The WAY that this most often happens is when an owner places a collar on the Chihuahua and then connects a leash to that.
Whether this is to keep the dog in place, to take him or her for a walk or for any other reason....When the other end of the leash is connected to something or is held in your hand, if the dog jumps or runs forward and the leash becomes taunt....this puts a LOT of pressure on the neck and the trachea can (and often is) damaged!
How can you avoid this? The #1 way to avoid this is to have your Chihuahua wear a harness whenever the dog is on leash. These can be obtained at any pet supply store, whether it is your local store that you can drive to or a pet supply store online (see below).
They are easy to put on, made of many different fabrics to choose from and come in many colors so that you can have 1, 2 or many to dress up your Chi when it is time for a walk.
With the harness, any pressure will be distributed over the chest, shoulders and back, NOT just on the neck. And this will keep your Chi happy and healthy.