|Mr. Justin Cobb
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
I appreciate that this is a patient driven site, but thought you
might be interested..
Thanks for the
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
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
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
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
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
|Dr. BrooksHi 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
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
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
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)
|Dr. De SmetDEAR 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
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 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
[li]there is no correlation in most of the systems between
head and cup.
[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
[li] It would be the best to use it for the cup because
there we have the most failures!
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
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
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 de smet
hipsurgeon amc gent krijgslaan 181 9000 GENT BELGIUM
anca clinic roma valle giulia ROMA ITALY
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
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
I hope this helps with this very complex issue.
Thomas P. Gross, M.D.
|Dr. SchmalzriedDear 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
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
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
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
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