J.J. is a nine-month-old Yorkshire terrier. He’s an adorable bundle of energy, so his owner was not surprised when J.J. managed to escape his pen two weeks ago. Since puppies, like children, frequently get bumped, bruised, strained, and sprained, his mom also wasn’t surprised that he was limping. “He probably pulled a groin muscle jumping out of the pen,” she concluded, and wisely tried to make him rest. Not an easy task. Ten days later he was only slightly improved, so she brought J.J.. to me to evaluate.”Let him walk around the room, ” I requested, observing his gait.
“When he plays, he puts the foot down,” she said. “But he holds it up when standing still.”
J.J. definitely had a slight hind leg hitch as he trotted up and down the office. With each step, he planted his paw on the floor without hesitation so I knew the problem was likely higher up the leg, but methodical examination is necessary to avoid oversights, so, as always, I started at his toes, then worked my way slowly up.
Toes, metatarsus, tarsus, knee. Could he have torn a cruciate ligament? Was anything swollen, crunchy, or painful? His kneecap slid a tiny bit off center when I pushed it firmly. Technically called luxating patellas, kneecaps that move out of alignment are fairly common in toy breeds. J.J.’s didn’t displace enough to be causing this limp. Now the hip. I rotated his leg in the socket. No reaction. Pretty normal range of motion. But it felt wrong. “Something just seems off to me here,” I stammered uncertainly. “He may have dislocated his hip.”
A normal hip joint consists of the big round ball that tops the thigh bone (called the femoral head) sitting in a cup-shaped socket in the pelvis (called the acetabulum.) The femoral head should have a smooth spherical shape and the acetabulum, a generous, deep pocket. A small piece of connective tissue called the round ligament anchors the femur to the inner surface of the acetabulum and the entire joint is encased in a fibrous capsule. In dislocation (also called luxation), the round ligament and joint capsule tear, and the ball pops completely out of the cup.
“I really think he just pulled a muscle,” his mom reiterated, hopefully. I shook my head. Ten days should be sufficient time for a simple strained muscle to resolve.
“Let’s take an X-ray,” I prompted. “So we can be sure his hips and knees are okay.” J.J. didn’t seem as painful or as lame as expected with a dislocated hip, but maybe it was a sub-luxation, I thought to myself. That’s when the femoral head is only slightly out of place but not all the way out the socket. We’d know soon enough. J.J. headed downstairs to get his picture taken. Ten minutes later I examined the film. J.J’s left leg had a deformed femoral head and marked degenerative joint disease in the hip.
Legg-Perthes Disease. LPD. Also known as Legg-Calves-Perthes disease, avascular necrosis of the femoral head, coxa plana, and coxa magna. An orthopedic disease of unknown cause, LPD typically affects toy breeds, terriers, and other small dogs between the ages of three and 13 months.
In Manchester terriers a “multifactorial inheritance pattern with a high degree of heritability” has been identified, so a genetic predisposition is presumed likely in other breeds as well. Lameness usually comes on gradually, although it may start suddenly, as it did with J.J.. In such cases, the joint was most likely already compromised by primary LPD, but acute trauma precipitates the onset of visible symptoms and leads to discovery of the underlying issue. More than 85 percent of LPD cases involve one hip, though occasionally both may be affected. J.J.’s age, breed, and radiographs were all spot on for a diagnosis of LPD.
Unlike dogs born with hip dysplasia, pups with LPD start out with perfectly normal-appearing hip joints. Then something goes terribly wrong. Based on the histological appearance of the lesions, it’s thought that for some unknown reason, there is a sudden infarction of the blood vessels supplying the upper end of the thigh bone. With the loss of circulation, this area of bone actually starts to die. The femoral head literally collapses. The body tries to repair the deteriorating hip by generating new bone, but it is unable to recreate a smooth, cup-and-ball socket that rotates effortlessly. J.J. is left with osteoarthritis — a rough, irregular joint that grinds and causes pain with every step.
“It’s not a pulled muscle,” I said, trying to break the news gently. “Looks like Legg-Perthes Disease. J.J. needs surgery.”
There is no known cure for LPD that saves the original bone. Treatment goals are to remove the damaged bone, eliminate pain, and maximize mobility. A teeny, tiny hip replacement is one option, but there is a far less expensive alternative with such a good outcome it is almost universally agreed upon as the treatment of choice. The procedure is called femoral head and neck osteotomy (FHO) and consists of surgically removing the upper portion of the femur and allowing the remaining thigh bone to basically “float” free. By removing the areas where the abnormal bone was grinding, we eliminate the pain. But can the dog walk like that, you ask? Yup. These little pups start using the leg within days after surgery and in a surprisingly short time don’t limp at all.
Without surgery, dogs with LPD usually get progressively worse over time, experiencing muscle atrophy, and chronic lameness and pain. If for some reason surgery is not possible, we prescribe long-term pain medication as well as supplements like glucosamine that are touted to support joints and reduce inflammation. Affected dogs should not be bred, due to the likely inheritable aspect. J.J. is seeing the orthopedic specialist this week. Early activity is encouraged very soon after surgery to improve use of the leg. I suspect he’ll be running and jumping out of his pen again in no time.