More and more workers are getting placed in MCOs when their claim is accepted by the WC insurer. An MCO is essentially a medical network. The original idea was that they would make it easier for workers to find doctors willing to do WC. In practice, my suspicion is that many of us Claimant's Lawyers would agree that what we see as the downsides of MCOs outweigh the purported benefits. Unfortunately, MCOs are enshrined in the Statutes so they're here to stay...at least until the Legislature decides to change things.
The most important thing a works should know and do is to read the Notice of Acceptance packet carefully! If you're claim is in an MCO, you'll get a letter all about it. Sometimes it's packaged with the Notice of Acceptance, sometimes it's separate. Regardless, you gotta read it because you'll probably have to find a new "attending physician" quickly...someone who's on the MCOs "panel" or list of doctors.
If you're represented by an attorney, call your lawyer because they might be able to recommend some doctors who are on the MCO Panel. However, if your MCO is, for example, Kaiser, you may end up "stuck" in the Kaiser system. Same with Providence, Legacy, etc.
Regardless of which MCO it is, read the papers carefully and be sure your doctors is in the network, or find a new doc who is in the network. Once your claim is accepted and in the MCO, only an MCO doctor can do some of the really important things...like authorize you to get paid lost wages if you're not able to work!