The sudden lameness of a dog may be caused by calcium deficiency, muscle strain, joint problems, long nails, injury, fatigue, etc. First check whether the dog has any trauma. If there is no trauma, it is best to take the dog Go to the pet hospital for a x-ray examination. It is necessary to trim the dog's nails regularly to prevent the nails from being too long and break. It is also necessary to supplement the dog's nutrition and calcium, and not to do strenuous exercise to avoid the dog being injured.