An implant for insertion between a pair of spaced vertebrae has two interfitted parts relatively shiftable along an axis and having outer ends turned axially away from each other and each formed with an axially outwardly directed part-spherical convex surface. Formations such as a screwthread engaged between the parts can axially shift them relative to each other and lock their axial positions relative to each other. Respective L-shaped mounting brackets each have one leg extending transversely across the axis and formed with a part-spherical concave seat complementary to and fitting with a respective one of the part outer ends and another leg extending generally axially outward. The brackets are adapted to be fitted to the vertebrae. Fasteners secure each of the other legs to the respective vertebra.