High Yield Overview
ANIMAL BITES
Microbiology and Surgical Management
80-90%Dog Bites
50%Cat Infection Rate
BugPasteurella
DrugAugmentin
Injury Classification
Puncture
PatternDeep inoculation (Cats). High infection risk.
Treatment
Laceration
PatternTearing (Dogs). Less infection, more tissue loss.
Treatment
Crush
PatternDevitalized tissue (Large dogs). Compartment syndrome risk.
Treatment
Avulsion
PatternSoft tissue loss requiring reconstruction.
Treatment
Critical Must-Knows
- Cats bite deep (Puncture) → Pasteurella multocida → Rapid infection (less than 24h).
- Dogs bite wide (Crush/Tear) → Polymicrobial → Slower infection (greater than 24h).
- Primary closure is CONTROVERSIAL but accepted for face (excellent blood supply) and large lacerations (loosely).
- Puncture wounds should NEVER be closed primarily.
- Augmentin (Amoxicillin/Clavulanate) is the antibiotic of choice.
Examiner's Pearls
- "Capnocytophaga canimorsus causes overwhelming sepsis in asplenic/immunocompromised patients.
- "Australian Bats carry Lyssavirus (Rabies-like). Do not touch them.
- "Eikenella corrodens is HUMAN bite, not animal.
Clinical Imaging
Imaging Gallery
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Antibiotic Guidelines
The Golden Rule
Augmentin (Amoxicillin + Clavulanate). It covers Pasteurella, Staph, Strep, and Anaerobes. Allergy (Penicillin): Doxycycline (or TMP/SMX) + Metronidazole (for anaerobes). Alternate: Moxifloxacin (monotherapy, covers all). Avoid: Cephalexin (Keflex) alone - it does NOT cover Pasteurella effectively.
- Prophylaxis: Indicated for all cat bites, deep dog bites, hand bites, and immunocompromised hosts. Duration: 3-5 days.
- Treatment: Indicated for established infection. Duration: 7-14 days. IV if systemic signs.
Complications
- Septic Arthritis: From direct inoculation. Destroys cartilage rapidly (chondrolysis). requiring serial washouts.
- Osteomyelitis: If bone is bitten.
- Tenosynovitis: Pyogenic flexor tenosynovitis requires urgent drainage.
- Rabies: 100% fatal if untreated. (Note: Australian Bat Lyssavirus involves bats, not dogs/cats, but protocol is similar).
- Post-Traumatic Stress Disorder (PTSD): Common after dog attacks.
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Rehabilitation
Acute Phase (Days 1-7)
- Splinting: Position of safety (Intrinsic plus) for hand bites to prevent contracture
- MCP joints flexed 70-90°
- IP joints extended
- Wrist in neutral to slight extension
- Edema Control: Elevation above heart level is critical
- Compressive dressing (non-circumferential)
- Active finger pumping exercises when permitted
- Wound Care: Daily dressing changes to monitor for spreading infection
Subacute Phase (Weeks 1-4)
- Mobilization: Early controlled mobilization once infection cleared
- Active range of motion within splint
- Passive range if tendon repair performed (modified Duran protocol)
- Scar Management: Silicone sheets, massage once epithelialized
- Strengthening: Gradual isometric then isotonic exercises
Late Phase (Weeks 4-12)
- Return to Function: Occupation-specific rehabilitation
- Desensitization: For painful scars or hypersensitivity
- Contracture Prevention: Night splinting if MCP or PIP stiffness developing
Rehabilitation Priority
In animal bites with tendon injury, the balance between infection control (immobilization) and adhesion prevention (early motion) is critical. Generally, err on the side of infection control first - a stiff finger is better than an amputated one.
Prognosis
- Infection Rate: With proper debridement and antibiotics, infection rate is low (less than 5% for dogs).
- Function: Depends on structural injury. Nerve repairs in dirty wounds have poorer outcomes.
- Cosmesis: Scar revision may be needed later.
Evidence Base
Primary Closure of Dog Bites
Paschos et al. • Meta-analysis / Cochrane (2014)
Key Findings:
- Analyzed primary closure vs leaving open
- No significant difference in infection rate for non-puncture dog bites
- Primary closure is acceptable if debrided well
Clinical Implication: You can close the face and clean body wounds.
Antibiotic Prophylaxis
Medeiros et al. • Cochrane Database (2001)
Key Findings:
- Antibiotics reduce infection in hand bites significantly
- Less benefit for superficial wounds elsewhere
- Supports universal prophylaxis for hand/cat bites
Clinical Implication: Hand bite = Antibiotics.
Pasteurella Bacteriology
Talan et al. • NEJM (1999)
Key Findings:
- Multicenter study of infected dog/cat bites
- Pasteurella found in 50% dog and 75% cat bites
- Anaerobes present in majority of deep wounds
Clinical Implication: Polymicrobial coverage (Augmentin) is essential.
Capnocytophaga Sepsis
Lion et al. • Lancet Infect Dis (1996)
Key Findings:
- Review of C. canimorsus sepsis
- Strong association with asplenia and alcohol abuse
- High mortality rate (30%) despite treatment
Clinical Implication: Warning for immunocompromised patients.
Irrigation Volume
Bhandari et al. • JBJS Am (2015)
Key Findings:
- FLOW trial (Open fractures but applicable)
- Soap vs Saline vs Pressure
- Suggests copious low pressure saline is standard
- Though soap was not inferior, saline is safer for tissues
Clinical Implication: The solution to pollution is dilution.
Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Scenario 1: The Cat Bite
EXAMINER
"A 45-year-old lady presents with a small puncture wound to the volar index finger from her cat 12 hours ago. It is red, swollen, and painful on passive extension. How do you manage this?"
EXCEPTIONAL ANSWER
This is classical Flexor Tenosynovitis inoculated by Pasteurella multocida. The puncture wound seals the bacteria in the sheath. It requires hospital admission, IV antibiotics (Augmentin/Penicillin), and urgent surgical drainage (washout) of the flexor sheath. Conservative management will likely fail and lead to tendon necrosis.
KEY POINTS TO SCORE
Recognition of Kanavel signs
High risk organism (Pasteurella)
Need for surgery (Sheath washout)
COMMON TRAPS
✗Prescribing oral antibiotics and discharge
✗Waiting for 'pus' to appear
LIKELY FOLLOW-UPS
"What incision do you use?"
"Brunner incisions or mid-lateral, opening the sheath distally (A5) and proximally (A1) for irrigation."
VIVA SCENARIOStandard
Scenario 2: The Face Bite
EXAMINER
"A 6-year-old child was bitten on the cheek by the family dog. There is a 3cm laceration, full thickness. Parents are worried about scarring. Can you close it?"
EXCEPTIONAL ANSWER
Yes. The face has an excellent blood supply, and the risk of infection is lower than the hand. I would perform thorough irrigation and debridement under anaesthesia (likely GA for a child), and perform a primary closure with loose sutures. I would prescribe prophylactic antibiotics.
KEY POINTS TO SCORE
Face = Low infection risk
Cosmesis is a priority
Primary closure is accepted
COMMON TRAPS
✗Leaving it open (poor scar)
✗Not debriding edges
LIKELY FOLLOW-UPS
"What about Rabies?"
"If it's a domestic dog in Australia, risk is zero. If overseas or bat involved, Lyssavirus protocol applies."
VIVA SCENARIOStandard
Scenario 3: The Late Presentation
EXAMINER
"A 30-year-old man presents 3 days after punching someone in the mouth (Wait, Human bite? No, let's say 'bitten by a dog on the MCPJ'). He has a swollen knuckle. X-ray shows nothing. What is your concern?"
EXCEPTIONAL ANSWER
My concern is a septic arthritis of the MCP joint or an extensor tendon sheath infection. The tooth may have penetrated the capsule. 'Nothing' on X-ray doesn't rule out cartilage damage or radiolucent foreign body. I would aspirate the joint (if possible) or proceed to surgical arthrotomy and washout.
KEY POINTS TO SCORE
Joint penetration risk
Septic arthritis masking as cellulitis
Need for surgical washout
COMMON TRAPS
✗Treating as cellulitis only
✗Missing the joint involvement
LIKELY FOLLOW-UPS
"What if the X-ray showed a small calcification?"
"That is likely a tooth fragment. It must be removed as it acts as a nidus for infection."
MCQ Practice Points
Microbiology
Q: Which organism is found in 50% of dog bites and 75% of cat bites? A: Pasteurella multocida.
Pharmacology
Q: Why is Cephalexin monotherapy inadequate for animal bites? A: It has poor activity against Pasteurella multocida.
Sepsis
Q: Which organism causes fulminant sepsis in asplenic patients after a dog bite? A: Capnocytophaga canimorsus.
Anatomy
Q: A bite to the thenar eminence most risks which nerve? A: Recurrent motor branch of the Median Nerve.
Wound Closure
Q: Which anatomical location allows primary closure of animal bites due to excellent blood supply? A: The Face. Primary closure (loose sutures) is accepted for facial bites due to cosmesis and rich vascular supply.
Antibiotic Choice
Q: What is the first-line antibiotic for animal bite prophylaxis? A: Amoxicillin-Clavulanate (Augmentin). Covers Pasteurella, Staph, Strep, and anaerobes. Avoid Cephalexin alone.
Australian Context
Australian Bat Lyssavirus (ABLV)
- Key Point: Australia is Rabies-free for terrestrial mammals
- Exception: ABLV is present in Australian bat populations (flying foxes, microbats)
- Transmission: Any bat scratch, bite, or mucous membrane exposure
- Protocol: Post-exposure prophylaxis identical to rabies:
- Human Rabies Immunoglobulin (HRIG) infiltrated at wound site
- Rabies vaccine series (Days 0, 3, 7, 14)
- Mortality: 100% fatal once symptomatic (only 1 survivor worldwide with Milwaukee protocol)
Tetanus Prophylaxis (Australian Guidelines)
| Vaccination Status | Clean Minor Wound | Tetanus-Prone Wound |
|---|---|---|
| Fully vaccinated (less than 5 years) | No prophylaxis | No prophylaxis |
| Fully vaccinated (5-10 years) | No prophylaxis | Booster (ADT) |
| Fully vaccinated (greater than 10 years) | Booster (ADT) | Booster (ADT) + TIG |
| Unknown/Incomplete | Booster (ADT) | Booster (ADT) + TIG |
Antibiotic Guidelines (eTG Complete)
- First Line: Amoxicillin + Clavulanate 875/125mg BD for 5-7 days
- Penicillin Allergy (Non-severe): Cefalexin 500mg QID + Metronidazole 400mg TDS
- Severe Penicillin Allergy: Doxycycline 100mg BD + Metronidazole 400mg TDS
Medicolegal Considerations
- Dangerous Dog Legislation: Varies by state/territory
- Reporting: Not mandatory in most jurisdictions unless dangerous dog involved
- Documentation: Photograph injuries, document animal details (breed, vaccination status, owner)
High-Yield Exam Summary
Diagnosis
- •History: Animal type, Time, Host factors
- •Exam: Neurovascular status, Tendon function
- •Signs: Kanavel signs (Tenosynovitis)
- •X-ray: Foreign body (Tooth), Fracture, Air in joint
Management
- •Irrigation: Copious saline
- •Debridement: Aggressive
- •Antibiotics: Augmentin (Golden Standard)
- •Prophylaxis: Tetanus +/- Rabies (Bats)
Surgical Decisions
- •Face: Primary Closure
- •Hand/Foot: Leave Open / Loose
- •Puncture: Never Close
- •Established Infection: Washout