England manager Martin Johnson confirmed Borthwick's appointment after the squad arrived in Portugal yesterday for a pre-tournament training camp.
The squad contained Worcester loose-head prop Matt Mullen and Leicester tight-head Dan Cole who have been called in for the tournament in place of injured front-row pair Andrew Sheridan and Julian White. Leicester scrum-half Ben Youngs and the loose-forward pair of Wasps No8 Dan Ward-Smith and Harlequins flanker Chris Robshaw have also been promoted.
England have further concerns over the fitness of James Haskell, who injured his knee playing for Stade Francais against Edinburgh at the weekend, but a decision over his availability will be delayed until after a scan. Youngs has been promoted as cover for Leicester team-mate Harry Ellis, who is battling a chronic knee problem.
Robshaw and Ward-Smith, whose inclusion takes the tally of New Zealand-born players in the squad to four, have replaced Joe Worsley, who is out for at least the first two games, and Tom Croft.
The absence of Croft's lineout ability after the Leicester flanker suffered a knee injury will only have strengthened the case for Borthwick to be retained in the second row.