An implant and method for insertion between two adjacent vertebrae includes an implant body having a leading end and a trailing end spaced apart by a longitudinal dimension of the implant, two diametrically opposed first and second shells, each of the shells having a body portion and a thread portion extending outwardly from the body portion, and a resilient support portion disposed between the two shells. The support portion may be made of an elastomeric material or may include a spring mechanism.