Re: Lower back sprain from not using Knees?
Can you see a physical therapist? A good therapist will help you figure out how to use your body mechanics the best that you can, given your limitations. A therapist will work out a good home exercise program for you to strengthen your core muscles, which should make it easier for you. There are also little things you can do to minimize the stress on your body, like repositioning the item to be lifted or using tools to help, such as a hook or strap.
Hope you can get some help.