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does not preclude the possibility of a bacterial bone or joint infection, and many
infections are preceded by a history of minor trauma. Septic arthritis is the most
serious infectious cause of joint pain and limp. It is more common in younger
children and typically presents with a warm, swollen joint (although swelling in
the hip is very difficult to detect clinically). Exquisite pain with attempts to flex
or extend the joint is characteristic of septic arthritis, and the degree of pain with
motion serves as a helpful clinical sign in distinguishing bacterial joint infection
from inflammatory conditions. A common diagnostic challenge is differentiating
septic arthritis, transient (or toxic) synovitis, and Lyme disease (in endemic areas)
in a young child with fever, limp, and pain localized to the hip. Transient
synovitis, a postinfectious reactive arthritis, follows a milder course. It is usually
preceded by a recent viral respiratory or gastrointestinal illness. Acute-phase
reactants may be elevated in each of these conditions, although usually less so in
synovitis. A unilateral joint effusion, which is better visualized with ultrasound
than plain films, may be present in each of these conditions. Bilateral effusions
are more suggestive of an inflammatory synovitis. Joint aspiration may be
required for a definitive diagnosis because a septic hip is a surgical emergency
requiring open drainage. Osteomyelitis is another potentially serious infectious
cause of limp, although the presentation is typically more chronic than that of a
septic joint. Osteomyelitis, which is also more common in younger children,
presents with pain and occasionally warmth and swelling, usually over the
metaphysis of a long bone. A reactive joint effusion may be present.
Occasionally, osteomyelitis and septic arthritis will coexist. Chronic recurrent
multifocal osteomyelitis (CRMO), also known as chronic nonbacterial
osteomyelitis (CNO), is a rare inflammatory condition that should be considered
in cases of suspected osteomyelitis that seem atypical in their response to
treatment. More detailed discussions of both septic joint and osteomyelitis are
found in Chapters 94 Infectious Disease Emergencies and 121 Musculoskeletal
Emergencies .