What is the best mode of investigation for osteomyelitis (infection of the bone)?

Best Mode of Investigation for Osteomyelitis

MRI is the modality of choice for suspected osteomyelitis due to its superior sensitivity for bone marrow abnormalities, excellent soft tissue contrast, and ability to delineate anatomic detail. 1, 2

Diagnostic Algorithm

Initial Evaluation

• Plain radiographs should be the first imaging test in all cases of suspected osteomyelitis due to their safety, low cost, wide availability, and ability to provide anatomic evaluation 1, 2
• Radiographs can reveal gas, foreign bodies, and suggest alternative diagnoses such as fractures or tumors, though they have limited sensitivity (43-75%) for early osteomyelitis 1, 3
• Early acute osteomyelitis may show only normal findings or mild soft tissue swelling on radiographs 2

Definitive Imaging

• MRI with and without contrast is the preferred next imaging modality when diagnosis remains uncertain after initial radiographs 1, 4
• MRI has a reported 100% negative predictive value for excluding osteomyelitis; a normal marrow signal reliably excludes infection 1, 2
• Positive cases show decreased T1-weighted bone marrow signal with increased signal on fluid-sensitive sequences such as T2-weighted fat-saturated and short tau inversion recovery 1
• MRI sensitivity for osteomyelitis ranges from 82-100%, with specificity between 75-96% 3, 5

Alternative Imaging Options

• CT scanning depicts cortical bone well and can detect periosteal reaction, bone destruction, sequestra, and sinus tracts 1

• CT is particularly valuable for identifying sequestra, foreign bodies, and soft tissue gas 1

• CT is superior to MRI for the diagnosis of sequestra, foreign bodies, and gas but has lower overall sensitivity (65-75%) 1, 6

• Nuclear medicine examinations are most appropriate when 1, 2, 4:

  • MRI is contraindicated
  • Infection is suspected to be multifocal
  • Infection is associated with orthopedic hardware
  • Chronic bone alterations from trauma or surgery are present

• PET has high accuracy (85.1% sensitivity, 92.8% specificity) comparable to MRI for detecting osteomyelitis, particularly valuable in chronic cases 4, 5

Special Considerations

Hardware-Associated Infection

• In patients with previous non-arthroplasty hardware, MRI can be challenging due to metal artifacts 1
• Combined nuclear medicine approaches, such as bone scan with labeled leukocyte scan, enhance specificity in hardware-associated infections 2, 3

Chronic Osteomyelitis

• CT is well suited for evaluation of chronic osteomyelitis, depicting periosteal reaction, trabecular coarsening, bone fragmentation, and fistulae 1, 4
• FDG-PET has shown 91% accuracy for detecting chronic osteomyelitis and may be particularly useful when hardware is present 4

Soft Tissue Involvement

• Ultrasound plays a complementary role, primarily for detection of soft-tissue infections, subperiosteal and soft-tissue abscesses, and joint effusions 1
• Contrast-enhanced MRI is particularly important when evaluating soft tissue involvement 2

Diagnostic Pitfalls to Avoid

• Relying solely on radiographs to rule out infection, as early osteomyelitis may have normal radiographic appearance 2, 6
• Misinterpreting post-traumatic changes as infection on MRI 2
• Failing to obtain contrast-enhanced MRI when evaluating soft tissue involvement 2
• Not considering multifocal involvement, which is more common in children but can occur in adults 2
• Overlooking the need for tissue sampling in cases where imaging findings are inconclusive 4

In conclusion, while multiple imaging modalities play important roles in diagnosing osteomyelitis, MRI stands as the gold standard with its superior sensitivity and specificity, particularly for early detection of bone infection and assessment of soft tissue involvement 1, 5.