Abstract: Objective To investigate the isokinetic strength of knee extensors and flexors in patients with knee osteoarthritis (KOA), and to establish the correlation between the isokinetic strength and function in patients with KOA. Methods 23 patients with bilateral KOA and 14 matched normal controls finished the isokinetic test of knee extensors and flexors, the Five Times Sit-to-Stand Test (FTSST), Gait analysis, and Balance test. The KOA patients were evaluated with Visual Analog Scale (VAS) for pain and Western Ontario and McMaster University Osteoarthritis Index (WOMAC). Results It was less of the peak torque, average peak torque, average power, max rep total work, total work of knee extensors and flexors in the mainly involved limbs than the contralateral limbs (P<0.05), and more of the hamstring/quadriceps peak torque (H/Q) percentage (P<0.05) in the patients. It was less of all the observed indicators of knee extensors and average power of knee flexors in the patients than in the normal controls (P<0.05), and was more of the H/Q percentage (P<0.05). The peak torque of knee extensors correlated with the results of FTSST, walking speed, walking distance, falling index, VAS, and WOMAC-pain (P<0.05), but the peak torque of knee flexors did not (P>0.05). Conclusion It is weak of the isokinetic strength of knee extensors and flexors in patients with KOA in the mainly involved limb, as well as the isokinetic strength of knee extensors compared with the normal controls. The changes in the extensors and flexors are not equivalent. The peak torque of knee extensors significantly correlated with the pain and functions of the knee.

Key words: knee osteoarthritis, extensors, flexors, isokinetic muscle strength, function, pain