just need some advice

My doctor that I have been seeing, Has a rule. you have to loose 20lbs before surgery, or he wont do it. My problem is I am on a 1200 calorie diet: and I have a blown out knee. So even though I am following the diet, I cant loose the weight, because i'm not burning the calories. I push myself as far as possable, but I have only lost 4 lbs in 5 weeks.