When I was a kid, we had a German Short Haired Pointer/Weimereiner cross, Priscilla (Pris). She was the runt of the litter. She lived to be like 18 with no health-related issues. However, when she was 13, my dad and I were out shooting his .22 pistol. She was with us, but was over near our truck, on the other side of some railroad tracks. A train came, she got scared and wanted to get back to us. Something on the train struck her and knocked her about 10+ feet backwards. When we got over to her, she was trying to stand up, but stumbling around. She had a quarter-sized hole in her head. My dad wanted to put her down, out of her misery. I wouldn't let him. We wrapped my sock around her head and the hole, and rushed to the vet. It was a Sunday, so we had to wait for him to get there. He finally showed up an hour later. He picked a couple skull fragments off her brain, and left one in there that was partially embedded, stitched her up and sent her home. After a couple weeks, she made a full recovery. She did start to lose her sight and hearing, but lived another 5 healthy years...
Anyway, the runt is just a word. The biggest, healthiest one can end up with the most health problems and vice versa.
~S