Bigger dogs can have chronic joint pain and arthritis. Their knees are also susceptible to injury, especially if they jump from high places or go up and down stairs a lot.
The most common problem dogs have with their legs is hip dysplasia, an inherited genetic disorder. The most common injury is a torn cruciate ligament, which is in the knee.
A dogs legs are pretty sensitive they can have problems with their legs from arthritis to a scratch making them limp and if the dog is suffering from an external injury there are times it will work its way internal.
Some dogs have a degenerate disease. German shepards are best known for that. They could have had been hit when they were younger. anything could happen. You'll never know when.
