Abstract: An endplate plunger for implanting a growth-promoting tether between opposed adjacent vertebrae. The endplate plunger includes resilient arm assemblies that store potential energy when the endplate plunger is in a retracted configuration. In transitioning from the retracted configuration to a deployed configuration, the potential energy is released in a burst of kinetic energy, causing tip portions at the distal ends of the resilient arm assemblies to be thrust into the adjacent vertebrae. In some embodiments, each tip portion forms a cleft in the respective vertebral endplate and deposits the tether therein. The tether is thereby anchored directly in the clefts, without need for separately formed anchors. In some embodiments, devices and methods are disclosed to route the tether through an implanted spinal implant.