When someone has arthritis of the foot, it can be difficult to treat because it’s hard not to use your feet. If medications and nonsurgical treatments don’t work, the next option is likely surgery. But to be able to rest the foot well enough for good results, the person must be able to move around without weight bearing and this usually means crutches. If someone doesn’t have strong enough arms or good enough balance, this can be difficult, if not impossible. Even if your father was to use a wheelchair after surgery, you do need strength in your arms to propel the chair.
It may be that this is one reason your father’s doctor is talking about exercising and increasing strength. The best bet is for your father or you, if your father permits, to ask the doctor the reasoning and what specifically you can be doing to increase the chances of a successful surgery.