A more thorough explanation:

The common-knowledge exception is a legal principle that allows non-expert witnesses to testify about routine or simple medical procedures in a medical malpractice case. This exception is a narrow one, and it only applies in some jurisdictions where a plaintiff is not required to present expert testimony to prove negligence.

For example, if a patient goes to a doctor for a routine check-up and the doctor fails to diagnose a common condition, such as high blood pressure, the patient may be able to use the common-knowledge exception to prove negligence. In this case, the patient could call a witness who has personal experience with high blood pressure and can testify that the doctor should have recognized the symptoms and made a diagnosis.

Another example of the common-knowledge exception is when a patient is given the wrong medication by a nurse. If the medication is a common one that most people are familiar with, such as aspirin, the patient may be able to use the common-knowledge exception to prove negligence. In this case, the patient could call a witness who has personal experience with aspirin and can testify that the nurse should have recognized the mistake and corrected it.

Overall, the common-knowledge exception is a useful tool for plaintiffs in medical malpractice cases who may not have access to expert witnesses. However, it is important to note that this exception is limited and may not apply in all cases.