Paediatrics: Infections: osteomyelitis

Infections: osteomyelitis

Infection of bone. The frequency of osteomyelitis is greatest in infants, with 33% of all cases in the first 2yrs, and 50% occurring by 5yrs. Male > female (2:1).

Pathogenesis

Infection usually seen in the metaphyseal region of bones. Most infections are spread via the haematogenous route from a p site of entry (e.g. res-piratory, GI, ENT, or skin sites). Infection may also occur by direct in-oculation (open fractures, penetrating wounds) or local extension from adjacent sites. In the infant, transphyseal vessels are patent and infection may spread to the adjacent joint causing a septic arthritis. In adolescents infection tends to spread through the medullary canal.

Types of osteomyelitis

•   Acute.

•   Subacute (2–3wks duration).

•   Chronic: may develop ‘sequestrum’ (dead bone) and ‘involucrum’ (new bone).

•   Bone abscesses may become surrounded by thick, fibrous tissue and sclerotic bone (Brodie’s abscess).

Aetiology

The yield for bacterial growth from synovial fluid and bone aspirate is small; therefore organisms are not always isolated. Staphylococcus aure-us is most common in children in all age groups. Other organisms seen include the following:

•   Neonates: group B streptococcus and Gram –ve enteric bacilli.

•   <2yrs: Haemophilus influenzae (rare).

•   >2yrs: Gram +ve cocci, Pseudomonas aeruginosa.

•   Adolescents: Neisseria gonorrhoeae.

Consider salmonella in SCD. Tuberculosis is rare.

Symptoms and signs

•   Neonates characteristically do not appear ill and may not have fever.

•   Older children have pain, limping, refusal to walk/weight bear, fever, malaise, flu-like symptoms. Overlying bone may be tender (+ warm), with/without swelling. Long bones principally affected: Tibia > femur > humerus.

Differential diagnosis

This includes:

•   JIA

•   Lyme/post-streptococcal arthritis

•   Acute leukaemia

•   Neuroblastoma

•   Neoplasm (e.g. osteoid osteoma, osteosarcoma, Ewing’s sarcoma).

•   CRMO.

•   LCH.

Investigations

• Blood: FBC, ESR, CRP, blood cultures (positive in 50%).

• X-ray of bone: early stages may be normal; soft tissue oedema may be visible. Late stages reveal metaphyseal rarefaction. Destructive changes in bone appear after 10 days.

• US-guided aspiration: for microscopy and culture.

• MRI: soft tissue assessment—bone marrow involvement; abscess formation, joint effusion, subperiosteal extension.

• Bone scans: good for acute osteomyelitis; can identify up to 90% of joint involvement (seen as hot spots) and differentiate joint from bone involvement; good for infections of pelvis, proximal femur, and spine.

• Open biopsy may be necessary.

• Consider immunological evaluation if atypical organism.

Treatment

• Medical: IV antibiotics for a minimum of 2wks, followed by oral antibiotics for 4wks. Early liaison with microbiologist required.

• Surgical: drainage and debridement if there is frank pus on aspiration or a sequestered abscess or collection (not accessible to antibiotics).

Prognosis 

Usually excellent if treated early. Disease recurrence/pro-gression to chronic infection is seen in <10%.

Complications

• Systemic: may include septicaemia.

• Local: pathological fracture, sequestration, growth disturbance.