I've had problems with my sternum ever since I rearended someone on a major highway because there was a ladder in the road(strap down your ladders properly or I will rip your tongue out through your *******). I locked my arms on the steering wheel and I don't think my chest even touched the seat belt. Ever since then, if I stretch my arms too far back, my chest will pop and I feel a deep pain across my sternum. I have wondered if I split it in the crash and keep resplitting it when I stretch. If it gives you any comfort, I have this happen often and the pain is relentless. I also doubt this will ever go away as this was over 4 years ago.