A question was posted in another area about weight lifting - particularly squatting - after a resurfacing. This got me thinking about stuff.
I'm not a doctor - nor do I play one on TV - but I've read general comments about the life of a resurfacing being 15 years or so. Why does it wear out?
When you look at the design of the natural hip it would appear that the femoral neck is in shear, as it sits at an angle to the socket in the pelvis. Logic would dictate, however, that it is primarily in compression - otherwise it's a bad design that evolution would have weeded out. It would seem logical that the loads on the femur would be primarily distributed throughout the hip socket, and not overly loaded at any one point.
This would also seem to be borne out by the emphasis in resurfacing at getting the cup angle "just right." A cup at the wrong angle puts localized load on one portion of the cup leading to premature wear. This would indicate that a cup placed at the right angle distributes the load on the cup more evenly, reducing localized wear. That would also indicate to me that the loads on a resurfacing implant are primarily compressive, and that the load on the femoral neck is primarily compressive, otherwise you would always be edge loading some part of the implant.
The only thing that would cause a resurfacing to need replacing would therefore be excessive wear, and likely all over the implant and not particularly localized. I guess. Maybe I'm wrong about that.
So what would cause excessive wear? If you look at three different exercises - biking, running, and squatting, what causes the most wear? In cycling the load is relatively light but there is a lot of repetitive motion. In running you have the repeated impact on the implant - momentary high loading. In squatting you have a heavy load but little impact, and for very short duration - maybe 3 to 20 repetitions.
Logic again would indicate to me that running would cause the most wear. It's going to take a certain amount of load before the force exceeds the strength of the metal, and I doubt cycling imparts really any more load than walking. Squatting imparts a heavier load but it is of short duration and I don't know that the load from squatting would be greater than the load from the impact of running. The impact of running may impart the greatest load of all, but does that load exceed the strength of the implant? Does a heavily padded running shoe, like the Hoka One One, reduce those loads in the same way a SAFER barrier reduces the localized load in an accident at a race track?
I don't know the answer to any of this, but maybe it will spark a discussion.....
The longevity of resurfacings is at the moment an unknown. The BHR has been out for just over 15 years and in the developers hands I believe has a retention rate of around 98% across the board. The predecessors to the BHR don't have the retention rate that the BHR does but some of those have now lasted 20+ years and are still in situ.
The key factor I believe is how long the devices will stay attached to the bone. The alloy the BHR is made from will never realistically wear enough that the device won't work. There are numerous THR's that was made from the same as cast alloy that are still in situ afte well over 40 years! The cup design of the BHR is unique as it has the porocast beads which create a really rough surface for the bone to weld to. You are totally correct that the positioning of the device is a huge factor! If the surgeon puts it in wrong it won't do well in the longrun.
Danny
Good discussion. Doctors have told me that if your bone density is not very good, it will increase with a hip resurfacing if the patient starts to walk and be active. Weight bearing activities increase bone density. The hip components really are depended on bone growth to keep them in place. So I am guessing there is some line between good weight bearing activities and those that continue to jar the heck out of the joint and device. Again, no one knows for sure about all of this. Even among runners, some people might have different styles and ways of placing the feet as the run to make a difference between the impact the joint receives. Not an easy thing to probably try to test, even thought they do a lot of medical testing.
I think if we all have our components placed properly and make sure we do some walking and weight bearing activities, we have the best shot at taking our hip resurfacings with us to the grave. And they say you can't take it with you! LOL :o
I'm sure your right pat bone quality and density will be the over riding key to longevity. I personally think that I'll one day have a revision but if mine lasts me 30 years I'll be ecstatic!
Thats my outlook as well Danny, although I'd be ecstatic at anything beyond 20 yrs.
The way hip surgery has moved in recent years, we may all have little to worry about that far down the line.
Hopefully, the revisions will be more of a straightforward operation. My aim is to treat my THR with respect but not have it hold me back and see what the future brings.
All thanks to this site, I might add.
Mr T wouldn't commit to a lifespan of the BHR when I questioned him on it he did however he did say that his 15 year stats were in the very high 90s and that they wouldn't just go from that to zero over night. He predicted that his 20 year stats will be almost the same as his 15 year stats. So I guess that's as close as you'll get to a UK surgeon saying these will really last a long time!
And mike as I've said to Anna there's numerous THR's still in situ after 40+ years. So touch wood yours will out last you mike! ;)
I've said this to several people close to me, if my BHR only gives me 5 years, then that's 5 years of a decent standard of living. I had zero life before. Anything more than that is a bonus.
Very true ruby but personally I wouldn't want to go under the knife for round 2 after 5 years! I'll be amazed if either of ours don't do atleast 20 years.
I obviously expect it to last a hell of a lot longer, as does Mr T, however I was that grateful that 5 years would do LOL.
OK, call me the ultimate optimistic guy but if you've ever held one of the devices you would be hard pressed to think it would wear out easily, the implants are designed to ride on a thin layer of synovial fluid produced by your body so wear would be greatly minimized, even if it did you have a lot of very strong metal.
Adhesion issues between the femoral component and the femur is one thing that will likely cause a failure, maybe, this has not shown it's ugly head. Once the cup is set properly bone growth will hold up for a very long time.
Everyday that goes by the more I am optimistic that our implants for the majority will last a lifetime and there is nothing that says differently, most times when you do have a failure it's happened in the first couple years.
I personally think the pounding from running could cause failure over the long term.
Of course this is IMHO.
Chuck
I'm not entirely sure what we're talking about here.
Are we talking about wearing out the BHR prosthetic bearing?
Or, are we talking about the longevity of the hip surface replacement as a whole?
It's an important distinction, because each has a different answer. It would be impossible for a human to "wear out" a BHR prosthetic bearing. We would have to live for hundreds of years for that to happen. The laws of metallurgy and physics dictate this.
Answering the other question is near impossible, because so many factors dictate the life of a hip surface replacement. Surgical technique, recovery, activity level, bone density, weight, health, diet, flexibility, metal allergies, accidents, cell turnover, vascularity, bone resorption, bone cement longevity... and probably a lot of things no one has figured out just yet.
I just had my six month with Dr. Pritchett yesterday. He says the best any doctor can tell anyone at this point, is what he told me: "This hip should last you a long time." Vague, but realistic.
I have an uncle who had a heart transplant at Stanford in 1990. Doctors gave him another 10 years at the most. He's still alive today and still one of the most cantankerous bastards I know.
If my hip gives me as long as his heart... I'll be happy.
Is a THR designed to work in the same way regarding synovial fluid lubricating the joint, or is that not a possibility with no femoral head?
I think that would depend on the THR mike ask Mr T next rime you see him.
I was referring to the overall life.
Adhesion is what will cause long term issues, Dr. Gross thinks that the cement will be the weak link in all of this but then again that has not shown to be the weak link. The more time goes on like I said the more I think we'll die with our implants walking straight lines. In the past failures were many times the results of the break down of the bearing surfaces.
You make a great point that how the device is implanted will determine the future, but more than often poor surgical technique shows up within the first 3 years, this is why the 4 year point is key.
Back in 2008 Dr. Gross was of the opinion that the possibility of long term survival of implants was more than likely.
Chuck
Quote from: Baby Barista on September 08, 2012, 10:50:16 PM
I'm not entirely sure what we're talking about here.
Are we talking about wearing out the BHR prosthetic bearing?
Or, are we talking about the longevity of the hip surface replacement as a whole?
It's an important distinction, because each has a different answer. It would be impossible for a human to "wear out" a BHR prosthetic bearing. We would have to live for hundreds of years for that to happen. The laws of metallurgy and physics dictate this.
Answering the other question is near impossible, because so many factors dictate the life of a hip surface replacement. Surgical technique, recovery, activity level, bone density, weight, health, diet, flexibility, metal allergies, accidents, cell turnover, vascularity, bone resorption, bone cement longevity... and probably a lot of things no one has figured out just yet.
I just had my six month with Dr. Pritchett yesterday. He says the best any doctor can tell anyone at this point, is what he told me: "This hip should last you a long time." Vague, but realistic.
I have an uncle who had a heart transplant at Stanford in 1990. Doctors gave him another 10 years at the most. He's still alive today and still one of the most cantankerous bastards I know.
If my hip gives me as long as his heart... I'll be happy.
Chuck I truly pray that we can all take our HR's to the grave! As everyone stresses on here all the time surgeon technique is THE most important factor!
Danny
Quote from: Baby Barista on September 08, 2012, 10:50:16 PM
I'm not entirely sure what we're talking about here.
Are we talking about wearing out the BHR prosthetic bearing?
Or, are we talking about the longevity of the hip surface replacement as a whole?
It's an important distinction, because each has a different answer. It would be impossible for a human to "wear out" a BHR prosthetic bearing. We would have to live for hundreds of years for that to happen. The laws of metallurgy and physics dictate this.
Answering the other question is near impossible, because so many factors dictate the life of a hip surface replacement. Surgical technique, recovery, activity level, bone density, weight, health, diet, flexibility, metal allergies, accidents, cell turnover, vascularity, bone resorption, bone cement longevity... and probably a lot of things no one has figured out just yet.
I just had my six month with Dr. Pritchett yesterday. He says the best any doctor can tell anyone at this point, is what he told me: "This hip should last you a long time." Vague, but realistic.
I have an uncle who had a heart transplant at Stanford in 1990. Doctors gave him another 10 years at the most. He's still alive today and still one of the most cantankerous bastards I know.
If my hip gives me as long as his heart... I'll be happy.
And this is actually what I was getting at. I liken the BHR device as functioning like an engine crankshaft bearing, with the synovial fluid acting like the engine oil. With an adequate number of main bearings supporting the crankshaft there will be essentially no wear to the bearing surfaces. I wonder if the loads placed on the hip from activity cause wear - if the synovial fluid is compressed to the point where you have metal to metal contact, or if failure would come from a skeletal problem - the cup or the cap loosening over time. I would think the skeletal bond would become greater over time and not less.
These thoughts came about because of a post on another topic where a doctor recommended against heavy squats after a resurfacing. I'm trying to figure out why - other than just taking a conservative approach. I can recall Kirk M. posting some time ago that he knew of a resurfacing patient that snapped of the end of the femur doing leg presses. I'm trying to understand why that would happen - if it would be because leg presses (or squats) place the femoral neck in shear instead of compression. It would seem more likely in that case that the femoral neck had not fully healed. Is there an issue after the femoral neck has fully healed?
I'm not a powerlifter and I'm not going to be doing 400 pound squats like Buster, but I cannot ever recall reading that powerlifting resulted in a structural failure - like a femoral neck snapping - in a natural hip. Powerlifters have muscle and tendon issues, and often skeletal issues in the spine, but I've never heard of a skeletal issue in the hip. Is the concern then that heavy squatting - or running - would cause the implant to move, or to wear?
I think even if all the synovial fluid was pushed out of the gap the vitalium alloy is soooooo incredibly resistant to wear that it wouldn't really do much. The fluid would be sucked back in pretty quickly when whatever the activity was ceased.
I really doubt that the femoral neck would fracture once fully healed. But be mindful that it takes 12 months for the bone density to "normalise".
Even if you had a situation where some of the synovial fluid was thin or non existent the surfaces are polished to the point where you can spin the femoral component in the cup and it spins and spins like crazy, and that is without any lubricant. The day before surgery Dr. G handed us the device and we had a good old time spinning it like a top.
As Danny has said, getting the right angles is so very important for the long term survival of the device. If you get Treacy or McMinn as your surgeon your chances of long term survivorship jumps, you would be hard pressed to find a failure of his on this forum, go ahead and do a search, we might have one from each, what do you say Pat?????
Chuck
Have the Synovial fluid pushed out under load is something I have thought about quite a lot. The same argument surely would apply to a natural joint, although cartiallage is way more slippery than anything else, about 10 times more slippery than black ice! The metal/metal surface, although very smooth, nowhere near natural cartiallage. Never the less with proper placement the combination of the Synovial and smoothness is obviously good enough for a long time. Also Synovial fluid is not like water, it is very viscous with a similar consitency to egg yolk so naturally with heavy load it should still be a good lubricant.
As for shear stress during squatting, the cap is precisely moulded to be a tight fit in all directions, having said that it is still an interface with two different materials so must probably is the weakest point, but how resilient is a good question. I wonder if there are any in lab tests fo this type of force. In my mind the only weak point would be if you tried to pull it off. So I would have thought that once the bone has healed and reshaped to it's new stress loading it would be fairly resilient. I still think that it is best to err on the cautious side when doing really deep heavy repetitive squats in case over time it worked lose. Just my thoughts.
I remember Rick Rubio posting that he was having a revision done to the cup after 5 years. Rick began running right after the resurfacing, and was running 5 miles at one month. The cup loosened up and apparently little or no bone grew into it. In that case, however, it seems likely that the impact of running was causing very slight movement in the cup from the beginning preventing bone growth, kind of like picking at a scab prevents it from ever healing. I would think after 6 months to a year of bone growth into the cup that wouldn't be an issue.
So here is a question. Does anyone know if a bone, say a thigh bone, flexes at all during activity, or is it completely rigid? I would bet a bone does have a tiny amount of give, and that give is reduced in the femoral neck area by the insertion of the metal pin in the center of the bone.
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.
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.
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.
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
Still amazed at how well you're doing, Jason. You're really taking this second chance by storm.
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
Ice that baby, Jason...
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
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
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.
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.
Yes I remember that chapter. Hell I think anything would screech with 1000lbs hanging off it! ;D
Do you know where I can get a copy of that book.
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 (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
Morph keep an eye on amazon mate I've seen them on there for around £50.
50 Quid !!!!!! is it bound with Gold?
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" !!!!!
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.
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
Good to hear Jason - mine are just about chest level right now, feeling fine.
I made the decision a long time ago that I wouldn't be returning to Thai pads and bag work as I think no matter how tough the devices are the sheer force I used to be able to create kicking the pads and bags it just can't be any good for the device. This however does not meen I will be giving up! I'll be adapting my style to make more use of my heavy hands and eventually do intend on having atleast 1 fight in the cage.
Looking forward to the report, Danny - good hands and grappling are pretty effective from my point of view.
If cage fighting is OK does that mean Rugby is too?
I would argue that mma is actually easier on the body than rugby. Mr T told me that running 100 miles a week and rugby were the only 2 things he asked patients not to do. However I don't think he quite understands how mad I can be! ;D he did say tho that he has patients who do both those and are still fine. If/When I go back to competition I will be totally changing my style to look after the bionic hip. Not sure you can do that with rugby. But ask Mr McMinn once your fully healed and see what he says!