Diagnosing the cause of cat or dog limping is often a much more difficult problem than diagnosing the cause of lameness in humans. When a cat or dog limps the owner frequently has no idea of how the injury occurred. The injured animal is often presented to the veterinarian with the complaint that the their pet is “just not walking right” rather than the dog is limping. The pet’s owner is often unsure or wrong about which foot or feet are involved. Many times the owner will think that their pet is lame on its left hind leg when in fact it is the right hind leg which is causing the abnormal gait. In fact the abnormal gait may turn out to be a neck or back problem with no injury to the limbs at all. Sometimes the lameness may involve more than one of the pets limbs and may be what veterinarians describe as a “changing leg lameness”. Often dog limping is intermittent; it is present one day and the next day its gone.
Finally, to the frustration of owner and veterinarian alike, it is not uncommon for animals that have been limping for days at home to come to the veterinary clinic and walk perfectly. Small breeds of dogs often have knee caps that “pop out” occasionally and result in lameness. These dogs walk normally when the knee cap is in its proper position. Careful observation of the pet in motion accompanied by skilled manipulation and probing of limb is what it takes just to figure out which part or parts of the animals body are involved in the problem. Keep in mind that, frequently, all a human physicians need to do is ask their limping patient “where does it hurt”.
Determining which of the animal’s limbs are involved is just the beginning of diagnosing the cause of lameness. The next step is to localize the pet’s pain to a more specific area on the affected limb, and then further narrow the problem down to whether it is a nerve, muscle, tendon, ligament, bone, or joint cartilage problem. If the area of injury is only mildly painful it is often difficult for the veterinarian to localize the problem since the pet may display little or no reaction to the probing and manipulation of the joints and muscles. Radiographs are often helpful in detecting osteoarthritis, hip dysplasia, fractures, dislocations, and ruptured disks but are of no assistance if the problem involves a muscle, tendon, ligament, or a nerve injury. When working on very tiny pets such as birds, hamster, gerbils and mice injuries such as hairline fractures may be so small that they are easily missed on x-ray. Rabbits that become suddenly lame in their hind legs may have a partially dislocated or fractured vertebrae in their back.
Lameness in animals is not always the result of pain. Lameness can be due to a malformation of a limb or it may be due to a weakness or a partial paralysis due to a nerve injury or nerve degeneration. Intervertebral disk problems in the pets neck or back can result in a paralysis or weakness in the front or back limbs. A standard radiograph, myelogram, neurologic exam, and electrical testing of muscle and nerve conduction are often necessary in diagnosing these problems.
To further complicate the issue, limb soreness may be the result of a more generalized problem in the body. For example infectious problems such as bacterial endocarditis, and Lyme disease can produce painful muscles and joints. Certain B vitamin deficiencies result in nerve degeneration. Cats can develop an intra vascular obstruction of blood flow into one or both limbs resulting in lameness or paralysis. Kidney tumors of birds often result in pressure on the sciatic nerve producing a single leg lameness. The metabolic disease known as Gout often results in very painful joints in dogs, cats and birds.
“Metabolic bone disease” in the Iguana and smaller lizards is a problem involving the parathyroid gland and the abnormal deposition of calcium in the muscle which eventually result in severe lameness and paralysis.
I am sure that from the above discussion you now have some sense of what your veterinarian is up against when asked to diagnose your dog’s limping . Lameness diagnosis is just one of the many times when your veterinarian is wishing that your pet could at least point if not talk. In the next issue I will continue the subject of lameness with a discussion of certain specific lameness problems and their treatments. Emphasis will be on the more chronic problems of the older pets including a discussion on both conventional and alternative methods of treatment.