Linda Lombardi

A number of studies have found a relationship in humans between anxiety and a condition called joint hypermobility syndrome (JHS). Now a study has found a parallel association in dogs. This provides insight into understanding this correlation in people, as well as providing something to think about in dogs with anxiety and dogs with hip problems.

Coauthor James A. Serpell, Ph.D., professor of animal ethics and welfare at University of Pennsylvania, says humans who suffer from this condition essentially have loose joints and are more prone to dislocations and osteoarthritis. They also have a higher prevalence of anxiety, fear, panic, and a range of psychiatric disorders than the general population.

“There’s a lot of speculation about what could be the possible connection between the two,” he says. “One theory is that loose joints cause people to be anxious because they’re constantly worrying about the health consequences of their condition.”

Testing Method

The researchers tested that hypothesis by looking at whether the correlation held in another species that was not capable of that kind of understanding and worry. It was possible to test this on a large scale using already-existing data for guide dogs. The organization The Seeing Eye routinely tests puppies for joint problems at 18 months. Puppy raisers also fill out the C-BARQ, a standardized behavior evaluation. Researchers looked at these records for 5,575 dogs.

“We found that there was a strong association between a behavior variable that we call excitability, but that you could also call hyperarousability, and loose hips in these dogs,” Dr. Serpell says.

Trait and Anxiety Linked?

While they did not find a direct link with anxiety, there is likely a link between that trait and anxiety. “The literature in humans suggests that the reason that some people become anxious is simply because they’re more reactive to things in their environment,” Serpell says.

Finding a link between the physical condition and similar behavioral traits in dogs, then, casts doubt on the “health worries” explanation for the association. “The conclusion is, it’s very unlikely that the reason that people with joint hypermobility are anxious is because they’re anxious about their health condition, because we’re getting the same thing in another species,” he says. “This suggests that there must be some underlying link between the two.”

The exact nature of that link is currently unclear, but it is known that people with joint hypermobility show differences in their brains, particularly in areas related to emotional response. “This would suggest that we would find a similar difference if we were able to look into the brains of these dogs, and that there’s a direct link between these changes in brain anatomy and physiology across species that is involved in this strange link between joints and brains,” he says.

“This study add one more relevant piece to the puzzle of the interaction between behavior changes and medical problems,” says Carlo Siracusa, DVM, Ph.D., DACVB of the University of Pennsylvania School of Veterinary Medicine. “There is a growing body of evidence showing that animal behavior is regulated by the same immune and inflammatory response behind medical problems. So, it is probably time to retire the question ‘Is it medical or behavioral?'”

Socialization Effect

Serpell says the fact that the association was indirect – the dogs were excitable, but not necessarily anxious – is likely due to the strong impact of early socialization. “So much of anxiety-related behavior in dogs is linked to poor early socialization,” he says. “So instead what we’re picking up is something at a deeper level–a tendency to react strongly to the environment, which my guess is, would be less likely to be influenced by early environment than something like anxiety.”

Guide dog puppies are particularly well socialized, reducing the chance that they’ll be anxious adults even if they have inherited a genetic tendency to excitability and anxiety. Serpell notes that they’ve also been selected for generations against that trait. “I should say this somewhat cautiously, but so in some ways this was the worst population to look for this type of association, because the amount of variation they show is rather limited, because of selection and because of very careful early socialization.”

The fact that an association was found anyway suggests that if we could look instead at the general population of dogs, the association might be even stronger. Another limitation of the study is that the breeds were limited to those typically used as guide dogs. There are breed differences in tendencies to both excitability and joint problems, so further research is necessary.

Another possible explanation for the association, that the anxiety is caused by constant low levels of joint pain, seems unlikely, says Serpell. These dogs are young enough that although they are likely to develop hip problems later in life, they’d be unlikely to be in pain now, and their ratings on the C-BARQ did not show touch sensitivity.

That said, osteoarthritis does occur in young dogs. Even puppies younger than one year can experience lameness and chronic pain from it so that explanation remains a possibility.

These findings can be seen as another argument for the importance of proper early socialization, particularly in puppies who are excitable, since the implication is that they are more likely to develop anxiety. Another possibility, not suggested in the paper, is that we might want to be more aware of the potential for joint problems in dogs with these behavioral tendencies.

“That’s certainly something we could think about,” says Serpell. “If you’ve got a highly arousable dog that reacts very swiftly to environmental triggers and is slow to calm down after it gets aroused, then maybe yes, we should be giving special consideration to the possibility of joint hypermobility, particularly if it’s a medium to large breed dog where the consequences of it are likely to be more severe.”

This article was reviewed/edited by board-certified veterinary behaviorist Dr. Kenneth Martin and/or veterinary technician specialist in behavior Debbie Martin, LVT.

Linda Lombardi writes about the animals who share our planet and our homes for magazines including The Bark, websites including National Geographic and Mongabay.com, and for the Associated Press. Her most recent book, co-authored with Deirdre Franklin, is The Pit Bull Life: A Dog Lover’s Companion.