If I lost my hearing after a total knee replacement, is this grounds for medical malpractice?

This could be a basis for a medical malpractice claim.  However, to prevail on the claim, you will have to prove that the hearing injury is a direct result of the doctor's malpractice.  To do this, you need to get a copy of your medical records and have them reviewed by another doctor.  If you're not sure how to do this, then consult with a medical malpractice attorney.  They can help you with procuring your records and finding an expert that will be appropriate for evaluating your case before you make the final decision on whether or not to file a med mal lawsuit.