First, for those who aren't fluent in legalese, a "statute of limitations" is a state law that puts a strict time limit on your right to go to court and get your lawsuit started. There are usually different deadlines depending on the case you want to file, and the time limit is expressed in years.
In Tennessee, the standard statute of limitations for medical malpractice cases gives you only one year to get your lawsuit filed. That typically means one year from the date on which the alleged malpractice occurred, but in some cases the "clock" doesn't start running right away. In Tennessee, if the patient's injury is not discovered within that one-year period, the statute of limitations period beings to run on the date on which the injury is discovered, and the filing deadline is one year from that date.
You can find this law online: Tennessee Code Annotated section 29-26-116.
In Tennessee, there is also a larger deadline for medical malpractice lawsuits which says that, regardless of when or if the injury was discovered, "In no event shall any such action be brought more than three years after the date on which the negligent act or omission occurred"—meaning three years from the date on which the defendant committed the underlying medical error.
The only exceptions to this over-arching three year deadline in Tennessee are 1) when a medical malpractice case involves "fraudulent concealment on the part of the defendant," or 2) "where a foreign object has been negligently left in a patient's body." In those situations, the one-year lawsuit filing deadline described above applies and there is no larger deadline.
If the deadline set by the Tennessee statute of limitations has passed, but you try to file the lawsuit anyway, the doctor or health care facility you're trying to sue will file a motion asking the court to dismiss the case, and the court will almost certainly grant the motion. So it's critical that you pay attention to the deadline as it applies to your case, especially in Tennessee, where the one-year statute of limitations is pretty defendant-friendly.