When a dog limps, he is usually doing so because one or more of his limbs hurt or because his normal range of motion has somehow been altered. The most important initial distinction to make is whether the limp is bad enough to prevent the dog from bearing any weight on the affected limb.
What to Look For
The next step is to try to first identify which limb has the problem and then to pinpoint exactly where the source of the problem is. To figure out which limb is bothering your dog, watch him walk for a while. Usually a dog will come down heavier on his healthy limb and avoid putting substantial weight on the limb that is bothering him. You can identify this by observing your dog's head when he walks. The comfortable limb will be placed on the ground and his head will go down at the same time. His head will tend to come up when the uncomfortable limb is on the ground.
Next, you'll need to examine the limb that's bothering your dog. I like to start by examining a limb that I'm pretty sure is uninjured, starting at the toes and working my way toward the body. This gives me an idea how the dog responds to pressure he is not accustomed to so I can compare it to his response to similar pressure on the affected limb. It may also instill some trust in a dog, who might otherwise think I'm trying to take advantage of his injury.
Examine each of the following areas:
Toes: First check each of the toenails for cracking or splitting. A cracked or split nail will expose the sensitive tissue and blood vessels beneath and can be extremely painful. A simple crack with no bleeding and a mild limp usually does not require veterinary intervention, but any crack that results in bleeding could require sedation, thorough cleansing, trimming, and possibly cauterization and bandaging. Examine each toe individually and gently move and squeeze them to check for possible injury. Bruised and even fractured toes will cause a limp but don't always require intervention. X-rays, however, are usually necessary to evaluate a toe that remains painful even after a few days of rest.
Webbing: The spaces between many dogs' toes are connected with soft skin that stretches and provides a large surface area for swimming. This skin is often sliced by sharp objects a dog is likely to walk on, such as glass and metal. If such a slice is bleeding, stitches and antibiotics are usually appropriate. In addition, foreign objects - such as gravel, tar, and thumbtacks - can get wedged in between a dog's toes, causing a limp that should resolve once they are removed. A variety of masses, cysts, and infections, however, can arise between a dog's toes and should be evaluated by your veterinarian.
Pads: Dogs have six protective pads on their front paws (this includes the one at the back of their carpi, or “wrists”) and five on their hind paws. These are usually leathery in texture and are simply a thicker form of skin than exists elsewhere on a dog's body, with a higher percentage of hardened protein-rich tissue called keratin.
Like the rest of a dog's paw, these pads can be sliced by sharp objects and can bleed if cut through the outer “horny” layer. They can also develop warts, become sensitive from walking on hot surfaces, and can grow abnormally hard, dry, or irritated due to chemical exposure or dietary imbalances.
Joints: Any one of the many joints in a dog's limbs can be the source of enough discomfort to result in a limp. Discounting the multiple joints of the paws, there are three major joints in each limb of a dog. A dog's front limb consists of the carpus (or wrist), the elbow, and the shoulder. The hind limb includes the tarsus (or ankle), the stifle (or knee), and the hip. Check each of these joints by applying light pressure and then increasing the pressure to moderate. If no discomfort is noted, try gently lifting the limb and slowly duplicate a normal range of motion. By supporting the entire limb, you can examine each joint in isolation and hopefully identify the source of the limp.
Bones: There are approximately 321 bones in a dog's body. Bruising or fracturing of many of them could cause enough discomfort to result in a limp. Check the leg bones by visual observation first. Look for swelling, bleeding, or other signs of injury or asymmetry. Similar to examining the joints, examine the long bones of the limbs by applying mild to moderate pressure along their entire length. You can verify any suspected irregularity or abnormality by comparing it to the other healthy limb.
What to Do
Exam complete, ask yourself the following questions:
Could your dog have suffered any trauma over the previous few hours? If the dog has been out of your sight, is it possible that he was involved in an accident of some sort, jumped or fell from a height, was bitten by another animal, or stung by an insect? If that's the case, refer to “My Dog Was Hit by a Car or Heavy Object”, “My Dog Fell from a Height” or “How to Treat Your Dog's Allergic Symptoms” [not available online].
How old is your dog? Your dog's age is important in trying to get to the bottom of the problem. Young dogs can experience limb discomfort from developmental issues that older dogs wouldn't have, and older dogs can suffer from various cancers and forms of arthritis that puppies would be less likely to experience.
Did you notice a cracked toenail? Refer to “My Dog Has a Broken Toenail” [not available online].
Do you suspect a fracture? If there is significant swelling and pain and your dog refuses to bear any weight on the affected limb, assume there is a fracture and get your dog to a veterinary hospital.
Are your dog's footpads dry or cracked? If so, see the chapter “My Dog Has Cracked Footpads” [not available online].
Does the pain appear to be isolated to a specific joint? If so, try treating with a weight-appropriate dose of a buffered or enteric-coated aspirin product. If that doesn't help within a day, see your vet for a more thorough evaluation.
Always proceed with caution when examining a dog suspected of being in pain. Extreme pain will cause a dog to revert to his most primitive instincts, which include biting any creature that approaches, even his beloved owners! With that in mind, a thorough yet cautious exam will usually reveal the reason for the limp. If at any time during the exam your dog indicates discomfort or pain, stop immediately.