Meaning of "threaded down"

[All Potted Out]

"When an epidural is administered, a very fine, hollow needle is inserted into the epidural space and the catheter, (thin tube) is threaded down the needle, which is then removed."

There are two things about this sentence that confuse me. First, shouldn't the comma after "catheter" be deleted? Second, what does "threaded down" mean?

[Yankee]

Hi apo

Yes, the comma should be deleted. I'd say that was just a typo.

Threaded down the needle:

Do you know how to sew, apo? When you thread a needle, you put the thread through the eye of a needle. In your sentence, the "thread" (catheter) has to be put through a different sort of needle: a long, hollow needle, and the "thread" is inserted at the top and must then go down to the bottom of the needle.

Amy