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Pre University Examination - Orthopaedics: Model Answers

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Q1. Clostridial Gas Gangrene (Clostridial Myonecrosis) [10 marks]

Definition

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Etiopathogenesis

• Clostridium perfringens - most common (80-90%)
• Clostridium septicum, C. bifermentans, C. sporogenes
• Non-clostridial gas-producing organisms (coliforms) are co-isolated in 60-85% of cases

• Crushing injuries, missile/gunshot wounds
• Compound fractures with devitalised muscle
• Ischaemic/vascular injuries
• Bowel surgery (spontaneous gas gangrene from C. septicum)
• Premature wound closure

1. Devitalised (ischaemic) tissue creates the anaerobic environment needed for spore germination
2. Incubation period: usually <24 hours (range: 1 hour to 6 weeks)
3. C. perfringens produces multiple exotoxins:
   • Alpha-toxin (lecithinase) - most important; destroys RBCs, WBCs, platelets, fibroblasts, and muscle cells
   • Phi-toxin - causes myocardial suppression
   • Kappa-toxin - destroys connective tissue and blood vessels
4. A vicious cycle ensues: bacteria multiply -> exotoxins cause local necrosis and vascular thrombosis -> further anaerobic spread -> gas (CO2, H2, N2) tracks along muscle planes
5. Systemic exotoxins cause severe haemolysis, leading to hypotension, shock, AKI, and ARDS

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Clinical Features

• Pain - earliest symptom; rapidly increases in severity (disproportionate to wound appearance)
• Tense, woody swelling of the limb
• Wound exudes serosanguineous (brownish, "dishwater") discharge
• Skin turns bronze/brown, then blue-black
• Haemorrhagic bullae (blisters)
• Soft-tissue crepitus on palpation (gas in tissue planes)
• Characteristic sickly-sweet odour

• High-grade fever, tachycardia, tachypnoea
• Altered mental status (restlessness, anxiety, then delirium)
• Hypotension progressing to septic shock
• Jaundice (from haemolysis)
• Oliguria/anuria (AKI)

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Investigations

• X-ray/CT scan - feathery gas shadows within muscle planes
• Gram stain of exudate - large Gram-positive bacilli, notably WITHOUT neutrophils (neutrophils are destroyed by the toxins)
• Blood tests - haemolytic anaemia, leucocytosis, metabolic acidosis, raised creatinine
• Culture - anaerobic culture of wound discharge confirms organism

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Differential Diagnosis

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Management

• IV fluid resuscitation, inotropes for shock
• Monitor urine output, ABG, renal function
• Blood transfusion for haemolytic anaemia

• Penicillin G (high dose) - first-line
• Clindamycin - inhibits toxin production (key adjunct)
• Third-generation cephalosporins added for polymicrobial cover

• Radical surgical debridement - all necrotic muscle must be excised
• Amputation - in established gas gangrene with systemic toxicity, amputation is life-saving and must not be delayed
• Wound is left OPEN (no closure); packed with saline-soaked gauze
• Re-exploration at 24-48 hours

• Recommended in severe cases if facilities available
• Inhibits bacterial growth in high O2 environment; may limit extent of debridement needed

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Q2A. Classical Hand Deformities in Rheumatoid Arthritis [5 marks]

1. Ulnar Deviation/Drift at MCPJs

• Most characteristic deformity of RA
• Pannus destroys the MCPJ capsule and collateral ligaments
• Flexor tendons bowstring towards the ulnar side
• Results in ulnar deviation of fingers at the MCPJs with radial deviation of the wrist (zig-zag deformity)

2. Swan Neck Deformity

• Hyperextension at PIPJ + Flexion at DIPJ
• Caused by: MCPJ synovitis -> intrinsic muscle tightness -> PIP hyperextension; or FDS tendon rupture
• Resembles a swan's neck in profile

3. Boutonniere Deformity

• Flexion at PIPJ + Hyperextension at DIPJ
• Caused by: attenuation/rupture of the central slip of extensor tendon -> lateral bands sublux volar to PIPJ axis -> PIPJ stuck in flexion, DIPJ hyperextends

4. Z-deformity of Thumb (Hitchhiker's Thumb)

• Flexion of IPJ + Hyperextension of MCPsJ (or vice versa)
• Three types (Nalebuff classification)

5. Caput Ulnae Syndrome

• Dorsal subluxation of the distal ulna due to DRUJ destruction
• The prominent ulnar head ("caput ulnae") can rupture the extensor tendons of the little finger first, progressing radially (Vaughan-Jackson syndrome)

6. Extensor Tendon Ruptures

• Begin with the little finger (EDM, EDC5), progressing radially (Vaughan-Jackson)
• Unable to actively extend the involved fingers

7. Mallet Finger

• Loss of active DIP extension due to extensor tendon attrition over a dorsal osteophyte

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Q2B. Bursitis Around the Knee [5 marks]

1. Prepatellar Bursitis ("Housemaid's Knee")

• Location: Subcutaneous, in front of the lower patella and upper patellar ligament
• Cause: Repeated kneeling (carpet layers, roofers, clergy)
• Features: Tender, fluctuant swelling directly over the patella; knee flexion is painful; joint itself is not involved
• Treatment: Rest, aspiration, anti-inflammatory drugs; surgical excision for chronic/recurrent cases

2. Infrapatellar Bursitis ("Clergyman's Knee")

• Superficial infrapatellar bursa: Between skin and patellar ligament below the tibial tuberosity
• Deep infrapatellar bursa: Between patellar ligament and the tibia
• Cause: Kneeling in a more upright position (prayer)
• Features similar to prepatellar bursitis but lower in position

3. Suprapatellar Bursa

• Located between the femur and the quadriceps tendon
• Normally communicates with the knee joint cavity
• Becomes distended in any knee joint effusion; best detected as a horseshoe-shaped swelling above the patella

4. Semimembranosus Bursa (Baker's Cyst precursor)

• Located posteromedially, between semimembranosus and medial head of gastrocnemius
• Becomes prominent and tense on knee extension
• More common in children; usually resolves spontaneously

5. Baker's Cyst (Popliteal Cyst)

• A herniation of the posterior synovial membrane through the oblique popliteal ligament
• Located in the midline of the popliteal fossa, slightly below the joint line
• Prominent on extension; disappears on flexion
• Often associated with intra-articular pathology (OA, RA, TB)
• On examination: transilluminates; Foucher's sign (becomes tense on extension, soft on flexion)
• Rupture can mimic DVT (pseudothrombophlebitis)

6. Pes Anserinus Bursitis

• Located medially, deep to the conjoined insertion of sartorius, gracilis, and semitendinosus
• Common in obese women with OA; pain on the medial side of the knee

7. Iliotibial Band Bursa

• Between the iliotibial band and the lateral femoral condyle
• Common in runners ("runner's knee")

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Q2C. Hangman's Fracture [5 marks]

Definition

Mechanism

• Primary mechanism: Hyperextension + axial loading of the cervical spine
• Classically described in judicial hanging (the noose forces hyperextension)
• In modern practice: high-energy trauma - road traffic accidents, diving injuries, falls
• Some patterns involve flexion-distraction

Classification (Levine-Edwards - Most Widely Used)

• Starr-Eismont variant: Fracture extends into the posterior body of C2; higher rate of neurological injury; needs halo vest or surgery

Clinical Features

• Neck pain, tenderness over C2
• Torticollis
• Neurological deficit is LESS common than expected because the bilateral pars fracture actually decompresses the spinal canal (the vertebral body shifts forward, widening the canal)
• However, severe displacement or disc herniation can cause cord injury

Investigations

• Plain X-ray: lateral view shows forward displacement of C2 body on C3; fracture through the pars
• CT scan (gold standard): precise fracture characterisation
• MRI: disc/ligament injury, cord signal changes

Management

• Type I and Type II without severe angulation: Rigid cervical collar or halo vest immobilisation for 8-12 weeks
• Halo vest complications (especially in elderly): pin site infection, loosening, dysphagia

• Type IIa, Type III, and Starr-Eismont variant: Surgical stabilisation
• Posterior C2-C3 fusion (most common)
• Anterior C2-C3 discectomy and fusion (for disc disruption)

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Q2D. Pathoanatomy of CTEV (Congenital Talipes Equinovarus) Foot [5 marks]

Definition

The Four Components of CTEV Deformity (CAVE)

Detailed Pathoanatomy

• Talus: The head and neck of the talus are deviated medially and plantarward (the talar neck is short and internally rotated)
• Calcaneus: In equinus (plantarflexed) and varus (inverted) position; the posterior part is pulled up by the shortened tendo-Achilles, making the heel feel "empty"
• Navicular: Displaced medially with respect to the talar head (talonavicular subluxation) - the most consistent pathological finding
• Cuboid: Displaced medially with respect to the calcaneus

• Ligaments: Calcaneofibular ligament and plantar calcaneonavicular (spring) ligament are shortened and thickened
• Tendons and sheaths: Posterior tibial tendon sheath, tendo-Achilles, tibialis posterior, flexor hallucis longus, and flexor digitorum longus are contracted
• Tendon sheaths contain contractile myofibroblasts (fibroblastic component)
• The lateral structures (peroneal tendons and their sheaths) are elongated

• Gastrocsoleus and posterior tibial muscles are smaller than normal
• Reduced myofibrils, increased connective tissue (possibly due to neuromuscular abnormality)
• Evertors (peronei) are weak

• The dorsalis pedis artery may be diminished in calibre
• Contributes to difficulty with healing post-surgery

• Deep medial crease and single posterior crease are characteristic
• All children have a smaller calf and foot on the affected side

Key Pathological Distinction

• In postural CTEV (intrauterine moulding): deformity is correctable and fully reducible; no structural joint/bone change
• In structural idiopathic CTEV: deformity is fixed; underlying bony and soft-tissue changes as above

Clinical Appearance

Classification

• Pirani score (0-6): based on 6 clinical signs; guides Ponseti treatment
• Dimeglio classification (Grade I-IV): grades reducibility and severity

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