Bianca Andreescu's twisted knee adds to concerns for teenager's career

• Andreescu retires against Karolina Pliskova at WTA Finals• Elina Svitolina wears down Simona Halep to reach semi-finals Bianca Andreescu was forced to retire with a left knee injury while losing 6-3 to Karolina Pliskova at the WTA Finals in Shenzhen as injuries continue to define the young Canadian's career. Andreescu had arrived for her second match of the tournament with all eyes on her back after she struggled towards the end of her three-set defeat by Simona Halep on Monday. Instead, s...