Postoperative Infection

KEY FACTS

Terminology

• Infection at surgical site within 1 month of surgery or within 1 year of prosthetic implantation

Imaging

• Mild soft tissue edema, fluid, & hyperemia are very common signs in early postoperative period
• Intensity & pattern of edema, fluid, & hyperemia helps differentiate infectious from noninfectious inflammation

Inflammation from surgical disruption of tissues & subsequent repair follows expected pattern & is usually mild in degree

Inflammation from postoperative infection is more severe & does not follow expected pattern
• Edematous tissue = hyperechoic if mildly edematous, hypoechoic if more intensely edematous
• Fluid may collect as discrete collection or as accumulation at fascial or tissue interface

Variable echogenicity

Cannot reliably differentiate between infected collection & noninfected collection

Check gravity-dependent areas around surgical site as fluid will tend to collect here
• US is not prone to metallic artifact & is more suited to assessment of postoperative patient
• US is not sensitive at detecting osteomyelitis

Top Differential Diagnoses

• Postoperative inflammation
• Hematoma
• Deep venous thrombosis

Diagnostic Checklist

• US helps to define site of soft tissue infection, isolate fluid, & provide aspirate for culture
• ± US-guided soft tissue biopsy if no fluid collection is present
• US-guided synovial biopsy helpful in confirming prosthetic joint infection if no fluid for aspiration

TERMINOLOGY

Definitions

• Infection at surgical site within 1 month of surgery or within 1 year of surgical implant

IMAGING

General Features

• Best diagnostic clue

Inflammation ± collection persisting > 1 week after surgery
• Location

Soft tissue, bone, or joint

Hip, knee, spine, or any operative site
• Morphology

From localized wound infection to acute osteomyelitis

Radiographic Findings

• Best initial investigation

Aids interpretation of subsequent US and other investigations

Progressive osteolysis is key to recognizing infection

Radiographs are normal in 50% of periprosthetic implant infections

CT Findings

• CECT

Multidetector CT is less prone to metallic artifact than MR

– CT (or MR) provide most useful assessment of infection after implant has been removed

Delineates bony abnormality and soft tissue infection

– ± CT-guided aspiration or drainage

MR Findings

• T1WI

MR imaging is often severely limited by metallic susceptibility artifact

Hypointense soft tissue swelling
• T2WI FS

Hyperintense soft tissue swelling ± hyperintense fluid or fluid collection
• T1WI C+

Infective, noninfective inflammatory, and reparative tissue all enhance

– Generally, the greater the enhancement, the more likely the infection

Useful at delineating fluid collections

– Degree of wall enhancement is greater with abscesses than with sterile collections

Ultrasonographic Findings

• US is not prone to metallic artifact

Good visualization of juxtacortical tissues
• US can access most operative areas
• Helps localize site of infection (superficial or deep), identify drainable collection, and guide fluid aspiration or tissue biopsy for diagnosis
• Mild soft tissue edema, joint fluid and capsular hyperemia are common early postoperative findings
• Intensity and pattern of edema, fluid, and hyperemia helps differentiate infectious from noninfectious inflammation

Inflammation from surgical disruption of tissues and subsequent repair follows expected pattern and is usually mild in degree

Inflammation from postoperative infection is more severe and does not follow expected pattern
• The greater the degree of soft tissue edema and inflammation, the greater the likelihood of postoperative infection
• Edematous tissue is hyperechoic if mildly edematous, hypoechoic if more intensely edematous
• Fluid may collect as discrete collection or along fascial and tissue interfaces

Usually accumulates at most dependent areas

Anechoic or hypoechoic or hyperechoic fluid collection

± echogenic debris

Usually unable to distinguish between infected collection, noninfected seroma, or liquefied hematoma

– Need to aspirate fluid for microbiological, cell count, and biochemical analysis

– Synovial fluid leukocyte count, percentage of polymorphonucleocytes, C-reactive protein, and other synovial fluid biomarkers are predictive of periprosthetic joint infection
• Synovial/capsular thickening is common after surgery

Joint capsule disruption during surgery or arthroplasty

– Limits development of postoperative effusion

If capsule has been disrupted, there may be little, if any, joint effusion even with infection as joint fluid drains into periarticular tissues

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Apr 9, 2020 | Posted by admin in MUSCULOSKELETAL IMAGING | Comments Off

KEY FACTS

Terminology

TERMINOLOGY

Definitions

IMAGING

General Features

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Postoperative Infection

Postoperative Infection

Imaging

Top Differential Diagnoses

Diagnostic Checklist

Radiographic Findings

CT Findings

MR Findings

Ultrasonographic Findings

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Postoperative Infection

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