Diagnostic performance of FDG-PET in differentiating septic from aseptic painful hip prostheses

Objectives Accurate non-invasive differentiation of aseptic loosening from periprosthetic infection in the painful hip prosthesis remains a challenge. This abstract serves to update our prior paper with new results assessing the diagnostic performance of FDG-PET to non-invasively diagnose infection in patients with painful hip arthroplasty.

Methods In an ongoing prospective study, FDG-PET was performed on 129 painful hip prostheses after clinical evaluation and laboratory data were inconclusive for infection. Images were interpreted in blinded fashion, with infection identified based on increased FDG activity at the bone-prosthesis interface of the femoral component of the prosthesis. Final clinical outcome was available for 99 hips, determined via surgical, microbiological, and clinical follow-up.

Results Of 99 hip prostheses with full follow-up, FDG-PET identified prosthetic infection in 15 of 19 (sensitivity=78.9%), with false positive (FP) results in 18 of 80 (specificity=77.5%). Seven of 18 FP readings showed extensive osteolysis or periprosthetic fracture non-union visible on plain film radiography; when these were removed, specificity improved to 84.9% (62/73). When patients with a mechanical cause for pain were excluded, FDG-PET had a PPV of 57.7% (15/26), NPV of 93.9% (62/66), and accuracy of 77.8% (77/99).

Conclusions These results demonstrate that FDG-PET is a highly accurate diagnostic tool for the evaluation of infection in painful hip arthroplasty. Specificity is decreased in patients with radiologic evidence of mechanical hip pain, and should be interpreted with caution.

Research Support This study was funded by a grantfrom the NIH.