Composite FDG-PET and 3-phase bone scan in suspected infections post open reduction and hardware fixation of fractures

Objectives Management of infection (INF) post open reduction and internal fixation (ORIF) of fractures is an ongoing dilemma, infection in the presence of hardware (HDR) mandates revision/removal of HDR; conversely early removal of HRD, in the presence of non-union, complicates management of both INF and fractures. PET-CT is emerging as a strong contender for evaluation of MSK infections; we evaluated the role of composite FDG-PET and bone scan (BS) in suspected INF post ORIF.

Methods Retrospective radiology archival review of all pts suspected of INF post ORIF and having undergone PET and BS scans from 2012 to current revealed 30 pts (male=21, female=9, mean age=42.5) scanned for suspected INF post ORIF. The PET-CT fusion images were reviewed interactively on a dedicated workstation, and planar 3-phase bone scans were reviewed as screen captures. Findings on composite PET and BS were correlated with cultures (CULT [no=9]), and/or clinical follow-up (f/u).

Results A total of 168 HRD (screws 126, wire loops 14, plates 11, rods 9, nails 5, chain plates 3) in 30 pts were evaluated. In 5 (4 screws and 1 wire loop) of 6 pts pos. for INF by CULT, the composite PET and BS were both true pos; in the 1 remaining pt pos. by CULT, composite PET and BS showed soft tissue inflammation. In all 3 pts neg by CULT, PET and BS were both true neg. In discordant cases; 8 pts. had BS +ve and PET -ve, BS was +ve due to the following: heterotopia (2), dislocation/subluxation (2), and soft tissue/deep ulcers (4). While, 2 pts. had PET +ve with BS -ve: heterotopia (1) and callus (1). Both PET and BS were +ve, one each in diskitis and callus, but localization by PET-CT ruled out osteomyelitis or INF. In the remaining 12 pts. with both PET and BS -ve, the composite bi-modality was considered to be true negative by f/u. Discussion: PET and BS were staunchly complementary. While neg. findings on both PET and BS essentially ruled out INF; however, when PET and BS were discordant (synovitis, ulcers, etc), PET was helpful in localizing the findings on BS; conversely, in pts with non-specific activity on PET, the findings of normal flow and blood pool on BS, improved the spec. of PET.

Conclusions Clinical utility and Limitations: The composite dual modality imaging allows for same day diagnostic work-up. Potentially improves accuracy of detection and localization of infected foci. Our study is limited by number of cultures obtained, and limited f/u. Conclusion: In our series, composite FDG-PET and BS appear to be highly complementary, a composite neg. study essentially rules out INF post ORIF, PET helps in localizing and clarifying pos. findings on BS, thereby increasing the sens. spec. and acc. of the composite dual modality.