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Hip Resurfacing News

I am Chair of Orthopaedics at Imperial College in London and have a research team working on nothing but hip resurfacing. Our particular interest is in doing the operation exactly right: we plan each operation with a CT scan, which enables us to plan precisely. We then navigate in surgery to achieve that plan. I append a couple of pics of a plan and a post op xray to show you the idea.

I appreciate that this is a patient driven site, but thought you might be interested..

Justin Cobb

 

Dr. Bose

Hi Pat,

Thanks for the mail.

Using computer navigation in  joint surgery is a double edged weapon. While potentially it can reduce the number of outliers,  it can also cause tremendous deviations and absurd placements which would never be done with conventional jigs. I have seen many examples of this done elsewhere and referred to me for revision surgery.

Generally the input to the computer is made by a technique known as bone morphing where the surgeon uses pointer probes to point out the various bony landmarks to the computer. If the surgeon makes an error in this step then it obviously carries on in all further steps leading to a faulty placement. To argue that it removes human  error is most irrational.

We have the brainlab navigation ( market leader in navigation)  in our unit since 2007 and I did a series of cases at that time ( about 80 cases) . I have to say that the femoral cap placement was inferior to my placement with traditional jigs. However I found it useful when one had distorted anatomy as in previous prox. femoral osteotomy. I still use it for such cases.
 
There are many reasons in my opinion by which the conventional jig is far superior to the navigation in hip resurfacing.
 
1. bone morphing with the pointer probes damages the neck capsule which I protect passionately during hip resurfacing surgery and which I am sure is one of the key elements for my success rate.

2. I  use navigation routinely  during my Total knee replacements as the aim of the TKR surgery is to allign the components to the hip and ankle which are not visible in the surgical wound. In contrast in hip surgery the goal is not to align hip component to the spine , pelvis or knee/ ankle. The aim is to align components to local landmarks in the surgical wound, the location of which is given to the computer by the surgeon.  Then the computer gives back the same information which the surgeon offered in the first place. ( this is unlike the TKR where the computer picks up the hip on merely moving the hip and not morphing). Arguments that the computer increases accuracy in hip surgery is frankly absurd and have to be dismissed as marketing techniques.
 
3. The concept of incorporating the  combined anterversion is now the key in operating on FAI ( Femoro- acetabular impingement) which is the pathology in over 95 % of male patients having primary osteoarthritis. This is a dynamic assessment and can be done only with a jig using a lat cortex pin and cannot be done with navigation.
 
Having said all of the above  one must make a distinction between what Prof. Cobb uses and what others use.

Prof . Cobb is the  only one to my knowledge who uses a CT based navigation. The CT gives information which the surgeon cannot access unlike imageless navigation with all other surgeons which depends on surgeon's input based on bone morphing that  defeats the whole purpose of navigation.

In conclusion I would like to say that imageless navigation has very limited role in hip arthroplasty ( eg previosely operated cases) and is an excellent tool in Knee arthroplasty.
CT based navigation for hips which is still not available commercially ( which prof. Cobb uses) may have a significant role in hip arthroplasty. This has to be balanced with the radiation dose for routine CT to be applied universally( approx 30 -50 conventional x-ray dose )
 
wishing you the very best
 
with best regards
vijay bose
chennai

Hi Pat,
 
Computerized navigation has been around for a long time, in total hips, total knees, and now hip resurfacing. A lot of surgeons, including me, have tried it out and not seen an advantage in all but very exceptional cases. Yet other surgeons use it on every case.
 
This is what I think about computerized navigation: It is a tool which can narrow the "bell-curve" of component position, but the curve still has some spread. That helps a surgeon avoid "outliers", or badly misplaced components. Navigation does not make component position the exact same every time, but it helps avoid those outliers. (If it was the exact same every time there would be no bell-curve at all.)
 
So, if a surgeon has no outliers, in other words if he is doing a good job of keeping his personal bell-curve narrow, there is no advantage to using computer navigation. Alternatively, if a surgeon thinks he might accidentally misalign a component so much that it would be considered an outlier, the computer may prevent that.
 
Like any computer, what comes out depends on what went in. Registering the anatomy (which tells the computer where everything is) at the beginning of a computer-navigated operation is not at all an exact science, but depends upon knowledge and experience. It's the same with mechanical alignment jigs. With either method, one should hope that the surgeon is ready to adjust the verdict of the computer or the jig to place the component accurately in the bones which are clearly visible.
 
Are there any downsides to using a computer? Well, there is the extra time involved, which prolongs the surgery (think infections, blood clots). There is extra expense. There is often one more person in the OR, and more traffic in the OR can lead to infection. There is the possibility of surgical complacency if the doctor believes in the infallibility of computers.
 
I have heard this discussed at resurfacing meetings, and people whom I respect more than any others in this field have tried navigation and declared it "useless", and a "waste of time". While unwilling to go quite that far, it does make me think I am fine in continuing with mechanical jigs.
 
Your question about doctors not having 100% "retention" due to component malposition requires a reply. Personally, I have not had any failures in almost 600 resurfacings due to component malposition. I have 1 femoral neck fracture due to leg presses 8 weeks after surgery, and one pelvis fracture resulting from trauma 2 years after resurfacing. That's it. But malposition is an important cause of fracture, wear-related failure, and possibly pseudotumors as well, so should be avoided.
 
Any surgeon "young" enough to learn hip resurfacing is certainly young enough to learn the much easier task of computer navigation, so people who consider someone too "old" to learn navigation are being silly.
 
Similarly, a patient who would choose his surgeon based upon their use of computer navigation is badly misguided. There are many much more important issues to consider.
 
Having said all this, I wouldn't be surprised if at some point in the future surgical navigation becomes more accurate, easier, cheaper, and quicker. Robots will substitute for doctors. Surgeons will look back on the old days and shake their heads in amazement that we used to do all this by hand.
 
Peter Brooks MD, FRCS(C)
Cleveland Clinic

DEAR PAT

WHAT ABOUT NAVIGATION

Today navigation is still a tool that is not easy to use and that needs a certain learning curve as resurfacing itself also has.

So it is not a useful tool today for resurfacing beginners, where it should be! It would be nice if it would be a help at the start of the learning curve.

So can somebody with experience use it or should they use it?

It is like doing a certain approach and having experience with it, so it feels better and confident.

Most of the experienced surgeons do feel they do not need it. MAYBE it could help.

BUT there are some things that have to be cleared out still today:

[list]
[li]there is no correlation in most of the systems between head and cup.
[/li]
[li] Most of the systems only look to the head, and nobody can tell us today what is now the best place to put the implant
[/li]
[li] It would be the best to use it for the cup because there we have the most failures!
[/li]
[/list]

BUT AGAIN the most problems will be with females, that easily have twisted pelvis on the table and smaller sizes, and it is not sure it will have a big influence here.

If it is a system with preop CT of the pelvis to do the acetabulum, the pictures are taken in SUPINE (lying down position!). The patients walk and run on their hips, they do not lie on them, and that can make a complete difference!

So we are not there yet, if something could help me to do better surgery it would be navigation, but as it is today, it is not a 100% proven project. I have today so designed instruments that I call it navigation without navigation; of course in other sites navigation really could help!

I do not know if the 7 malpositioned cups in my series of 3000 would have benefited with navigation, possibly yes, but maybe would have had others where then the placement was worse?

It is the future?, maybe, but not there yet at present for everybody. That is why not everybody is using it, not just because we would be to lazy, to old, to stubborn or whatever.

If it would be used tomorrow in all cases from the start, the worry is also there, that if the navigation fails we do not know anymore what to do. All these facts should not be used for marketing or publicity issues but left to the orthopaedic community to make it better, try it and try to succeed better, what prof.Cobb, myself and all others I think try to do.

KOEN

koen de smet

hipsurgeon amc gent krijgslaan 181 9000 GENT BELGIUM +3292525903 www.heup.be

anca clinic roma valle giulia ROMA ITALY www.ancaclinic.it

Dr. Gross

Dear Pat, 

Thank you for the work you do, it helps so many. Computer aided navigation is an interesting concept. However, there is no evidence that it leads to better clinical outcomes and fewer failures. On the other hand, there is ample evidence that surgeon experience has a dramatic effect on outcomes and complications. 

One way to conceptualize this is that the experienced surgeon’s brain is a computer with much more sophisticated "software" than a navigation computer. When a computer is programmed, an algorithm must be created which has certain inherent limitations. Furthermore additional significant sources of errors are introduced by the registration of anatomic points for the navigation computer in surgery.

My personal opinion is that navigation that is based on a pre-operative CT scan data, which is being pioneered by Justin Cobb, has tremendous promise in the future to improve the results. At this point, we are still in the early development phase. It will probably add several thousand dollars to the cost of each operation. 

In summary, I believe the right kind of navigation surgery based on accurate 3D CT scans holds tremendous promise for the future. It will still require an extensive amount of preliminary development work before it is ready for routine use. 

I hope this helps with this very complex issue. 

Best regards,

Thomas P. Gross, M.D.

Dear Pat,

There is some data indicating that navigation can improve the accuracy of femoral component placement in hip resurfacing.  The real issue is "compared to what?"  For an inexperienced surgeon, navigation may help him avoid component positioning problems that have been associated with "the learning curve".  However, for an experienced surgeon, who has an established mechanical alignment system with a high success rate - it is difficult to demonstrate an advantage to him with a navigation system.  Further, the registration process takes a little time – so the cost-to-benefit ratio for the experienced surgeon in a busy O.R. is questionable.  The navigation systems are not hard to learn to use, even for old guys like me!

A bigger challenge is acetabular component positioning.  This is true for total hips, and even more important for resurfacing.  There are 2 parts to the acetabular positioning problem.  The first is identifying the desired position for that patient and the second is putting the cup in that position.  Keeping the pelvis in one position and finding accurate pelvic/acetabular landmarks can be challenging.  The lateral opening angle is the easier part.  Most surgeons today agree that between 40 and 50 degrees is desirable.  Version is more complicated because the desired acetabular version is dependent on femoral version.  Acceptable version is also related to the lateral opening angle and the resultant bearing contact area.  Again, the issue is experience.

If I have any doubt about component positioning, I get an intra-operative x-ray.  Admittedly, there can be some challenges to getting a good intra-operative view.   For what it’s worth, we did an x-ray review of my first 500 resurfacings (minimum 1 year follow-up).  I have never had a femoral neck fracture and all sockets are below 50 degrees lateral opening.

Best wishes.

Thomas P. Schmalzried, M.D.

I was at the Annapolis conference last week and listened with great interest to the discussions on this topic. As you can well imagine the navigation companies have been trying very hard to sell their equipment to the hospitals. I have resisted thus far because I never felt the cost was justified in either total knees or primary stemmed hips because the anatomy is easily directly visualized and my accuracy was already excellent in placing the components with the available instruments.

For resurfacing the anatomy is not so easily visualized because the pin is placed in the center of the femoral neck and can't be directly visualized. Additionally the neck is not fully visualized because the capsular attachments are preserved to maintain blood supply to the femoral head.

I went back this week and reassessed my pin placements on my first 50
resurfs and found that my pin placement was very accurate and that all the pins that were more then 2 degrees off ideal (total of 2) were in the first 10 cases. That said there have been a few times where although the pins were placed accurately I was a little unsure until the post op x-ray confirmed things. There are a number of ways to check placement with the neck feeler gauges prior to reaming over the pin and once one learns how to do this it works well. As I have done more I now rarely have those feelings of uncertainty and would agree that computer navigation might not offer much at this stage.

The role I see for navigation is in a surgeons early cases not to be the only way to place the pin but rather as a way to check placement of a conventionally placed pin to confirm proper position and allow repositioning if needed. That would prevent misplacement in the early cases while allowing a surgeon to gain experience and confidence in conventional pin placement.

Although I am now confident in my pin placements I am going to try a navigation system once or twice just to see. After that the hospital would need to buy the system and for now I don't think the cost will be justified. I will keep everyone informed of my opinions after I give it a try.

Scott Rubinstein M.D.
Illinois Bone and Joint Institute
Chicago, Illinois
 

Dr. Bose

I was one of the first to try out computer aided surgery for resurfacing. This has no advantage except in patient who have had previous surgery like a osteotomy . It has a very important disadvantage of removing all the capsule and soft tissues on the neck of the femur ( to take a computer reading known as bone morphing). This will compromise blood supply. I have to say that currently for resurfacing computer aided navigation is only a marketing tool for surgeons/ companies. Computer aided navigation is very beneficial in knee replacements where one has to align the knee components to the hip and ankle and I use it routinely for knee replacements.

Wishing you the very best

With best regards
Vijay bose
chennai
 

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