I was fortunate enough to have a chance discussion with a Vet recently and as the conversation about the common complaints amongst humans and animals unfolded over a beer he informed me that:
“You know, Dogs don’t get Disc bulges…”
“So what” I hear you growl….
Well, I think this is pretty fascinating. You see, Humans get a a fair few disc bulges in the spine. The intervertebral disc is a squishy cartilaginous tissue that separates the spinal bones (vertebrae), it gives flexibility to the spine. Disc bulges are very commonly seen in the neck and the lower back on MRI scans (see Becky’s great blog on this “Dont despair at disc degeneration). They are exactly as they sound, a soft structure that has started to bulge a little due to degenerative changes over time. Sometimes they can bulge out towards nerve tissue but they cause little compression and hence little in the way of symptoms. Sometimes the soft inner part of the disc can push out a lot further and this can cause compression on nerve root leading to pain and dysfunction, these are quite different to bulges and we refer to them as disc prolapses.
Unfortunately, in the past a lot of attention was drawn to disc bulges as the cause for peoples back pain and and as such we got pretty obsessed with them. However as we have gained more knowledge on how people feel back pain we now understand that actually they don’t cause much pain and are a relatively irrelevant finding on MRI scans, but interestingly…. Dogs don’t get them.
I am told by my Veterinary friend that Dog’s do get problems with discs, though these are often much more severe prolapses of the disc that require surgical intervention to fix the problem, however scans rarely show small bulging of the discs like in humans. This got me curious. What is it about a canine spine that is so different to a human spine that seems to prevent this degenerative change?
Of course the fact that dogs walk on all fours and carry their spines in a horizontal manner must be part of the cause, but there are some other factors….
You could argue that Dogs are much more active than most humans. Dogs don’t sit and drive to work, sit at work all day then sit and drive home for another hour, struggling to fit in their 30 minutes of activity a day due to busy lifestyles. Dogs will walk/ run a significant distance (they have smaller legs than us!) every day and have you ever noticed how much they stretch out when laying out all cosy and comfy in front of the fire? All of this exercise and stretching is of course very helpful for the spine and the absence of prolonged sitting in their daily routine may lead to less weakening of the disc wall which can lead to disc bulging. Though I’m not convinced this is the only reason we don’t see as many disc bulges in dogs….remember to see a disc bulge you have to scan the back.
Dogs don’t often have MRI scans for back pain, this is something that I think is a key point. They will have an MRI scan when they have a functional problem, ie the owner notices that they cannot jump up into the car as easy as they used to, as this may be caused by a nerve in their back being compressed by a prolapsed disc. Unless we are Dr Doolittle, it is pretty unlikely that we will know Rover the Labrador will have been complaining of back pain too much.
In the past the medical community has been quite quick to arrange MRI scans for humans with simple mechanical back pain. We know now that very often this doesn’t help and often shows up normal age related changes in the spine that in the past have been erroneously attributed to the cause of peoples back pain. So if they don’t have a lot of MRI scans maybe this is another reason why we don’t see a lot of disc bulges in Dogs.
Very often patients will ask for a scan of their spine if they are in pain and the point I am trying to make here is that very often for simple mechanical back pain an MRI scan will not help us much as it doesn’t identify a particular tissue at fault and it wont change the outcome. Physiotherapists have significant training in spotting signs and symptoms during your assessment which help us to identify people who will benefit from a scan (particularly if the pain doesn’t appear to be mechanical back pain) but the vast majority of back pain will ease with exercise, stretching , keeping active and fully mobile – just like our four legged friends.