My nearly five-year-old Pomeranian has been suddenly lifting a back leg and hopping without putting weight on it — what could be wrong?

A back leg that won't bear weight can result from injury, muscle disease, joint disease, a fracture, or a neurological problem. Carefully check the leg for any trauma and treat it promptly. Pomeranians have fragile bones and are prone to kneecap dislocation, so if no injury is visible, have a vet take x-rays to find the cause.