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What is the NCP - Neck Capsule Preservation - Approach in Hip Resurfacing?
Dr. Su's Article
The NCP approach, at least the way that we mean it, is a different
way to incise the capsule in order to gain access to the hip joint.
Usually with THR, the capsule is detached from the femoral neck and
flipped back. It is usually preserved and repaired in order to avoid
dislocation.
With the NCP approach in hip resurfacing, we cut the capsule along the femoral head, so
the capsule along the neck is not disturbed. This preservation of the
neck capsule should help preserve important blood vessels along the
femoral neck, which may in turn preserve blood supply for the femoral
head. This will hopefully improve longevity of the resurfacing.
This is all in theory at present, but the results of Dr. Bose speaks
in favor of it. At the end of the operation, the capsule is sewn
together. This should help prevent dislocation and may help other
things such as lubrication of the joint.
So the NCP is more about preserving blood supply during the
approach. I don't think that it would have a difference on range of
motion, but the fact that I can get a nice capsular closure gives me
confidence to allow patients immediate range of motion of the hip
without restrictions.
Hope that is helpful.
Regards
Dr. Su
Dr. Bose's Article
There are of course many views and opinions amongst surgeons regarding the
best approach and what to preserve during the surgical approach. Failures in
resurfacing which occurs due to faulty approaches and vascularity issue ,do so
at the 3-6 yrs mark ( slow varus collapse with loosening of femoral component ie
AVN of the entire head) . Hence, it is difficult to prove or disprove any
concept regarding this issue with statistical proof. One needs a large number of
cases followed up carefully for a long time and have an opposite approach as a
control group. This would be very difficult in a clinical setting.
Therefore, the best option would be to adopt a common sense path based on some
consensus that has already emerged in the resurfacing fraternity.
It is now more or less accepted that the anterior, anterolat or post approach
really has no influence as regards to the blood supply to the femoral head.
(However other factors like muscle damage, etc, may differentiate the Clinical
result from these approaches.)
There are two components of blood supply to the femoral head intra osseus (
within bone ) and extra osseus ( from outside bone). The relative importance of
these two blood supply is again a source of great controversy amongst surgeons.
There is agreement however that in primary osteophytic OA, there is more of the
intraosseus component and in non -OA cases there is less of the intraosseus
component.
The intraosseus blood supply can be preserved by using a vent during femoral
preparation. This prevents fat and cement debris blocking the small veins in the
head of femur and neck. Though some surgeons would not subscribe to this theory
no one will argue that venting the femur causes any harm. Hence it an excellent
idea in my opinion and this was developed by Derek Mcminn.
The extraosseus blood supply is maintained by preserving the retinacular vessels
on the femoral neck. This has been experimentally again proved by Prof. Sugano
and there is a consensus on this. The best insurance one has in preserving the
retinacular vessels would be to preserve the capsule. In theory one can take the
capsule off and preserve only the synovium to retain the retinacular vessels.
This may be alright but more risky and technically difficult to achieve. Again
no one can argue that preserving the capsule does any harm. Hence I advocate
this strongly.
Therefore not venting the femur and not preserving the capsule could potentially
cause great harm with femoral component failure at the 3-6 year mark. Surgeons
who do not advocate this may be influenced by their early success with
resurfacing but will have to wait 6 years before they can say with conviction
that these technical issues are not important.
The added advantage of preserving the neck capsule is the ability to repair
capsule to capsule at the end of surgery which accelerates the immediate rehab .
It may restore proprioception to an extent.
The NCP approach (Neck Capsule Preserving approach )was developed at the ARCH
centre in Chennai, India and is being increasingly adopted by surgeons the world
over for hip resurfacing surgery.
Vijay Bose
Chennai
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