A bi-directional fixating transvertebral (BDFT) screw/cage apparatus includes an intervertebral cage having a plurality of internal angled screw guides and screw members and a screw locking mechanism. The screw locking mechanism has leaf springs mechanically interacting with ratcheted screw heads of the screws and allowing the ratchet teeth of the screw heads to rotate only in a penetrating direction and preventing rotation of the screw head in an opposite direction. The intervertebral cage is adapted for posterior lumbar intervertebral placement, anterior lumbar intervertebral placement, anterio-lateral thoracic intervertebral placement, or anterior cervical intervertebral placement.