Magnetic Remanence of Stainless Steel and Titanium Alloy Orthopaedic Implants

Stainless steel and titanium alloys are common materials for orthopaedic implants. However there is a lack of information and studies on magnetic remanence of  implants used in clinical practice. The aims of this study are to investigate the composition and the presence of magnetic remanence for these two orthopaedic implant materials. These two factors may cause implant instability and heat problems as well as degradation of the images quality if the patients undergo magnetic resonance imaging (MRI) examination. The magnetic hysteresis loop and remanence status of stainless steel and titanium alloy orthopaedic implants were investigated with a vibrating sample magnetometer (VSM). Both samples of stainless steel and titanium alloy had been exposed to external magnetic fields up to 1 T (10000 G) and 1.4 T (14000 G), respectively. The compositions of these two orthopaedic implant materials were studied using a scanning electron microscope with energy dispersive X-ray analysis (SEM-EDX). The results of the study demonstrated that ferrous and nickel compositions in stainless steel alloy orthopaedic implants contributed to the residual magnetism, as shown in the hysteresis loop. The titanium alloy orthopaedic implant sample does not contain any ferromagnetic elements. After exposure to a magnetic field, the stainless steel values of retentivity, coercivity and magnetisation are significantly higher compared to those of the titanium alloy. The stainless steel orthopaedic implant sample demonstrates a typical hysteresis loop that suggests the existence of magnetic remanence. In contrast, the titanium alloy orthopaedic implant sample showed no significant remanence phenomenon. By considering the existence of magnetic remanence in the implant is important as potential effect on the MRI image quality.