Infection in Bone 1: Acute & Chronic Osteomyelitis

Question 1

Who tends to get acute osteomyelitis?

Answer 1

Mostly children

• Adults with comorbidity (diabetes, rheum arth. immune compromise)

Question 2

How does acute osteomyelitis tend to spread?

Answer 2

• Haematogenous spread (most common in children and elderly)
• Local spread from site of infection (surgery / open fracture / joint replacement)
• Secondary to vascular insufficiency
• Infected umbilical cord / boils / abrasions / UTIs / arterial line

Question 3

What organism is the most common cause of acute osteomyelitis?

Answer 3

Staph Aureus

Question 4

What are some other organisms that cause osteomyelitis in children and adults?

Answer 4

Children:
- Group B Strep / E. Coli / Strep pyogenes

Adults:

• Coagulase negative staphylococci & propionibacterium spp (both common in prostheses)
• Myobacterium TB / pseudomonas aeroginosa

Question 5

What are the common sites for acute osteomyelitis to occur?

Answer 5

Metaphysis of long bones
- Distal femur / proximal tibia / proximal humerus

Joints with intra-articular metaphysis:
- Hip / radial head of elbow

Question 6

Describe the progression of an acute osteomyelitis infection

Answer 6

1. Starts at metaphysis
2. Causes vascular stasis
3. Inflammation & suppuration (increases pressure)
4. Release of pressure (sub-periosteal / into joint etc)
5. Sequestrum +/- Involucrum (necrosis of bone +/- formation of new bone)
6. Resolution OR Chronic osteomyelitis

Question 7

How does acute osteomyelitis tend to present in infants?

Answer 7

• Failure to thrive
• Metaphyseal tenderness & swelling (swelling not immediately visible, later stage sign)
• Decreased ROM
• Positional change of limb / joint (stop pain)
• Commonest around knee
• Infants < 1 month old often present with multiple sites of infection

Question 8

How does acute osteomyelitis tend to present in children?

Answer 8

• Severe pain
• Reluctant to move (neighbouring joints held flexed, avoid weight bearing)
• Fever (swinging pyrexia) / tachycardia
• Malaise / nausea / toxaemia

Question 9

How does acute osteomyelitis tend to present in adults?

Answer 9

• Thoracolumbar spine is most common area: complain of backache
• History of UTI / urological procedure / diabetes / immunosuppression / are elderly

Question 10

What is the most common type of acute osteomyelitis in adults?

Answer 10

Secondary acute osteomyelitis

• After surgery (ORIF) / open fractures
• Commonly see a mixture of organisms in these patients

Question 11

What investigations are used for suspected acute osteomyelitis?

Answer 11

• ESR / CRP / FBC (neutrophil leucocytosis)
• Blood culture (done 3x, at peak temp.)
• MRI / X-ray (normal for 1st 10 days) / USS (pus)
• Isotope bone scan / labelled white cell scan (both glow at site of infection)

Question 12

How would you expect X-rays of a patients bone throughout the process of infection to look?

Answer 12

1. No change within first 10 days
2. Early changes: X-ray appears darker due to medullary lysis of the bone (destruction of cells)
3. Further darkening due to destruction and sequestrum of bone
4. Whitening of the bone due to involucrum (new bone formation)

Question 13

What are some possible DDx for acute osteomyelitis?

Answer 13

• Acute septic arthritis
• Trauma (fracture / dislocation)
• Acute inflammatory arthritis
• Transient synovitis
• Soft tissue infection

Question 14

List the different methods of microbiological diagnosis of acute osteomyelitis

Answer 14

• Blood cultures (not always positive in surgery / open fractures)
• Bone biopsy / aspiration
• Tissue swabs from around debridement in prosthetic infections

Question 15

Treatment of acute osteomyelitis?

Answer 15

• Supportive (analgesia / fluids)
• Rest & splintage
• Antibiotics
• Surgery (biopsy / abscess drainage etc.)

Question 16

Describe the antibiotic treatment given when acute osteomyelitis is diagnosed. Which antibiotics are used at first, before microbiology results are in?

Answer 16

• Start with IV antibiotics, switch to oral (usually at about 7-10 days)
• Antibiotic treatment usually lasts 4-6 weeks (depends on clinical response & ESR)
• Fluclox & Benzyl Pen usually used at first (bc usually either S Aureus or group B strep)

Question 17

Why can antibiotics fail in treating osteomyelitis?

Answer 17

Resistance / poor penetration

• Bacteria can also hide in dead bone and lie dormant for years due to antibiotics not reaching these areas of un-perfused dead tissue

Question 18

When is surgery needed to treat acute osteomyelitis?

Answer 18

• Biopsy
• Pus drainage (abscess drainage)
• Debridement of infected tissue
• Replacement of infected joints

Question 19

What are some possible complications of acute osteomyelitis?

Answer 19

• Metastatic infection / septicaemia
• Septic arthritis
• Altered bone growth
• Pathological fracture
• Chronic osteomyelitis

Question 20

What causes chronic osteomyelitis?

Answer 20

May follow acute osteomyelitis

De Novo: Surgery / open fracture / immunosuppressed

Repeated breakdown of “healed” wounds

Retained sequestra / involucrum / dead bone

Question 21

What organism tends to cause chronic osteomyelitis?

Answer 21

Usually a mixed picture with multiple:

• S. Aureus
• E. Coli
• Strep. Pyogenes
• Proteus

Question 22

Treatment of chronic osteomyelitis?

Answer 22

• Long term antibiotics
• Surgical eradication of infection
• Deformity correction / reconstruction / amputation

Question 23

What are some possible complications of chronic osteomyelitis?

Answer 23

• Chronic sinus discharge & flare ups
• Metastatic infection
• Pathological fracture
• Growth disturbances +/- deformities