Disobedience causes scare

Every parent faces the issue of telling a child not to do something, and the child disobeys.
Recently, disobedience led to an emergency room visit and x-rays.
My youngest child blatantly disregarded both my husband and myself in our instruction to NOT climb onto our garbage can.
The child was barefoot, as he prefers to be. We happened to be outside, watching the approach toward the green can that stands approximately four-feet tall.
Our response was to tell the young man, "Do not climb up there!"
We repeated our command several times, and he proceeded to do exactly as we had instructed him not to.
All is fine up to this point, and I approach the child in order to remove him and discipline him from the garbage can. Before I reach him, he jumps from the can to the uneven ground beneath him.
He complains at this point. His foot hurts, but he says he is okay.
This kid is tough, and he has apparently done this many times before, he let me know.
I administered discipline I had originally intended for the disobedience, receiving his complaint in return, and he resumed his activities of playing with the other children.
Problem taken care of, my husband and I return to the confines of the house.
Later, our son goes into the house and tells us his foot "really hurts."
I place an ice pack on it and give him a children's Tylenol.
The following morning, my husband informs me the foot is swollen, and he will not be going to daycare.
I figure, "This too shall pass."
After running over the different scenarios as to what diagnosis a doctor might have for that swollen foot, I decide I need to at least have the foot examined.
I take him to the local hospital after work and have the foot x-rayed in case any of those tiny little bones in his foot might have a break.
Children have growth plates in their feet, and I have been told that injury to a growth plate is very serious. And, in such a case, surgery is some times necessary.
Fortunately, the results of the x-ray did not show any breaks. The physician informed me that I did, however, make the right decision because the damage could have been very bad.
Another measure of being blessed is that bones in children's feet are very flexible.
So, my son was able to leave with instruction to give him Tylenol if the foot bothered him. It was just soft tissue damage and the foot will be tender for a while. But, otherwise he is fine.
What I am not fine about is the fact that I would have to go to such extremes just to ensure my son's antics don't cause him serious injury.
It is frustrating to be a parent.
But, the child's response to the whole matter would be cute if I weren't so upset with the incident. He said, "Mom and Dad, you were right. You are the smartest parents in the world."