I had surgery on my back six months ago. The surgeon used a device that screws into the bone to hold it in place. Everything was going well until last week when part of the device broke. My doctor told me that the bone had healed. What could have caused the screws to break?

Screws of this type can break after surgery. Screw breakage doesn't necessarily mean that the bones haven't grown (fused) together. The bone fracture may have healed, but the device was overloaded. This can happen with certain movements or excessive, repeated movements.