How can I prevent swelling on my ankles due to lymphedema (caused by abdominal surgery)?

Compression. Lymphedema is cause impaired circulation of lymph. Normally the compression of muscles propels the lymph through lymphatic system, however if the is obstruction it need extra help. That can from compression stockings, lymphatic massage, or compression boots or pumps that inflate. All of these things give an extra boost to lymph circulation.
Compression hose. These problems are best dealt with in lymphedema clinics...All large cites have these clics attached to university medical centers...Compression hose in the 40 mm range should be of benifit if applied before getting out of bed and taken off only when back in bed at night.
Lymphedema treatment. As drs. Wright and bein said, the treatment is manual lymphatic drainage, compression stockings, decongestion exercises, weight loss (if needed), and intermittent pneumatic compression. Sometimes inelastic compression works better and is easier to use than compression stockings (see www.Circaid.Com). It is important to see a lymphedema therapist for treatment, education, and other recommendations.