Dual mobility acetabular cup vs traditional implant #2

[Going4fun]

I talked to my surgeon about the ball size ... Basically he estimated 36mm would be the size of the ball he put into me ... he says beyond that ... the thickness of the cross-linked polyethylene liner would be compromised ... But he was clear 36mm was only an estimate and that he makes the final decision during surgery.

@sfbaylover, there are so many variables to consider for stability ... and the ultimate determinant, it seems to me, is the skill and judgment of the surgeon ... A mediocre surgeon could place a big ball and it would mean nothing if the surgeon doesn't place the device in the best way and doesn't repair your tissue in the best way. That's the challenge with hip surgery, it seems to me. There are an infinite number of variables ... so focusing on one variable (say the device) doesn't get us very far ... No matter how great a device is (and Josephine makes the point that they are quite similar) ... if the surgeon isn't skilled and experienced at placing the device, there is no gain.

I found two surgeons (after looking a lot) who were incredibly skilled and who were comfortable with patients resuming athletic activity at a high level after the surgery. I think that's the most important point ... find that skilled surgeon who you trust ... and make sure they're on the same page with you as far as your goals afterwards. I wouldn't assume that the bigger the device the better ... though of course that seems like common sense ... In hip surgery ... which is so complicated, we are way beyond common sense. (I am reminded of how strange this all is when I tell people that most devices these days are uncemented and will fuse with bone. People shake their heads.)

There was the big deal about a decade ago when surgeons began using large bearing metal-on-metal replacements ... The metal-on-metal devices didn't require a lining ... so they could use large balls ... which was supposedly better ... and then there emerged all kinds of problems with metal allergies and metal debris forming ... and corrosion. Surgeons beat a quick retreat away from metal-on-metal replacements.

Same with the approaches ... no one approach is clearly better than the others ... and pretty much surgeons will say they use their particular approach NOT because they think the data indicates their approach is better than another ... but rather because they like it, feel safe using it, feel comfortable cutting that way and because they believe THEIR patients have the best results with that approach.

 

[Josephine]

One surgeon said he would likely use a 36mm ceramic head, the other surgeon said he would likely use a 32mm ceramic. Naturally, in this case, I assume that bigger here is better, but maybe not?

I really don't think that 4mm is that much of a difference!

I realize that the larger the head, the greater the potential for bearing wear

Wear hasn't been an issue for some years. The only cup that has wear is the polyethylene one and even that wear has been much reduced with the cross-linke ploy and the Vit E.

I simply want my hip to feel and function as normally as possible.

It will, whatever device is used. Don't swallow all the manufactures' hyperbole on this!

 

[dlp]

Since this thread was initially about Dual Mobility, don't forget that DM femoral heads are smaller than the "regular" models. So just keep in mind when discussing these things, the implant makes a difference. Most of the ceramic heads start at 28mm (and I think I've even seen 22mm mentioned for some)

As @Going4fun points out, there's more to this whole process - and more to what may or may not cause you to dislocate than just the head size of your implant. I have 2 x 28mm ceramic heads on my Stryker ADMs - and I don't feel unstable, I don't feel at risk, and I trust that my surgeon made the right choice based on my physiology.

There are so many things to fret over when it comes to this surgery, worrying over a few millimeters is something I definitely didn't have time for. (Same goes for approach.) Discuss your lifestyle, your plans, your hopes and dreams for post-surgery living with your surgeon. If you trust him/her, then trust that they make the right choice to allow you to continue/achive that lifestyle. Unless you read your surgery report, you will never be able to measure it yourself anyway

 

[dapplega]

I agree with @dlp.
I am curious what your surgeon shared with you regarding why he chose the dual mobility for you over traditional. Was there something particular where it suited your lifestyle plans or is it just his/her preferred implant of choice?
I believe my surgeon is using the dual mobility in all his patients (I'll ask at my 1 year). I know he has used it in many patients my age and older.

I know I can't tell the difference in my hip (other than mentally knowing I had surgery less than a year ago). I can stand and place my palms nearly flat on the floor. I used to go farther but do start to feel a bit worried... ...
My ceramic head is 28 mm but remember that is inside of the much larger articulating poly head. My cup is 50mm so the poly head that is the second articulation is 50mm - that is where the stability comes from. In a traditional implant if you have a 36mm head in a 50mm shell your poly liner would be 7mm thick whereas the liner is 11mm thick in my dual articulation.

Other than the 2 wearing surfaces (debatable based on available information), the only other concern I've found is that there are also 2 potential dislocation areas. The main one would be the poly head from the shell (similar to dislocation in a traditional implant). There is another, very small risk, that the ceramic head dislocates from the poly liner (as I believe it is snapped in place). There have been very few occurrences of this that I've found (only one study even mentioning it...) but perhaps that is because the numbers don't exist yet. Time will tell as dual mobility seems to be gaining popularity in the US.

 

[dlp]

Hi @dapplega

My surgeon told me that he uses the same implant pretty much across the board. He's been using it for quite a few years, apparently, and said that's he never had a male dislocation since switching. (I did not think at the time to ask how many females - I was a little bit preoccupied making sure I got all of my questions answered). My acetabular cups are both 56mm, so somewhat larger than yours. Not sure of the thickness of that liner.

The numbers seem to look good for dual mobility. I've read a few things over the past year or so that have been indicating better/lower dislocation rates with DM than traditional. (like this one from earlier in the year https://www.hss.edu/newsroom_aaos2018-dual-mobility.asp) I think that my Stryker implant has been around since 2010, and some of the earliest DM implants go back to the 90s in Europe.

I don't do anything - intentionally - that would potentially cause me to dislocate my hip. Accidents happen, but thats true with or without titanium hips so I don't fret about it. For me, I'm more worried about life, longevity, and wear of the implants. Definitely see the advantages to the ceramic over metal, and I'm hoping to be cremated with the hip (Do they melt, leaving my wife with a titanium/ash hybrid nugget in the urn?? ). But that being said, I'll gladly take another surgery down the road if required. Getting rid of the OA pain now is totally worth a few weeks of discomfort.

 

[dapplega]

Thanks @dlp - I now have cup envy... ;)
Appreciate the link to that study.
Have a great Labor Day Weekend!

 

[Josephine]

don't forget that DM femoral heads are smaller than the "regular" models

Actually that's an optical illusion!

Inside are two components - the ceramic head which is captive inside the poly head. The ceramic is usually about 22-24mm and the external diameter of the poly head is 28mm - as a rule! Just thought you'd all like to know!

 

[dlp]

Thanks @dlp - I now have cup envy... ;)
Appreciate the link to that study.
Have a great Labor Day Weekend!

Hah - I didn't even know the sizing until recently. Decided to get copies of my records for my files.
Weekend should be nice and quiet - which is fine by me Hope yours is good, too!

Actually that's an optical illusion!

Inside are two components - the ceramic head which is captive inside the poly head. The ceramic is usually about 22-24mm and the external diameter of the poly head is 28mm - as a rule! Just thought you'd all like to know!

Ahh, good to know. So are the 2 measurements added together to get an equivalent of a traditional implant? Probably not since that pushes things into 40mm+ I imagine.

Since the traditional implant sizes seem to be in the 30mm range, is the acetabular cup probably less shallow for them?

 

[dapplega]

@dlp - actually I think you have it right - for dual mobility the head size of the poly liner would be higher. I think (famous last words) it is fairly simple math. Let's assume your inner cup diameter is 56mm. Since your liner articulates it acts as a large head size of 56mm. If your inner ceramic head is 32mm then the thickness of the liner would be 12mm (12mm * 2 = 24mm + 32mm ceramic head = 56mm). That's how it was explained to me and also how the pictures portray it. Anyone please clarify if my math or understanding is wrong...
BTW - interesting article here.

 

[Josephine]

So are the 2 measurements added together to get an equivalent of a traditional implant?

No! Certainly not!What would be the point of that. The external diameter of the larger one is the crucial one.

My numbers might be a bit out of date, I'm afraid!

If your inner ceramic head is 32mm then the thickness of the liner would be 12mm (12mm * 2 = 24mm + 32mm ceramic head = 56mm).

@dapplega I long ago out-lived my math! So I'll have to take your word for it!
However, the numbers between the smaller, captive head diameter and the external diameter of the whole are largely academic to my way of thinking!

 

[dlp]

Heh - yeah - Math isn't my thing either And while I'm not really concerned about it, the nerd in me loves trying to dig into the specs/facts/figures of this stuff!

 

[Andy P]

I'm completely against traditional bearings now, the 36 and below wont give you a full range of movement. Which means your hip wont return to its fullest muscle balance. With bearings over 36mm there starts to be lubrication issues and greater potential for wear (as you've mentioned), but this doesnt make them a bad choice, its just that they are away from the average replacement and surgeons tend not to want to drift from the most proven direction. With a modern CoC or CoP implant, the wear is so tiny 0.001 per year, that even speeding that up by 100% still isnt going to be an issue.

Dual mobility is said to have the most natural feel and gives an outer bearing of 44mm + which compared to my natural hip (52mm), is actually a decent compromice

 

[MrDIY]

the 36 and below wont give you a full range of movement.

What are the differences in range of motion between implants? Range of motion seems like a highly individual metric. Are you a gymnast?

your hip wont return to its fullest muscle balance.

What does this mean?

Dual mobility is said to have the most natural feel

How is this measured?

 

[Josephine]

I'm completely against traditional bearings now, the 36 and below wont give you a full range of movement.

Andy, where is your evidence for this? There are numerous athletes out there who have traditional hip replacements yet have gone back to their professional level performance. I'll have the look up the ones I'm thinking about at this moment but one that does spring to mind is Nick Skelton, who, if you recall, won gold at the 2012 London Olympics when he was less than one year out from his THR!

 

[Andy P]

This is purely anecdotal and does not refer to ROM, yes, sure you can still run and jump with a traditional hip replacement.

There are studies on ROM with regard to bearing size, but my main concern is dislocation which has happened to a relative of mine and its something that I really want to avoid.

With regards the bio-mechanical benefits or DM, this was my very first question on this forum, but it should follow that the more you are able to stretch out your muscle then the greater your sense of balance.

 

[Josephine]

but my main concern is dislocation which has happened to a relative of mine

I'm so sorry to hear that but I would suggest that it was nothing to do with the DM directly. People with every other type of hip replacement device get dislocations too!

and its something that I really want to avoid.

Well of course you do! But if I may use a rather trite comparison, that's a bit like saying you'd never drive a Ford because someone you know once had a serious accident in one! It's happenstance, that's all.