biotherapy with leeches

Patients with arthritis of the knee joint are in constant pain and sometimes even have to take morphine. The regular use of leeches could free 60% of these individuals from pain for at least a few months. To treat such a patient with leeches the doctor places three to 12 of these little vampires on the painful sites and waits until, after about a half an hour, the animals are satiated and fall off.
Are leeches just disgusting or are they useful?