Please don't take my advice as 100% truth because I am just going to tell you my personal experience.
I have had about 6 traffic infractions (speeding, red light violations, talking on cell phone etc) and one serious infraction (driving on a suspended license). Only 1/6 of these previous convictions were "spent" when I applied, but I did the following:
1. Got ORIGINAL copies of my violations from the courts that issued the violation. If I couldn't get original copies, I got the clerk to certify the print out showing my name, violation type, consequence (fines) and the fact that I paid.
2. I declared every, single, infraction according to the visa directions. On my Tier 4 visa application, it asked for all of my violations, so I gave everything I had, even things 9 years old.
I got a Tier 4 visa and a Tier 2 visa with no issue. That being said, your situation is different because
-you have a misdemeanor which is more severe than my traffic infractions
-your violation has been spent
I suggest that you retrieve those original documents ASAP because the courts can sometimes take ages to send them to you. The most important thing you need to do is to declare everything. If they know you are transparent, they should be fine. Also, take a look in the "general guidance for refusals". It shows what types of violations they MUST refuse someone for. As far as I can remember, it was offenses that result in a consequence of jail time, but please look to be sure.