An implantable metallic spring designed to be placed alongside the spinal column to enable curvature correction and lengthening in children with early onset spinal deformities (e.g., scoliosis). It is a component of an implant assembly that uses two long rods, two small anchor rods, springs, and sliding bearings, whereby the spring-based distraction force drives axial displacement of one long rod with respect to the other to achieve continuous spinal correction and lengthening, without the need for post-implantation invasive interventions. It is placed over the rods along their axes, the rods filling the springs hollow lumens.