If your dog is having difficulty using his or her back legs, there are several things you can do to help. First, take your dog to the vet for a checkup to rule out any medical causes of the problem. If no underlying health issues are found, there are a number of ways you can help your dog regain strength and mobility in his or her back legs. One way to help is by providing physical therapy exercises for your dog to do at home. There are many different exercises that can be helpful, and your vet or a professional physical therapist can show you how to properly perform them. Another way to help is by providing nutritional support in the form of supplements specifically designed to support joint health. These supplements can be found at most pet stores or online. Finally, it is important to keep your dog's weight at a healthy level. Excess weight can put unnecessary stress on joints and muscles, which can make it even harder for your dog to use his or her back legs. If you are unsure about what a healthy weight is for your dog, talk to your vet. With a little help, your dog should be able to regain strength and mobility in his or her back legs in no time!