Dewclaws are similar to the thumbs and big toes in dogs. They are not directly equivalent to human structures, but they are somewhat similar.
Dewclaws can be firmly attached to a dog's foot or only attached by skin. Front dewclaws are usually bone-attached, while rear ones are more mobile.
Dewclaws provide extra traction and help stabilize the carpal joint when dogs run at high speeds or turn. Some dogs use them to climb trees or hold objects.
Front dewclaws should not be removed unless there's a very good reason. Rear or double dewclaws may be removed to prevent injury, but this is debated.
Dewclaw injuries are relatively rare but can occur. Any nail can become partially or completely pulled off, broken, split, infected, or ingrown.
Dewclaw injuries are usually best assessed by a vet. They can remove damaged nails or trim ingrown ones, and prescribe any needed antibiotics and pain relievers.
Dewclaws are no different from your dog's other nails. Regular nail trims are needed to keep their nails at a healthy length, especially for dewclaws.