Knee osteoarthritis is serious epidemiologic problem. Knee prosthesis is successful treatment for many of patients with advanced knee osteoarthritis but there are important numbers of patients, which are not appropriate candidates for such surgery treatment. For them ,any treatment which could relieve pain in their knee would have good impact on quality of life. Adductor canal block is successfully used for relieving postoperative pain after knee surgery. Official approval from ethics committee of Republic Slovenia was obtained for this study. After being informed about the study and potential risks, all patients giving written informed consent will undergo an orthopedic examination and those with confirmed diagnosis of knee osteoarthritis lasted more than 6 months will be included in the study. Prior to start they filled Knee injury and osteoarthritis outcome(KOOS) form and estimate maximal and minimal intensity of pain in the knee .They repeat self assessment of pain at the same manner using 11 point numeric rating score(NRS) 1 week and 1 month after blockade.Measurement of maximum voluntary isometric contraction of quadriceps muscle (MVIC) ,time up and go test(TUG) and 30s chair stand test are performed by physiotherapist before block of adductor canal on the ipsilateral leg ,1 hour,1 week and 1 month after block..Block of adductor canal is performed by the same and trained anesthesiologist at the proximal part of the leg using 14 ml of Levobupivacaine and 100 mcg Clonidine mixed in the same syringe.At the conclusion of study patients filled the Knee injury and osteoarthritis outcome(KOOS) form once again.