I'm working on a character for my story. He is an active-duty US Army Ranger performing combat missions. I would like him to have had a previous injury suffered in the line of duty in which foreign objects entered his body and were not removed during treatment of the injury.
Obviously, once the initial injury had healed, these foreign bodies would have to be non-life-threatening, and not cause significant impairment.
However, what I don't know is what sort of injury might result in retained foreign bodies, that would not result in the soldier being reassigned or being medically discharged.
So my question is: What previous injuries might a modern-day US special forces soldier have suffered during combat that would result in retained foreign objects that would allow them to continue serving as a special forces soldier after recovery from the injury? Answers should include the type of object, approximate location, reason for non-removal and why it has not resulted in loss of capabilities. Time to heal from the injury in question would also be useful.
The foreign object(s) should (each) be big enough to see easily with the naked eye if they had been able to be removed.
Preference will be given to answers detailing initially more serious injuries requiring surgery and longer recovery times over minor injuries that would have short recovery times and minimal medical intervention. i.e. the worse the injury, the better... as long as the soldier can still be an active-duty US Ranger and serve in combat operations. It would be even better if the soldier could have continued to fight immediately after receiving the injury and receiving basic first aid.
'None' is an acceptable answer if any foreign objects retained after an injury would result in the soldier being reassigned from an active-duty combat role in a US special forces unit.