My husband is a disabled vet who's been fighting a bad leg for 40 years. Finally had to amputate at the hip in October as they found a big cancer blob in it. He won't get a prosthetic until spring, so he's in a chair, or walker, or crutches for now. This pants modification lets him carry stuff around without an extra bag and looks way better than safety pins, or a big knot.
This should work for any amputation at knee or above. Not sure there's enough pant leg left for lower amputations.
Warning - This project requires sewing with a machine or by hand. Sewing uses sharp pointy things like pins, needles, and scissors. The writer is not responsible for any damage you do to yourself or your customer or your customer's pants.
Step 1: Test Pin for Fit
Fold pant leg up with 3 folds and pin at top outer edges. The bottom/ankle level fold should be fairly short. Work with your customer to get a comfortable overall length and crotch to top edge length. To long and it will flop around and get in the way while moving. To short and it will be to constricting and the pocket will be to little. Measure/mark lengths, pin points, and fold lines.
For my customer, we already had all his sweats pinned at his preferred length, so I just went with that. If your customer hasn't done that, pin the pants and have them wear them around for a couple of days to make sure they are right. Folded pant legs do weird things when in a wheelchair and transferring.
MAKE SURE YOU ARE WORKING ON THE CORRECT LEG! (Yes, I did the wrong leg the first time. He had pinned them himself and was wearing them backwards. Sweatpants do weird things when there's only one leg in them.)
Step 2: Stitch the Ankle Fold
Take out the test pins. Turn the bottom of the leg inside out, lay flat and stitch across at the ankle fold line. Back stitch the start/finish to reinforce. This stitch line forms the bottom of the pocket.