Nathan Horton, as usual, had a giant smile on his face.

So did a lot of other people around the Bruins yesterday afternoon at the United Center, where Horton was a surprise participant in the B’s off-day practice before tonight’s Game 2 of the Stanley Cup finals.
Horton skated on a few line rushes with regular linemates David Krejci and Milan Lucic (with Tyler Seguin alternating in for a few reps), and appeared to be able to handle and shoot the puck fine. He did not speak to reporters after practice.

Horton, of course, left Game 1 near the middle of the first overtime, when a seemingly minor bump with Chicago defenseman Niklas Hjalmarsson aggravated a left shoulder subluxation initially suffered in an April 20 fight against Pittsburgh’s Jarome Iginla.

Needless to say, that injury has not been confirmed by team officials — who truly do not know whether Horton will play tonight.

“We won’t know (this) morning, either,” said general manager Peter Chiarelli. “You see him in practice (yesterday) and he got some (shots) off. But I don’t know what’s going to happen.”

After he was knocked out of Game 3 of the 2011 Cup finals by a concussion and missed last year’s playoffs with another concussion, Horton is hungry to stay in the lineup.

“I would think so,” said Chiarelli. “Hopefully Horty will find a way to play. I understand if he can’t. I mean, he got injured. At the end of the day, it’s the player’s call. I do think this is a case where having the extra two days helps.”

Chiarelli also said part of the decision-making process is weighing the potential value in holding Horton out of Game 2 — if the two extra days of rest and healing might allow him to play the rest of the series’ games.

NHL players have been known to play with shoulder subluxations. The shoulder may be heavily taped, limiting the range of motion and hopefully preventing the joint from dislocating again. And, although no one speaks about such matters, there could be one or more painkilling injections involved.

The term “Dr. Feelgood” was heard in numerous conversations at the rink yesterday.

Horton is certainly a key to the B’s Cup hopes. Despite sitting out the final six games of the regular season after he hurt the shoulder, Horton has enjoyed a sensational playoffs — with seven goals, 17 points and a plus-22 in 17 games.