Magnetic resonance imaging of painful total hip replacement: detection and characterisation of periprosthetic fluid collection and interobserver reproducibility.

PURPOSE: The purpose of our study was to demonstrate the diagnostic value of magnetic resonance imaging (MRI) when measuring and characterising periprosthetic fluid collections in patients with painful hip prosthesis and to provide an estimation of interobserver reproducibility.
MATERIALS AND METHODS: Nineteen patients (mean age 59±13 years) with painful total hip replacement and clinical suspicion of infection underwent MRI. Images were reviewed blindly by two musculoskeletal radiologists with different levels of experience who evaluated the presence/absence of soft tissue oedema or fluid collection (when present, three-plane maximal diameters were measured; involvement of skin/subcutaneous/deep tissues or prosthesis were estimated; fluid was classified as serous/purulent/haematic according to signal behaviour). Interobserver agreement was calculated (Cohen's ).
RESULTS: A total of 26 MRI studies were carried out (three patients underwent two and two patients underwent three MRI examinations). Both readers detected soft tissue oedema (13/26, 50%) or fluid collection (21/26, 81%) and characterised the fluid as serous (9/21, 43%), purulent (8/21, 38%) or haematic (4/21, 19%). The collection involved skin/subcutaneous tissues (16/21, 76%), deep soft tissues (19/21, 91%) or the implant (12/21, 57%). For all evaluations, interobserver agreement was complete (=1). No significant differences were found between the measurements of the collections (p>0.258).
CONCLUSIONS: MRI is highly reproducible in detection, localisation, quantification, and characterisation of fluid collections when the presence of implant infection is clinically suspected.