“Can a spinal block cause permanent damage?”

Absolutely not if done correctly

There are possible permanent and dangerous complications associated with any procedure and also with spinal anesthesia. The rate is very low, and should be discussed as part of the proper informed consent taking by your Anesthesialogist.

Yes, but it’s rare.

If you examine the anatomy of a spinal block, you will be reassured that the common fears about it are unwarranted. It is more properly called a subarachnoid block because the needle and medication goes into the subarachnoid space which is the cerebrospinal fluid filled space below the level of the spinal cord. The risk of some type of permanent damage is extremely small. The medications commonly used have been proven safe with many years of effective use. Depending on the type of procedure or purpose of the block, there can be some transient side effects that are easily treated with intravenous medication. There is about a 1-3 percent chance that you could develop a post dural puncture headache. This headache is
easily treatable if it is severe enough. When considering medical treatment or anesthesia, you and your physicians should always consider the risks, benefits, and alternatives of any plan. Spinal anesthesia is safe and effective for the vast majority of patients when it is a recognized alternative for your particular condition or procedure.

Most unlikely except for very, very rare case of infection, which should not occur when given by a board certified anesthesiologist in a reputable hospital/clinic.

It's a rare complication, but could happen.