An implantable device includes a spacing member and an elongate member. The elongate member includes a body portion having a first end coupled to the spacing member and a second end having a retention member. In a system for maintaining disc space between adjacent vertebrae, the implantable device is used in conjunction with a spine fixation member. The spine fixation member includes bone anchors and a spinal rod for releasably securing the retention member of the elongate member thereto in order to prevent expulsion of the spacing member from the disc space. Methods of using the system include unilaterally and bilaterally replacing diseased or damaged intervertebral discs from a posterior or transformational approach.