Re: negatives for hip resurfacing?

July 20, 2003

" Bone cement " is not part of the articular surface of the artificial joint and

so should not " wear " in the sense that the polypropylene cup is worn away by the

metal femoral head of a THR joint. Concerns about cement in THRs are pretty well

limited to the increased " clean up " involved when the old THR device is removed

and the site is prepared for a new revision device.

In the arena of resurfacing, the acetabular component is non-cemented and

depends on a " press fit " for initial stabilization and eventual boney ingrowth

for final strength and stability. The femoral component is cemented with varying

amounts of space around it for the cement. This provides good initial fixation

and seems to allow good survivability of the bone within.

I have argued that a cementless femoral component would provide a better

physiologic environment for this bone, but there have been technical problems

that have limited the success of this type of device. For one thing, the

intimate fit on the femoral head that is necessary for osteo-integration (boney

ingrowth) seems to be difficult to achieve. I've included an excerpt from the

JRI website with some discussion of this problem here:

<<On the femoral side the cementless components almost without exception became

fixed (whether TiAlloy/CP Ti mesh or the later beaded cobalt chrome) but the

components often tilted during insertion creating gaps between the bone and the

component in some areas which apparently added to the vulnerability to debris

penetration.>>

I happen to think that these problems will be overcome with better device

designs and improved surgical techniques in the near future. In fact some

surgeons are using cementless C2Ks in England with good success right now.

Another extract from the Corin Group's discussion group:

<<A few of our surgeons only ever use uncemented now in all their cases. One in

the UK has done hundreds this way - every single one of which is doing well.>>

This is very; intriguing to those of us who would prefer to avoid the cement

issue altogether but at this time these devices are not available in the US

where I am planning to have my surgery. In short, although I like the idea of a

cementless femoral resurfacing component, I believe the outstanding results that

are routinely achieved with the current cemented devices combined with my own

level of discomfort and desire to proceed with the surgery ASAP make me

comfortable with resurfacing techniques currently used.

That said, I look forward to a time when a cementless option is available.

MLTDMD

Re: negatives for hip resurfacing?

Has there been any info as to whether metal implants shed less wear

particles than other materials? (eg., ceramic) Do all OSs use the same cement,

which I assume also sheds wear particles? Also I wasn't quite clear on why you

said that cement has been given a bad name (wrongly). If it sheds particles like

all the other materials, isn't it just as bad as all the rest?

Sharry

July 20, 2003

hi micheal-

thanks a ton for your repsponses and caveats. i think you are absolutely right

in your approach to this board, strong opinions are not bad at all as long as

they are backed up with clear thinking and offered for the benefit of our

collective understanding.....as your comments most certainly are.

sincerely, jeff

DISCLAIMER.....

read the schpeel at the bottom of micheal's last post!

Re: Re: negatives for hip resurfacing?

Jeff, a sidebar to the non-cemented femoral resurfacing head question....

You asked why various changes have beem made, specifically in the move towards

cementing the head and changes in the " spherocity " of the acetabular component.

Months ago, I came across some research that I've lost track of now. It

described some early efforts with non-cemented resurfacing devices in England

and reported that after suffering a 15% failure rate, the technique was

abandoned. 15% is unnacceptable to the patients whose devices failed, but the

other 85% may have results that are quite acceptable to them.

It was my impression that many of the early resurfacing patients were actually

in such poor condition that resurfacing would probably not be offered to them

today. Their failure rates may have been much lower with better patient

selection. At any rate, cementing the femoral head makes resurfacing surgery

less technique sensitive and availabe to a broader patient population.

The modifications to the acetabular cup have mostly been to reduce incomplete

seating of the component. Since the cup is dependent on intimate contact with

bone for " osteointegration " this is critical. Various fixation screws and fins

are used with THR cups to ensure fixation and close approximation of implant to

bone. Most manufacturers seem to have this worked out pretty well now and most

surgeons seem to understand the importance of adhering to their crtieria.

I'm intrigued by the cementless femoral cup and view it as a natural extension

of the techology, requiring only more experience and research to fine tune

present systems and designs for the most successful application. There are

questions about the physiology of the bone whithin the femoral component that I

really don't know about and that I suspect will be large issues for resurfacing.

Bone is an active tissue that requires a good blood supply to remain healthy,

much less to heal. Bone recieves it blood via internal (marrow) and external

(periosteum) sources. If you shave off the external surface of the femoral head,

you've just eliminated one of the sources of blood supply. If the vessels of the

marrow are compromised by AVN, diabetes, athrosclerosis or other conditions,

there will be less potential for osteointegrations (boney ingrowth) and a

cemented head might be a better solution.

I doubt many surgeons, much less insurance companies will volunteer to do the

screening, testing and metabolic scans that might be neccessary to determine the

potential for good bone physiology within the femoral head post surgically, so

the criteria will probably be more subjective.

Is the patient young, generally healthy with good circulation? Do they smoke?

Are they diabetic? Have they had any problems with healing broken bones in the

past? Is the radiologic comformation of the femoral head relatively normal? Is

there AVN or cystic development? How motivated is the patient to have

non-cemented over cemented?

These and other screening questions will probably be used to establish whether

non-cemented femoral resurfacing is appropriate for an individual patient. If no

" red flags " pop up, then my personal opinion is that a non-cemented femoral

resurfacing would be preferable over cemented.

BUT - I don't know... and I don't think the OSs know, what other conditions

and situations might make non-cemented devices fail. Does the removal of the

periostium reduce the blood supply too much? Does the insertion of the " stem "

dissrupt the marrow's blood supply too much? What goes on under the femoral cap

where x-rays don't penetrate and any direct examination is very invasive? These

are BIG questions.

When faced with the very good results we are getting with cemented femoral

caps in the very clear and encouraging present, do I want to be one of the first

to " try out " non-cementation? Do you? It's a very difficult question and I'm

hard pressed to answer it, as my surgery approaches.

I'm keeping my " ear to the ground " here in this discussion group and wherever

I can glean more information. What a great thing it is to be facing this now

when the choices are between good things instead of between THR and the misery

of waiting.

MLTDMD

July 20, 2003

Sharry,

It's very difficult to define the amount of debris accumulated from metal to

metal hip surgery. The following factors being variables depending on the

patient:

Weight

Size of joint

Activity

Life expectancy

etc. etc.

One thing that can be said is that metal to metal THR has a history of 40+ years

with no known problems. There is conjecture and surveys carried out but nothing

found of a detrimental nature. Debris does accumulate to some level in the body

but in 40 years no evidence has been recorded against metal on metal.

Polyethylene did have a problem but the debris of the latest cross linked grade

is said to overcome this. A lack of history means short term data is the only

confirmation

Ceramic also has a lack of history.

Cement was thought to cause Osteolysis in the 70's and as a result cementless

THR became more prominent. In time the occurrence of Osteolysis was even more

predominant in the cementless THR's. The culprit was the polyethylene liners in

the joint (A different grade is used today which is claimed doesn't have the

problem). Cementation was cleared but mud sticks.

As far as I know all cement used is the same'

Rog

negatives for hip resurfacing?

Hi Jeff

To reinforce what has recently posted I attach the following Canadian

site:

http://www.canorth.org/thumbsup.htm

There are a number of articles but the following is an excerpt from 'A

Lasting Bond'

A Lasting Bond

Tissue resorption at the interface of implant and bone - what clinicians

call " peri-prosthetic osteolysis " - remains the single greatest obstacle to

hip-implant longevity. When osteolysis continues unchecked, the bone around the

implant becomes porous and brittle. Components can loosen and eventually break

away from the surrounding bone. Usually the remaining bone of the femural shaft

is first to fracture and give way, since it's subjected to the combined

mechanical forces of weight-bearing and motion.

At first, scientists attributed the symptoms to " cement disease " - a

localized inflammatory reaction supposedly caused by the body's rejecting PMMA

bone cement as a foreign substance. This dominant school of thought inspired

so-called " cementless " implants, which rely on bone tissue's natural tendency to

grow into porous surfaces to form a strong and durable bond. The problem

appeared to be solved. Then in the 1980s, osteolysis caused several

porous-coated stem-designs to fail sooner, more severely and more frequently

than cemented stems. Cement disease had become " cementless disease. "

The answer came to light, you might say, in 1992 when scientists used a

special polarization microscope to examine activated white blood cells, called

macrophages, that were collected from patients undergoing hip-revision surgery.

Macrophages act as the immune system's gatekeepers, sounding the alert for a

full-fledged inflammatory response when they encounter invaders. Macrophage

means " big eater " in Greek, and the name is apt, since these immune-system cells

gobble up foreign particles, protein fragments, bacterial by-products and so

forth, which they seek in the bloodstream and lymphatic system.

Under polarized light, the researchers noticed an unexplained colour shift

in the macrophage's innards - somehow the cells had acquired reflectors that

refracted light. The phenomenon could only be reproduced with other macrophages

harvested near hip implants. More powerful electron microscopy subsequently

revealed that the macrophages had consumed many, many, sub-micron particles (a

micron equals a millionth of a metre) of polyethylene plastic - indigestible

wear debris from the hip socket. Indeed, later experiments demonstrated that, if

wear particles of any kind - cement, metal, ceramic, plastic - in the right size

and in sufficient number are encountered by the immune system, it triggers a

foreign-body inflammatory response that can accelerate bone resorption. Thus,

the quest for the most elegant solution to osteolysis - a " no-wear " hip implant

- continues.

Rog

P.S.There are plenty more sites that say the same sort of thing. Once

cementation had been given a bad name (wrongly) mud sticks.

July 21, 2003

Hi jeff,

Couldn't help replying .......... it seems to me that you are really getting

into a lot of worry here........... so I thought I would thow in a few more

for you......... there are sadly several other points that can have long

term implication which could well outweigh any decision made about the type

of implant......... Like the surgeons skill, how his life is going right

then, the infection rate of the hospital in which you get implanted, the

state of your femur, your own bodies immune system, how your own health is

right there and then and how you have treated your body up until then, what

your family history is of health issues - i.e whether prone to osteoporosis

etc, and last if not the most important, the sort of luck you as an

individual have..........which is why I find the stats trotted out very

suss.

I personally know an owner operator truck driver with 2 THR;s of plastic

nature who has gung ho operated his business for many a long year now

accompanied by his bilateral replacements......... often working long hours

and hauling/lifting etc. But this man is one of those people who has a

certain degree of luck in his life........ you know the variety that always

wins the local raffles etc. on a regular basis. BTW noone told him he had to

worry about going to the dentist either or looking after this teeth...... so

none of the problems of taking antibotics for dentist visits for

him.......groan. Very typical of the Australian male attitude of 'she'll be

right mate'.......... I am willing to bet he will be one of those stats of

people doing well at 20 years......... whereas others trying to do a tiny

bit of his life would have dislocated a dozen times by now..........

It is also interesting that all these prothesis issues seem of deadly

importance preop, but once you have whatever prothesis you get, that one

alone gets to be the best.........and life quickly finds many other

facinating things as one regains the use of the body...........

Edith LBHR Dr. L Walter Sydney Australia 8/02

>

> i just read that canadian article.

> it seemed clear to me though, that polyethylene was the main culprit

refered to in in this article for cases of osteolysis, cemented &

non-cemented. i think it is unfortunate that it does not refer to any

metal-on-metal statistics. perhaps this may show a difference in results, at

least that is what the various hip resurfacing websites tell us.

>

> i would like to clarify my thinking/understanding on this, please tell me

if it seems off :

>

> causes of osteolysis :

> 1. poly-metal = non-absorbable wear debris = macrophages = osteoclasts =

bone resorbtion = loosening = revision

> 2. poly-ceramic = non-absorbable wear debris = macrophages = osteoclasts =

bone resorbtion = loosening = revision

> 3. ceramic-ceramic = non-absorbable wear debris = macrophages =

osteoclasts = bone resorbtion = loosening = revision

> 4. cr-cobalt metal-metal = absobable wear debris = no concentration of

particles = no macrophages

>

> conclusion : lack of polyethylene = lack of osteolysis = much lower

failure rates

>

> acetabular cups :

> 1. any poly paticles present will comprimise any cup fixation

> 2. cemented fixation = bad

> 3. pressfit w/ porous surface & HA = good = standard practice

> 4. pressfit with screws = good = used when necessary i.e. dysplasia cup

>

> conclusion : cup w/ no cement = current obvious choice

>

> articulation combinations :

> 1. metal-poly = bad

> 2. metal-metal thr w/ cement stem = pretty good

> 3. metal-metal thr non-cement stem = very good

> 4. metal-metal resurf = better......regardless of cement/non-cement head

> 5. metal-metal resurf w/o cement head = still trying to find clear info to

address this specific question

>

> general conclusions :

> 1. poly = bad

> 2. osteolysis is generally not a problem with metal-metal thr or resurf.

> 3. large diameter metal cup - metal head is desirable for better ROM &

lack of dislocation & natural feel.

> 4. resurf is more desirable than thr if you expect to live for 20 more

years due to eventual need for revision.

> 5. cement fixation of femoral resurf head is common practice with great

results for up to 10 years and probably more.

> 6. non-cement fixation of femoral resurf head is less common practice w/o

clear data for or against it.

>

July 21, 2003

Jeff,

You continue to ask some very good questions....

<< i have also read that bone is an organic material that the body continually

absorbs & regenerates, unlike glue and cement.

and, that bone growth will bond to porous metal surfaces, but not to cement

surfaces. true? not true?

The bone / implant interface is studied very closely in dentistry. A true

organic bond would histologically consist of hemidesmosomal units within living

bone bonded to the substance of the implant. This does not occur. The best we

get, even with up to six months of unloaded contact with the implant, is

" intimate " boney ingrowth into surface irregularities of the implant surface. I

have not seen any histology of living bone juxtaposed on PMMA. The idea of

coating dental implants with plastic prior to implantation has never been

seriously considered to my knowledge.

Healthy and actively metabolizing bone must be reasonably tolerant of PMMA

though. I presume the cement can be loaded immediately because of larger

irregularities that mechanically lock the femoral cap in place. Later, boney

ingrowth should increase retention, stability, and resistance to infiltration by

osteolytic stimulating debris / bacteria / or whatever. For now, the initial

fixation in non-cemented components is achieved by " press fitting " them into

slightly under contoured boney cavities so they stick in place mechanically

until bone can grow and stabilize them more securely.

There are some mechanical problems with doing this using the resurfacing

device's femoral component. It must fit intimately with the bone for boney

ingrowth to occur. It must " seal " the margin between the cap and the neck of the

femur so debris / clotted blood / serum / bacteria can't penetrate the spaces

under the cap and wreak havoc with the delicate process of building bone. Until

these problems can be addressed and reliably taken care of, cemented resurfacing

caps will be the norm.

Those nasty little macrophages you mentioned are products of the body's

inflamatory response to irritating " junk " (listed in part above) present within

it. They upset the normal physiology of bone which is constantly being removed

by " osteoclasts " and renewed by " osteoblasts " by tilting this balance more

toward inflammation and destruction of bone, hence the loosening and failure of

implants, both dental and orthopeadic.

I digress... as far as a true bond to either metal or PMMA goes, the best we can

hope for is a connective tissue interface at a microscopic level and boney

ingrowth into surface irregulatities at the macrosopic level. The width of this

connective tissue interface can vary according to how happy the tissue in

question is being close to the implant surface material, how much loading and

movement is created by the patient's activities, as well as the health and

resilience of the patient and their own tissue in question. I would give a

nickel to see some actual histology of tissue/metal vs tissue/PMMA interfaces in

patients of various ages and states of health and activity levels.

<<if someone would invent some form of organic bone bondo that acts as cement in

the short term and acts as bone food to encourage bone growth while it breaks

down and get absorbed, i'd be psyched....any bio-chemists out there?

AAHHHH.. the holy grail of implantology!

The trouble is you want strength so you can go home and resume your life as soon

as possible, but you want it to be soft and porous so blood vessels can

infiltrate it and osteoclasts can produce new bone. So far we haven't found that

magical substance yet. We have several types of grafting materials in dentistry

that come close, but none that I know that you can walk on!

I hope this helps... I certainly feel verbose in all the pontification I've been

doing here. This is a fascinating subject to me. I hope I haven't become too

much of a bore.

MLTDMD

July 21, 2003

Rog

Thanks for clearing up my questions

Sharry

negatives for hip resurfacing?

Hi Jeff

To reinforce what has recently posted I attach the following

Canadian site: