Federal and media watchdogs have for years been exposing Medicare scams involving power scooters and wheel chairs paid for with tax dollars and given to people who don't medically need them or who use them for convenience instead of walking. So how can the fraud still be happening?

Of 100 prescriptions reviewed by the Department of Health and Human Services' Inspector General, 47 were given out wrongly, often because a doctor had never even seen the patient. Medicare pays more than $500 million annually for an estimated quarter million wheelchairs, power scooters and related products.

The sample of 100 was limited to cases where billing codes showed that Medicare hadn't paid a doctor for an exam in addition to paying for the wheelchairs, which cost $2,400. It also excluded $84 million in payments that raised red flags for a variety of other reasons.

That left $87 million in payments, or about 15 percent. In the sample of 100, the nearly half where a doctor hadn't seen the person, or didn't provide evidence that he needed a power scooter or wheel chair, would represent $35 million, according to the inspector general.

Even that was not the full extent of such payments. Other reviews have highlighted doctors that see dozens of patients a day for cursory exams that almost always prescribe Medicare-paid scooters or wheelchairs. And none of those totals include Medicaid, which pays for medical services for the poor.

"Previous Office of Inspector General reviews found that a high percentage of PMD claims were un-allowable because they did not comply with federal requirements," the inspector general said.

HHS "did not require [durable medical equipment] Medicare contractors to match suppliers'" claims with physicians' records to identify claims. In 19 cases, the doctor never met with the patient.

In five of the 100 cases reviewed, wheelchair sellers produced fake doctors' signatures. One wheelchair seller concocted notes about a wheelchair exam and added them to unrelated checkup notes.

In 28 cases, the doctors didn't say why a less expensive alternative like a cane or manual wheelchair wouldn't work, or why the patient truly needed it.