Abstract: A fusion implant apparatus for facilitating fusion of adjacent bone structures includes a threadless implant member which is positioned between adjacent opposed bone structures. The implant member defines a longitudinal axis and first and second longitudinal ends and has an outer wall which is dimensioned to engage the opposed bone structures upon positioning therebetween in supporting relation therewith. The outer wall defines an internal cavity for the reception of bone growth inducing substances and includes a plurality of apertures which extend therethrough in communication with the internal cavity to permit fusion of vertebral bone tissue. The implant member also includes an intermediate portion which defines a cross-sectional dimension transverse to the longitudinal axis which is greater than the respective cross-sectional dimensions of the first and second longitudinal ends of the implant member.