You may not like this answer, but some of us have pockets of fat that resist diet and exercise. Like you said, you can weight 110 pounds & still have fat in pockets that won't go away. That's the beauty of genetics. I get frustrated when people say they are genetically predisposed to be morbidly obese....I want to tell them "No, you're not genetically predisposed to be morbidly obese, your're genetically predisposed to a have a certain body type that holds on to fat in certain areas, such as knees or hips or abdomen!" You can certainly trim down your knees through total body fat burning aerobic exercise & strengthen your leg & knee muscles through lower body strength training such as lunges & squats.
Liposuction is designed exactly for these pockets of fat that resist diet and exercise. Lipo is not the answer for weight loss, but it is the answer for fine-tuning your "trouble spots" once you've reached your target weight and are in top shape.