A ligament-tensioning device (1) for preparing the implantation of an articulated implant consists of a base body (5) comprising first claws (6, 6') provided with first bearing surfaces (7, 7') applied to a first bone part (33) and second claws (13, 13') provided with a second bearing surfaces (10, 10') applied to a second bone part (34). The claws (6, 6'; 13, 13') are displaceable with respect to each other with the aid of parallel-displacement devices (12, 12'). In addition, the invention provides for a first scale (31) disposed on the base body (5) of the ligament-tensioning device (1) and second medial and lateral scales (32, 32') corresponding to the first scale (31), wherein the second scales (32, 32') are disposed on a guiding body (3) which is movably mounted with respect to said base body (5) by means of the parallel-displacement devices (12, 12). The scales (31, 32; 31, 32') can be brought into congruence in such a way that the height of an implant insertable into the treatable joint is separately medially and laterally presettable.