cadera / hip - Active Congress.......

MIÉRCOLES / WEDNESDAY
102
ing system (Table 1) with a score >3 representing
a 12 fold increase risk in early failure
or adverse radiological changes. In addition,
when Amstutz and associates25 reported on
the overall experience in the fi rst 400 hybrid
metal on metal SA, a SARI >3 had a survivorship
of 89% at four years versus 97% with a
score < 3.
Currently, the posterior approach is the most
commonly used for hip resurfacing. However,
as discussed in this issue by Nork and associates30
the choice of a surgical approach
for hip resurfacing must factor in different
anatomical considerations than when performing
a standard total hip replacement.
With preservation of the femoral head and
neck, issues such as vascularity and adequate
visualization with minimal trauma to
tissues and nerves must be considered10,30 .
For example, the choice of a surgical approach
compromising femoral head blood
supply10,30,31 and causing osteonecrosis could
lead to femoral loosening32 or femoral neck
fracture33 if the lesion is suffi ciently large. In
addition, because of its conservative nature
and goal to closely reproduce the normal
anatomy of the proximal femur positioning of
the implants may have a greater impact on
implant survivorship and patient function than
with a standard hip replacement.
In the 1982 OCNA issue on surface arthroplasty,
Hedley31 emphasized the importance
of maintaining femoral head vascularity when
considering intervention in early stages of arthritis
whilst in the more advanced stages an
intramedullary source would be suffi cient34 .
The discussion at that time was not so much
what surgical approach to use since most
were using a pure anterior35 or extracapsular
trochanteric osteotomy36 but can one safely
dislocate the native hip joint without causing
osteonecrosis. Subsequent retrieval analysis
papers of failed surface arthroplasty failed to
identify any major osteonecrotic segments. 37-
39 , however the massive granulomatous
reaction from the polyethylene wear debris
combined with bone resorption secondary
to implant micromotion did not leave much of
the bone at the implant interface intact. And
more importantly, most surgeons at that time
where performing hip resurfacing through
approaches which left the obturator externus
tendon intact protecting the branch of the medial
circumfl ex artery 40 . In addition, there is
recent evidence that the blood supply pattern
in advanced arthritis is not signifi cantly different
than in the non arthritic state 41 . Recent
work on arthritic femoral heads, presented
at the annual Orthopaedic Research Society
meeting in Washington, DC (February 2005)
demonstrated using laser doppler fl owmetry
that damage to the extraosseous blood supply
to the femoral head (retinacular vessels)
can cause a signifi cant decrease (greater
than 50%) in blood fl ow. Further followup and
research will be required before we can fully
assess the role of femoral head vascularity
on the clinical outcome of hip resurfacing,
however the choice of a surgical approach
which minimizes the risk of damaging the
blood supply to the femoral head need to
be strongly considered. This may become
even more crucial as we consider cementless
fi xation on the femoral side and earlier
intervention in the arthritic process to avoid
the development of femoral head cysts.
Finally, one must consider the underlying diagnosis
when evaluating a patient for surface
arthroplasty. In cases of dysplasia, acetabular
defi ciencies combined with the inability
of inserting screws through the acetabular
component may make initial implant stability
unpredictable. This deformity in combination
with a signifi cant leg length discrepancy or
valgus femoral neck could compromise the
functional results of surface arthroplasty, and
in those situations a stem type total hip replacement
may provide a superior functional
outcome 51 . Finally, the presence of a metal on
metal bearing leads to an increase in metal
ion release 9,52 . Consequently, because the
information on the systemic distribution of
metal ions and their interaction with living
cells is limited, patients with compromised
renal function and a history of metal sensitivity
are probably not good candidates for a