Arguably the most important part of arthritis treatment is working the affected joints through their entire range of movement and stregthening the supporting muscles.
The frog legs is an exercise that achieves both of these for both the hip joint and knees.
It is very important, as knee joints wear to keep the inner leg muscles strong especiallly if there is also a problem in the hip. this is because the muscles on the outside of the leg will be favoured. This results in flabby muscles their and a lack of support for the inflamed knee joint.