Spinal implants and methods of extending pre-existing spinal implant constructs. For example, one disclosed embodiment comprises a sensor for measuring an electrical characteristic of a power line, electrical generator, or electrical device; a network interface; a processor; and one or more computer-readable storage media storing computer-executable instructions. In various examples, the fastener includes a single stud rivet or includes a two legged staple. For saturation values of image points of the first type whose brightness values lie in the established brightness value range, a frequency with which these saturation values occur in the image region of the first type is determined.