Judging by the stake visible among the stems it was originally being trained as a standard. I've never gown one of those so maybe someone else will come along and help you rejuvenate it. Alternatively you could give up on the standard look and give it a sturdy trellis and Google pruning Wisteria as a vine.

Once it is fully leafed out you can safely cut out any dead bits for starters.

Where are you located? Somewhere a lot warmer than here as mine are still dormant and it'll be almost a month before we will see flowers on ours!

Both our Chinese and Japanese ones are grown as standards, which makes them much easier to prune and control. It looks like that one is out in the open away from anything it could latch onto and overwhelm...? If so, that's a good thing which would also make it easy to see and remove root suckers.

The stake is definitely inadequate! You need a very sturdy wood post (e.g. 6" diameter sunk deeply) or a strong metal one (e.g. 3/4" or sturdier angle-iron sunk deeply - our Japanese one is supported between two angle-iron posts.)

See if you can lift up the fallen part of the trunk - they remain surprisingly flexible.... If you can lift it into a vertical position, and if you can install a suitably sturdy support, I'd try to re-establish it as a tree. Once you get it up and supported, I'd cut a lot of the skinny growth back hard. Can you see a bulge near the base that would indicate a graft union? If there is no obvious graft union, perhaps this is a seed-grown plant - but at least the flower says that it has an attractive flower and the plant is mature enough to flower. If you can see a graft union, remove any shoots/stems that arise below that point.

Cutting it back will result in an explosion of new growth! There are very detailed - fussy - instructions for pruning/training wisteria. I ignore most of it :-) The Chinese wisterias - like yours - that do the showy flower display in spring before most of the foliage emerges display well when encouraged to form flowering wood from 'top to bottom'. So simply pruning most of the whippy, curly new shoots back to 6-10" will promote lots of flowering wood - and most likely prompt a secondary flush of flowers in summer too. We prune the new growth on ours almost every week when it's growing! Long-arm pruners are an essential tool! Once the leaves drop in the fall, we remove and discard into the garbage all seed pods in order to prevent seeding around.

Wow, thanks! I could tell the stake inside was too small; the vines had grown around and broken it in several places. I just hadn't got that one pulled out yet. I don't know when the previous owners staked it originally. We are in central Indiana, USA, right on the line between zones 5/6.