Explain the surgical
approaches to hip resurfacing and what approach you prefer
Most hip replacement and resurfacing surgery in the USA, about
80%, is performed through a posterior approach. About 20% of US
hip surgeons prefer some variation of an anterior approach (antero-lateral,
direct lateral, trans-gluteal, or true anterior). Anterior
approaches are also more common in Europe and Canada.
In the posterior approach, the incision, dissection, and
dislocation of the hip joint are all performed posteriorly
(toward the buttock). The large gluteus maximus is split, and
the gluteus medius and minimus muscles (hip abductors) are
retracted, but not cut. A number of smaller muscles, the “short
external rotators” including piriformis, obturator internus,
gemelli, quadratus, and obturator externus, are cut, and the
tendon of gluteus maximus may also be partially divided. With
these out of the way, the posterior hip capsule is incised, and
the hip is dislocated posteriorly by turning the foot toward the
ceiling. The acetabulum and femoral head are then resurfaced,
the muscles and capsule are repaired, and the incision closed.
In the direct lateral approach, (or trans-gluteal approach as it
is also known), the incision is on the side of the hip, and from
there the dissection proceeds towards the front of the hip
joint. The hip abductors (gluteus medius and minimus) are split
in the line of their fibers, peeled off the greater trochanter
of the upper femur in continuity with upper fibers of the vastus
lateralis, and retracted anteriorly, allowing the anterior
capsule to be cut, and the hip to be dislocated anteriorly, with
the foot pointing down to the floor. During closure, these
muscles all tend to lie back where they belong, and since they
have not been cut across their fibers, there is no tendency for
their repair to pull apart. The antero-lateral approach is
similar, but retracts or detaches, rather than splits, the
abductors.
The true anterior approach can be adapted to hip resurfacing,
actually better than for hip replacement, since exposure to the
shaft of the femur is difficult (and not needed in resurfacing).
It is not popular among surgeons who operate on adults, but is
fairly common in pediatric orthopedics.
Different approaches have different issues. The posterior
approach is very well known in the USA, and BHR developers Mr.
McMinn and Mr. Treacy use it routinely as well. Theoretically it
should have a higher dislocation rate, due to the fact that
dislocation almost always occurs posteriorly, and this approach
disrupts all the potential restraints to posterior dislocation.
But dislocation after hip resurfacing is much less of a problem
than it is with hip replacement, due to the very large head
size. The blood supply to the femoral head stands a greater
chance of damage through the posterior approach, since that is
where the vessels mostly are. The important hip abductors
(gluteus medius and minimus) are left completely intact.
The direct lateral (trans-gluteal) approach has the advantage of
a lower dislocation rate, and less likelihood of damage to the
blood supply of the femoral head. In addition, no muscles are
actually cut across; they are just split, or teased apart in the
line of their fibers, which should lead to more reliable
healing. The exposure of the socket is a “straight shot”, since
the acetabulum is an anteriorly facing structure. The
disadvantages are that there is nonetheless surgical trauma to
the abductors which, if substantial, could cause a limp. There
are also reports of heterotopic ossification, although this may
occur with any approach.
The true anterior approach can be associated with injury to a
sensory nerve responsible for the side of the thigh (lateral
femoral cutaneous nerve), and the location of the incision in
the groin is not the cleanest part of the body. It is also by
far the least commonly used of these incisions for adult hip
surgery, so at least for the time being, we do not have a lot of
data.
The main thing to keep in mind is that any of these surgical
approaches can work just fine. All have been modified in many
ways as surgeons find better ways to do things. The most
important thing for a patient to decide is who will do their
surgery, not how it will be done. The surgeon, drawing on his or
her own training, experience and beliefs, will decide what works
best in their hands.
What Hip Resurfacing
Device Do You Prefer?
I prefer the BHR (Birmingham Hip
Resurfacing). It has the longest track record, and better
results on the Australian Registry and Oswestry Outcomes Study
than others. There are quite a few variables in instrumentation,
cement technique, device dimensions, clearance between the ball
and socket (for self-lubrication), and metallurgy. With all
those variables, no one can be sure what the very best
combination would be, other than to look at long-term data. That
is what the BHR group provides. Lab testing, although important,
is less compelling.
Take a look at the 2007 Australian National
Joint Replacement Registry
http://www.aoa.org.au where they report on many different
resurfacing systems available in that country. There is a wealth
of information there. It shows, for instance, that in men < 55,
resurfacing does better than hip replacement (HT19, HT25). It
also shows that the BHR outperforms other commonly used devices
in terms of revision rates, apart from Adept and Mitch that were
recently released and are promising (HT37). This may of course
change with time, due to learning curves or other factors. I
have an open mind, but for now the BHR has the largest series,
and the best data.
I should also point out that I am a paid
consultant on hip issues for Smith and Nephew, which markets the
BHR. However, I receive no remuneration based on whether I
implant BHR's or not.
What Surgical
Approach Do You Use?
I use the direct lateral approach. This is a type of anterior
approach. Post-operative limp is not a problem.
There is no difference in the results of
anterior vs. posterior approach, although that is surprising in
that the blood supply to the femoral head is disrupted more
during posterior approaches. The most important thing is the
experience and preference of the surgeon, 80% of whom in the US
are using the posterior approach.
How do you feel
about cementless devices? Do you prefer cemented and why?
The BHR femoral component, being cemented, is fully secured to
the bone immediately. The femoral issue is that the freshly
shaped bone is weak, has to heal, and remodel according to new
loads. That takes many months. During that period, there is a
small risk of femoral neck fracture. On the socket side, the
hydroxyapatite coating on the rough surface facilitates bone
ingrowth over several months. I do not allow running and jumping
for 1 year.
In general I use cementless total hips and cemented total knees.
The difference is due to the fact that to cement a traditional
hip stem, you fill up the femoral canal with doughy cement,
which, when it hardens, is extremely difficult and destructive
to ever get out if you have to. On the other hand, cementing a
knee prosthesis requires only a thin layer of cement, which is
easy to revise. Of course, data is important here too.
Cementless total hips and cemented total knees do extremely
well.
What about resurfacing? The BHR is "hybrid",
in other words, a cemented femoral component and a cementless
socket. The developers tried fully cementless resurfacing and
fully cemented resurfacing. Their data showed that the hybrid
was better, so that is the direction they went. And in hip
resurfacing, as in knee replacement, the cement is just a layer,
not a column of cement down the femoral shaft, so it is easy and
safe to revise if necessary.
Does the length of
incision influence the rehabilitation?
The length of the incision has to do with the amount of early
post-operative pain, but not directly with the speed of
recovery. That depends upon how the tissue inside, like muscles,
are dissected, handled and repaired. That in turn is dependent
upon the techniques and skills of the surgeon and assistants.
Do you preserve the
hip capsule during your hip resurfacing surgeries?
I do not preserve the anterior capsule. This is removed during
the surgical approach, and that is a good thing, because it is
normally shortened and contracted by the arthritic process. If I
repaired it, that might limit full extension of the hip, which
in turn could stress the lower back. That is one reason why
posterior surgeons make a point of also cutting the anterior
capsule and leaving it to stretch out, while they repair the
posterior capsule to prevent dislocation and help the blood
supply.
The more important posterior capsule is left
entirely alone in my surgical approach. This means the
dislocation rate in my practice is practically zero in hip
replacement, and is zero in BHR's. Interestingly, there were
quite a few dislocations in the early US BHR experience,
probably related to learning curves and the posterior approach.
Why is Hip
Resurfacing better than a THR - for the proper candidate?
I prefer hip resurfacing over hip replacement, in the proper candidate,
for many reasons:
- It is much more conservative with respect
to bone loss, on the femoral side. On the acetabular (socket)
side, there is a slight increase in bone resection, but most
failures are not socket-related, so that is less important. Why
would you want to cut away 3 inches of healthy femur, especially
in a young person, when the only problem is damage to the
cartilage surface? Just replace the surface!
- The above argument only holds water if the
results of resurfacing are comparable to replacement. They are,
in the right candidate: younger, healthy bone which is not too
distorted, active, good kidney function, no nickel allergy, not
a woman of child bearing age.
- It is more natural. Subsequent bone loading
is exactly how nature designed it, on the upper bone of the
femoral head, from the top down. Hip replacement actually
reverses normal loading. As stresses from weight bearing are
applied to a conventional hip replacement, they pass down the
stem, bypassing the remaining upper bone, and overloading the
bone farther down the thigh. The end result is that years later,
the bone in a resurfaced patient is closer to normal, but the
bone in a replacement patient is weak in the upper femur, and
strong down below.
- It hurts less. You don't get a root canal
of your thigh bone.
- It feels better. I have an interesting
group of patients with a replacement on one side (from years
ago) and now a resurfacing on the other. They all prefer the
resurfacing.
- There is some evidence from gait studies
that function may be better than hip replacement.
- Most resurfacing patient ultimately get
back to completely normal activity. Most hip replacements do
not. Of course, some of that is due to the younger population we
are resurfacing.
- It is less likely to result in leg length
inequality.
- It is less likely to dislocate, by a factor
of 10.
- Range of motion has the potential to be
normal. This depends on many factors.
- Most importantly to younger patients, is
the ease of revision. If you need further surgery in the future,
and you have already had a total hip replacement, you may be
facing a revision of your stem. Revisions can be a big deal. If
the stem is loose, if cement has to be removed, if the upper
bone is weakened (see above), if there is a fracture, or
infection, you are likely to need a revision-style stem. These
are long, larger diameter stems, perhaps modular, maybe
requiring bone grafting, extended trochanteric osteotomy,
cortical windows, wires, cables etc. The long-term results of
these stems is nowhere near as good as first time hip
replacement.
If you need further surgery, and your hip was
previously resurfaced, guess what? You get a first-time total
hip stem, with all the attendant excellent results of that, and
if your socket is still fine, the surgeon will leave it alone,
put a big metal head to match it on your stem, and you're done.
Half the work of a hip replacement, with the excellent wear
properties, range of motion, and resistance to dislocation of
the big head.
That alone would be enough to convince most
young patients to try a resurfacing, even if the results were
not quite as good as hip replacement. The fact is, the results
are just as good, or even better in some reports.
