An expandable intervertebral implant (10) having an external member (12) and an internal member (14). The implant includes a locking arrangement (50) having a first interlocking teeth structure (56) formed on the external member and a second interlocking teeth structure (58) formed on the internal member. The interlocking teeth structures of the external and internal members have engagement surfaces (76, 86) arranged in a non-perpendicular orientation relative to the direction of implant expansion. The locking arrangement is configured such that walls of the internal member are pulled or flexed toward the walls of the external member when compressive forces are applied to the implant.