I feel a bit silly telling this since you are the medical doctor and I am not, but there are smaller solutions than the plate and screws. For a collar bone ruptured near the middle, the surgeon uses a wire to attach the two pieces together. That is far less invasive surgery and may even be removed under local anaesthesia in some cases. That may be a better solution for a rib bone.
There is another problem I was warned about: the capacity to synthesise Vitamin D from UV diminishes with age, so that it may be insufficient even under the California sun. Maybe a moderate additional supply of Vitamin D would help you better regrow that rib bone?
