Diagnostic values of positron emission tomography versus triple-phase bone scan in hip arthroplasty loosening

The most frequent complications of total hip arthroplasty are septic and aseptic wear-induced loosening. A reliable differentiation between septic and aseptic loosening with current diagnostic tools is not possible. Therefore, we examined the diagnostic valency of positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) in cases of septic or aseptic hip arthroplasty loosening compared with conventional triple-phase bone scan (TPBS).

Fifty patients with 70 total hip replacements (symptomatic n=50, asymptomatic n=20) were examined by means of FDG-PET and TPBS to detect septic and aseptic loosening and differentiate between the two. A differentiated algorithm subdivided into categories I-V was developed for FDG-PET. Additionally, standardized uptake values (SUV) were calculated from the lesion with the highest FDG uptake. Interpretations of the TPBS were done according to the criteria described by Wilson. The final diagnosis was based on operative findings including microbiological and histological examinations (n=50), while the remaining asymptomatic arthroplasties (n=20) were integrated into a clinical follow-up (> or =9 months).

Sensitivity/specificity of FDG-PET was 91%/92% (accuracy 91%) compared with 78%/70% (accuracy 74%) for TPBS. A high correlation could be proved between FDG-PET investigation and operative histopathological findings (r(Spear)> or =0.9). No significant differences were found regarding cemented and uncemented implanted hip arthroplasties (p> or =0.05). Calculation of the SUV turned out to be inappropriate as a sole criterion for image interpretation.

FDG-PET is a promising, highly accurate examination method to detect polyethylene and metal wear-induced chronic inflammation followed by periprosthetic osteolysis. In addition, FDG-PET has a significantly higher sensitivity and specificity than TPBS for differentiating between aseptic loosening and infection.