Breeder Education Part Of Effort To Raise Awareness About Pes Varus
Though some breeders believe that pes varus has occurred in Dachshunds for about 40 years, others are still learning about the potentially crippling orthopedic disorder known in layman's terms as bowlegged syndrome.
Andra O'Connell of Kerhonkson, N.Y., first encountered pes varus in 2003 when a Standard Longhaired Dachshund puppy from a litter she bred developed the condition. O'Connell, who breeds under the Amtekel prefix, had bred Dachshunds for 30 years but was not familiar with the disorder. When the puppy was sold around 12 weeks of age, there was no indication of the condition.
The owner noticed signs of lameness and a bowlegged conformation when the puppy was 4 1/2 months old. The veterinarian diagnosed the puppy as having damaged growth plates. "There was never any mention or discussion of pes varus or a genetic inheritance," O'Connell says.
The puppy had corrective surgery, and today, at age 8, is healthy.
Pes varus cropped up again in 2010 in two of seven puppies that O'Connell line bred. One of the puppies is mildly affected, and the other one is considered severely affected because it is completely crippled. "It has been upsetting to have this disorder show up in two litters," says O'Connell.
Pes varus affects less than 1 percent of Dachshunds, yet the condition has the potential to detrimentally impact quality of life, says Dan Burke, D.V.M., a clinician at the Veterinary Centers of America in Phoenix and a Dachshund breeder for 40 years. "I have been seeing more and more cases of pes varus over the last 10 years," he says. "The important thing to realize is that this is a genetic-based problem."
Experts suggest that the condition, medically known as angular hock deformity, has an autosomal recessive mode of inheritance, meaning affected dogs inherit a copy of the gene mutation from both the sire and dam. Carriers are not affected by the disease but can pass the mutant gene to 50 percent of their offspring.
Charlotte Borghardt, chairwoman of the Dachshund Club of America Health Committee, says pes varus has become more common in recent years. "We seem to have quite a few cases in our breed all of a sudden," she says. "It's important to get the word out to breeders and owners, so they will be aware of the condition and know what signs to look for."
A Bowlegged Appearance
Pes varus is a Latin term that combines pes (foot) and varus (inward) and describes a deformity in which the distal tibia is turned inward toward the body. The disorder occurs when the distal tibial (shinbone) growth plate closes prematurely, causing asymmetrical growth of the tibia that results in a bowlegged appearance and lameness.
E. Mayrhofer first reported pes varus, describing it as metaphyseal dysplasia of the tibia, in an article in the German veterinary journal Kleintierpraxis in 1977. Stuart G. Johnson, D.V.M., and his colleagues at Texas A&M University were the first to use the term pes varus, reporting favorable results from type-II linear external fixation devices to treat the condition in five Dachshunds in an article in Veterinary Surgery in 1989.1
The disorder also occurs in horses and humans. In people, the musculature deformity is called club foot and generally is corrected without surgery.
All bones have growth plates, called epiphyseal or ephiphysis plates. Immature, non-calcified cells comprise the soft, spongy matter that makes up young bones. As a puppy matures, the long bones of the legs grow from the immature cells located at the ends of the bones. When dogs are around 8 to 11 months of age, the distal ephiphysis growth plates close, a process in which they mineralize or become hard with calcium and minerals. Until these growth plates close, the bones continue to grow in length.
"In dogs with pes varus, the medial side of the distal growth plate closes prematurely, thus stopping growth, whereas the lateral side of the growth plate continues to grow," Burke says. "This causes an uneven growth of the tibia and a varus angulation of the distal tibia. While the lateral side of the growth plate functions properly, the medial side does not. Because the distal portion of the affected tibia is not level to the ground, the affected leg looks bowlegged."
In the early stage, pes varus is noticeable when a dog puts weight on the affected leg, with the body's center of gravity shifting toward the side of the affected leg. Viewed from behind, the heel is in the inward position. As the tibial deformity progresses, laxity of the knee joint and lateral dislocation of the patellar occur, causing a dog to walk with a limp or with the affected leg lifted.
Pes varus has been documented in all three coat varieties and in both Miniature and Standard Dachshunds. The disorder occurs globally, with cases reported in Dachshunds from Finland, the Czech Republic and Japan.
The disease ranges from mild to severe and can be unilateral or bilateral, meaning it can occur in one or both hind legs. The bowing of the legs usually is the first sign. Besides lameness, the disease can cause an inability to run and play, with dogs often stopping to rest after a few steps. When both legs are affected, one leg typically is more severely affected. Puppies with mild pes varus may show no clinical signs.
"The younger the age in which the growth plate closes, the more severe the deformity," says James Tomlinson, D.V.M., DACVS, professor of surgery at the University of Missouri College of Veterinary Medicine. "Dogs that are mildly affected generally have no long-term problems as long as they maintain a reasonable weight. Many moderately affected dogs adapt well with seemingly no pain or limitation in their ability to get around."
Surgery to correct pes varus, called an open-wedge osteotomy, generally produces good to excellent results, with most dogs making a full recovery within eight to 12 weeks. Without surgery, osteoarthritis is inevitable and dogs may have problems with corresponding joints such as joint incongruity and instability. Unfortunately, the procedure, which averages around $3,000 per leg but varies based on the geographical location, is cost-prohibitive to some owners.
"The open-wedge osteotomy involves cutting across the tibia bone, close to the curvature, while leaving a portion of the contralateral cortical bone intact," Tomlinson explains. "This creates a hinge on the lateral side of the tibia. As the bone is straightened, a pie-shaped wedge or deficit is created. Bone graft tissue is then inserted into the osteotomy site. Stabilization is done with a veterinary T-plate, a type of bone plate, or a modified external fixator."
Advantages of the bone plate include a low risk of postoperative infection. "Since the plate is embedded in the body, the affected limb can be used soon afterward and the hardware does not need to be removed," says Tomlinson. "The greatest chance for successful transplantation of live bone is with a cancellous autograph, which means the tissue comes from a dog's own body."
Cancellous bone, also known as trabecular of spongy bone, is harvested from the upper end of the humerous or the wing of the ilium. In Dachshunds, this is a small area of bone that is often difficult to harvest, Tomlinson says. An alternative is using cancellous allograft, or tissue harvested from a donor dog, or a collection of cancellous autograft tissue mixed with allograft tissue.
Avoiding a Genetic Bottleneck
When Jeanne Rice of Yatesville, Ga., bred her first litter of Miniature Dachshunds in 1970, one of three puppies developed a curvature of the tibia around 4 months of age. "Back then, breeders referred to this as bowlegged syndrome," she says. "No one really knew what it was."
Between 1970 and 1991, Rice had six litters (Longhair, Wirehair and Smooth) in which one puppy in each litter developed a unilateral curvature. Several veterinarians and orthopedic specialists examined and took radiographs of the dogs, but none was able to name the condition. Though she never learned definitely that the dogs had pes varus, Rice believes that this was the cause of their bowlegged appearance.
"When I tried to correlate the pedigrees and affected puppies, I could not find a commonality," Rice says. "Though I still don't know with a certainty that it was pes varus, I believe that the description of the condition and signs were similar."
Though pes varus is believed to be an inherited condition with an autosomal recessive mode of inheritance, there is no genetic test available to identify carriers. "This makes it difficult to offer solid recommendations to breeders," says Paula Henthorn, Ph.D., professor of medical genetics at the University of Pennsylvania School of Veterinary Medicine.
"You want to remove the deleterious genes, but not necessarily at the cost of removing all affected dogs and their immediate relatives (sires, dams, offspring and littermates) from the gene pool," Henthorn continues. "Doing so could create a bottleneck effect in which you inadvertently increase the risk for other diseases or conditions that are more complicated or life-threatening."
Henthorn advises breeders to consider all of a dog's attributes in choosing breeding partners. "It also is important to keep accurate records," she says. "If the mode of inheritance is autosomal recessive, a dog may be clinically normal but a carrier for pes varus."
Though no genetic research is planned to identify the causative mutation for pes varus, Borghardt is optimistic that a project could come about in the not-too-distant future. Research support via funding and sample collection will come through educational efforts, she believes.
O'Connell, who has begun submitting blood samples from her affected and normal Dachshunds, agrees. The samples are stored at the DNA Repository at the Canine Health Information Center (CHIC), a canine health database sponsored by the Orthopedic Foundation for Animals and the AKC Canine Health Foundation.
"If other breeders of affected and normal dogs would collect and store DNA, we would have a larger DNA collection ready when the research begins," O'Connell says. "That's my goal. I hope that one day we'll know much more about this disease in Dachshunds."
Purina appreciates the support of the Dachshund Club of America and particularly Charlotte Borghardt, chairwoman of the DCA Health Committee, in helping to identify topics for the Purina Pro Club Dachshund Update newsletter.