Osteomyelitis

Question 1

Define

Answer 1

There is infection of the metaphysis of long bones

Adjacent to the epiphysis (growth plate) which is highly vascular

Question 2

Causes

Answer 2

MOST COMMON sites:
1. Distal femur
2. Proximal tibia

But- any bone can be affected

Modes of transmission:
1. Usually due to haematogenous spread of the pathogen
2. Direct invasion from a contiguous infection (e.g. cellulitis)
3. Direct inoculation (e.g. trauma or surgery)
4. Most infections are caused by Staphylococcus aureus

Other causes include:
1. Streptococci (Group A and B)
2. Haemophilus influenzae (if not immunised)
3. Kingella kingae (gram negative organism in the oral microbiome)

Sickle cell anaemia is associated with an increased risk of staphylococcal and salmonella osteomyelitis

Risk factors: SCD, immunodeficiency disorders, DM, sepsis, minor trauma coincident with bacteraemia, indwelling vascular catheters

TB can also cause osteomyelitis, especially in immunodeficient children

Question 3

Presentation

Answer 3

• Most chronic in onset and less severe than septic arthritis (i.e. over a week rather than a day)

1. Markedly painful, immobile limb (pseudoparesis)
2. Acute febrile illness
3. Swelling and exquisite tenderness directly over infected site
4. Movement of the limb causes severe pain
5. Sterile effusion of an adjacent joint
6. Back pain (in vertebral infection)
7. Limp or groin pain (infection of the pelvis)
8. The skin is swollen directly over the affected site

IMPORTANT: presentation may be more insidious in infants

Occasionally, there are multiple foci e.g. disseminated staphylococci or H. influenzae infection

NOTE: kids may still be able to walk around and pain is considered to be LESS SEVERE than septic arthritis

DDx: bone tumour, septic arthritis

Question 4

Investigations

Answer 4

Blood cultures (usually positive)

WCC and CRP are raised

X-rays are initially normal, other than soft tissue swelling

After 7-10 days, subperiosteal new bone formation and localised bone rarefaction become visible

Brodie abscess - “moth sign” may be visible

Brodie abscess | Radiology Reference Article | Radiopaedia.org
USS may show periosteal elevation at presentation

Joint aspiration and MC&S to rule out septic arthritis

MRI allows identification of infection in the bone (subperiosteal pus and purulent debris in the bone), also differentiates bone from soft tissue infection

Radionuclide bone scan may be helpful if the site of infection is unclear