You're discovering why pots with narrow necks are a pain in the long run. I've ended up smashing a pot in the past. It won't hurt a robust wisteria to cut roots if necessary.

If you mean for the plant to remain viable, and in reasonably good vitality, you'll need to be proactive and repot the plant. Root congestion begins to limit vitality at the approximate point in time when the root and soil mass can be lifted from the pot intact. As root congestion increases, growth rate and vitality decreases in a direct relationship until such time as the plant is so weakened it will be taken by insects, disease, or it will simply run out of the energy it takes to keep its systems orderly and succumb to the stress.

In a necked-down light purple pot that happens to be a favorite. From a cutting, I started a species of potentilla that will form a single trunk (sp fruticosa). It's highly unusual in that it produces light purple blooms, which are nicely complimented by the shade of the pot. It's become a very nice bonsai, and one of my favorites. Because of its unusual bloom color, I wouldn't want to lose it, so come spring, I plan on breaking the pot.

Your plant is naturally vigorous, which is a genetic trait. Given the right conditions, it's a plant that's hard to stop and quick to recover. Vitality (or 'health', if you prefer) is not a genetic trait. Vitality is a measure of how ably your plant is dealing with the current cultural hand its been dealt. Since the tendency will be toward decline in vitality as the root congestion increases, I would suggest you separate pot from root/soil mass and get after fixing all the root issues before the plant awakens in spring. You might be able to do that w/o breaking the pot, but there's no way to tell w/o a sense of what you have to deal and work with.

This is a Hyde brand scraper you can find at most paint stores. I have ground down the bottom straight edge so it's radiused, and honed it so it's very sharp. It's made of spring steel, so it holds an edge quite well. I push the tool along the outer edge of the pot to cut through roots and free up the root/soil. I just thought of something. An offset frosting spatula used to ice cakes would be very flexible and should work well - especially if it's sharpened so it will cut roots instead of mangle them. See one

Al