Why do I set off airport metal detectors after my surgery? Don't want to do my BBL before clearing this up.

I was set to get a BBL in November 2016. In August, I learned I had large fibroids and had open surgery that month to remove them. I postponed by BBL until late January 2017 to give my body healing time. Over the holidays, I did some traveling and on 3 separate occasions, I set off the AIT screening machine (the one where you lift your arms over your head). Each time, it highlighted my left groin area. Why do you think this happens? Should I get an xray? Don't want to do my BBL before clearing this up.