Background Magnetic Resonance (MR) offers the potential to identify early loosening and assess peri-articular soft tissue structures in patients with metal joint prostheses. Unfortunately, conventional MR is currently incapable of assessing the prosthesis-bone interface in patients with joint replacements because of field inhomogeneity resulting from metal related paramagnetic and ferromagnetic effects. New Slice-Encoding Metal Artefact Correction (SEMAC) techniques have been developed that may allow visualisation of the bone and soft tissues close to metal work.
Objectives In order to explore the clinical utility of the technique, we conducted a retrospective audit of conventional MR and the newer metal suppression techniques.
Methods Patients who had previously received hip prostheses and were undergoing clinical review were imaged using both conventional and metal suppression MR techniques using a Siemens Avanto 1.5T MR scanner as part of their routine clinical care. T1 TSE and STIR coronal and T1 and STIR SEMAC sequences were assessed. The femoral and acetebaular components were consensus scored by two experienced musculoskeletal radiologists for diagnostic quality. Each prosthesis zone was scored using a five point scale: (0) definitely non-diagnostic; (1) probably non-diagnostic; (2) possibly diagnostic; (3) probably diagnostic; (4) definitely diagnostic.
Abnormalities were assessed on both radiographs and MRI using a four point scale: (0) none; (1) mild; (2) moderate; (3) severe. Effusion and bone-cement interface were assessed by prosthesis zone. These abnormalities were defined as increased signal on STIR sequences with intermediate signal on T1 scans.
Results Images were reviewed from 19 patients (mean age = 64; SD = 12 years) with a variety of hip prostheses (Charnley = 4, Corail = 7, Furlong = 1, Metal-on-Metal = 7). SEMAC increased the number of diagnostically useful images (defined as ≥2) in all Gruen zones for both STIR and T1 images (Table 1). Importantly, this also translated into to an increased ability to identify abnormalities: Use of SEMAC enabled identification of more abnormalities in all Gruen zones and doubled the number of effusions visible (Table 2).
Conclusions The use of SEMAC sequences substantially improved image quality and enabled identification of more peri-prosthetic complications in patients with metallic joint prostheses.
Disclosure of Interest None declared