"Ryan and Mike are two outstanding players," Blues chief executive Robert Norster said. "With Robert Howley also joining us as backs' coach, the two of them will particularly benefit from his expertise and our future prospects are enhanced by their presence."
"All teams require strong selection options and competition for places, especially when injury takes a hand as it has in such pivotal positions for us this season.
"We have been particularly unfortunate at scrum-half. Now Ryan is back to full fitness and with Mike coming on board we have just that."