Magnesium implants in orthopaedic surgery create a diagnostic conundrum: A radiology case series and literature review

During a routine post-operative orthopaedic radiograph reading session, repeated unusual radiographic soft tissue and bone appearances became evident. It was discovered that these patients had received biodegradable magnesium implants which have recently been introduced into orthopaedic clinical practice. To the untrained eye, the combination of peri-metallic bone resorption with associated soft tissue gas, could easily be mistaken for post-operative infection. The aim of this study is to properly characterise the radiographic post-operative appearances of biodegradable magnesium orthopaedic hardware. We retrospectively evaluated radiographs of all patients who underwent magnesium screw implantation for fractures over a 6 month period. Four patients, mean age of 9.75 (range: 6-15) years who underwent magnesium screw fixation following fracture were included in the study. Follow up duration was 100 days (range: 75-122) with a mean of 2.5 postoperative radiographs being performed per patient during this period. All cases demonstrated post-operative peri-metallic radiolucency which developed around the magnesium screws on x-ray, which subsequently resorbed over time. Peri-metallic soft tissue gas was observed in all patients. In two cases, magnesium implants fractured. As the use of biodegradable metal implants becomes more common, it is important for radiologists to be aware of their imaging characteristics. Prior to reporting a case, it would be prudent to know if biodegradable screws have been utilised and whether there exists a clinical concern for post-operative infection in patients with these particular implants, in which case it would be critical not to dismiss peri-prosthetic radiolucencies and soft tissue gas as merely a sequela of the natural metal degradation process.