Thank you very much for contacting healthcare magic. You have problem of constipation after knee surgery that may be because of inactive lifestyle. For treatment of constipation problem you have to modify your diet like..... Eat high fiber foods like whole grain,black beans... etc. Avoid gaseous foods like cabbage, cauliflower, broccoli etc. .... Drink more water. Eat fresh fruits and green vegetables. Avoid spicy foods and oily foods. Avoid alcohol drinking and smoking. Don t ignore to go toilet. After taking this much care still constipation problem is present than you can take bulk forming agent like psyllium or methyl cellulose. ... osmatic laxative can use like polyethylene glycol . I hope my advise helpful to you. Thank you very much.