Pluto is the only ex-planet (now a dwarf-planet) in our solar system to have this orbital characteristic. This is caused by its very elongated orbital path. Most planets travel around the Sun in an elliptical orbit that is closer in shape to a circle. They pretty much remain the same distance from the Sun during their annual trip. This is true of Neptune. But Pluto's orbital distance from the Sun varies by over 1.86 billion miles (about 3 billion km), enough to cause its orbital anomaly.
Don't worry about Pluto colliding with Neptune though. Pluto's different in that respect as well. Rather than orbiting on a relatively flat plane as the other planets do, Pluto's orbit brings it above and over the orbit of Neptune. Their paths don't cross.