An intervertebral implant adapter for the L5-S1 juncture comprises a wedge shaped body of biocompatible material having upper and lower surfaces with the upper surface having a slot which provides slidable interlocking engagement with a motion or fusion implant. The lower surface is provided with any convenient bone anchoring mechanism. The adapter mates with an upper implant which is implanted after the adapter so as to provide an implant which matches the lordotic angle but which, in its multiple piece form, is no bigger than the posterior disk height.