Osteomyelitis (MSK)

Question 1

Define osteomyelitis.

Answer 1

Inflammatory condition of bone caused by an infective organism

Question 2

What organisms commonly cause osteomyelitis?

Answer 2

• most commonly Staphylococcus aureus
• Salmonella species more common in sudden cardiac arrest patients
• infants: Group B Streptococci, E. coli, Candida albicans
• children: GAS, Streptococcus pneumoniae, H. influenzae, Pseudomonas, Kingella kingae

Question 3

What are the two classifications of osteomyelitis?

Answer 3

• haematogenous osteomyelitis - results from bacteraemia and usually monomicrobial –> most common in children
• non-haematogenous osteomyelitis - results from contagious spread of infection from adjacent soft tissues to the bone, or from direct injury/trauma to the bone and usually polymicrobial –> most common in adults

Question 4

What are some risk factors for haematogenous osteomyelitis? (4)

Answer 4

• sickle cell anaemia
• IV drug use
• immunosuppression
• infective endocarditis

Question 5

What are some risk factors for non-haematogenous osteomyelitis? (3)

Answer 5

• diabetic foot ulcers/pressure sores
• DM
• peripheral arterial disease

Question 6

How many bones does osteomyelitis usually involve?

Answer 6

A single bone

Question 7

What is the basic pathophysiology of osteomyelitis?

Answer 7

Bacteria –> bloodstream –> bone (affects periosteum –> bursts –> abscess)

Later: cytokines induce bone resorption –> replacement with fibrous tissue –> new bone formation around necrotic one (involucrum - chronic)

Question 8

What happens in acute osteomyelitis?

Answer 8

• immune system destroys all invading bacteria
• if viable bone then osteoclasts + osteoblasts begin to repair damage

Question 9

What happens in chronic osteomyelitis?

Answer 9

• affected bone becomes necrotic + separates from healthy bone (sequestrum)
• osteoblasts may form new bone that wraps the sequestrum in place (involucrum)

Question 10

What are the clinical features of osteomyelitis? (5)

Answer 10

• limp or reluctance to weight bear - common in children
• non-specific pain at site of infection
• malaise, fatigue, fever, chills
• inflammation, tenderness, erythema, swelling
• Hx preceding skin lesion, sore throat, trauma, operation

Question 11

What might we see on examination of osteomyelitis? (8)

Answer 11

• localised erythema
• tenderness or spasm
• swelling
• warmth
• painful/limited movement of affected limb
• seropurulent discharge from wound/ulcer
• reduced sensation in diabetic foot
• previous scars, flaps or fractures

Question 12

How might native vertebral osteomyelitis present?

Answer 12

Local back pain with systemic symptoms

Question 13

When should you suspect acute osteomyelitis?

Answer 13

Unwell child with a limp OR in an immunocompromised patient

Question 14

When should you suspect chronic osteomyelitis?

Answer 14

Adults with history of open fracture, previous orthopaedic surgery or discharging sinus

Question 15

When should you suspect native vertebral osteomyelitis?

Answer 15

Patient with new back pain and systemic symptoms

Question 16

What are some risk factors for osteomyelitis? (7)

Answer 16

• penetrating injury
• IVDU, haemodialysis (contaminated needles)
• diabetes (–> foot ulcers)
• HIV / immunocompromised
• recent surgery e.g. dental extraction of infected tooth
• distant or local infection e.g. cellulitis, RTI, Varicella
• SCA, RA, CKD

Question 17

What are the first-line investigations for osteomyelitis? (4)

Answer 17

• FBC - high WCC
• ESR & CRP - elevated
• blood culture - before Abx
• plain XR of affected area

Question 18

What does XR show in osteomyelitis?

Answer 18

• periosteal thickening, osteopenia, soft tissue swelling, intramedullary scalloping, cavities
• ‘fallen leaf sign’ - when a piece of endosteal sequestrum has detached and fallen into medullary canal
• acute - may initially be normal, osteopenia appears after 6-7 days

Question 19

What is the most definitive imaging modality for osteomyelitis?

Answer 19

Bone MRI

Question 20

What are the gold standard tests for osteomyelitis?

Answer 20

Bone sample + bone biopsy (balance invasiveness of test with need for accurate aetiological diagnosis)

Question 21

What investigations are needed before starting Abx in osteomyelitis? (2)

Answer 21

• blood culture
• bone biopsy (if indicated)

Question 22

What are some differential diagnoses for osteomyelitis? (9)

Answer 22

• septic arthritis (can co-exist)
• juvenile idiopathic arthritis
• transient synovitis (2-12y, moderate hip pain and limp)
• reactive arthritis
• slipped capital femoral epiphysis
• Legg-Calve-Perthe’s disease
• cellulitis
• necrotising fasciitis
• metastatic bone cancer

Question 23

What is the management for osteomyelitis?

Answer 23

Abx therapy for 2-4 weeks - flucloxacillin (IV) + supportive care

Clindamycin if penicillin allergic

Cefazolin/cefuroxime/flucloxacillin if child

Vancomycin if MRSA

Question 24

When do we do surgery for osteomyelitis?

Answer 24

• peripheral osteomyelitis - if limb deteriorates and dead bone is established
• vertebral osteomyelitis - progressive neurological deficits, deformity + spinal instability despite antimicrobial Rx

Question 25

What do we do in chronic osteomyelitis?

Answer 25

Refer to specialist team, staging and assessment

Question 26

What are some complications of osteomyelitis? (7)

Answer 26

• drug reactions
• infection recurrence
• fracture
• infection spread –> joints, skin, muscle, blood vessels
• neurological impairment secondary to abscess or bony collapse
• amputation
• growth disturbance in children

Question 27

Describe the prognosis of osteomyelitis if diagnosed promptly and treated adequately.

Answer 27

For most patients with acute osteomyelitis, they will recover with no long-term complications