Injuries

Paw injuries can be due to cuts, splinters and the affected paw can become  swollen. Especially if they are accompanied by damaged nails, this type of injury is likely to become infected.
Muscle pain comes from prolonged contraction. The muscle becomes swollen and the animal cannot move the injured joint. Chronic muscle contractions contribute to changes in movement.
Injuries to tendons and ligaments are a major source of canine pain and can lead to arthritis.  

A torn cranial cruciate ligament can occur when a dog turns or suddenly stops while running. This injury commonly occurs in large breeds, especially if they are overweight.

Tendon tears, which are less common than ligament injuries, can occur with excessive running or jumping.
The dog will immediately start to limp following a tendon or ligament injury. Pain will be felt when pressure is applied to the area.

Bone fractures can occur in the case of trauma (e.g. a road accident) or excessive pressure on the skeletal system. Bone fractures happen in numerous places, sometimes the bone breaks the skin, sometimes not. A dog with a broken bone will refuse to put any weight on the leg.