A distractor device (1) comprises a distracting element that includes a fixed plate (3) and a mobile plate (4), said mobile plate (4) being translatable by means of an actuator with respect to a body (2) of said distracting element between a first position where it is in contact with said fixed plate (3) and a second position where it is spaced therefrom. The distractor device further includes at least one rod (10) suitable to be introduced in the medullary cavity of a femur (F) and provided with a stem (10a) and an abutment plate (10b) fixed at one end of the stem (10a) and inclined by a known angle (α) with respect thereto, said abutment plate (10b) being suitable to receive in abutment the mobile plate (4) in said second position, and one between the mobile plate (4) and the fixed plate (3) being also rotatable with respect to the other, the angle of rotation of the rotatable plate (3, 4) determined by the contact between the mobile plate (4) and the abutment plate (10b) being measured by means of a graduated scale (5d) and an indicator (4a) secured to said rotatable plate (3, 4). Thanks to these features, the distractor device according to the invention allows to check in situ and to correct the theoretical valgism angle of a patients knee determined during a pre-surgery phase, thus allowing to correctly place the jig for the first distal resection of the femur.Linvention concerne un dispositif distracteur (1) qui comprend un élément distracteur qui comporte une plaque fixe (3) et une plaque mobile (4). La plaque mobile (4) peut se déplacer au moyen dun actionneur par rapport à un corps (2) de lélément distracteur entre une première position où il est en contact avec la plaque fixe (3) et une seconde position où il est à distance. Le dispositif distracteur comporte en outre au moins une tige (10) conçue pour être introduite dans la cavité médullaire du fémur (F) et pourvue dune tige (10a) et dune plaque de calage (10b) fixée à une extrémité de la tige (10a) et i
