Accurate differentiation between loosening and infection is very important in the optimal treatment of patients with painful lower-limb arthroplasty. The distinction is very difficult, time consuming and expensive. FDG-PET has shown to be a powerful tool in the diagnosis of infection and inflammation. FDG-PET is particularly valuable in the evaluation of chronic osteomyelitis, sarcoidosis, fever of unknown origin, the acquired immunodeficiency syndrome and infected prostheses and also holds promise to monitor disease activity and response to therapy.

FDG-PET is an effective modality in the diagnosis of infection associated with lower-limb arthroplasty. Overall sensitivities range from 90% to 100% and specificities of 81% to 89% have been reported. In contrast to conventional nuclear medicine and radiologic techniques (Particularly MRI), PET is not affected by metal implants used for orthopedic procedures. Bone marrow uptake is minimal in these patients who usually are elderly. Furthermore, better spatial resolution of PET compared with conventional nuclear medicine modalities allows the detection of small and subtle lesions that can go unnoticed with other tecniques. When PET imaging is used to diagnose periprosthetic infection, certain cautions should be taken into account when interpreting the scans. The criteria to be used to distinguish infection from aseptic loosening should be clearly defined. Increased FDG uptake must be present along the interface between prostheses and bone to suggest infection. Often a significantly increased FDG uptake is found around the neck and/or head portion of the prosthesis following arthroplasty. Nevertheless, without increased FDG uptake along the interface between bone and prosthesis, a diagnosis of infection can not be made with confidence. For knee prostheses this diagnostic criterion is not as optimal as in the hip prostheses resulting in more false-positive results. Surgical intervention usually results in increased FDG uptake for up to 6 months. However, nonspecific increased FDG uptake caused by uncomplicated arthroplasty persists for an extended period of time.

As a metabolic modality, FDG-PET is superior to anatomic imaging techniques in the diagnosis and treatment of patients with prosthetic infections and inflammations that rely on the presence of hyperemia and increased perfusion. Novel PET tracers are being tested that may further enhance the role of this technique.