This is a two part blog post written in conjunction with Hannah Oliver-Byrne of Combined Physio. You can find her post on physiotherapy for hip arthritis here.
We’ve all heard it – “My dog’s got hip arthritis”, but what does this actually mean? Well arthr… means “joint”, and anything ending in -itis means “inflammation” (e.g. appendicitis is inflammation of the appendix). So arthritis = joint inflammation. Sometimes we hear the term “osteoarthritis” meaning inflammation of the bone within or around the joint.
Now we’ve got that out of the way, we can talk about hip arthritis. The hip is a ball and socket joint. The ball sits on top of the long bone in the leg (the femur) and fits into a cup or socket on the pelvis and is held there by fibrous rope-like ligaments. The bony ball and socket are covered with a soft rubbery material called cartilage. Hip arthritis means inflammation of the bone or cartilage anywhere in this joint.
Injury to any tissue in the body immediately starts the healing process. Usually we see bleeding, followed by clotting, followed by fibrosis where fibrous tissue is laid down, and ultimately final repair. In bones, we see an extra step after fibrosis where calcium is deposited to stiffen the repair and ultimately form bone. This process results in an increase in blood supply, swelling, heat and pain due to the release of certain chemicals – we call this “inflammation”. In a damaged hip we can use xrays to see the extra bone being formed as the body tries to repair and stabilise the joint.
So what causes the damage that eventually results in arthritis?
Wear and tear – just like any machine, the longer we use it, the more wear we produce. Cartilage gets bruised and ligaments get stretched. As our dogs get older their healing response becomes less and less effective, ligaments lose their elasticity and cartilage becomes more fragile. Trauma tends to increase as exercise levels drop and weight increases, putting more strain on the joint. Eventually we see damage to the joint outpacing the body’s ability to heal. The continual trauma creates a permanent repair mode in the joint; and as we’ve just seen, repair=inflammation.
Hip dysplasia – What does this exactly mean? Anything ending in -plasia means growth, and dys… means “faulty”. So dysplasia = faulty growth. The reasons why dogs’ hips don’t form properly are shrouded in a mist of genetics, obesity and exercise issues but the ultimate outcome is the same: a ball on top of the femur that doesn’t perfectly fit the socket on the pelvis.
Visualise it like this- make a cup shape with one hand, then push your other hand closed in a fist into it. Make sure your fist is snugly cupped by the other hand then gently rotate it. This is how a normal hip joint should operate. Rotation is smooth and load is distributed evenly across the joint as it’s such a good fit. Now slightly open the hand that cups the fist and move the fist around. Notice how the fist can now skid around the cup a bit like a mortar and pestle. Because the curve of the socket doesn’t fit the curve of the ball, load is focussed over a smaller area causing pressure. The ball can skid across the cup and crash into the other side causing bruising. This deformity eventually results in a chronic repair site, and chronic painful inflammation.
It’s worth pointing out at this point that this chronic inflammation further disfigures the hip joint as extra fibrous tissue and bone is laid down around the joint due to the repair processes. This extra tissue physically restricts joint movement, and is painful as it is stretched by joint movement. You can see the extra bone in the xray above under the red spot.
So whatever caused the problem in the first place, a dog with hip arthritis ends up with a joint that is painful and restricted in motion. As time goes by and the dog uses the joint less, muscle wastes the joint becomes even less functional. The dog becomes lame, and may adopt a “bunny hopping gait”:
Remember- if your dog is lame, it is painful.
So what can we do to treat this?
I like to think of treatment for arthritis like a pyramid. We add on layers of treatment starting with ones that have fewer side effects and are cheaper first. We build up the pyramid using progressively more difficult treatments until at the top we end up with pharmaceuticals and surgery.
Layer 1: Remove the root cause! Not much we can do about ageing, but we can get our dogs to lose weight. In doing so we’ll reduce the force acting through each joint and so reduce trauma. Think about changing beds to memory foam and putting down rugs on slippery floors to reduce the chance of further injury.
Layer 2: Physiotherapy- I’ll leave this for Hannah to talk about, but suffice to say that it’s essential! You can see her post here…
Layer 3: Neutraceuticals (or supplements). The evidence for much of these supplements is mixed to say the least. Chondroitin, glucosamine, green lipped mussel extract, devils claw and tumeric have all been used with varying degrees of success. There may be some action we don’t understand here so give them a go and see if any of them help to reduce the pain. (I’m going to lump homeopathy and magnetic collars in here too – no evidence to support their use but some of our clients swear by them)
Layer 4: NSAIDs. Now we’re looking at the big guns. (N)on (S)teroidal (A)nti-(I)nflammatory (D)rug(s) are the mainstay of pharmaceutical relief. The most common human drugs are ibuprofen and meloxicam, and in dogs meloxicam and carprofen (ibuprofen is pretty toxic for dogs). Brand names to look out for are Rimadyl, Metacam and Loxicom.
These drugs work by suppressing the production of inflammatory chemicals within the joint.
No inflammatory chemical = less inflammation = less pain and slower disease progress
Unfortunately this suppression also reduces the production of the protective lining of the stomach.
Less protective lining = acid damage = ulceration
Not every dog suffers from this problem, but a minority are very sensitive. Higher dosage means a greater danger of side effects. So what happens if your dog can’t cope with these drugs?
Layer 5: COX-2 inhibitors: remember how NSAIDs suppress the production of inflammatory chemicals? Well it does this through suppressing an enzyme called cyclooxygenase (COX), of which there are two forms: COX-1 produces the stomach lining, COX-2 produces the inflammatory chemicals. COX-2 inhibitors are a more modern NSAID- by preferentially suppressing COX-2 we can save the stomach lining and hence reduce stomach ulcers. Brand names to look out for are Onsior and Previcox. Unfortunately they still have some effect on reducing stomach protection, and some dogs can’t even cope with these.
Layer 6: Anti-inflammatory steroids e.g. PLT (prednoleucotropin) Expensive and have the same side effects of steroids, which no-one wants! Nevertheless can still be useful.
Layer 7: I’m going to call these non-anti-inflammatory pure pain killers. NSAIDs, COX-2 inhibitors and steroids work by reducing inflammation in the joint. By doing this they will slow down the process by which the arthritis worsens. There are other drugs around that are pure pain killers, but crucially don’t do anything for the inflammation and so don’t slow down the disease process:
- Fentanyl patch
So a dog with hip arthritis will commonly be put on a diet, given supplements and physiotherapy and be on some form of anti-inflammatory and/or pure pain killer (don’t forget anti-inflammatories are also pain killers). So what if we still can’t control the pain?
Surgery is the last resort for patients which do not respond to any of the therapies mentioned above. For dogs early in life that look have hip dysplasia we can consider surgery such as juvenile pubic symphysiodesis or triple pelvic osteotomy. These surgeries aim to move the cup of the pelvis further over the ball of the feumur and hence reduce trauma; although hip arthritis is still inevitable, it will hopefully be less serious and later in life.
For dogs that have pre-existing hip arthritis we can looks at pectineal myotomy, femoral neck and head excision, or even total hip replacement. With costs for these surgeries ranging up to £6,000, prevention is definitely better than cure!