Cartilage gets squished when you stand

Reprinted from Coleman et al 2012, yes with permission. It cost me $20 just to use it!
You can see the cartilage of a healthy human joint outlined in yellow (from an MRI).

I recently came across a great little paper on knee joint thickness by Coleman et al. It confirms what we may have already known or guessed.... but it does it beautifully and in a highly quantified manner. The data is from humans, but I would expect that similar would be seen with doggies! Very sophisticated experimental techniques, and modelling with some lovely beautiful pictures (!) and well controlled data.
Read the paper here Coleman et al 2012
The paper shows that there is a physical squeezing and compressing of cartilage when you stand up.  This has all kinds of ramifications to scientists who work in the area (like us!!).
The difference in thickness is quite small between day and night, but certainly significant in the knees.
Snippets of the data are that men's cartilage is much much thicker than womens'... and of course, there is a significant correlation between cartilage strain and body mass index (BMI).
...So if you want nice thick knee cartilage; be a chap, spend the day in bed*... but don't eat too much!!!

*...but seriously: it is generally accepted that moderate exercise is good for healthy joints, but excessive weight is an absolute no no......

Other blogs pertaining to osteoarthritis and exercise:
What Gives People and Animals Arthritis
Is Running Good for Your Health
Exercise and osteoarthritis

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Is Running Good For Your Health?

Here is the update on this blog:  
For a proper academic review of this subject see  Hunter and Eckstein 2009.

Exercise and osteoarthritis, two recent reports have been published with apparently conflicting conclusions:The medically orientated Nature Reviews in Rheumatology suggests there is (as I suggested in the previous blog optimal joint usage for healthy cartilage), and a sports medicine journal article from Dr Williams suggests that long distance running decreases risk of osteoarthritis.  

Naturally, from the Twittersphere, those people who love running feel their pursuit has been justified.  those people who commercial promote exercise will use it as propaganda.  I find it sad that on this issue, just like so many, people pick the evidence that suits their believes rather than balancing evidence.

Now lets start with a reminder.  Osteoarthritis is a condition of painful joints, which involves the whole joint, but one of its hall marks is the loss of cartilage.  Cartilage lines the hip and knee joints.  The cells that make it (chondrocytes) actually sit within the the cartilage of the joint.  They respond to the loads placed upon the joint by producing cartilage... within reason.  If you don't use a knee and hip joint at all, you would expect the muscles to waste away, the bones to become thin and brittle, and the cartilage become thin also.  I think we can probably all agree on this.  However, cartilage is a living tissue.  It is not shoe leather.  Part of the confusion is caused because cartilage has no blood vessels so it does not bleed, and it has no nerve fibers running out of it so you don't feel pain from the cartilage itself.  But it still needs to be loved!  We know for absolute certainty that excessive weight (high BMI) promotes you getting osteoarthritis, even the Dr William's paper shows this.

There is clearly debate as to how much usage is ideal.  The sporty paper could be used to support the argument that "it's the more the merrier", but there are huge confounding variables.  The author did what he could, but it is difficult!!! The analysis was not able to exclude two possibilities (1) That slimmer people (with lower BMI) may run more and (2) That people could start to run less when they get painful joints. If you believe that either (1) or (2) could be true they presumably you will come to the conclusion that this new paper does not really answer the key question of how much usage is ideal.

So the other paper, the Nature review?  Well it is just a few line summary of a very thorough paper in the "Osteoarthritis and Cartilage" journal.  But This is what is reported.  The LEAST active elderly people loose cartilage, but so do the MOST active!!!  Activity is assessed with a PASE survey, and yes age and BMI is taken into account.  Also, the study tracks people and so ceasing activity due to joint pain is less of a factor.  Now bare in mind this is activity assessed by PASE not running marathons!  PASE asks a number of activity questions, see Table 1. They then considered the top 15% and bottom 15% activity rates and compared against the middling people.
...BUT and here is the elephant in the room.  The health crises we have at the moment is due to obesity and lack of exercise of people, not over exercise, so whilst I would suggest that the jury is out on how much exercise is good for your joints.... for the rest of you LOTS of exercise is clearly a great thing.  ...and for me too, but I am lazy :-/

 So the conclusion:  Everything in moderation? 

Table 1: PASE Activities, Performances and Weight Scores
PASE stands for: Physical Activity Scale for the Elderly

Activity	Answer	points
Walking and bicycling	Hour/day	20
Light SRA	Hour/day	21
Moderate SRA	Hour/day	23
Heavy SRA	Hour/day	23
Muscle strength/endurance	Hour/day	30
Paid/unpaid work	Yes/no	21
Light housework	Yes/no	25
Heavy housework	Yes/no	25
Home repairs	Yes/no	30
Lawn work	Yes/no	36
Gardening	Yes/no	20
Caring for others	Yes/no	35

 

What causes arthritis in people and animals/dogs

I am hoping to expand this section greatly, but for the time being lets keep this very simple:

In people there are two (common) very clearly distinguishable types of arthritis, rheumatoid arthritis and osteoarthiritis.  Hallmarks (according to a rheumatoid consultant colleague of mine) of rheumatoid are initial stiffness, whereas osteoarthritis tends to being with pain.  In dogs, arthritis is most commonly osteoarthritis, very similar to that seen in humans.  In all cases, there is some inflammation (so this includes swelling and stuff)... but rheumatoid is an autoimmune disease, where the body's own defence system attacks itself.

There are several treatments available, but the sad fact is none of them are terribly brilliant. Many will help a bit, prolong mobility and reduce pain, but there are no cures. 

Causes:  I think we would have to say rheumatoid is mostly genetic. Osteoarthritis is very clearly multifactorial.  There are several genetic factors which pre-disopose to osteoarthritis, but joint injury, excessive joint usage and obesity appear to be the cause in several cases.

What can you do about it?  The only thing we are reasonably confident of; is that keeping your own weight and the weight of your dog down.  Keep up regular exercise, but be aware that excessive force applied to joints could result in later development of osteoarthritis.