Joint Infection
KEY FACTS
Imaging
IMAGING
General Features
Ultrasonographic Findings
Cardinal sign of septic arthritis
± clumps of echoes or multiple fine echoes within joint fluid
Anechoic joint fluid does not exclude septic arthritis
In some nondistensible joints (e.g., acromioclavicular, sternoclavicular, sacroiliac joints), effusion is minimal
Amount of joint fluid decreases as chronicity of infection increases
Viscosity of joint fluid increases as chronicity of infection increases
without synovial proliferation due to acute septic arthritis (Salmonella enteritidis). Note the clear visualization of cartilage 
and posterior glenoid labrum 
.
with a small effusion 
in a patient with juvenile rheumatoid arthritis. This may be due to either infective or inflammatory arthritis. Joint aspirate yielded Moraxella species.
at the suprapatellar pouch with severe synovial proliferation 
due to chronic joint infection with Staphylococcus aureus.
on the dorsum of the index metacarpophalangeal joint 
. There is a small erosion 
of the 2nd metacarpal neck. This arthritis was due to tuberculosis confirmed by histology and microbiology following surgical exploration.
