We needed some sort of leg brace for Tiny Tim to go along with the traditional crutch. The leg brace needed to be easy to remove by an actor onstage (as Bob Cratchit helps Tim get ready for bed), be adaptable to our two different child actors (with a 4" height difference), and be durable (the theatre is planning on bringing this show back year after year).
While searching google I found this image which served as my inspiration. The leather straps and the wooden base are just what I was looking for.
I bought three similar brown leather belts at a thrift store for $1 each. I stained some scrap lumber and bought a small strap hinge for the knee joint.
The joint looked far too open with just the strap hinge, and didn't really give the appearance of a supportive, functional medical device. I went back to the hardware store and found this sliding hinge. It is designed to support the lid of a box or trunk. After some tinkering to remove pieces that controlled the speed and direction the hinge could slide (prevented the hinge from sliding past 90 degrees) I screwed it on.
The brown leather belts were all cut long enough to go around the boy's legs and then I drilled new holes for the belt buckles (use a bigger drill bit than you think as the leather will stretch around the bit and close back on the hole). I used extra screws to screw the leather to the wooden base, an then stained it all dark.