Andy
I had a friend shatter a forearm and, as part of the repair, get an electronic growth stimulator. Sounded pretty bogus to me so I slogged through the scientific literature (I've got the background that I can do that). The results were interesting and positive, though they still aren't sure of the details of what is going on. Informed speculation is either
1) a weak alternating current gives the bone growing cells an axis to align with (as opposed to growing in random directions which they usually do) so they grow more quickly along the line of current flow, or
2) the A.C. causes the cells to be more active and grow faster.
Most likely some mix of both. The surgeons align the flow along the direction that needs to heal first and bone grows that direction fastest. Be glad you've got a more recent version of the stimulator. The original Russian version had stainless electrodes driven directly into the bone from the outside and you were attached to a signal generator. Made Frankenstein's Monster seem plausible.
Jim