Leyton Orient have agreed a six-month contract for defender Sam Oji.
The 22-year-old centre-half spent the early part of this season on loan at Brisbane Road and, having been released by Birmingham, has been snapped up by Orient manager Martin Ling.
"We all know about Sam from his loan spell and he impressed us during that time," Ling told the club's official website.
"His attitude was first class and he did well whenever he was called into the team.
"He will offer us good cover both at right-back and centre-back, which will be especially important over the next three or four weeks due to Alton Thelwell's injury."
In three and a half years at St Andrews, Oji made only one substitute appearance for Blues.