Non union sternum after 4 yrs of valve replacement

I had an aortic valve replacement 4 yrs ago. My sternum has always hurt some but was told it was normal. Just recently I have been hurtling in my chest and short of breath.  A ct scan was done and shows non union sternum. Has anyone heard of this.  I see a surgeon on Thursday.  I exercise and eat healthy. Thought I was doing great