An extender system is configured to couple a vertebral bone anchor that has been previously implanted in a vertebra, or is newly implantable in a vertebra, to an adjacent bone, which can be an additional spinal level or an occiput, for example. The extender system includes an extension member having a body and an engagement member coupled to the body. The extension member defines an aperture extending through the engagement member. A screw is configured to attach the extension member to the vertebral bone anchor. The extension member can be fastened to the adjacent bone.