I'm not a believer in standard physical therapy, with its muscle-oriented approach, to treat PFPS (patellofemoral pain syndrome). So if I'm right, and it doesn't work, why then does it sometimes work? (Thus the paradoxical title of this entry.)
I think the easiest way to understand what's going on is through what I call the "socket wrench analogy."
Let's say you're trying to remove a nut from the end of a bolt. You're up on a ladder and you've spotted the bolt, attached to a brace that helps hold in place the rain gutter, which you're trying to rehang in a different location.
As any casual weekend handyman (or woman!) knows, removing the nut can be accomplished several ways. You can get a pair of pliers, squeeze the jaws around the sides of the hexagonal nut, and try to loosen it. Or you can use a socket wrench, a tool that has various snap-on pieces that fit various-sized nuts. A socket wrench is expressly designed to loosen and tighten nuts.
Here's what will happen if you reach for the pliers: In a certain number of cases, you'll succeed just fine. Pliers aren't designed to remove nuts from bolts, but they'll do the trick in a pinch. But then sometimes you'll come across that hard case, where the nut is stubbornly frozen. Using the pliers, you stand a good chance of not only failing but stripping the sides of the nut, thus making it almost impossible to remove some other way.
Now, with the socket wrench, you stand a much better chance of achieving your goal. Because this tool is specifically designed for the task.
So if your success rate with pliers is 55 to 65 percent, then your success rate with the socket wrench would be higher, maybe 90 to 95 percent.
With PFPS, if the success rate with standard physical therapy is 55 to 65 percent, then I would estimate that with a joint-focused approach, it would be significantly higher.
Standard physical therapy tries to save your knees through your leg muscles. I think it does work sometimes, and I suspect it works best for the milder cases of PFPS (just as that pair of pliers will remove the nuts that aren't too stuck). Strong legs do protect weak knees, so it's not as though having stronger muscles is a bad thing. Quad-strengthening exercises may overtax a weak knee, but if the joint isn't too weak (as with mild PFPS), perhaps no damage will be done.
Once you get a hard case of PFPS though, I bet that standard physical therapy often fails. Why? It's the wrong tool to fix the problem. Your problem isn't your leg muscles; it's your joints. So why not apply the right tool (joint-friendly exercises) in the first place to fix what ails you?