Hooked epinephrine auto-injector devices in children: four case reports with three different proposed mechanisms

The prevalence of epinephrine auto-injectors (EAI) use is on the rise. Our objective was to describes children with hooked EAI needles that were embedded in soft tissues. Results: Two children self-injected in their shins. The embedded EAIs required removal in the Emergency Department. Both needles were hooked and splayed at the tip. A boy in anaphylaxis kicked his leg during EAI injection and the hooked needle embedded under his skin and was difficult to dislodge. The exposed needle was curved. A girl had an EAI administered for anaphylaxis, which was also difficult to dislodge. On removal, the distal needle tip was hooked approximately 160 degrees. Images of the device revealed that the needle fired off-center from the device and the device components were cracked. We propose three different explanations for these hooked EAI needles. The first is that the needle could hit bone during injection and curve rather than penetrates further. Secondly, the needle could bend when the patient moves during injection. Thirdly, if a needle fires sufficiently off-center to hit the cartridge carrier, this could hook the needle prior to injection. Awareness of the reasons for needle hooking, damage observed, and challenges and successful approaches to their removal, can better prepare the provider for these uncommon events. Teaching parents, children and educators about safe EAI storage and appropriate restraint during use may prevent some of these accidental injuries. Reporting device failures may lead to improvements in device performance and design.