Can I use a 2011 iMac 21.5 lcd on a 2010 model?

Well it isn’t that simple, Apple altered the mounting frame between the systems so you will need to remove the raw LCD panel from it. If we look at the panel its self we can see its not the same 2010: LM215WF3 (SD)(A1) or LM215WF3 (SD)(B1) where we have LM215WF3 (SD)(C2) for the 2011 system. So clearly they are not exactly the same.

So before you make the jump how about giving us a bit more. There is a common failure which is quite repairable. If you take the display off you can gain to the backside of the panel to fix the LED backlight strip connector which often comes unsoldered from the other side.