A surgical tool for tensioning a flexible member (14, 58) of a vertebral device having a body, said flexible member (14, 58) having at least one end portion to which tension is applied, said tool comprising: - a longitudinal member having a longitudinal axis, a first end provided with an element for securing in rotation the at least one end portion of said flexible member (14, 58) with said first end of the longitudinal member, and a second end provided with a handling element, wherein the first end of said longitudinal member is designed for rolling said at least one end portion of the flexible member (14, 58) when said longitudinal member is rotated; and - a guiding member comprising a first end adapted to be applied against said body of the vertebral device, and guiding elements for guiding in rotation said longitudinal member about said longitudinal axis, said guiding member maintaining the longitudinal axis of the longitudinal member with respect to said body, whereby the rotation of said longitudinal member with said handling element produces the tensioning of said flexible member (14, 58); characterized in that: said guiding member is a tubular member having first and second ends (130b, 130a) and adapted to receive said longitudinal member in rotation and in that said first end of said tubular member is provided with an engaging piece to be applied against said body of the vertebral device for securing in rotation said tubular member with respect to said body and said second end of the tubular member is provided with a second handling element. - a longitudinal member having a longitudinal axis, a first end provided with an element for securing in rotation the at least one end portion of said flexible member (14, 58) with said first end of the longitudinal member, and a second end provided with a handling element, wherein the first end of said longitudinal member is designed for rolling said at least one end portion of the flexible member (14, 58) when said longitudinal member is rotated; and - a guiding member comprising a first end adapted to be applied against said body of the vertebral device, and guiding elements for guiding in rotation said longitudinal member about said longitudinal axis, said guiding member maintaining the longitudinal axis of the longitudinal member with respect to said body, whereby the rotation of said longitudinal member with said handling element produces the tensioning of said flexible member (14, 58); characterized in that: said guiding member is a tubular member having first and second ends (130b, 130a) and adapted to receive said longitudinal member in rotation and in that said first end of said tubular member is provided with an engaging piece to be applied against said body of the vertebral device for securing in rotation said tubular member with respect to said body and said second end of the tubular member is provided with a second handling element. said guiding member is a tubular member having first and second ends (130b, 130a) and adapted to receive said longitudinal member in rotation and in that said first end of said tubular member is provided with an engaging piece to be applied against said body of the vertebral device for securing in rotation said tubular member with respect to said body and said second end of the tubular member is provided with a second handling element.