RECENT REPORTS
ON THE RESULTS OF SURFACE REPLACEMENT OPERATIONS
18 / 03 / 2004
SURFACE HIP REPLACEMENT – a breakthrough at last
Surface hip
replacement has been discussed more among the patients than among
the total hip surgeons. The majority of surgeons were aware of the
catastrophic failure rates of this method in the past. A small group
of surgeons, however, were convinced that bad materials
(polyethylene cup components) used for manufacture of the device
were responsible for the past bad results. (see
also the chapter
Surface hip replacement
for more details).
These surgeons
developed a new surface hip replacement device. In this new surface
hip device, both shells are made from cobalt-chrome-alloys. What
hampered the spread of this device was the lack of reliable reports
about the results of this new surface replacement hip.
This may by over
now. In the January issue of the prestigious Journal of Bone and
Joint Surgery (American volume) there appeared a report from the
Californian surgeons working at the Joint Replacement Institute on
the results with one model of the surface hip replacement device.
Now, in the March
issue of the British volume of the same journal, there appear three
reports about the results with a British model of surface hip
replacement device. Two reports are authored by British surgeons
( Daniel 2004, Glyn-Jones
2004), one report is authored by Japanese surgeons (Kishida
2004). Speak about the spread of the hip surface replacement method!
In the report about
the Birmingham surface replacement device (Daniel 2004), the authors
followed 384 patients with 446 hip resurfacings for a mean of 3
years. The results showed that there was only one revision operation
in this group, making the incredibly low rate of failure of only
0.02% !
The patients have
had much improved function in their hips and relief of pain. The
patients were encouraged to continue with their work and leisure
activities as usual; 30 % of patients thus continued with heavy job,
and over 90% of all patients continued to participate in sports.
The Birmingham hip
resurfacing (BHR) arthroplasty is a
metal-on-metal prosthesis. The femoral component (shell) is cemented
whereas the cup component is cementless.
No medium term results (5 years) or long-term results (>10 years)
have been published as yet. Thus, the critics may say that present
results are good, but how will it be in the future? There is,
however, a roentgenological method that
in may predict the long-term behavior of the resurfacing device.
The method is based
on the following observation: A total joint prostheses that shift
their position relative to the surrounding skeleton already during
the first two postoperative years are in reality loose, although not
causing inconvenience to the patient. The majority of these
prostheses, however, will continue to increase loosens and
eventually fail. The movements of the total hip components are very
small and need a sensitive x-ray measurement method to be disclosed.
With the use of roentgen stereophotogrammetric
analysis (RSA) the
roentgenologist can disclose even very small movements and
shifts in the position of the device already during the first two
years after the surgery.
A group of British
surgeons thus measured whether the femoral component of the
Birmingham hip replacement device moves early after the surgery (Glyn-Jones
2004).
Migration of the
femoral component in 22 patients was measured by
RSA at intervals of three, six, 12 and
24 months. At 24 months the total three-dimensional migration of the
head was 0.2 mm. This movement was so small that it was probably
caused by the error inherent in the measurement method. Simply
stated: all the femoral devices were rock steady!
There is always a
fear that the total hip replacement will weaken the skeleton around
the hip prosthesis, making it prone to the fracture. The
surgeon speak about the "stress shield
effect" (for details see the chapter
Function of the THP
/
stress shielding effect).
A group of Japanese
surgeons studied the stress shielding effect of Birmingham surface
hip replacement device (Koshida 2004).
They measured the bone mineral density (BMD)
of the femur close to the hip replacement device on 26 hips in 25
patients.
The patients were
divided in two groups. Group A consisted of 13 patients (13 hips)
who had undergone resurfacing hip arthroplasty with the
BHR system and group B of 12 patients
(13 hips) who had had conventional cementless
total hip arthroplasty.
The measurements
showed that surface replacement device preserved the bone stock
close to the prosthesis much better than did the
cementless total hip replacement
prosthesis.
Conclusion of all
three reports: The Birmingham surface hip replacement is an
excellent device which has almost no complications, does not change
the skeleton, and will have also excellent long term results. It
seems as all patients, or at least the younger active patients
should have this replacement device. The conventional total hip
replacement prosthesis seems in comparison almost obsolete!
There is only one
snag in the whole. Doctor Amstutz and
his team originally used the Birmingham hip surface replacement
device too but abandoned it; in their report the American surgeons
say "loosening of the McMinn design in the short term (less then two
years postoperatively...led us to adopt a new design".
I will follow this
question closely and return with more information. The failure rate
of 0.02% in the British report seems to me incredibly low.
Your opinion?
____________
References:
Daniel J et
al.: J
Bone Joint Surg-Br 2004; 86-B: 177 - 84
Glyn-Jones
K et al.:
J Bone Joint Surg-Br 2004; 86-B: 172 - 6
Kishida
et al.:
J Bone Joint Surg-Br 2004; 86-B: 185 - 9
11 / 02 / 2004
LEG LENGTH - IT WILL NOT CHANGE AFTER SURFACE HIP REPLACEMENT
Many young patients with congenital (inborn) deformation of the hip joint develop so-called secondary osteoarthritis of the hip joint and seek help for their painful hip. (For more information see also the chapter Hip diseases- congenital hip dysplasia). The congenital deformation of the hip anatomy usually resulted in shorter and more vertical femoral neck, this deformity is called short femoral offset. At the same time the musculature around the hip of these patients is weak. So that often these patients suffer not only from painful stiff hip joint, but also from a shorter limb and from limp caused by weaker musculature.
When these patients seek operative treatment for a painful stiff hip joint, they will often ask the surgeon if it will also be possible to correct the leg length and improve the muscle function in one operation.
Operation with a total hip joint may fulfill all three objectives.
By choice of a suitable total hip device with longer neck and greater offset (see the chapter Function of the total hip prosthesis - offset for details) of the femoral component, the surgeon may be able to create a longer artificial hip neck and at the same time the artificial neck will be placed in a more anatomical position.
First, the longer neck of the femoral component will equalize the limb length.
Second, the more anatomically placed neck will increase the lever arm of the muscles and thus increase the muscle force of the weak abductor muscles (the muscles that push the leg from the midline). The increased muscle force may reduce limping.
Third, replacement of the worn out hip joint will relieve the pain and stiffness..
Can surface hip replacement achieve all these goals too? Unfortunately, not.
Surgeons from the well known Joint Replacement Institute in Los Angeles, USA, studied the biomechanical effect of surface hip replacement on 40 surface replaced hips in young patients and compared it with the biomechanical effect of 40 total hip replacements done on slightly older patients (Silva 2004).
Basically, the authors measured the leg length difference and the offset of the femoral neck on the preoperative x-ray pictures and compared these values to the values found on the postoperative x-ray pictures.
It appeared that femoral offset was practically unchanged in patients operated on with surface replacements, whereas it increased with 9 mm in patients operated on with total hip replacement. Surgeons believe that increased offset of the femoral component increases muscle force, increases the range of motion, and decreases the wear of polyethylene from the cup component. So these nine millimeters with which the offset increased in total hip replacements are indeed important.
Leg length increased in mean with 4 mm in patients operated on with surface replacement and equally much in total hip replacement group. However, the leg length in surface replacement never increased more than 12 millimeters.
So the authors conclude that limb lengthening of maximally 1 cm can be achieved by surface replacement operation, but femoral offset and thus the muscle force will be essentially unchanged by hip resurfacing. Patients with limbs that are more than 1 cm shorter than the contralateral (other side's) limb due to dysplastic hip or that have annoying limp due to a short vertical femoral neck (short femoral offset) may be better served by a contemporary total hip replacement. These patients should be informed about these limitations of surface replacement surgery.
This recommendation seems to be a common sense: the surface replacement operation is in essence putting two shells on reamed hip joint surfaces, nothing more. Thus, these shells cannot restore anatomical deformations of the hip joint caused by an inborn error to normal.
Not every patient, however, who wishes to have surface replacement of his/her hip joint knows this simple fact and it is good that the authors caution the surgeons to tell it to their patients.
Your opinion?
_ _ _ _ _ _ _ _
References:
Silva M.et al.: The biomechanical results of total and resurfacing hip arthroplasty. J Bone Joint Surg-Am 2004; 86-A: 40 46
03 / 02 / 2004
SURFACE HIP ARTHROPLASTY - RELIABLE RESULTS AT LAST
Several young
patients and patient support groups were discussing the advantages
(and disadvantages) of the surface arthroplasty of the hip joint.
These debates have been sometimes hefty, because the solid arguments
– the results – were lacking.
Now a well-known hip
surface replacement surgeon, professor
Harlan Amstutz from Los Angeles, USA,
published his long awaited report in the leading
orthopaedic journal, The Journal of Bone
and Joint Surgery (Amstutz 2004).
Doctor
Amstutz and his colleagues followed 355
patients who have had totally 400 surface hip replacements. The mean
length of follow-up was 3.5 years and almost no patients were lost
to observation.
Doctor
Amstutz used in all patients the
Conserve Plus surface hip replacement device produced by Wright
Medical Technology. Both components of
this device are manufactured from cobalt-chrome alloy, the femoral
component is cemented on the prepared rest of the femoral head, the
cup component is impacted in place in the prepared hip socket
without cement.
Doctor
Amstutz and colleagues call the results
achieved with this device "encouraging". During the 3.5 follow-up
years, there were in general 6 % failures that needed revision
operation to total hip replacement. The results were influenced
strongly by the patients’ age, activity, and the diagnosis of the
hip disease.
The authors
developed a so-called risk index to assess the risk of the failure
of the surface hip replacement. Young, very active patients with
more deformed and small hip joints with large voids (cysts) have a
high risk index and thus were at four times greater risk for early
failure (11% failed surface hip devices during the 3.5 follow-up
years) than the rest of the older, less mobile patients with less
deformed hips (only 3% of failures).
What are the
"encouraging" facts? The rate of failures so short time after
operation is certainly high in young patients, but then this
category of patients is always at greater risk of failure whatever
hip operation the surgeon carries out.
Perhaps the good
news is that the failures engaged almost exclusively the femoral
head component, whereas the metallic cup did not loosen. In the
"old" models of surface replacement devices with polyethylene cups,
the loosening of the polyethylene cup components was one of the main
causes of failures of the surface replacement prostheses.
The bad news?
There were 0.7% hip dislocations among these patients; one of them
needed revision to a total hip device. The dislocation rate is of
course low, but this surface replacement hip operation is still no
guarantee against hip dislocation.
What was not
revealed? Doctor Amstutz says that
initially he used the McMinn’s surface
replacement device. He was forced to abandon it, however, because
this device has had unacceptably high rate of early failures. What
is an "unacceptably high rate"? How many were these unlucky
patients? How were the results of their revision operations? There
is a reference to a report presented at one conference in the text,
but no numeric data.
Conclusion:
In my opinion this
is a very comprehensive and well-balanced report. The authors of
this report concede that "certain types of patients do
better with this procedure, at least as it is currently
performed, than others do".
Paradoxically, the
young, active patients with small, deformed hip joints who are often
told that surface replacement operation is especially suited to them
as a procedure to "spare time" before a more radical total hip
operation, have had worst results.
Let me cite what the
authors of this report have to say about this topic:
"Ultimately, the
control of postoperative factors is up to the patients,
but it is the duty of the surgeon to properly inform them
of the potential risks. At the present time, we do not
have definitive contraindications to the surgery, but patients
who have compromised bone stock, particularly large femoral
head cysts and small femoral heads, warrant special scrutiny
as candidates for the procedure. Patients also should be
informed that high activity levels (especially impact
sports), although they have not been found to be
significant at this time, are likely to shorten the life
of the implant in a manner similar to the way in which
those activities affect a total hip replacement".
You got it?
Other issues, such
as high levels of metal in the blood are mentioned in the report,
but the time is too short to evaluate its possible effects.
_ _ _ _ _ _ _
References:
Amstutz
H.C. et al.:
J Bone Joint Surg-Am 2004; 86-A: 28-39