At first the hospital issued him a very basic one, the type with small wheels on the front legs and tennis balls for feet on the back. He found this walker cumbersome when dealing with uneven surfaces, however.
We upgraded him to one with much larger wheels and hand-operated brakes. The model we got was the "Ultra-Light Rollator", made by Medline and distributed by Walgreen's.
This was a huge improvement. He found it much easier to navigate around obstacles and more secure to lean on, but it had one flaw. The walker folds easily so it can be stowed in the back seat or trunk of a car. However, there's nothing to keep it folded. It tends to unfold while the user is trying to pull it out of the back seat, making the operation difficult for someone who already has mobility problems.
This simple project adds a 3D printed catch which locks the walker in the folded position. It is sized so that only a little pressure is need to latch or unlatch it. It was printed in ABS plastic on the MakerBot Replicator using 2 shells and 10% infill. (I made it at TechShop. www.techshop.ws) It attaches to the frame of the walker with a single zip-tie.
Although the design is extremely simple, the result is a big increase in usability for the patient. And the 3D printed part makes a difference, too. I originally made a temporary catch from coat-hanger wire. It worked, but the 3D printed version is easier to operate and doesn't rattle when the walker is moved around.
The CAD file is attached, in Autodesk Inventor format and as an STL file.