The researchers assigned patients at random to receive either leech therapy or treatment with diclofenac gel. The leech therapy patients had 1 treatment session during which the researchers applied 4 to 6 leeches to the affected knee. The leeches stayed on the knee until they detached themselves (about 70 minutes), and then patients rested the knee for 12 hours. The researchers instructed the diclofenac group to apply the gel to the affected knee at least twice a day. Patients could use other oral osteoarthritis medicines as needed. After 3, 7, 28, and 91 days, the researchers measured patients' pain, stiffness, and function by using standard questionnaires.