If this Celtics season had any sort of turning point, it came Jan. 27. The Miami Heat had brought their talents to TD Garden. A national television audience tuned in. And the Celtics were down a key player, one of their leaders. But, in front of a leather-lunged crowd that spent much of that Sunday afternoon on its feet, the Celtics, without Rajon Rondo, fought to an emotional double-overtime win. Including that game, the Celtics have won 16 of their last 22, reversing a season that before the Miami game seemed headed nowhere, as Boston’s record then sat three games below .500. That win also began an 11-game home winning streak, the Celtics’ longest such streak since they won 13 straight home games during the 2008-09 season. But Miami soon began its own streak. After splitting their next two games, the Heat kicked off what has stretched into a 22-game winning streak, tying them for the second-longest streak in NBA history with the 2007-08 Houston Rockets. (The longest is 33 games in a row by the ’71-72 Lakers.) Monday night, Miami and Boston reunite in TD Garden. A national television audience again will tune in. And the Celtics, already short Rondo, again could be down a key player, another leader, as veteran center Kevin Garnett is questionable to play because of a left adductor strain. Coach Doc Rivers said that Garnett, who missed Saturday night’s game and didn’t practice Sunday, is “50-50 at best” to play because of the injury, which is located in the thigh area. Rivers stressed that the injury wasn’t that serious, “but it’s just a point in the year where you’re not going to play him if he’s not feeling great.”