Riddle Me This

What, precisely, are five-year-old boy knees made of?

(Hint: skin, bones, and cartilage is the wrong answer.)

I can't say for sure, myself. But this I do know: from almost exactly the moment he turned five, Son has been busting through the knees of his pants legs as if his pants were made of butter and his knees were hot knives. Seriously, the rate of decay of brand-new blue jean knees is something deserving of a Guinness world record -- if only I knew whom to call to show this off.

In the past few months, I have patched blue jeans and heavy cotton twill pants. Multiply. Carefully. Using heavy denim patches, and numerous rows of stitching. Yesterday I noticed that even the most recent patches are disintegrating. If I didn't know better, I might think his knees are actually radioactive.

Just this morning, I found the beginnings of a hole -- a threadbare patch in which only the horizontal fibers were remaining -- in a pair of canvas army pants. These particular pants even have gussets in the knees (you know, those seams stitched halfway across the knee region, to make the knee a tiny bit baggy), which in theory would be just the thing to combat Pointy Knee Syndrome. And yet, they too are failing.

Yesterday, he tore a horizontal slash across the knee of a favored pair of corduroys.

There seem to be no pants immune to the scourge of the razor sharp knees of this child.

Here's what else I don't understand. Daughter has blue jeans that she inherited from Son, some of which he had inherited from the older sons of our good friends. THOSE four-children-later blue jeans are still intact. I can't figure it out. It's not clear to me that my two children play that differently. There seems to be something particular that happens on a fifth birthday that makes the difference, though, since his knees did not have this particular sword-like property when he was younger.

Hence, I am at the point of hiding the one pair of inky dark blue jeans Son has that don't yet look like Swiss cheese, just so he can have one intact pair of pants to take with us on our trip to New York. We're not leaving for a month, and it seems a shame to waste a whole month of chilly weather without letting him wear these presentable jeans. But I cannot bear to buy another pair of blue jeans before we leave, and it is absolutely certain that if these pants go into the rotation, they will not last a month in a contest with those particular knees.

The knees always win.

So here's what I want to know: is there anything I can use for these patches that will make a difference? Should I be lining his pants legs in lead? Will he outgrow this?

And, the $64,000 question: once we get into shorts weather, and whatever is forming the abrasive force on the other side of his pants legs is going head-to-head with his knees, will his knees finally lose? Is my choice knee patches or ER visits?