O&T SC078: Musculoskeletal Infection

Question 1

***Musculoskeletal infections that cannot be missed

Answer 1

Bone / Joint infection:
1. Septic arthritis
2. Osteomyelitis (acute / chronic)

Soft tissue infections:
1. Paronychia (not urgent but significant pain)
2. Soft tissue abscess
3. Infective tenosynovitis
4. Necrotising fasciitis
5. Gas gangrene
Etc.

SpC Revision:
- Skin and soft tissue infection: Not require surgical drainage
- Septic arthritis, Necrotising fasciitis, Infective tenosynovitis, Infected implant —> ALL require surgical drainage

Question 2

Paronychia

Answer 2

• Collection of pus under nail fold / bed
• Significant pain, swelling, numbness due to swelling

Cause:
- Minor injury / Outside-in puncture wound

Causative agent:
- MSSA

Treatment:
1. Incision and drainage
- over lateral side of finger
- deep cut from lateral to central (need to cut ***through septum otherwise residual pus inside —> recurrent / persistent infection)
2. Daily dressing + packing
3. Antibiotics (Augmentin)

Question 3

Osteomyelitis

Answer 3

• Infection of bone caused by bacteria

Causes:
- Common in paediatric patients (rich but **slow blood flow from nutrient artery over growth plate —> bacteria accumulate in **metaphysis —> abscess formation —> osteomyelitis —> if not treated properly —> chronic osteomyelitis)
- Implant-related infection

Pathogenesis:
- Bacteria travel through metaphyseal vessel (**Haematogenous spread (e.g. **UTI))
—> **Seeding of infection around metaphysis (stopped by growth plate (but if significant enough can still go through))
—> **Abscess formation
—> **Subperiosteal abscess (grow from inside to outside and accumulate underneath periosteum (thick in children))
—> **Sequestrum formation (bone necrosis) + **Involucrum (reactive bone formation) + **Sinus tract formation (~ fistula tract)
—> Cloacae (discharging pus + bone)
—> Chronic osteomyelitis

Classification:
1. Acute (<2 weeks) / Subacute (<3 months) / Chronic (>3 months)
2. Stage of infection: **Cierny-Mader classification (based on **site of infection)

**Cierny-Mader classification:
Stage 1 (Medullary osteomyelitis):
- Etiology: Haematogenous
- Necrosis limited to medullary contents + endosteal surfaces
- **Antibiotics, Unroofing, Intramedullary reaming

Stage 2 (Superficial osteomyelitis):
- Etiology: Contiguous soft tissue infection (e.g. implant-related)
- Necrosis limited to exposed surfaces
- Antibiotics, Debridement

Stage 3 (Localised osteomyelitis):
- Etiology: From stage 1 / 2, Trauma, Iatrogenic (e.g. implant-related)
- Well marginated + stable before and after debridement
- Antibiotics, Debridement

Stage 4 (Diffuse osteomyelitis):
- Etiology: From stage 1 / 2 / 3, Trauma, Iatrogenic (e.g. implant-related)
- Circumferential / Permeative
- Antibiotic, **Debridement + **Stabilisation (by external fixation) + **Bone cement with antibiotic (provide structural support + release antibiotic locally) + **Bone graft after removing bone cement

Clinical features:
1. Pain
2. Swelling + redness
3. Pus collection
4. Reduced ROM

Investigations:
1. X-ray
2. CT, MRI
3. CRP (preferred over ESR ∵ more sensitive due to shorter half life)

Treatment (**Acute vs **Chronic):
Acute:
1. ***Antibiotics (Broad spectrum) (e.g. Augmentin)
2. Surgery

Chronic:
1. ***Debridement
2. Antibiotic (may need long-term)

Length and Route of antibiotics:
- Start with **IV antibiotics —> Change to **Oral if improvement —> ***6-8 weeks depending on clinical condition
- Monitor:
—> Clinical signs: Pain, swelling, ROM
—> Biochemical markers: CRP, ESR

***Indications for surgery in Osteomyelitis:
1. Failed medical treatment
2. Sepsis
3. Pus / Abscess formation
4. Sequestrum formation (very good medium for bacterial growth + prevent bone healing)

Question 4

Septic arthritis

Answer 4

Clinical features:
- **Hot, swollen, tender joints
- Fever, systemic upset
- **Gross limitation of motion
- Knee: patient usually hold in 30o flexion

Risk factors:
1. Age >60
2. **Recent bacteraemia (e.g. chest infection —> patient may complain of sudden joint pain)
3. Immunocompromised
- **DM
- Malignancy on treatment
- Cirrhosis
- Renal disease
- Long term steroid
4. ***Drug abuse (needle sharing)
5. Recent dental procedures (without antibiotic cover)

Classification based on **severity: **Gachter classification (Arthroscopic + Radiographic findings)
Stage 1: Opacity of fluid, redness of synovial membrane, No radiolographic changes
Stage 2: Severe inflammation, fibrinous deposition, pus, No radiolographic changes
Stage 3: Thickening of synovial membrane, compartment formation, No radiolographic changes
Stage 4: Aggressive pannus with infiltration of cartilage, undermining the cartilage, **Subchondral osteolysis, possible **osseous erosion, cysts

Investigations:
1. Blood
- CBP, CRP, ESR
- Blood culture
2. X-ray of involved joint
- **soft-tissue swelling / hip joint capsular distension (with **widening of joint space / even **subluxation)
- radiographic changes in the proximal femoral metaphysis: osteomyelitis
(- **Shenton’s line broken
- osteopenia)
3. MRI
- useful to detect any **co-existing osteomyelitis
- not routine —> only used when chronic pain after septic arthritis + persistent pain + persistent CRP
- maybe most useful test to distinguish from osteomyelitis
4. **Joint aspiration
- Colour, appearance
- WBC, %PMN
- Gram stain, Culture + sensitivity (Bacteria, AFB, Fungal)
- Crystal
- Protein (High), Glucose (Low)
5. Radioisotope scan (localise infection)

Treatment:
1. Antibiotic
2. Surgery
- Excisional **debridement + **drainage (to clean up infection)
- ***Arthroscopy / Arthrotomy (similar results)

Complications (from SpC O/T Seminar: Common Hip Disorders):
1. **Secondary OA
2. **Pain (∵ joint incongruency and chondral damage)
3. Stiffness (∵ ankylosis + soft tissue contracture (flexion + adduction contracture))
4. **Deformity: angulation, coxa vara, shortening
5. **Instability, Dislocation
6. **Leg length discrepancy
(From JC O/T:
7. **AVN
8. **Pathological fracture
9. **Chronic infection (osteomyelitis)
10. ***Sepsis)

Question 5

Pyogenic flexor tenosynovitis

Answer 5

• Closed space infection of flexor tendon sheath of hand (Inflamed synovium + Pus in synovium) —> can cause Tendon ischaemia
• 2.5-9.4% of all hand infections

Causative agents:
1. MSSA (up to 75% of positive cultures)
2. MRSA (up to 29%)
3. Staphylococcus epidermidis
4. Streptococcus species
5. Gram -ve + Anaerobes
6. Culture -ve (20-68%)

Clinical features:
***Kanavel’s cardinal signs:
1. Tenderness over + limited to flexor sheath
2. Symmetrical enlargement of digit (“Fusiform”)
3. Severe pain on passive extension of finger (> proximally)
4. Flexed posture of involved digit (∵ pain)

Mode of spread:
- Haematogenous
- Direct inoculation (Laceration, Puncture wound, Bite)

Management:
- Prompt clinical diagnosis

Treatment:
1. Antibiotic
- Empirical covering Staphylococcus + Streptococcus species
- Cover Gram -ve rods + Anaerobes if immunocompromised patients
- **<48 hours after injury (i.e. **early presentation, only ***1-2 Kanavel’s cardinal signs)
- Examine affected hand frequently
- No improvement after 24-48 hours —> Surgery indicated

3. Surgery
   - Often needed due to delayed presentation (e.g. **3-4 Kanavel’s cardinal signs ∵ patient not seek medical help immediately)
   - **Debridement + Drainage + Irrigation
   - ***Zig zag incision (avoid flexion contracture)

Risk factors for amputation:
- DM
- Renal failure
- Peripheral vascular disease

Question 6

Necrotising fasciitis

Answer 6

• ***Orthopaedic emergency
• Involves superficial fascia —> spread **fascial planes (between superficial and deep fascia)
  —> **NO clinical signs in the beginning (∵ not involve epidermis / dermis)
  —> ***High index of suspicion
• Breakage of skin (e.g. lacerations, insect bite, needle puncture)
• Significant demands on health care system

Causative agents:
1. **Group A Streptococcus
2. **Vibrio species

Risk factors:
1. **Immunocompromised
- DM (57%)
- Renal failure
- Liver disease
2. **Alcohol abuse
3. Exposure to NSAIDs (∵ inhibit prostaglandins which alter inflammatory response to microorganisms + induce acute renal failure)

Pathogenesis:
Organisms / Spores introduced into soft tissue and release exotoxins
—> Local tissue + vascular endothelium damage by exotoxins (NOT much clinical sign)
—> Erythema + Swelling
—> Bullae + Ecchymoses
—> **Deeper tissue infected + **Larger venules / arterioles occluded
—> Necrosis affect all tissue layers

Clinical diagnosis:
1. History of minor trauma to extremities
2. **Disproportionate pain
3. **Generalised erythematous rash, swelling and toxic appearance
4. **Low platelet count
5. Bedside procedure
- **Incision —> **Lack of bleeding + necrosis, **Foul smelling dishwater pus, ***Minimal tissue resistance to finger dissection (∵ necrosis)

Staging:
Stage 1: **Tenderness, **Erythema, Edema, Warm skin, Fever
Stage 2: **Blisters + Bullae
Stage 3: **Tissue necrosis, **Hyposensitivity, **Anaesthesia (necrosis + damage to peripheral nerve), ***Tissue crepitation, Haemorrhagic bullae

Sequelae if not treated promptly:
1. Amputation
2. Death (mortality rate 20-75%)

Management:
- Early diagnosis

Treatment:
1. **Broad spectrum antibiotic (IV Ampicillin + Cloxacillin 1gm Q6H (SpC OT))
2. Early **Radical debridement

Question 7

Limb salvage vs Amputation

Answer 7

Limb salvage:
- Good past health
- Not life-threatening state
- Multiple sites
- Responsive to inotropic support

Amputation:
- Concurrent medical disease with high anaesthetic risk from multiple operations (e.g. poorly controlled DM, valvular heart disease)
- Myonecrosis
- Unremitting shock
- Concurrent peripheral vascular insufficiency
- Rapidly progressive infection
- Large area of tissue necrosis (heel pad and sole skin loss)

Question 8

Gas gangrene

Answer 8

• ***Orthopaedic emergency

Causative agent:
- **Clostridium perfringens (common in **farm) —> ***Gas-forming bacteria

Clinical features:
- Rapid clinical onset + Rapidly progressive soft tissue infection
- Swelling
- Sudden onset of pain
- Crepitus (characteristic)
- Blisters containing foul smelling brownish liquid with ***gas bubbles
- Soft tissue induration + discolouration (may also be present)
- Fever

Investigations:
- X-ray —> Gas density inside soft tissue

Treatment:
1. Antibiotic
- Empirical to cover **Clostridia + Gram +ve cocci
- Augmentin + **Metronidazole (Flagyl)
2. Early ***Radical debridement +/- Amputation
3. ICU support

Question 9

General management of Orthopaedic infections (SpC Revision)

Answer 9

1. Drainage of collection
2. Collection of specimen for culture + sensitivity
3. **IV broad spectrum antibiotics **after collection of specimen (unless septic —> take blood first)
4. ***Surgical debridement
5. Coverage of open defects when possible
6. Temporary immobilisation
7. Rehabilitation after infection controlled
8. Follow reconstruction ladder

Control of baseline factors:
1. DM
2. Smoking
3. Immunosuppressants
4. Nutrition

Question 10

Fist-bite injury

Answer 10

• Highly prone to infection
• Routine surgical irrigation + debridement recommended