Some Random Thoughts on the Life of a Resurfacing

[morph]

I think bones are pretty rigid and would probably snap before flexing. The muscles and the ligaments absorb alot of the forces through the body. With good walking/running posture the body is quite efficient at abosorbing shock it's when there are muscle imbalances etc there could be problems. But running on a relatively new device before muscles have properly healed let alone bone is risky.

The metal pin is purely for guiding the the ball into position and does not take any load or stress, so if there was any flex in the bone it would not have an impact on the resurfacing.

BTW I seem to remember at the beginning of the year something about a graphite lubricated coating on retrieved MOM devices. Anyone else remeber that.

[hernanu]

Well, everything flexes, including steel.

The bone's structural components are the hard external layer (compact osseous tissue) and the spongy osseous tissue. The compact tissue is probably what we're talking about here, it's composed of repeating circular structures called osteons.

Those are concentric circles of mineral layers with a central canal, which contains both a blood and nerve supply. These individual units combine to form the actual bones, so they provide strength without the brittleness that something that doesn't flex would have.

Osteocytes, which are the mature bone cells, are responsible for maintaining the bone matrix and for repairing bone. They are capable of breaking down bone and rebuilding it, inserting more cells in response to stimuli like exercise, making the bone denser and stronger. If the bone breaks down faster than the existing osteocytes can rebuild it, then you lose bone mass and the bone gets weaker.

In our case, during recuperation we are trying to help these cells to repair bone mass and hopefully to build more mass. Our walking, then increasing exercise under the surgeon's overview is crucial to promoting the bone growth that locks our implants into place, then continued exercise keeps that bone strong.

I assume (and have tried to recuperate that way) that since we are so under stress initially and our osteocytes have to work overtime to get new bone growth going to replace what we lost or may lose due to the surgeries, to anneal the bone to the devices. Doing moderate exercise and taking good care of the hip initially tips the scale to let the osteocytes increase bone mass, gets the blood flow going within the bone and locks the bone onto those implants.

Conversely, putting too much pressure early on, puts the osteocytes on a slippery slope of trying to repair the damage from the surgery, trying to grow into the implants and responding to the extra pressure of too much activity too soon. In some cases the osteocytes and their owner lose out.

Just my opinion, I'm not a medical person, just an interested osteocyte owner.

[morph]

Interesting Hern cheers,  I am at 13 week so need to be a bit carefull, I believe at around 3 months the bone is at its most fragile.

[Jason0411]

Basically Hern has just descrribed the lead up to my fracture. I over did it totally then at 7 weeks tripped stamped my foot down hard to stop my self and wallop cap moves down by a centimetre crushing the bone beneath it. Obviously I had not given my bone a chance. I have now though.
:D

[hernanu]

Still amazed at how well you're doing, Jason. You're really taking this second chance by storm.

[Jason0411]

Over did it a bit on saturday. Decided to walk from a river to a pub nearby. Trouble is the pub wasn't as near as I thought, ended up walking nearly 3.5 miles unaided. Have been a little uncomfortable but noting major. Walking with one stick most of the time as instructed but do tend not to bother for short walks or around the house.

~Jas

[hernanu]

Ice that baby, Jason...

[Tin Soldier]

and have a pint.

With regards to the strengh of the device, sort of a dead horse here, but McMinn's chapter 2 or something like that in "Modern Hip Resurfacing" has some discussion on early development of HR (specifically BHR). He shows a 500 pound weight pendulum that is used to run hundreds of cycles on various fluids in an early BHR.  They did it dry on one test and found no wear.  They used cow blood, human syn fluid, engine oil,... and I think the results pretty much said that you don't need any fluid.  We probably have a similar "dry" test, with lower weight of course, in our hips when we hear the vibration or squeak that folks mention.  I've had that 3 times and it does seem to be related to dehydration, and not over exercise.  I don't like it when it happens, and so I generally shut down the activities for the day and drink a lot of water.  It goes away by the next day.  In summary CoCr alloy is super resistant.  Slippery too.

Pritchett was interviewed by TV station about Floyd Landis' hip and while Dr. P is talking on the interview, he is spinning a BHR.  Yes, top like.  You can see it on Pritchett ortho's website.

If we look at the 3 sports mentioned in the first post, which one has the most joint degration throughout the whole leg for a normal non-arthritc hip?  Cycling is probably the easiest on the body altogether, so I would think cycyling would also be the easiest on the HR'd joint.  Why would the mechanics of degedration be any different with HR?  Not sure it all matters, since the HR device itself has been shown th last a very long time.   

Great discussion.  Thanks

[Jason0411]

I played with a BHR in McMinns office spinning it in the socket with no sound or friction it just spun and spun. I commented on how smooth it was and he told me that the one I had in my hand was a reject. So if a reject is that smooth just how smooth are the perfect ones.

Jas

[Dannywayoflife]

I have a copy of a publication by McMinn and Treacy that details the whole development and clinical results of the BHR it's very interesting stuff. It has also created confidence for me in the longterm survivorship of the BHR.

[Tin Soldier]

I reread the chapter on development of the BHR in McMinn's book "Modern Hip Resurfacing" and I made a couple mistakes in my ealier post.  The pendulum weight affectionately called Big Ben, was actually 500 Kilograms, not pounds (duh, this is in the UK), and McMinn did find trouble with the dry run, screeching and obvious signs of friction.  I think I was thinking of a different test maybe that Charnley did before McMinn.  However there was very little difference between the various fluids used for lubrication on the early BHR.  Also, the test was geared towards looking at the friction differences between various sized components as well as the different fluids.  Very interesting. 

[Dannywayoflife]

Yes I remember that chapter. Hell I think anything would screech with 1000lbs hanging off it! ;D

[morph]

Do you know where I can get a copy of that book.

[Pat Walter]

It is a bit expensive.

http://www.amazon.com/Modern-Hip-Resurfacing-Derek-McMinn/dp/1849967261/ref=sr_1_1?ie=UTF8&qid=1347716423&sr=8-1&keywords=McMinn%27s+book+%22Modern+Hip+Resurfacing

I was very fortunate to get a free one signed by McMinn at one of the hip resurfacing courses. If you attended one of his presentations, you received the book.  It was a great gift.  I really appreciate it.

Pat

[Dannywayoflife]

Morph keep an eye on amazon mate I've seen them on there for around £50.

[Jason0411]

50 Quid !!!!!! is it bound with Gold?

[Jason0411]

It must be made of Gold or I haven't bought a book for a long time. Just looked on Amazon, not wishing to sound like a Yorkshire man but "Ow Much" !!!!!

[Dannywayoflife]

Ha we Yorkshire men are know for our short arms and deep pockets jas!  ;D I don't know why it costs so much but once I've saved up I'll buy a copy.

[Jason0411]

My Bruvs LBHR is working well he was doing some pad work at Karate and went for a head kick but the guy holding the pad dropped it slightly at precisely the wrong moment. Full on temple with no pull back. Apparently he hit the floor quite hard and had a bit of a headache for a while. Nick said he felt a bit rusty as hadn't done any hard pad work for a while and was really starting to feel like he was flowing nicely so went a bit higher. Oops. The bloke who took the hit is 6ft and Nick is 5 10 so the old boy can still do it.

He did say after the session of hard pad work he knew he had done it and pobably won't make tto much of a habit of it.

Jas

[hernanu]

Good to hear Jason - mine are just about chest level right now, feeling fine.