False Magnetic Resonance Imaging Persistence of a Biodegradable Anterior Cruciate Ligament Interference Screw With Chronic Inflammation After 4 Years In Vivo

Surgeons should be aware that the degradation kinetics of biodegradable implants likely influence the rate of osseous integration, and depend on numerous factors such as polymer weight, crystallinity, and stereocopolymer ratio. We present a case of inflammatory reaction at a polylactide tibial interference screw site more than 4 years after primary anterior cruciate ligament (ACL) reconstruction. This inflammation was presumptively treated as an infection with surgical irrigation and debridement. Preoperatively, the screw was clearly delineated by magnetic resonance imaging (MRI), yet was grossly absent at surgery. Postoperative MRI confirmed thorough debridement and complete absence of the screw. This report shows that not only can a late inflammatory reaction occur, after up to 4 years in vivo, but that the MRI may show a persistent screw despite significant biodegradation. False MRI-persistent screws should be considered when critically reviewing studies that use MRI in the methods for evaluating biodegradable implants. More importantly, false MRI-persistent screws may have significant ramifications when planning revision surgery after primary ACL reconstruction having used interference screws that can degrade over several years.