Amir Johnson found it hard to find an available jersey number with the Celtics

The Boston Celtics have retired 21 jersey numbers, a record for a North American sports franchise and a mark of the team's tremendous success in obtaining 17 NBA championships and 21 conference titles. It's something to be proud of for the franchise, its fans, and anyone who has ever been involved with the Celtics.

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But there's a dark side to that rich history — new Celtics can have a really, really difficult time finding a suitable jersey number. With most of the standard basketball numbers taken by existing players or retired for all-time greats (in some cases because legends like Bill Russell popularized those digits in the first place), offseason additions such as veteran big man Amir Johnson must dig deep to find numbers that hold special meaning in their lives.

Johnson's journey ended with No. 90. How did he settle on such an odd choice? Adam Himmelsbach of The Boston Globe has more (via Reddit):

“Every number 1-34 is basically retired. My first initial number, I picked No. 5, but I know there was going to kind of be some controversy with that because Kevin Garnett won a championship. So I knew that was pretty much out the water. My number [15], of course, was retired. And I recently posted a picture on my social network, I don’t know if you guys checked it out, it was a team back in the ’90s, like ’97, ’96, I played for my first organized basketball team, which was the Burbank Celtics. It was a Celtics team. So I just kind of just put that together. The ’90s were good. I was born in ’87 but the ’90s were good.”

And here's that photo of Johnson as a young Celtic:

Johnson is close — 17 numbers from Robert Parish's 00 to Reggie Lewis's 35 have been retired, so he had few choices not already taken by his teammates. He could have gone with No. 30, the closest multiple of his favored No. 15, but I suppose that's just a pale imitation of the real thing.

The result is that Johnson has picked a jersey number that stands in for an entire decade, which are probably just as good reasons as any others. At the very least, we cannot accuse the 10-season veteran of unoriginality. No Celtic has ever worn No. 90, and only P.J. Brown and Roy Rogers Jr. have ventured into the 90s.

Perhaps Johnson can make No. 90 his own and lend an unlikely jersey some cultural cachet. If that doesn't work out, though, then he'll have a chance to impress the man in control of No. 15. Celtics legend and longtime announcer Tommy Heinsohn does usually take to gritty, hustle-minded players like Johnson.