-97%) - most common
• Mechanism: abduction + external rotation (e.g., falling on outstretched arm)
• Humeral head moves anteroinferiorly
• Bankart lesion: avulsion of anteroinferior glenoid labrum - causes recurrent dislocation
• Hill-Sachs lesion: compression fracture of posterosuperior humeral head
• Axillary nerve injury: loss of sensation over "regimental badge" area (lateral arm) + deltoid paralysis

• Most commonly affects supraspinatus tendon
• Presents with painful arc (60-120° of abduction)
• Common in overhead athletes and the elderly

• Fibrosis and contraction of the joint capsule
• Painful restriction of all movements, especially external rotation
• Common in diabetics and middle-aged women

• Can occur with shoulder dislocation or fracture of surgical neck of humerus
• Results in: deltoid paralysis (loss of abduction), loss of sensation over lateral arm

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Sources: THIEME Atlas of Anatomy; ROSEN's Emergency Medicine; Gray's Anatomy for Students; Miller's Review of Orthopaedics

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1. Draw a shallow cup on the left = glenoid cavity, with a small rim = labrum
2. Draw a large circle fitting into the cup = humeral head
3. Draw a dashed oval around the joint = capsule
4. Add the acromion as a shelf above (flat hook shape)
5. Add the coracoid process as a beak below-front
6. Label the 3 GH ligaments (superior, middle, inferior) on the anterior capsule
7. Draw 4 small arrows around the humeral head for SITS rotator cuff
8. Add the biceps tendon coming out of the top of the joint

• Glenoid labrum
• Articular capsule
• Inferior GH ligament (most important!)
• SITS muscles (especially supraspinatus on top)
• Axillary nerve below the joint
• Acromion + coracohumeral ligament

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Movements at the Radioulnar Joint

1. Introduction

• Proximal radioulnar joint (PRUJ) - at the elbow
• Distal radioulnar joint (DRUJ) - at the wrist

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2. The Two Joints

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3. Movements: Pronation and Supination

• In supination: radius and ulna lie parallel to each other, palm faces anteriorly (up)
• In pronation: radius crosses over the ulna, palm faces posteriorly (down)
• The ulna remains fixed - only the radius rotates around it

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4. Range of Motion

• Supination: 0° → 90° (from neutral/anatomical position)
• Pronation: 0° → 85°
• Combined functional range used in daily activities: ~170°

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5. Muscles Producing Movement

Memory tip: Supination is the stronger movement (turning a screwdriver, tightening a bolt). Biceps brachii is the most powerful supinator - hence elbow must be flexed for maximum supination power.

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6. Role of Interosseous Membrane

• A strong fibrous sheet connecting radius and ulna between the two joints
• Transmits forces from radius to ulna (e.g., a fall on outstretched hand)
• Functionally links PRUJ and DRUJ - movement at one joint requires movement at the other

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7. Clinical Correlations

• Common in children under 6 years
• Sudden pull on the child's hand causes radial head to slip under the annular ligament
• Child holds forearm in pronation and refuses to move it
• Treatment: Supination + flexion manoeuvre to reduce

• Fracture of distal radius - disrupts the DRUJ
• Affects pronation and supination

• Injury at the radial neck/arcade of Frohse
• Supinator muscle denervated → weakness of supination
• No sensory loss (pure motor nerve)

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Sources: Gray's Anatomy for Students; THIEME Atlas of Anatomy; Rockwood & Green's Fractures in Adults

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Movement at the Radioulnar Joint - Quick Summary

Two Joints, One Movement

• Proximal RUJ (pivot joint) - radial head in radial notch of ulna, held by annular ligament
• Distal RUJ (pivot joint) - head of ulna in ulnar notch of radius, stabilized by articular disc
• Linked by the interosseous membrane

Only Two Movements

Muscles

Clinical Points

• Pulled elbow (children) - radial head slips under annular ligament; treat by supination + flexion
• Colles' fracture - disrupts DRUJ
• Posterior interosseous nerve palsy - weak supination

Drawable Diagram

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Movements at the Radioulnar Joint (10 Marks)

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1. Introduction

• Proximal Radioulnar Joint (PRUJ) - just below the elbow
• Distal Radioulnar Joint (DRUJ) - just above the wrist

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2. Proximal Radioulnar Joint (PRUJ)

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3. Distal Radioulnar Joint (DRUJ)

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4. Interosseous Membrane

• A strong fibrous sheet running diagonally between the radius and ulna
• Fibres run obliquely downward and medially from radius to ulna
• Functions:
  1. Mechanically links PRUJ and DRUJ - so both joints always move together
  2. Transmits force from radius to ulna (e.g., fall on outstretched hand transfers force proximally)
  3. Gives attachment to deep muscles of forearm

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5. The Two Movements: Pronation and Supination

Axis of Rotation

Easy Drawable Diagram:

How to Draw This in Exam (2 minutes):

1. Draw two vertical forearms side by side
2. Left = two parallel bones (radius lateral, ulna medial) - label SUPINATION, palm UP
3. Right = radius crossing over ulna forming an X - label PRONATION, palm DOWN
4. At top of each: small circle = Proximal RUJ + ring around radial head = Annular ligament
5. At bottom: label Distal RUJ + Articular disc
6. Middle: diagonal lines between bones = Interosseous membrane
7. Dotted line through both = Axis of rotation

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6. Range of Motion

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7. Muscles Producing Movements

Supination Muscles

Key point: Biceps brachii is the most powerful supinator - it works best when the elbow is flexed at 90°. When elbow is extended, supinator acts alone.

Pronation Muscles

Key point: Pronator quadratus is the primary pronator at all positions of elbow flexion. Pronator teres assists and acts as accessory.

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8. Nerve Supply Summary

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9. Applied Anatomy / Clinical Correlations

A. Pulled Elbow (Nursemaid's Elbow / Chassaignac's Paralysis)

• Age: Most common in children 1-4 years (annular ligament is lax and weak at this age; becomes stronger with age)
• Mechanism: Sudden axial traction on the child's outstretched, pronated forearm (e.g., swinging a child by the hands, pulling child upstairs)
• Pathology: The annular ligament slips forward and becomes entrapped between the radial head and capitellum of humerus
• Clinical features:
  • Sudden pain at elbow
  • Child holds arm in slight flexion and pronation (pseudoparalysis - "arm looks paralyzed")
  • No swelling or bony tenderness
  • Refuses to move the arm
• Treatment: Supination + flexion manoeuvre OR hyperpronation technique
  • A click is felt/heard on successful reduction
  • Child is symptom-free within minutes after reduction
• X-ray: Usually normal (clinical diagnosis); done to rule out fractures

B. Galeazzi Fracture

• Fracture of middle/distal third of radius + dislocation of DRUJ
• DRUJ is disrupted and unstable
• Treatment: ORIF of radius fracture to restore DRUJ stability

C. Monteggia Fracture

• Fracture of proximal third of ulna + dislocation of radial head at PRUJ
• Anterior dislocation most common (Bado type I)
• Anterior interosseous nerve or radial nerve may be injured
• Treatment: ORIF of ulna + reduction of radial head

D. Posterior Interosseous Nerve (PIN) Palsy

• Compression of PIN in the arcade of Frohse (fibrous edge of supinator)
• Denervates supinator and extensors
• Weakness of supination (biceps partially compensates)
• No sensory loss (pure motor nerve)

E. TFCC (Triangular Fibrocartilage Complex) Tear

• Common in fall on outstretched hand or forceful rotation
• Presents with ulnar-sided wrist pain worsened by forearm rotation
• Diagnosed by MRI arthrography
• Treatment: Arthroscopic debridement or repair

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10. Summary Table

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Sources: THIEME Atlas of Anatomy; Gray's Anatomy for Students; Tintinalli's Emergency Medicine; Campbell's Operative Orthopaedics

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