How common is lymphedema?

Surprisingly common. According to lymphnotes.Com (http://www.Lymphnotes.Com/article.Php/id/401/), in the U.S., just within the medicare age population, the number of persons afflicted with lymphedema, or at risk of developing it, exceeds 6.8 million individuals. That would include all causes of lyphedema both primary (don't know the cause) and secondary ( due to cancer, radiation, surgery, etc.).
Unpredictable. Most people do not suffer long term lymph edema with elective surgery - unless the lymphatic system is already compromised before surgery. Lymph edema is more common when you have soft tissue problems such as crush injury, infection, cancer invasion, radiation or other complication involving host metabolic dysfunction.
Fairly common. Any swelling is lymphedema - very common after injury, inflammation - acute edema resolves quicker vs chronic which becomes a problem.