The number one cause of injury is overuse: working too much, too fast, too soon, or too often. As riders, it is a huge responsibility to protect your horse from these training errors. It is tempting to overdo it when there are shows you want to go to, or if you have a young and talented horse. There is a limit to how much training the body can absorb. Rest and recovery are as important as hard work. Realigning the body with massage therapy is another key to preventing injuries. Flexibility is an important indicator in the prevention of injuries. The horses I know that avoid injuries and are at the top of the leader board are the ones who are on a carefully planned fitness program, have superior nutrition, regular body work, are ridden on good footing, and have knowledgeable farriers.
Pain is a warning signal that needs to be listened to. Pain is an important signal that something is about to go very wrong. If you saddle up your horse and he has a strong reaction, pay attention to that. If your horse starts refusing jumps, listen to him. If your horse comes out of the stall very stiff, or is taking longer to warm up, there is discomfort present. If dealt with early, many sources of pain can be alleviated through deep massage. If pain signals are ignored, they will inevitably get worse. Something minor can lead to something very serious, or permanent, in a muscle, tendon, ligament, or joint. When in doubt, use the cold laser, or have body work done. Needless suffering can very often be avoided.
Once an injury occurs, scar tissue forms as it heals. This tissue is not as elastic as the original and thus is more prone to re-injury. As I keep saying, prevention is the key to a long and successful athletic career.