Dr. Kurtz had an article online that had concerns about the head neck rations of hip placement. We wanted to provide potential hip resurfacing patients with opinions of other top resurfacing surgeons to explain their views.
Thanks for the mail. I read Dr. Kurtz thoughts on hip resurfacing in his
His concerns are very valid but I cannot agree with his conclusions.
In short , his concerns only underline the fact that bad results of
resurfacing are due to badly done resurfacings.
The head neck ratio is an important determinant of range of movement and
prevention of impingement.
In a patient with normal anatomy, if one is careful to restore anatomy the
range will be like pre-0p range of movement before the onset of arthritis. This
is a simple concept.
However many patients especially young osteoarthritis will have FAI ( Femoro
– Acetabular impingement) as the source of their arthritis. It is of paramount
importance to recognize it and deal with it time of surgery. Again patients with
an mild unrecognized slip in their earlier years will have OA in the later
years. Here again it is crucial to recognize and deal with it at the time of
As the head component in a resurfacing is centered on the neck and not the head
, correct placement will restore the head neck offset to a large degree.
During the surgery the metal cap will look very eccentric on the head.
Surgeons with less experience in resurfacing will think this is wrong and
will just put a cap on the translocated head resulting in very low head neck
ratio which will lead to problems postop.
In some severe cases , even if done correctly there may not be adequate head
neck offset. This is very rare and in this instance one has two choices. In a
very young patient , I would trim the ant neck to re-create the offset. In an
older patient I would proceed to use a stemmed component with the same acetabular cup. One cannot underestimate the importance of bone conservation in
a young patient.
In a patient whose head – neck offset is carefully restored to ‘normal ‘
during surgery and the acetabulum inserted in correct orientation , patient will
have ‘normal’ movement postop. Only a contortionist will need more than ‘normal’
movement. Although in theory a large head THR can have supra normal movement,
this never happens in clinical situations because apart from the head neck ratio
there are many other factors determining ROM like muscle tension etc.
By stating 69 degrees as the functional ROM In resurfacing , is Dr. Kurtz
suggesting that resurfacing patients will not be able to sit in a chair as that
would require 90 degrees?
The mathematical calculations is very different from actual clinical results
in the human body.
The most practical example of this is in India where most patients would sit on
the floor even if the surgeon advises them not to as it is a very important
We did a study in our unit and found that 20 % of conventional THR were able
to sit and 76% of resurfacing patients were able to sit. This again reiterates
the importance of surgical technique.
Purely by choosing a particular prosthesis one cannot guarantee a near normal
ROM- it has to be installed correctly. However the resurfacing/ anatomical head
is the best tool in the surgeon’s hands to restore near normal ROM.
Dr. Kurtz also has mentioned component height which would give a prominent head
neck junction if not seated. I fully agree with this and it would cause serious
problems if not seated. The bottom line is again technique related and one must
fully seat the component.
The next issue is impingement which he has raised. The concern in very valid
because resurfacing acetabular components typically subtend a larger angle at
the periphery than conventional THR cups.
Therefore it is more difficult to bury the anterior edge beyond the bone
margin in a resurfacing . I would do this in all cases and would never accept
ant edge of the cup to be more proud than the bony margin. Therefore the issue
of neck- prosthetic impingement does not arise in my opinion. Again is a matter
of surgical technique.
Some of his statements, are simply not true. – like the ones given below
One does not remove more acetabular bone in the acetabulam than in a THR. – if
someone is doing this he is doing something seriously wrong. I have explained
this concept earlier. If any resurfacing surgeon is doing this he must be
The incision for resurfacing is not bigger than for THR . It has been published
by Derek McMinn that Hip resurfacing can be done by MIS and results are same.
My incisions for both resurfacing and THR is about 10 to 14 cms and the
length variability depends on the constitution of the patient and not on the
procedure. If a surgeon is using larger incision for resurfacing than for THR,
it is not wrong but is in the learning curve of the procedure. Arguments like
that of the removal of labrum and cutting of the capsule in a resurfacing will
cause problems sounds to be weak attempts to pick holes in the outstanding
functional results that have so far been achieved in the last 12 yrs in
resurfacing. The capsule is not removed in a resurfacing but carefully preserved
and stitched back capsule to capsule ( the NCP approach or the neck capsule
preserving approach for resurfacing). It is certainly true that the surgeon has
to give much more importance to the preservation of neck capsule in resurfacing
than in a THR.
It appears to me surgeons confuse many aspects of resurfacing. The old poly
resurfacings results must not be mixed with the modern metal on metal
There are two dif concept in a resurfacing which was introduced to the
orthopedic community at the same time and hence gets mixed up. The first is the
use of an anatomical sized bearing. This implies the head diameter to be the
same as that of the native head. It is important to understand that the aim is
not to put in the biggest sized head that is possible. If a larger than a native
size is uses, it will bring a dif. set of problems. Anatomical sized bearing
can be done with a resurfacing or with anatomical metal on metal THR ( people
refer to this wrongly as large head — it is actually the correct head and all
other heads are indeed small heads). Now , currently one can use the BMHR as
well. I have attached the pics which illustrates it. Hip Resurfacing is not
the aim here – the goal is to restore an anatomical bearing which would be best
attempt at restoring near normal function. One has to use the best devise to
achieve this goal.
Restoring an anatomical bearing is the
goal in a high value hip.- high value hip means in
patient who have a lot of demand out of their hips. An
elderly sedentary patient can have any hip and any
articulation. It would make no difference. However an
wear resistant anatomical bearing is the goal in a
patient who has demand of the hip for occupational ,
recreational or social customs.
This is the first aim. The next issue is of bone
conservation . Importance of bone conservation is
determined by relative importance of 3 factors, namely
the age , the activity level and the bone stock. Bone
preservation is not a static concept. Bone conservation
would be of immeasurable value in a 25 yrs old and would
be probably be a contraindicated in 80 yrs old due to
the risk of femoral neck fracture. I have attached a pic
to illustrate this point.
Thus there are two dif issues here –
the use of an anatomical sized bearing & bone
conservation. These are independent issues . As both
these concepts came simultaneously with the advent of
resurfacing there has been a hotch-potch with many
confusing these two.
Dr. Vijay C. Bose
Consultant orthopedic surgeon Chennai, India