From October, 2015 to May, 2016, 42 old females with KOA were divided into two groups equally. They received hip strengthening (HS group) and quadriceps strengthening (QS group) for two weeks, respectively. The pain, stiffness and physical function scores of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were measured. Isokinetic strength peak torque (PT) was assessed for knee extensors and flexors, and 6-minute Walk Test was also evaluated. They were followed up two months later.

Before exercise, there was no significant difference in all the indexes between two groups (P > 0.05). Two weeks after exercise, the knee flexor PT (t = -4.038, P = 0.001) and 6-minute walk distance (t = -2.474, P = 0.022) increased in QS group; the pain, stiffness and physical function scores of WOMAC (t > 2.487, P < 0.05), the knee extensor and flexor PT (|t| > 6.370, P < 0.001), and 6-minute walk distance (t = -2.241, P = 0.037) improved in HS group; the scores of WOMAC were lower (t > 2.087, P < 0.05) and the knee extensor PT was higher (t = -5.028, P < 0.001) in HS group than in QS group. At two-months' follow-up, the drop-out rate was significantly lower in HS group than in QS group (χ² = 13.480, P < 0.001).

Hip muscles strengthening is a good choice for KOA in the early stage of treatment, which could avoid the pain in quadriceps training, increase quadriceps strength and improve physical function.