Chronic pain in dogs – Canine osteoarthritis

Osteoarthritis – what is it?

Osteoarthritis is a disease commonly caused by developmental abnormalities of the joints.

It is progressive, disabling and non-curable and one of the most common causes of chronic pain in dogs, affecting one in five dogs. It is commonly diagnosed in older dogs, aged eight and above, but can also develop earlier. It can be very painful and affect the whole quality of life. Chronic pain has been linked to depression and anxiety in many studies, so it is very important to treat the pain with efficient treatments.

Reluctance in jumping or moving as usual can be a sign of osteoarthritis. Photo: Adobe Stock

What happens inside?

In developmental osteoarthritis, usually the joints don’t move as smoothly as they should and this results in damages to the structures within the joint. Osteoarthritis can also be acquired. It means that due to injuries and trauma, infection or immune-mediated disease, osteoarthritis can develop without genetic likelihood to have it.

In osteoarthritis, the cartilage breaks down faster than it repairs itself and that process results to degeneration of the cartilage. The inflammation in the joint causes pain and swallowing.

Osteoarthritis, destruction of cartilage – human model. Photo: Adobe Stock

The degeneration of cartilage has been thought to be the primary change, but it has been found that a combination of cellular changes and biomechanical stresses cause also several secondary changes. Those secondary changes can be subchondral bone remodelling, the formation of osteophytes, the development of bone marrow lesions, change in the synovium, joint capsule, ligaments and periarticular muscles, and meniscal tears and extrusion. (Man & Mologhianu 2014)

What is pain?

Pain itself is a way of the body to tell that something is wrong. Acute pain is severe, rapid and comes with a pain response that is usually recognizable like whining, yelping, limping… Chronic pain lasts for longer than a normal tissue would heal and is usually associated with a pathological condition that doesn’t heal. It progresses slowly and symptoms are more subtle.

Pain starts with painful stimulus and the stimulus is then converted into a chemical signal at the nociceptor cell which is also known as pain receptor. Then the signal is transmitted to the brain via the spinal cord, which creates a pain response. There are two types of nociceptors: A-delta fibres which conduct rapid pain signals to the spinal cord and causes acute pain and C fibres, which control slow, persistent pain reaction.

 

How pain stimulus is becoming pain response

 

Osteoarthritis usually progresses in time and can be described as musculoskeletal chronic pain. Chronic pain alters the brain and nervous system because the painful stimulus occurs often. Central sensitization might happen, which means that the nervous system gets regulated in a persistent state of high reactivity. It means that it lowers the threshold for feeling pain and the body is in alert mode all the time. This usually leads to behavioural changes, as the body of the dog has heightened sensitivity to pain and the sensation of touch.

Can my dog have osteoarthritis? The most common signs of pain

Chronic pain is developing little by little and the first signs of pain are very subtle. Dogs are very good at compensating the pain and they find alternative ways to move, which don’t cause that much pain or stress to the sore joint. Compensating in movement can create problems elsewhere, as then some areas are used more than they should be. It is very hard to see the signs of chronic pain as they develop slowly and the owner gets used to the changes. Changes in movement and behavioural changes are signs that should be looked into.

Changes in movement

Usually, the first signs of pain are changes in the way the dog moves – for example, the dog is more reluctant to jump into a car/sofa, the dog is more often pacing instead of gaiting or goes from walking straight to galloping. Changes in how the dog is laying down, if getting up is looking more difficult or changes in the posture can be signs of musculoskeletal pain. Clear signs of strong pain are limping or whining when moving.

Limping is a sign of severe pain. Photo: Adobe Stock

Behavioural changes

Overall mental state and mood of the dog are good indicators of pain. Increased sleeping and lameness are usually signs of that something is wrong. Increased aggressive or fearful behaviour are common behavioural changes in dogs with chronic musculoskeletal pain. In a study by Mills et al (2019) for example defensive behaviour, changes in learning and performance, house-soiling problems, attention-seeking behaviour, obsessive-compulsive types of behaviour, pica (eating inappropriate things, for example stones) and other behavioural problems were linked to pain. Over aroused or excitement in stressful situations can also be one coping mechanism as the behaviour produces adrenaline and dopamine, which can mask the feeling of pain.

 

If your dog wants to sleep more, he might be in pain. Photo: Adobe Stock

Behavioural changes are a complex set of pain indicators, which can sometimes lead to misinterpretations. Some behavioural problems can be just learned habits that can be trained with positive reinforcement and behavioural modification, but sometimes those are signs of pain. Central sensitization commonly plays a big role in behavioural changes and aggressive behaviour towards people and other animals. As the nervous system of the dog is alert all time, it can lead to aggressive or avoidance behaviour to avoid touching or other things that cause pain in the individual. Central sensitization can lead to other heightened senses also and humans with chronic pain sometimes report sensitivities to light, odours and sounds. This may also affect the behaviour of the dog. And as the nervous system is responsible also for emotions and if it is stuck in a persistent state of reactivity – the dog will be literally nervous which can be seen as anxiety-like behaviour.

 

Aggressive behaviour is usually linked to pain. Photo: Adobe Stock

How to assess if your dog is in pain?

It is very important to assess the pain of the dog with a validated pain score outline – it helps with making the diagnosis and keeping on track on how the pain is developing. It helps both the owner and the veterinarian to have a clear view of the state of the dog and to decide the relevant treatment. Veterinarian always makes the final diagnosis by medical examination.

Helsinki Chronic Pain Index is made by Anna Hielm-Björkman and it is easy to use on daily basis. HCPI is designed to assess chronic pain in dogs.

You can download a printable version from here:

Helsinki Chronic Pain Index (HCPI) – this version is translated and made by Four Leg Rehab Inc

Osteoarthritis is a common and non-curable condition, which causes chronic pain. The pain can be prevented or prolonged by keeping the dog in normal weight and in good muscular condition. The pain can be treated to some point with medical support, which should be planned with a veterinarian.

Key sources

Canine Arthritis Resource and Education CARE – www.caninearthritis.org
Canine Arthritis Management – https://caninearthritis.co.uk/
Tassuapu – www.tassuapu.fi
Institute for Chronic Pain – www.instituteforchroicpain.org
Science Translational Medicine Journal
PAIN® Journal
Preventive Veterinary Medicine (Could it be osteoarthritis? How dog owners and veterinary surgeons describe identifying canine osteoarthritis in a general practice setting, Belshaw et al, 2020)
Animals (Pain and Problem Behavior in Cats and Dogs, Mills et al 2020)
Journal of Medicine and Life (Osteoarthritis pathogenesis – a complex process that involves the entire joint, Man & Mologhianu 2014)
Notes from lectures Mechanisms of Behaviour; Behaviour and The Nervous System, Behaviour and The Endocrine System, The Pain Pathway. By Jo Bond, University Centre of Sparsholt

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