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INTRODUCTION
Revision
of loosened acetabular implants has generally given
disappointing results 1
3
7
9.
At the 1989 SOFCOT Symposium, Salvan 9
reported 22.9 % of recurrent loosenings, and 22.9 % of
potential loosenings, i.e.only 54.2 % of favourable results
among 210 cases of simple revision for acetabular implant
loosening.
The
use of a Müller-type reinforcement ring gave better
results 5
6,
and using this technique in 1993 Pascarel
6
reported only two failures in 141 cases at four years of
follow-up. However, the long-term results of these rings
wich cannot be incorporated remains an open question.
Remarkable
results at over ten years of follow-up have been recorded in
first-line surgery with impacted hemispheric acetabular
implants whose treated surface is treated surface allows an
osteointegration.. Can this technique be used in revisions?
Will grafting be necessary to restore bone stock?
To
address these questions, we studied a continuous series of
229 acetabular revisions by impacted implant with a mean
follow-up of six years and four months (four to nine
years).
MATERIALS AND METHODS
Between
January 1987 and September 1992, 229 acetabular implant
revisions by impacted implant were performed : 144 women
and 85 men, 121 right and 108 left,mean age 66 years (18
to 90 years), 20 patients were over 80 years of age and
77 over 70 (30 %).
Acetabular
destruction was stage I in 47 cases, without substantial
loss of substance, stage II in 146 cases, with enlarged
cavity trough substance loss but without major
deterioration of the columns and lower edge, and stage
III in 36 cases, with marked acetabular
deterioration.
Series A 1 :
From
1987 to 1989 we used the Esop 1 acetabular implant (split
hemispheric implant covered in a 1.5 mm layer of sanded
titanium, with 4.5 mm diameter screws) (91 cases). In
each case we reconstructed bone stock by impacting in the
acetabular cavity small cubes taken from femoral
heads stored in a bone bank. The implant was impacted
in this morsellized graft, and the screws transfixed the
grafts and were fixed in the healthy bone of the roof and
columns. Most of these acetabular implants were small :
50, 52 and 54 mm.
Series A 3 :
Since
1989 (138 cases), we have used the Esop 3
hydroxyapatite-coated implant (2.5 mm titanium coating,
optional 6.5 mm screw, hydroxyapatite surface). A large
Esop implant was impacted to fill the bone cavity and
ensure extensive contact between the surfaces of the
implant surface and the healthy acetabular bone. Little
or no bone grafting was done and the implants were large
: mostly 56 , 58 , 60 and up to 68 mm (Series A 3).
Follow-up at review was a mean six years and four
mounths (four to nine years).
Clinical
evaluation was done using the Merle d'Aubigné
scoring system. Radiographic assessment was done using
topographic classification into three zones:
supraexternal, two central, three inferointernal.
Survival was estimated by the actuarial method.
FAILURES AND PATIENTS LOST TO FOLLOW-UP
Series A 1 :
Of
91 patients with grafts, 25 died due to causes unrelated
to the implant and six were lost to follow-up. Among the
remaining 60 patients (66 %), there were eight (13 %)
acetabular failures and nine femoral failures. The
nine-year survival rate was 88 % (table I). Forty-three
patients were reviewed, 15 at nine years of follow-up, 20
at eight years, six at seven years, and two at six years.
Series A 3 :
Of
138 patients, nine were lost to follow-up and 20 died.
Among the remaining 109 patients (80 %), there were three
(3 %) acetabular failures and five femoral revisions. The
eight-year survival rate was 97 % (table II). One hundred
and one patients were reviewed, 12 at four years of
follow-up, 38 at five years, 34 at six years, 14 at seven
years, and three at eight years.
Failures
The
eight failures in series A1 were due to resorption of the
grafts with secondary migration of the implant. As the cup
held by fixation screws could not follow this resorption of
the grafts, it was subject to painful micromotion with
rocking of the implant.
The
three failures of series A3 were related to an error in
indication : they were stage III cases with considerable
substance loss and disappearance of the lower edge.
Protrusion occured in the months following surgery. We
should have used a peripherally supported reinforcement
ring.
RESULTS
Clinical and
functional
Series A 1 - 43 revisions:
Results were excellent in 22 cases (51 %), very
good in 12 (28 %) and mediocre in 9 (21 %). Pain was
rare, and was absent (D6) in 38 patients, rare and slight
(D5) in two, and troublesome (D4) in two. Mobility was
good (M6) in 40 patients, moderate (M5) in two, and
mediocre (M4) in one. Function was generally less
satisfactory with frequent persistence of limping : no
limping (F6) in 26 patients, slight limping (F5) in six,
and clear limping and use of a stick (F4) in 11.
Series A 3 - 101 revisions.
Results were excellent in 48 cases (48 %), very
good in 30 (30 %), good in 20 (20 %) and mediocre in 3 (2
%). Pain was absent (D6) in 71 patients, slight (D5) in
17, and troublesome (D4) in 13. Mobility was good (M6) in
95 patients, moderate (M5) in two, and mediocre (M4) in
four. Function was less satisfactory in this series: no
limping (F6) in 59 patients, slight limping (F5) in 31,
and with clear limping and use of a stick (F4) in 11.
Radiological results
Series A 1:
In the 43 cases, there was no reactive line 1 in
20 cases and a limited, nonprogressive reactive line in
zone 3 in 12 cases. Six reactive lines were complete in
zones one, two and three, five migrations of over 2mm
were seen, of which one with fracture of screws. The
latter 11 cases, with extensive reactive lines or implant
migration, were obviously compromised and will probably
progress to failure, requiring surgical revision.
Series A 3:
In 85 of 101 cases (84 %) there was no reactive
line, and nonprogressive reactive lines were seen in 16
cases in zone 3. No migration and no complete reactive
lines were seen in this series (table III). On the
contrary, the periprosthetic cavities were filled.
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DISCUSSION
The
clinical results in the two series were poorer than for
premary implants. This is common and due to the repeated
surgical interventions with periarticular sequelae dominated
by muscular involvement.
Two very different surgical techniques were used
successively and gave very distinct results.
In
the first series, we used small cups impacted on large
grafts of bone bank fragments. There were 8 failures, 11
problable loosenings (6 complete reactive lines and 5
migrations), i.e. 19 unfavourable results in 60 cases (32
%)
In
contrast, when we used large hydroxyapatite-coated cups with
little or no grafting, we observed only three failures in
109 cases (3 %).
This
comparison between two series done over different periods
and with distinct follow-ups is debatable
since it may introduce various methodological biases.
However, the very significant difference in failures and
loosenings (32 % versus 3 %) is in favour of technique A 3.
Although the follow-ups differ, the first signs of migration
occured very early in series A 1 (in the year following
surgery). The minimum follow-up of four years in series A 3
prevented this biais.
Although
the hydroxyapatite coating certainly plays a part in the
quality of the results, we believe that the essential cause
of the failures in the first series was the resorption of
the bone bank grafts. This viewpoint is shared by
Hooten 2,
Knight 4
and Pollock 8
who report failure rates above 30 % in their series
of revision with grafting and impacted acetabular implant.
We know, moreover, that these cementless acetabular implants
only give good results when there is secondary stabilization
by osseointegration. This is why technique A3 should be used
for an impacted hemispheric implant : large cup ensuring
substantial contact with the healthy acetabular bone. Use of
fixation screws is optional : when the primary stability is
sufficient through simple impaction, screws are not
desirable since in the long term they may promote migration
of polyethylene debris to the acetabular roof.
Is
it necessary to restore the bone stock? The good results
obtained without grafting allowed the reconstruction of a
continuous acetabular wall that is thin but whose trophicity
is satisfactory, with disappearance of the cavities and
harmonization of bone structure as revealed by radiography.
The large implant-bone contact area achieved through use of
large cups ensures optimal distribution of stresses, thus
avoiding long-term protrusion. Tanzer and Harris 11
are of this opinion : they used large impacted cups in 121
revisions and experienced only two failures. The main
drawback is that the centre of the hip is raised, although
Schutzer and Harris 10
have shown that this has few functional consequences. In our
experience, osteolysis generally extends both downwards
(lower edge) and upwards (roof), and the centre of rotation
of the hip was therefore little affected.
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