Aseptic loosening of knee replacement

Case contributed by Dr Michael Morris


A 62 year-old male presents with left knee pain 12 years following left knee joint replacement. The patient has a normal WBC count, midly elevated ESR/CRP, and a painful left knee. There is clinical suspicion for prosthetic infection, so In111-WBC and Tc99-Sulfur colloid scans are performed together for evaluation.

Patient Data

Age: 62
Gender: Male

Uptake on both WBC scan (left) and Tc99 Sulfur Colloid marrow scan suggests aseptic left knee joint replacement.

Negative for infection. 

Case Discussion

Evaluation for infection in the setting of hardware can be a diagnostic dilemma for orthopedic surgeons. Even if a joint replacement may require surgical revision regardless of whether there is infection or not, which may be the case in this scenario, the presence of infection requires altered management and delayed definitive repair.

The WBC scan, is sensitive for inflammation, however false positives can occur in the setting of aseptic loosening. In order to improve specificity when concerned for osteomyelitis, a Tc99-Sulfur Colloid scan be performed simultaneously. On the Sulfur Colloid scan, areas of increased uptake on the WBC scan that represent infection should show decreased uptake. Increased uptake on both studies is therefore suggestive against infection.

In this case, the patient was able to have revision surgery without the need for a temporary antibiotic impregnated replacement thanks to diagnosis by this study.

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