"I've got arthritis, there's nothing you can do about it" 

If I had a dollar for every time someone..........

As long as I didn't have to fork out a dollar for my response: "how long have you been like this for?"

Osteoarthritis/degeneration/wear and tear (as distinct from inflammatory arthritic diseases) is part of the ageing process and in some people and some joints it happens faster than in others, sometimes for a reason, but often for no reason. The only way any of us will avoid getting it in every joint is if we die before it happens!

It doesn't necessarily mean you can't be helped via Physiotherapy. Sure, we're pushing uphill in someone who has central canal stenosis and has had gradually increasing leg pain over years. Or someone with no chondral cartilage in their knee. 

But what if their pain level has spiked only recently? Maybe via an incident or not but if they've only been adversely affected for a month or less I start to get interested.

The injury almost certainly looked the same on x-ray, CT or MRI three months before. If they weren't too bad before they flared up, then it's not just their radiology or, logically, they should have been crummy back then! There's a good chance joint stiffness and/or weakness for whatever reason is now contributing to their increase in symptoms.

Joint stiffness we can change.

And of course muscular/proprioceptive support via increased strength around a joint will always have value in the patient prepared to put in, as instructed!