Mayflower was a six-pound, nine-week-old rescue puppy arriving on the Vineyard from an animal shelter in Tennessee by way of Rhode Island. Her papers said she might be a Boxer cross…or maybe part Chihuahua. Now there’s an interesting mix. “I’ve only had her five days,” her mom reported when she brought May for an introductory checkup. “She’s the cutest little thing, but I just noticed today there’s something wrong with her front leg.” I took a look. Mom was right. Mayflower was pretty darn cute…and her front leg was definitely abnormal. The wrist portion, technically called the carpus, buckled forward, giving her a kind of “double-jointed” appearance. “She doesn’t seem to be in pain,” her owner added, “but it sure looks strange.” “Let’s take a few X-rays,” I suggested.
“Juvenile carpal flexural deformity,” I announced 20 minutes later, after finding no bony abnormalities on the films. “Also called ‘puppy flexor deformity.'” I couldn’t recall seeing a case exactly like May’s before, but my veterinary database was full of pictures of pups with identical, odd-looking forelimbs.
Usually occurring in dogs less than four months of age, this syndrome is actually one of two conditions collectively called “carpal laxity syndrome.” In flexural deformity, the wrists bulge forward. In other words, they are hyperflexed. Conversely, the wrists may be hyperextended, dropping down toward the floor, giving the dogs a sort of bowing appearance. Carpal laxity syndrome is thought to be the result of an inequity between the growth rate of the bones and that of the tendons. Some propose that malnutrition or, conversely, overnutrition, especially in rapidly growing large breed puppies, may weaken muscles and tendons or contribute to irregularity in the tension load, leading to the abnormal positioning. Hyperextension laxity is seen primarily in large breed dogs with some studies suggesting Doberman Pinchers and Shar Peis may be predisposed. Carpal laxity can affect only one front leg or both. It can occur in one leg and then later develop in the other. Occasionally it may resolve and then recur.
Although the funny, wobbly appearance of May’s forelegs might lead one to think they should be splinted, that is not the case. Splinting doesn’t change the course of this syndrome. Hyperflexion usually resolves all on its own in two to four weeks. Hyperextension also typically self-corrects though may take a bit longer, up to several months, depending on the severity.
“Make sure May is being fed a nutritionally adequate diet,” I advised, “but also that she is not being oversupplemented. Keep her on surfaces with good footing,” I continued. “And avoid too much exercise and activities like climbing stairs or jumping out of the car until her legs look normal again.”
Carpal flexural deformities also occur in the young of other species like calves and foals. Now, the closest I’ve gotten to a horse in 20 years is dropping my daughter off at the barn for her riding lessons. (Okay, I tried getting back in the saddle once or twice but ultimately succumbed to my fear of…well, horses. And broken bones.) But I digress. The point is, I’m going to tell you a bit about carpal flexural deformities in newborn foals, often called “contracted tendons,” but I’m no horse doc. If you’ve got a foal with funny forelegs, talk to an equine veterinarian.
Foals with carpal flexural deformity may look like they are standing on tippy-toe, or wearing high-heels. Proposed causes include genetics, malpositioning in the uterus, rapid growth, nutritional deficiencies, or conversely, feeding an excessively nutrient-rich diet. Each case is individual and must be assessed as such. Affected foals may have difficulty nursing due to pain and an inability to stand steadily, making them more prone to aspiration pneumonia, failure to thrive, and infections. In mild cases, if the foal can actually get the bottom of the foot flat down onto the ground, the problem may resolve spontaneously as the weight of her growing body helps stretch the tendons.
Listen carefully to your veterinarian’s advice about any recommended changes in feeding and exercise. Some exercise is good. Too much is bad. A balanced diet is good. Too much or too little of certain nutrients is bad. There is no one-size-fits-all prescription. As long as you see progressive improvement, then no further intervention may be needed.
More serious cases warrant more aggressive treatment. One technique commonly used involves giving the foal oxytetracycline, an antibiotic, administered very slowly intravenously and then applying a temporary splint to the leg. Why an antibiotic? Is there infection in the legs? Nope. Besides its antimicrobial action, oxytetracycline also binds calcium in the system, which temporarily causes muscles to relax. As the muscles loosen, the leg relaxes into a slightly more normal position and a splint can be applied. Your veterinarian will likely want to check your foal’s kidney function before and after this treatment, and give her pain medications and gastric protectants as well. The oxytetracycline may be repeated every other day for a few times and the splints are usually left on for only short periods of time. For foals that do not respond to conservative medical treatment and splints, surgery may be required. Carpal flexural deformity can also occur in mature horses, usually as the result of injury or malnutrition, in which case you should definitely be getting advice from someone besides me.
For little Mayflower, however, I was confident about sending her home with a prescription for “tincture of time.” Her owner very sensibly was content with our “wait-and-see” attitude and the recommendations about diet and activity, while we gave Mother Nature a chance to straighten things out. Three weeks later May’s legs look right as rain…but I still can’t decide if she’s more boxer or Chihuahua.