When a patient met the inclusion criteria and consented to participation, the study physician opened the lowest numbered envelope, which determined the group of assignment. Leech therapy was carried out as previously described and tested in our pilot study (11, 16). In summary, 4 to 6 medicinal leeches (Hirudo medicinalis, ZAUG GmbH,Biebertal, Germany) were applied once to the periarticular soft tissue of the affected knee, with preference to maximally painful points during examination and palpation.