The general case over arbitrary number fields has been treated by Loïc Merel. A good place to start would be Bas Edixhoven's Bourbaki exposé Rational torsion points on elliptic curves over number fields, Séminaire Bourbaki, 36 (1993-1994), Exposé No. 782.

There is also an excellent set of notes by Joseph Œsterlé which were to be found on the ICTP website.