ReviewAcute osteomyelitis, septic arthritis and discitis: Differences between neonates and older children
Section snippets
Nomenclature
The term osteomyelitis refers to infection of bone and/or bone marrow. Depending on both the virulence of the organism and the immune response mounted by the host, osteomyelitis may be acute, subacute or chronic. Acute osteomyelitis is not common in adults [1]. Conversely, in neonates osteomyelitis is usually acute [2].
Septic arthritis refers to infection of a joint. While this may occur in isolation, in neonates it is much more likely to occur as a consequence of bony infection (osteomyelitis)
Pathogenesis
Infection may reach the bone (or joint) via three main routes:
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The bloodstream, i.e. haematogenous spread. This is the commonest route of infection in the neonate.
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Direct contamination, e.g. penetrating or puncture wounds, surgery. This route of infection is commoner in older children and adults.
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Indirect contamination from a nearby infection, e.g. cellulitis.
The causative organism depends on the age of the patient, and in the neonate is most commonly Staphylococcus aureus. Other organisms include
Anatomical considerations and pathophysiology
The unique vascular anatomy of the epiphyses in neonates and infants accounts for the frequency with which osteomyelitis and septic arthritis co-exist.
The reduced rate of blood flow within vessels at the metaphysis renders this region more susceptible to haematogenous seeding of infection [13]. Before the appearance of secondary ossification centres, the cartilaginous epiphyses receive their blood supply directly from metaphyseal blood vessels. Hence, septic arthritis is a relatively common
Clinical presentation and laboratory findings
Osteomyelitis and arthritis are commoner in young children than in older children and adults, peaking at around the age of 3 years for osteomyelitis and 2 years for septic arthritis [2], [3], [4], [5].
Compared to older children and adults, there are fewer clinical signs and the diagnosis of osteomyelitis and/or arthritis may therefore be harder to make. This is largely because of the poorly developed immune system of neonates, rendering them less able to mount an immune response. For this
Imaging
The role of imaging is to confirm the presence and site of infection, to differentiate unifocal from multifocal disease, to locate and guide aspiration of collections and to identify present or impending complications such as joint or extradural involvement.
Radiography is usually the first radiological investigation in a neonate with suspected osteomyelitis/septic arthritis/discitis. Other modalities include ultrasound (US), bone scintigraphy, magnetic resonance imaging (MRI) and computed
Complications
Considerable morbidity may be associated with neonatal osteomyelitis and/or septic arthritis. Early diagnosis and treatment are critical if complications are to be minimised. This is particularly true of septic arthritis, as damage to articular cartilage (secondary to proteolytic enzymes released from synovial cells) begins rapidly [4]. Complications include:
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damage to the growth plate with premature and/or asymmetrical closure of the growth plate;
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avascular necrosis of the femoral head with or
Summary
There are anatomical and pathophysiological differences that account for differences in the patterns of musculoskeletal infection seen in infants and young children compared to older children and adults.
The various imaging techniques outlined above each play an individual role in the diagnostic work up of a neonate with suspected osteomyelitis and/or septic arthritis. They should be seen as complimentary tools [29], and any particular child will often have multiple investigations.
The sequelae
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