Abstract: An apparatus includes a support member having an outer surface configured to be disposed between adjacent spinous processes and a retention member rotatably coupled to the support member. A first end portion of the retention member is spaced apart from the outer surface by a first distance along an axis substantially normal to a longitudinal axis of the support member when the outer surface is disposed between the adjacent spinous processes. A second end portion of the retention member is spaced apart from the outer surface by a second distance along the axis substantially normal to the longitudinal axis when the outer surface is disposed between the adjacent spinous processes. The first end portion of the retention member and the second end portion of the retention member are configured to cooperatively limit movement of the support member relative to the adjacent spinous processes.