A flexible connection unit for use in a spinal fixation device is provided. The flexible connection unit includes an elongated member, such as a vertebral rod, having a first end portion and a second end portion opposite each other with a transition portion extending therebetween. The first end portion of the vertebral rod comprises an oval shape and the second end portion contains an oval or non-oval shape. The major diameter of the oval shaped first end is parallel to the sagittal plane of a patients body and provides the higher stiffness for fusion to resist flexion in the sagittal plane. The second end portion of the vertebral rod is perpendicular to the sagittal end of a patients body and provides the lower stiffness for fusion.
