Why do doctors use a new thread of the same kind for each stitch instead of using a single thread for the entire stitch?
Using a single thread for a suture also known as continuous stitching has a major con that it has higher risk of failing if the suture is cut in just one place. So it is generally avoided eventhough it is very easy to do.
On the other hand interrupted stitching ( one thread for each stitch) is favoured because of lesser risk of failing, eventhough it is time consuming than continuous stitch.
If they used a single thread, then a single break in that thread would cause the entire thread to fall out of place. Using multiple threads means that if a break were to occur, the rest of the stitches would still be able to hold their place.
One time I had 5 stitches in my hand while I was snowboarding. Sometime during the day I fell down and one of the stitches came out; there was a lot of blood, but it was probably nothing compared to how much blood there would've been if it was a continuous thread and the whole wound opened.