World Athletics Championships 2013: Perri Shakes-Drayton ruled out of 4x400m relay due to knee injury The Londoner's coach Chris Zah has accompanied her on the flight home, where the injury, which is to her left knee, will be fully examined. She had an ultrasound scan on Thursday night, having said after the race it "felt funny." It certainly hampered her running badly as she hit hurdles and lost her rhythm entirely as she clocked her slowest time of the year. Tiffany Porter had no problem with the barriers in the 100m hurdles as she looked very smooth in winning her heat in 12.72secs to cruise into Saturday's semi-finals. The 25 year-old, an outside medal hope, finished ahead of London 2012 silver medallist Dawn Harper-Nelson, who was back in third. She said: "It was just a matter of working off the cobwebs and just focusing on running a clean race and qualifying. The main focus this whole season has been here, the World Championships, so hopefully I can put my races together and come out victorious.