The method and apparatus as shown in FIGS. 8-10 in which a fluid expandable member (208) is positioned in concentric relation about a needle (202). The fluid expandable member (208) is expanded into the nucleus pulposus potential space bordered by the annulus fibrosus of an intervertebral disk. Then, thermoplastic material in a flowing state is injected by a needle (202) within the annulus fibrosus to collapse the fluid expandable member (208) and occupy the space formerly occupied by the fluid expandable member (208).