Summary

Acute Haematogenous Osteomyelitis is a bacterial infection of the bone marrow, primarily affecting the rapidly growing metaphyses of long bones in children. The sluggish blood flow in the metaphyseal venous sinusoids allows bacteria to settle and proliferate. The most common pathogen is Staphylococcus aureus, though Kingella kingae is increasingly recognised in toddlers. Clinically, it presents with fever, pain, and refusal to weight bear ("Pseudoparalysis"). X-rays are usually normal for the first 10-14 days. MRI is the gold standard for early diagnosis. Treatment involves prolonged IV antibiotics, with surgical decompression reserved for abscess formation or failure to respond. [1,2]

Key Facts

• Definition: Infection of the bone marrow.
• Route: Haematogenous (via blood) is most common.
• Site: Metaphysis of Long Bones (Distal Femur, Proximal Tibia).
• Pathogen: Staphylococcus aureus (80%).
• Age: < 5 years (50% of cases).
• Imaging: MRI shows marrow edema. X-ray shows nothing (early).

Clinical Pearls

"X-rays are useless early": Do not be reassured by a normal X-ray. It takes 10-14 days for 50% of the bone mineral to be destroyed before lytic changes appear. A normal X-ray in a febrile, limping child does NOT rule out osteomyelitis.

"Pseudoparalysis": In neonates/infants, they can't say "my leg hurts". They just stop moving it. If you lift the leg and it flops down without resistance (but the child cries), think infection or fracture.

"The Four Intra-capsular Metaphyses": Usually, the growth plate blocks infection from entering the joint. BUT, in the Hip, Shoulder, Ankle, and Elbow, the metaphysis is inside the joint capsule. Therefore, osteomyelitis here can burst directly into the joint causing Septic Arthritis.

"Puncture through a Sneaker": If a child steps on a nail through a rubber-soled shoe, the pathogen is Pseudomonas aeruginosa (it lives in the rubber). You must use Ciprofloxacin.

         CHILD WITH FEVER + BONE PAIN
                    ↓
        BLOODS (CRP/ESR) + BLOOD CULTURES
        X-RAY (exclude fracture/tumour)
                    ↓
        HIGH SUSPICION? -> MRI
                    ↓
        START EMPIRIC IV ANTIBIOTICS
       (Flucloxacillin / Cephalosporin)
                    ↓
        IMPROVEMENT IN 24-48 HOURS?
        ┌───────────┴───────────┐
       YES                     NO / ABSCESS ON MRI
        ↓                       ↓
   CONTINUE IV            SURGICAL DECOMPRESSION
   (Switch to oral        (Drill / Washout)
    when CRP drops)

1. Medical Management

• Antibiotics: The mainstay.
  • Agent: Flucloxacillin or Cefazolin (covers MSSA). Clindamycin (if MRSA).
  • Duration: Traditionally 6 weeks IV. Modern "OVIVA" trial evidence suggests switching to Oral once fever settles and CRP < 20 is safe (usually 3-5 days IV, then 3 weeks Oral).
• Immobilisation: Splint the limb for comfort.

2. Surgical Management

• Indications:
  • Subperiosteal Abscess on MRI.
  • Failure to respond to Abx after 24-48h (Persistent fever).
  • Sequestrum formation (dead bone).
• Procedure:
  • Cortical Window: Drilling a hole into the metaphysis to vent the pus ("Drill hole osteotomy").
  • Washout: Massive irrigation.

• The Phantom Germ: For decades, "Culture Negative" osteomyelitis was a mystery.
• Discovery: Improved culture techniques (inoculating blood culture bottles directly) revealed Kingella kingae.
• Features:
  • Gram negative coccobacillus.
  • Commensal of the oropharynx.
  • Affects ages 6m - 4y (daycare age).
  • Mild presentation (Low fever, normal WCC).
  • Treatment: Amoxicillin/Cephalosporins (Resistant to Clindamycin!).

Key Studies

1. OVIVA Trial (NEJM 2017): Oral vs IV Antibiotics for Bone/Joint infection. Showed Oral is non-inferior to IV (after initial stabilization). Revolutionised practice (kids go home sooner).
2. Cierny-Mader Classification: Staging system for Adult Osteomyelitis (Anatomic + Physiologic host status).

What is Osteomyelitis?

It is a bacterial infection inside the bone marrow. It's like having a boil, but deep inside the thigh bone.

How did it get there?

Bacteria are usually in our blood transiently (e.g., from brushing teeth or a grazed knee). Usually, the immune system kills them. Sometimes, they get stuck in the slow-moving blood vessels at the end of the bone and start multiplying.

Does he need surgery?

If we catch it early, antibiotics alone can kill the bacteria. If a collection of pus has already formed, we need to operate to drain it, just like lancing a boil.

Will the bone grow normally?

Usually yes. However, if the infection is very close to the growth plate (the growing end), there is a small risk of damage. We will need to monitor his growth with X-rays over the next year.