When Flash, a sweet little Yorkshire terrier, was less than a year old, he started limping one day. Now, when young dogs get too rambunctious, it’s not particularly unusual for them to strain or sprain something. They’re like kids who overdo it at the playground or at soccer. But when Flash came to see me, something didn’t feel right with one hind leg. “Let’s take an X-ray,” I suggested. “I just want to make sure he hasn’t partially luxated his hip.” When the films were done, it was immediately apparent that something was wrong with the head of his left femur, the part of the big thighbone that articulates with the pelvis.
What exactly did I see on his radiograph? Let’s review the anatomy first. The hip joint, technically called the coxofemoral joint, consists of a “cup” portion in the pelvis (the acetabulum) and a “ball” portion of the thighbone (called the head of the femur) that nestles in the cup. Flash’s X-rays were consistent with a condition called Legg-Perthes disease, also known as aseptic or avascular necrosis of the femoral head. In Legg-Perthes disease, there is a disruption of the blood supply to the head of the femur. That’s right — bones are alive, and need to have a viable blood supply. Without adequate blood supply, the head of the femur starts to die, and little micro-fractures occur. The bone deteriorates and eventually collapses, leaving a misshapen “ball” portion of the ball-and-socket joint that causes instability of the hip … and pain.
Mild cases can sometimes be managed medically and with proper physical therapy. Painkillers. Nutritional supplements for joint health. Weight control. Exercise restriction. But more often than not, the best thing for the dog is surgery. That’s a hard thing for the owner of a vibrant, active pup to grasp. How can this happen to such a youngster? It’s precisely because Flash was so young that Legg-Perthes disease was at the top of the differential diagnosis list. This disease classically affects the hip joint in small-breed dogs under the age of 1. It is thought that there is a genetic component underlying the syndrome. It is seen most commonly in little terriers such as West Highland whites, Maltese, and Yorkies, as well as other toy breeds like miniature pinschers and poodles. Lameness and pain often come on gradually over a few weeks, but can present suddenly, like Flash’s did. In most cases, only one hip is involved.
Why surgery? Can’t the bone heal? I’m afraid not. In trauma-related fractures, such as when a dog is hit by a car, the broken bones often still have intact blood supply. As long as that is true, all the veterinarian needs to do is stabilize the pieces of bone in good alignment and restrict an animal’s movement for six to eight weeks, while Mother Nature works her magic. But in Legg-Perthes disease, the affected bone does not have a functional blood supply. It cannot heal. Period. The good news is that the surgical treatment is straightforward. The procedure is called a femoral head osteotomy (FHO) or femoral head and neck osteotomy (FHNO). The surgeon goes in and simply removes the necrotic femoral head and neck, leaving the remainder of the thighbone in place. That’s it. After surgery, Flash is supposed to get up and moving as soon as possible.
But wait. How is Flash supposed to walk and run without a hip joint? You’d be amazed at how quickly these little dogs bounce back. The muscles and connective tissue in the thigh and hip area all contribute to support the leg, and as scar tissue develops, the body can form a “false joint” that stabilizes things even more. It helps that most dogs with Legg-Perthes disease often weigh less than 15 pounds, and have the vitality of youth to aid in their recovery, but I have seen much larger dogs who have undergone femoral head osteotomies for other reasons, such as hip dysplasia, return to excellent function and mobility. I once was taking abdominal X-rays of a 60-pound, 12-year-old rescue dog when we discovered incidentally that he had undergone an FHO some time in the past. The owners, who had adopted him a decade ago, had no idea until we happened to see it on these films. The big dog had never had any evidence of a limp. Total hip replacement is theoretically also an option for treatment of Legg-Perthes, especially for dogs who do not respond well after an FHO procedure, but this is more expensive and involved, and usually not necessary.
The prognosis for Legg-Perthes disease is excellent with surgery and appropriate physical rehabilitation. Flash recovered beautifully. Three months later, however, he fell out of bed and broke the femur on the same side. So back to surgery he went, this time for a metal plate to repair the bone. Again, Flash recovered well. In addition to all this, the little guy also has a condition called medially luxating patellas, a common problem in small-breed dogs in which the kneecaps have a tendency to slip out of alignment. Over the years this can lead to significant arthritis in the knees.
Flash is 12 years old now. Kudos to his owner for an amazing job, always getting Flash the care he has needed, and keeping him active and happy. He recently made a visit to be evaluated by his orthopedic surgeon, who reported that the FHO and old fracture repair looked good. Not surprisingly, he has mild arthritis in his right hip, an expected consequence of FHO, since the remaining hip joint does a bit more than its share of the work over time. The orthopedist noted advanced arthritis in Flash’s knees, and suggested this was likely the main source of the mild lameness he has been exhibiting, not his FHO. Our challenge now is to find the best combination of medications to continue to keep Flash as mobile and pain-free as possible through his senior years.
