We know this is shaping up as a really good year in the Big Ten.

How good? A month before the teams gather in Indianapolis for what ought to be a raucous conference tournament, we don’t know.

Will the Big Ten, which had three teams ranked in the top five until early January, finish what it started? That’s going to be the big March Madness question for the Big Ten, which has a pretty good claim to being the nation’s best league. For now.

That’s one of the perils of having a really good top-to-bottom league: Supposedly lesser opponents can sneak up on you. Or flat-out punch you in the mouth.

When they were jumping out to a combined 49-1 start, Michigan State (18-1), Ohio State (15-0) and Wisconsin (16-0) all seemed to have Final Four credentials.

Then the Spartans lost two of three, the Buckeyes lost four of five and the Badgers lost five of six.

Give Michigan State, with a set of injuries that would have broken a lot of teams, a world of credit for staying on track. If the No. 9 Spartans, led by top Big Ten MVP candidate Gary Harris, can stay healthy, they have all the ingredients to put Tom Izzo in his seventh Final Four.

The situations of No. 22 Ohio State and No. 21 Wisconsin look more basic. With Aaron Craft on guard, the Buckeyes are only allowing 58.9 points a game, tops in the Big Ten. But they are ninth in scoring (71.9) and don’t have a proven go-to guy when they need a basket.

The Badgers, meanwhile, have a more versatile offense than Bo Ryan usually puts together. They have shot the three well, and major freshman-of-the-year candidate Nigel Hayes adds a needed front-court dimension to a team that can score a lot of different ways when it’s in a groove.

Wisconsin’s flaw? Its usually stout defense gave up nearly 78 points a game during a three-game skid, and then it was beaten at its own buttoned-down game by Northwestern and Ohio State.

When all the games have been played, NU’s 65-56 win at Wisconsin on Jan. 29 will remain a great example of the Big Ten’s balance. Is the Badgers’ loss to a team they had led 40-14 at halftime on Jan. 2 a sign of Wisconsin’s vulnerability or the Wildcats’ improvement?

The answer will have a different spin when the Badgers have taken their shot at putting Ryan in the Final Four for the first time.

What’s pretty clear now is that this is a banner year for Big Ten depth. When NU, rallying on defense behind Drew Crawford’s All-Big Ten-caliber leadership, gets off to a 5-5 league start, when Nebraska can win four of six, when Penn State can put together a three-game winning streak, those are solid accomplishments.

What’s really intriguing is that the league’s other top-25 teams, No. 15 Michigan and No. 16 Iowa, look like they have the ingredients to go deep in March.