There is a well-established relationship between joint hypermobility and anxiety in humans, that has not previously been investigated in other species.
A population of 5575 assistance dogs were scored for both hip hypermobility and 13 behaviour characteristics using previously validated methods.
Our results suggest a positive association between hip joint hypermobility and emotional arousal in domestic dogs, which parallel results found in people.
Since our first observation of the strong association between anxiety and joint hypermobility1, in people, a number of additional studies in clinical and non-clinical groups have supported the association between joint hypermobility syndrome (JHS) and anxiety, and with underlying features such as affective reactivity.
Human patients with JHS exhibit significantly greater manifestations of fear, agoraphobia and panic 4.
Suggested mechanisms in people include indirect effects on emotional and mental state through dysregulation of autonomic responses 5, involving brain regions such as the insular cortex, amygdala and anterior cingulate cortex, which are linked to increased autonomic arousal that intensifies emotional states6.
Also, it has been proposed that anxiety could be linked to pain and a greater perception of joint instability in human patients with JHS8.
This makes it sound like they’re saying anxiety leads to a greater “perception” of joint instability when I believe it’s the other way around: perception of my joint instability leads to anxiety.
Here we present the first evidence for an association between hip joint hypermobility and behavioural arousal in a non-human species.
This suggests that the link between hypermobility and behaviour regulation is phylogenetically old and could potentially be a universal trend among mammals.
It has been suggested in the literature that a human patient’s conscious awareness of the negative consequences of joint instability for their health might be the primary source of their stress and anxiety.
The findings of the current study challenge that interpretation.
Finally, proof that the pain arising from the defective connective tissue around our unstable joints (and other body parts, large and small) is NOT biopsychosocial.
If an animal can have the same link between JHS and anxiety, then our anxiety is a manifestation of a physical state, NOT our psychology or social conditions.
We selected the domestic dog (Canis familiaris) as a candidate species as it presents physical health problems related to JHS and experiences naturally occurring behavioural disorders that show face validity, and potential homology, with previously defined psychiatric disorders in humans10.
Hip joint hypermobility is a risk factor for canine hip dysplasia (CHD), one of the most prevalent developmental orthopaedic diseases in dogs worldwide.
radiographs of the hip joint are taken under extension and the extent to which the head of the femur can be displaced from the acetabulum is measured 12.
The C-BARQ sub-scales include
- stranger-directed aggression,
- owner-directed aggression,
- dog-directed aggression/fear,
- familiar dog directed aggression,
- stranger-directed fear,
- non-social fear,
- separation-related problems,
- touch sensitivity,
- attachment/attention seeking, and
We found 4 clusters of dogs based on their DI
Binary logistic regression (BLR) allowed us to identify behaviour and demographic factors associated with membership of the two clusters with the highest and the lowest hypermobility scores.
Females were 3.66 times more likely to be in the high hypermobility group than males, which is consistent with findings in humans 8.
With regard to behavioural traits, higher scores for excitability and aggression towards familiar dogs were associated with belonging to the high hypermobility cluster.
Excitability is a fundamental characteristic of emotional responses.
Emotional reactions to stimuli consist of two dimensions; valence and arousal.
Valence refers to the negative or positive character of the response, and arousal to its intensity.
In the method of behavioural assessment used in our study, excitability is an indication of the ease with which an individual enters a state of high emotional arousal in response to an external stimulus or event, regardless of emotional valence.
The C-BARQ describes a highly excitable dog as one that shows marked behavioural arousal, including barking or yelping at the slightest disturbance, rushing toward and around any source of excitement, and having difficulty calming down.
In humans, increased arousal has been linked to anxiety symptoms even in the face of neutral stimuli17.
When interpreting the apparent association between hypermobility and behavioural characteristics found in our results, pain should be considered a potentially influential factor.
Pain is never a “potentially influential”. For all animals, including humans, pain is “always influential”.
In summary, our results in Seeing-Eye dogs suggest that the link between hypermobility and emotional arousal is not limited to human beings.
Also, we hypothesise that overall excitability could be a key underlying trait involved in the development of anxiety-related disorders both in humans and animals
However, since this study involved a selectively bred population of assistance dogs, further work is required in order to determine whether these findings can be generalised to other types of dogs.
Coincidentally, I adopted a dog, Jordie, almost 10 years ago who has exactly these traits.
He’s as flexible as any cat and has the extremely loose skin usually found only on puppies. Additionally, he has terrible anxieties of all kinds, like abandonment issues and PTSD (from previous abuse?).
Since I was a teenager, I’ve clipped nails on my own dogs and even on other people’s dogs, but none have responded with the hysteria I face with Jordie every couple of months when I have to do this task.
He’s afraid of being “held down” and afraid of having his nails touched even with my fingers alone, making this bi-monthly task torture for both of us, no matter how careful I am.
But he also displays the positive side of his hypersensitivity: he’s joyously happy to see us if even if we’ve only been gone a few minutes and he greets anyone he knows with leaps and bounds of happiness, jumping into the air and twirling around with wild abandon.
So Jordie precisely fits the description of hypermobile dogs in this article, for better and for worse.