I have planted a brussels sprout before and it turned in to a whole plant (but bolted straight away ... presumably because it's an annual and the hormones for flowering were already activated)
I assume you mean when you buried the whole stem? Amazing idea either way - a good chance of an immediate crop of sprout 'broccoli' - which I love.
If it was a bought sprout then you can get seed of a variety that might be new (especially if they're red) - and you've tested its flavour. If it's home grown you're getting fresh seed - without being stuck with a manky 100x60cm plant that's probably in the wrong place.
If you bought the stem then the same advantages apply, it's still a great idea for dealing with the leftovers, and well worth the experiment. This thread can be read as meaning they have a reasonable chance of rooting and sprouting.
I may experiment with this year's home grown stems to see what chances a bought stem might have next November when they appear in the shops. I might even pop into the big posh food halls in the city to see if there's a wider range (they are a good source of anything unusual or special - you can often get red Jartichokes etc. to plant and delicious stuff to eat, like yellow pitaya fruits [with tiny but viable seeds for friends in warmer climes] and yellow passionfruit [that are just as nice with their mandarin background flavour as the normal ones that are hyper-raspberry flavour]).
Ideally you'd leave any damaged or immature sprouts on there for a quick result (you wouldn't want to mollycoddle the stick for a whole year - unless there was some chance of more sprouts). Maybe you could cut just the bit of the sprout that goes in the pan - in my house that would leave quite a few buds behind for every sprout taken.
It's crazy- I've been smashing the stems with a lump hammer so they will rot in the heap, but by doing that I was throwing away food that's actually fresher than what I paid for!
What's even more annoying is I found some sticks of a lovely red sprout in Lidl last Xmas - I love red sprout broccoli even more!
I understand that this type of epiphany is what they now call "life hacks" - maybe we should have a new category for them?
Cheers.