The invention relates to a device for determining a relative position of a femur (F) with respect to a tibia (T) comprising at least: - a first measuring member (4) intended to be 10 positioned against the tibia and comprising means (11) for collecting an absolute position of the tibia and means (12) for generating a signal representing this position - a second and a third measuring member (20 30) 15 intended to be positioned relatively to the femur by each surrounding the thigh (2) associated with the femur at different heights, the second and third measuring member each comprising means (55) for generating a signal representing a position of the 20 associated measuring member - a calculating member (100) comprising communication means (101) for receiving at least the signals generated by the first, second and third measuring members, comparison means (102) which 25 compare the signals of the second and third members in order to deduce an absolute position of the femur and processing means (103) which analyze the signal of the first measuring member and the absolute position of the femur in order to deduce a relative 30 position of the femur with respect to the tibia.La invención se relaciona con un dispositivo para determinar una posición relativa de un fémur (F) con respecto a una tibia (T) comprendiendo por lo menos: - un primer miembro de medición (4) destinado a ser colocado contra la tibia y comprendiendo medios (11) para recolectar una posición absoluta de la tibia y medios (12) para generar una señal que representa esta posición - un segundo y un tercero miembros de medición (20 30) destinados a ser colocados de manera relativa al fémur al rodear cada uno el muslo (2) asociado con el fémur a diferentes alturas, el segundo y tercero miembros de medición comprendiendo cada uno medios (55) para generar una señal que representa una posición del miembro de medición asociado - un miembro de cálculo (100) comprendiendo medios de comunicación (101) para recibir al
