Infection

Radiographic Features:

Soft tissue infection

Increased soft tissue density and volume will be associated with both soft tissue and bone infection; however, its presence is not diagnostic since inflammation secondary to other etiologies presents similarly. If the infection is secondary to a gas-producing bacteria, air-like dentities will be vissible in the soft tissues.

Bone Infection (Osteomyelitis)

The radiographic visibility of acute osteomyelitis may lag two weeks behind the clinical presentation. Classic osteomyelitis ultimately will present radiographically as osteolysis. However, rarefaction, periostitis (periosteal reaction) and/or erosion may be seen prior to osteolysis. The majority of foot infections are direct extension from the soft tissues or via implantation.

Chronic osteomyelitis, defined as a previously diagnosed acute osteomyelitis that does not heal and remains indefinitely, presents with a triad of findings: involucrum, cloaca, and sequestration.

Occasionally one may encounter infection of bone that arises from hematologic origin. This form of osteomyelitis, known as bone or Brodie's abscess, are considered to be a "subacute" infectious process. The characteristic radiographic picture is a soitary lucnet lesion with diffuse surrounding sclerosis.

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Here are examples of infection in the lower extremity:

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  • Case 2
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  • Case 3
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  • Case 4
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  • Case 5
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  • Case 6
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  • Case 7
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  • Case 8
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DP periostitis

DP periostitis

DP view. A fairly well-defined periosteal reaction (P) is present along the lateral aspect of the fourth toe proximal phalangeal diaphysis proximal 2/3. This is accompanied with an increased soft tissue density and volume. Diagnosis: infectious periostitis.

osteomyelitis

osteomyelitis

DP view. An ill-defined erosion is seen along the lateral aspect of the fifth toe proximal phalangeal head. Diagnosis: osteomyelitis.

gas gangrene

gas gangrene

DP view. A well-defined air-like density (arrow) is seen in the soft tissues adjacent to the medial aspect of the first metatarsal head. This finding is surrounded by increased soft tissue density and volume. Diagnosis: soft tissue emphysema.

bone abscess

bone abscess

DP view. A geographic (or, oval-shaped) decreased density (L) presents within the mid-diaphysis of the third metatarsal. It is surrounded by a diffuse, sclerotic margin (S). Diagnosis: bone abscess.

DP gas gangrene

DP gas gangrene

DP view. Multiple geographic air-like densities (G) of varying size and shape are seen throughout the soft tissues of the forefoot. Diagnosis: soft tissue emphysema.

Lateral oblique osteolysis

Lateral oblique osteolysis

Lateral oblique view. There is osteolysis of the hallux proximal and distal phalanges such that the entire head is absent in the former and the majority of the base and shaft of the latter. Multiple ill-defined bone segments (sequestra, s) can be identified. Diagnosis: osteomyelitis.

osteomyelitis

osteomyelitis

DP view. There is significant increased soft tissue volume and density involving the entire third toe. The middle and distal phalanges are absent as are the shaft and head of the proximal phalanx. (These bones were entirely present only 10 days earlier.) Diagnosis: osteomyelitis.

chronic osteomyelitis

chronic osteomyelitis

AP ankle view. The distal end of the tibia is deformed. Other findings include mixed lucency (L) and sclerosis (S) throughout this region as well as a linear-like decreased density superiorly in the mid-diaphysis (cloaca, C). The ankle joint (AJ) is not visible. Diagnosis: chronic osteomyelitis.

Should a radiographic study be ordered for suspicion of bone infection?

Definitely yes.

What are the best views to order?

At a minimum order DP/AP and lateral views. Oblique views can be valuable adjunct views and are advocated. My preference, in the scenario of possible bone infection, is to obtain all views that can provide visualization of the area in question. Findings may be subtle and only visible in one view.

Other information

The radiographic presentation of infection in the diabetic foot is no different than in the nondiabetic foot. However, neuropathic osteoarthropathy, a complication associated with diabetes, may appear identical to osteomyelitis. Furthermore, previously existing neuropathic osteoarthropathy in the same location significantly complicates the differentiation of osteomyelitis radiographically. In cases of superimposed pathology, additional imaging studies (MRI, technetium scan) may be necessary for further evaluation.

References:

  1. Resnick, D: Bone and Joint Imaging, 2nd edition, WB Saunders, 1996.
  2. Christman RA: Foot and Ankle Radiology, 2nd edition, Lippincott Williams & Wilkins, 2015.