Septic arthritis is a destructive arthropathy caused by an intra-articular infection that usually is related to severe symptoms such as pain and decreased range of motion. This condition requires prompt treatment aiming to avoid permanent damage to joint, which may result in chronic deformity or mechanical arthritis.
The diagnosis of joint sepsis is often considered straightforward. Patients often present with a painful joint, fever, and purulent synovial fluid.
Risk factors for septic arthritis include bacteraemia, advanced age, an immunocompromised state, rheumatoid arthritis, intra-articular injections, and prosthetic joints.
In the absence of trauma or recent instrumentation of the joint, septic arthritis is usually secondary to haematogenous seeding. S aureus is the most commonly isolated agent (31.3% of casesref).
Large joints with abundant blood supply to the metaphyses are most prone to bacterial infection, with the most commonly affected joints theoretically being the shoulder, hip, and knee.
Imaging generally plays an adjunct role to arthrocentesis in the diagnosis of joint sepsis. If synovial fluid cannot be retrieved, however, radiologic studies become of the utmost importance.
- X-rays may be normal in the very early stage of the disease
- joint effusion may be seen
- juxta-articular osteoporosis due to hyperaemia
- narrowing of the joint space due cartilage destruction in the acute phase
- destruction of the subchondral bone on both sides of a joint
- if left untreated, reactive juxta-articular sclerosis and, in severe cases, ankylosis will develop
- useful in superficial joints and in children
- shows joint effusion
- echogenic debris may be present
- colour Doppler may show increased peri-synovial vascularity
- can be used to guide the joint aspiration
- CT features of septic arthritis are similar to those spotted on radiographs
- a fat-fluid level can be a specific sign in the absence of trauma
- sensitive and more specific for early cartilaginous damage
- T1: low signal within subchondral bone
- T2: perisynovial oedema
- C+ (Gd): synovial enhancement
Treatment and prognosis
If unrecognised and left untreated, septic arthritis can result in irreversible joint damage within 48 hours of the onset of infection due to the proteolytic enzymes of the white blood cells that flood the infected synovial space. Osteonecrosis is also an important sequela of septic arthritis due to effusion and increase in intra-articular pressure compromises blood circulation.
Conversely, approximately 90% of patients with septic arthritis will recover with appropriate antibiotic treatment. Therefore, timely diagnosis and treatment are critical.
- 1. Fayad LM, Carrino JA, Fishman EK. Musculoskeletal infection: role of CT in the emergency department. Radiographics. 27 (6): 1723-36. doi:10.1148/rg.276075033 - Pubmed citation
- 2. Karchevsky M, Schweitzer ME, Morrison WB et-al. MRI findings of septic arthritis and associated osteomyelitis in adults. AJR Am J Roentgenol. 2004;182 (1): 119-22. AJR Am J Roentgenol (full text) - Pubmed citation
- 3. Weissleder R, Wittenberg J, Harisinghani MG. Primer of diagnostic imaging. Mosby Inc. (2003) ISBN:0323023282. Read it at Google Books - Find it at Amazon
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