Which findings on radiographs are characteristic of septic arthritis (SA)?

Updated: May 12, 2016
  • Author: Lourdes Nunez-Atahualpa, MD; Chief Editor: Felix S Chew, MD, MBA, MEd  more...
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Answer

Answer

The earliest plain film radiographic findings of septic arthritis are soft tissue swelling around the joint and a widened joint space from joint effusion; however, uniform narrowing of the joint has also been described. [15]

With progression of disease, plain films reveal joint-space narrowing as articular cartilage is destroyed, loss of continuity of the white cortical line as bone destruction begins, and development of marginal erosions when the bone is further destroyed. Bone debris within the joint space may also be seen in chronic untreated disease, which in adults may be mistaken as a neuropathic hip. [15]

Findings of superimposed osteomyelitis may also be identified, such as periosteal reaction, bone destruction, and sequestrum formation.

During the progression of infectious arthritis of During the progression of infectious arthritis of the hip, this image was obtained early in the disease and shows only concentric joint-space loss.
During the progression of infectious arthritis of During the progression of infectious arthritis of the hip, subchondral erosions and sclerosis of the femoral head are present.
During the progression of infectious arthritis of During the progression of infectious arthritis of the hip, subchondral erosions and sclerosis of the femoral head are present.

Mycobacterial infection presents as unilateral, focal, or diffusely decreased bone density, with eventual loss of the joint space that can evolve to ankylosis. Further studies, such as ultrasonography, can identify small to moderate joint effusion, accompanied by synovial thickening and enhancement on MR imaging. [16]

A triad of radiographic abnormalities known as the Phemister triad  is characteristic of tuberculous arthritis: peripherally located bony erosions, juxta-articular osteoporosis, and gradual narrowing of the joint space. [5]

Gas within the joint or adjacent soft tissues can sometimes be seen in infection secondary to gas-forming organisms, such as E coli or Clostridium perfringens. However, gas within the joint is usually secondary to prior aspiration or the vacuum phenomenon, which can occur secondary to limb traction during positioning while under examination or a recent dislocation.

Plain radiographic findings in the infant hip include obliteration of soft tissue planes, swelling, displacement of the fat pads, and juxta-articular osteoporosis. Hefke and Turner also described the obturator sign, which consists of swelling of the obturator internus in septic arthritis of the hip. [17]  Subluxation or dislocation of the femoral head secondary to intra-articular fluid can occur. However, this can be difficult to identify if the femoral head is not ossified.

In children, lateral displacement of the femoral epiphysis relative to the contralateral hip signifies a joint effusion. [18] As little as 2 mm of asymmetry in the distance measured from teardrop of the acetabulum to the medial metaphysis of the femoral neck is considered pathologic.

Inadequately treated SA can show osteomyelitis, osteoarthritis, ankylosis, periarticular calcifications, subchondral bone loss, and sclerosis.

Fluoroscopic imaging can help in the guidance of aspirations and to identify sinus tracts. [19]


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