19/10/2025
🔥 Investigation of Infected Orthopaedic Implants (Chronic Osteomyelitis)
Clinical Context:
Chronic infection around a tibial stainless steel plate often presents with sinus formation, pain, and non-healing wound.
Choosing the right imaging modality is critical for accurate diagnosis and surgical planning.
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🧠 Key Concept:
MRI is the best imaging tool for soft tissue and marrow changes…
but it’s limited by metallic artifact from stainless steel.
Nuclear scans (functional imaging) overcome this limitation and detect active infection even when hardware obscures the anatomy.
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🧩 If the plate is Stainless Steel:
MRI is not reliable due to severe magnetic artifact.
Best investigation:
🔹 Indium-111 labeled WBC scan → Highly specific for infection.
🔹 Tc-99m triphasic bone scan → Sensitive but not specific (useful screening).
Interpretation tip:
Increased uptake in all three phases = active infection (osteomyelitis).
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⚙️ If the plate is Titanium:
MRI artifact is minimal because titanium is paramagnetic.
Best investigation:
🔹 MRI with gadolinium contrast → Excellent for defining abscess cavity, sinus tracts, and bone marrow edema.
Added advantage: differentiates infection from aseptic loosening.
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🎯 Summary (Exam Focus):
Stainless steel implant → Indium-111 WBC scan (most specific).
Titanium implant → MRI with gadolinium (best visualization).
Triphasic bone scan → initial screening or when WBC scan unavailable.
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💬 Clinical Pearl:
> “When metal blocks your view — switch from MRI to molecular imaging!”
Functional scans see the battle, even when metal hides the field.
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