Weak in the knees

HUBLOTIs "weak in the knees" correctly used here?

No.
You can say: "By the time we got home, my knees were aching."

For the idiomatic expression "weak at the knees", which does not fit the context above, have a look here:

'Weak in the knees' is possible. COCA has 54 citations.

Thanks a lot, teechr and 5JJ.

Does "weak in the knees" sound right in the dialogue to you, 5JJ?

HUBLOTDoes "weak in the knees" sound right in the dialogue to you, 5JJ?

If I may **** in, it only sounds right to me if it's intended to mean that Lucy was emotionally shaken in some way on the hike—by being chased by a bear while on the hike, perhaps? Or, less likely, by being overcome by the natural beauty of the area she hiked in?

Having sore knee

CJ is right. When you're weak in the knees, you feel that you'll collapse because your knees aren't steady enough to hold you upright, but the reason lies with a mental shock not with any problem with ligaments.

HUBLOTDoes "weak in the knees" sound right in the dialogue to you, 5JJ?

It does to me. In fact, I used exactly those words to my wife yesterday, when I declined her invitation to go up to the top of yet another tower for yet another splendid view. However, I seem to be in a minority here, so perhaps there aren't many of us left who would say this,

Thanks a lot, everybody!

If Lucy had been physically tired, should she have said "By the time we got home, my knees were wobbling"?