Over those last 22 games, Youkilis undid a lot of the good of his 2011 season. He hit just .190/.304/.342, and dragged his season line down from .273/.388/.486 to .258/.373/.459. Even his pre-final stretch numbers were likely dinged by injuries -- check out his injury report from 2011, courtesy of Baseball Prospectus's injury database:

Date On	Date Off	Games	Side	Body Part	Injury	Severity	Reaggravation
04/22/11	04/23/11	1	Left	Ankle	Contusion	Foul ball	----
04/28/11	04/28/11	0	Left	Hip	Soreness	felt it jammed	----
05/01/11	05/02/11	1	Left	Hip	Soreness	soreness	Yes
05/03/11	05/04/11	1		General Medical	Illness	-	----
05/05/11	05/05/11	0	Left	Thumb	Contusion	-	Yes
05/14/11	05/14/11	0	Left	Hip	Soreness	-	Yes
05/25/11	05/26/11	1	Left	Hand	Soreness	-	----
06/17/11	06/17/11	0		General Medical	Illness	-	----
06/30/11	06/30/11	0	Left	Foot	Contusion	foul ball	----
07/05/11	07/06/11	1		Back	Contusion	HBP	----
07/26/11	07/27/11	1	Left	Thigh	Soreness	Hamstring	-
08/11/11	09/02/11	20	-	Low Back	Tightness	-	-
09/09/11	09/09/11	0	Left	Hip	Inflammation	Bursitis	-
09/09/11	09/13/11	3	Left	Abdomen	Sports Hernia	-	-
09/16/11	09/29/11	13	Left	Abdomen	Sports Hernia	-	Yes
10/04/11	10/04/11	0	Left	Pelvis	Surgery	Sports Hernia	-

There are 16 entries for injuries here, all from just last season. His hip was bothering him as early as late-April, and he dealt with hop soreness at various points throughout the year. Eventually, he required surgery for a sports hernia, the effects of which you can see in the cascade of injuries on the left side of his body from time spent trying to adjust to pain.

It's likely Youkilis, now 33 years old and averaging just 119 games a year over the last three seasons, will miss time again in 2012. The injuries have worn him down as the year has progressed, so given this pattern, he might not lose time until much of the year is behind us.The Red Sox have some plans in place to replace him when that happens-- Mike Aviles could slide over from short, and Jose Iglesias might be ready to assume a big league role by the time Youkilis is out for the count, or maybe Will Middlebrooks would have solved Triple-A by then -- but there's nothing on the roster that can replace Youkilis outright. Not that there could be, either: look at the chart up top again, the one that says he's one of just five major league hitters like him over the last three years (and this while dealing with these myriad injuries) -- and try to say with a straight face the Sox could easily replace him when he's down.

This is what makes him so important to the Red Sox, despite the missed time, and will also make next winter difficult, when his $13 million club option comes up. The Red Sox could use that $13 million to stay under the luxury tax threshold, but they could also have Youkilis relatively cheap for his production. That's a worry for another day, of course, and one clouded by dreams of prospects being as ready as we'd love them to be right when we want them to. Right now, the Red Sox just want Youkilis healthy and productive, because Boston is at its best when this is so. Squeezing 140 games out of Youkilis rather than 120 could be the difference between October baseball and another fall at home.