Denver Broncos center JD Walton will miss the rest of the 2012 season. Walton was placed on injured reserve yesterday after fracturing and dislocating his left ankle in the second quarter of Sunday’s 37-6 win over the Oakland Raiders. The third-year pro had only missed one snap in his career before the injury. Veteran Dan Koppen will replace Walton in the lineup. Linebacker Joe Mays, who was suspended for Sunday’s game, will take Walton’s place on the 53-man active roster.