Jack Collison's knee has caused him to retire. Former West Ham and Wales midfielder Jack Collison is retiring from football at the age 27 due to injury. After making 121 appearances during an injury-hit time with the Hammers, the midfielder moved to Peterborough in the summer hoping to kickstart his career. Collison made 12 appearances for the League One outfit, but has now decided to call time on his career due to persistent knee problems. The midfielder, capped 17 times by Wales, dislocated a kneecap playing for West Ham in 2009 and will now...