If you were fired from your job right after disclosing facts about a serious medical condition, and one that involves a work injury, you may have rights under workers compensation and the laws that prohibit discrimination.
Even though the employer terminated your employment, you can still pursue a workers compensation claim for medical benefits and lost wage/temporary and permanent disability benefits.
Also, the employer may have violated Wisconsin and Federal law that prohibits discrimination because of a serious medical condition, known as disability discrimination. This may be a claim if the employer disciplined you (written warnings) or terminated your employment motivated by the fact that you have a serious medical condition. The state and federal laws have different definitions of disability, so you may want to pursue one or both claims, depending on the medical facts of your condition and its limitations on your ability to work and perform major life activities. I recommend that you see an attorney experienced in handling discrimination claims for an evaluation and further direction. Don't delay, though, as you must file a complaint of discrimination with either the EEOC or the Wisconsin Equal Rights Division within 300 days of the discriminatory act, generally.
I am not sure where you got "recordable" injury from, but there is no such thing under the Wisconsin workers compensation law. An work related injury is just that a work related injury and as such is covered under the Wisconsin workers compensation laws. It does not matter if there were stitches, surgery or if it was only a muscle strain. From what you write, it would appear that the ER and/or their agents were trying to convince you not to pursue a workers compensation claim and tried to intimidate you with the write up on an extraneous (and seemingly pretextual) reason. With regard to your termination, you probably have a cause of action under the Wisconsin workers compensation statutes for an unreasonable refusal to rehire, which occurs when an individual is fired or denied rehire for asserting their rights under the workers compensation statutes.
In addition to the potential discrimination claims mentioned by Attorney Leech, because worker's comp is involved, there is a claim known as an unreasonable refusal to rehire claim you could also potentially pursue. You will want to contact an employment attorney ASAP and also apply for unemployment insurance with the State if you haven't done so already.