Doctors were among the more than 30 suspects arrested in a major Medicare fraud bust by more than 200 federal agents in New York, Louisiana, Boston and Houston.

Some of the businesses targeted in the raids gave patients "arthritis kits" that included heating pads and expensive knee and shoulder braces, the Associated Press reported. Even though the kits were unnecessary and many patients never received them, clinic owners billed Medicare between $3,000 and $4,000 for each kit.

Another scam targeted by federal authorities involved false billing for liquid food for patients who can't eat solid food. Clinic owners involved in the fraud never distributed the liquid food products to patients and, in some cases, billed Medicare for patients who were dead when they supposedly received the products, the AP reported.

This is the third major Medicare fraud action since May, when the U.S. Health and Human Services Department added millions of dollars and dozens of agents to deal with a problem that costs the country billions of dollars a year.