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On Thursday night, the Lakers will make their first return to Boston since their humiliating 131-92 defeat in Game 6 of the Finals last season. For both sides, the cast of characters looks remarkably similar.

Once again, L.A. will play without center Andrew Bynum, and once again, he won't be back for some time. That leaves the Lakers with the same starting five they had in June, and aside from upping Trevor Ariza's minutes and replacing Ronny Turiaf with Josh Powell, it leaves them with the same bench, as well.

The Boston side of the equation is mostly unchanged, too. The biggest difference is that sixth man James Posey is gone, and Tony Allen doesn't quite replace everything his predecessor provided. Also missing is P.J. Brown. Glen Davis has taken his place and is performing much better of late after a rough start to the season.

Those minor differences aside, the two sides will come in just as they did on June 17. So if something is to change, it probably has to be something that isn't easily seen from the outside.

And to change the result from a season ago, that something would pretty much have to be the Los Angeles defense. This is why Bynum was thought to be such a key for the Lakers -- with his presence clogging up the middle as he swatted away shots, L.A. seemed to have a much better shot against bigger, physical teams such as Boston.

That proved to be the case on Christmas Day, when the Lakers beat the Celtics to end Boston's 19-game winning streak, and has been the case for most of this season. L.A. has been in the league's top five in defensive efficiency all season. When combined with the league's top-ranked offense, that's a devastating combo.

Unfortunately, that elevated ranking depended on Bynum's presence, and he won't be in the lineup Thursday night. We can't even be sure he'll return this season.

L.A. has to make up for his absence with an improved spirit on D. Look back at last season's Finals, and you'll see countless moments when the Lakers' problem seemed to be not a lack of size or ability but mostly a shortage of intestinal fortitude. L.A.'s capitulation in Game 6 was the bottom of the barrel, but other moments in the series were nearly as egregious -- the coast-to-coast dunk the Lakers gave up to Leon Powe in Game 2, for instance, and the 83 points they surrendered in the final three quarters of their Game 4 collapse.

Unfortunately, the Lakers don't seem to have changed their stripes -- at least if you go by their results since Bynum went out. Yes, Kobe Bryant's 61-point game in MSG was amazing, but L.A. also gave up 117 points on 106 trips to the Knicks' middling offense. And in Toronto on Wednesday night, it was more of the same -- again, the Lakers' offense carried it to victory while the D permitted 107 points in 99 trips, and this to a team playing without a point guard.

Two games constitute a small sample, yes, but the results are not encouraging. If L.A. is to change last season's outcome in Bynum's absence, it has to change its stripes on D first. So far, we've seen little evidence of such a change happening. Although the threat of a Kobe onslaught will still give the Lakers a puncher's chance Thursday night, that chance seems unlikely to come to fruition unless they defend with a lot more zeal than they have in the past two games.

John Hollinger writes for ESPN Insider. To e-mail him, click here.