What can I do to help my hunched back?

It sounds unusual that you lost so much weight and muscle mass as a result of the hip replacement surgery. Were there complications to the surgery and did you happen to be sedentary for a long time after as a result? Or is there something else going on medically? Regardless, it would be good to speak with a dietitian about what the best foods are to help you build muscle mass. I would also make sure you tell your physicians of this loss of weight and muscle mass. There are a few simple things you can do to help your hunched back. Whenever you are in a static position over time (like sitting watching TV or sleeping) make sure you are supported in such a way that you aren't encouraging that rounded curvature of your spine. So don't use too many pillows to prop your head up at night, and make sure you have good low back support in your chairs so you can sit with better posture. Exercises that emphasize core strength and stability would also be helpful for you, such as yoga and pilates. It is important for you to stretch your chest/pectoral muscles and to strengthen your back and shoulder girdle muscles. Exercises with the foam roll can be helpful if you can tolerate lying on it lengthwise. If you really are leaning over quite a bit, you may want to consider a cane to help counteract this force of gravity. It would be best to meet with a physical therapist to make these decisions and to review these exercises so you are doing them safely and targeted toward your needs. Best of luck to you.