We previously reported the results of revision total hip arthroplasty after
an average duration of follow-up of 10.4 years (range, 8.5 to 12.7 years) for
thirty-four patients (thirty-six hips), from an original pool of forty-four
patients (forty-six hips), in whom a cementless acetabular component
(Harris-Galante I or Harris-Galante II; Zimmer, Warsaw, Indiana) was placed at
least 35 mm proximal to the interteardrop line because of severely compromised
bone stock1. All
components but one were fixed with multiple screws after line-to-line reaming
of the acetabulum (Fig. 1). The
average hip center was 43 mm (range, 37 to 77 mm) proximal to the
interteardrop line. The femoral component was revised simultaneously in
thirty-three of the forty-six hips, but no well-fixed femoral components were
revised. The mean age of the patients at the time of the revision surgery was
fifty-two years (range, twenty-five to eighty-one years).
At the time of the ten-year follow-up, one of the original forty-six hips
had undergone re-revision of the acetabular shell because of aseptic
loosening, with one additional shell scheduled for re-revision because of
aseptic loosening. In three other hips, the acetabular shell had been removed
because of infection. Nonprogressive pelvic osteolysis was noted in two of the
thirty-six hips that were followed for ten years or more, and two hips
demonstrated a continuous nonprogressive radiolucent line about the acetabular
component. The mean Harris hip score was 81 points (range, 56 to 100
points).
The central purpose of the present report is to update the results of
acetabular reconstruction with use of one type of cementless acetabular
component, placed at a high hip center, after a mean duration of follow-up of
16.8 years (range, fifteen to 17.9 years). We also report the results for the
femoral components, which were quite varied in design, fixation method, and
duration in situ.
Of the original group of forty-four patients (forty-six hips), twelve
patients (twelve hips) had died, two patients (two hips) were too ill to
return for follow-up, four patients (four hips) were lost to follow-up, and
five patients (five hips) had undergone re-revision of the acetabular shell,
leaving twenty-one patients (twenty-three hips) available for the present
study. The two patients (two hips) who were too ill to return for follow-up
had not required repeat revision. In the group of twelve patients (twelve
hips) who had died prior to the minimum fifteen-year follow-up, the average
interval from the index revision to the time of death was 9.82 years (range,
four to fourteen years) and no patient had undergone re-revision or
reoperation for any reason. Twenty-one hips had current radiographs and
clinical follow-up, one had clinical follow-up only, and one had radiographic
follow-up only. In the case of the one patient who lacked current radiographs,
the most recent radiographs (made eleven years after the index revision)
demonstrated no osteolysis or evidence of cup loosening. In the case of the
one patient without current clinical follow-up, the most recent Harris hip
score (determined twelve years after the index revision) was 84 points.
Clinical and radiographic data on the twenty-one patients (twenty-three
hips) had been collected prospectively, and the minimum fifteen-year data were
evaluated retrospectively. The average age of the patients at the time of the
latest follow-up was 64.9 years (range, forty-four to eighty-nine years).
Institutional review board approval was obtained before the start of this
study.
Physical examination was performed, radiographs were made, and clinical
evaluations (including determination of the Harris hip
score2 and the
University of California at Los Angeles
[UCLA]3 functional
index) were performed. Designation of radiographic signs of loosening and
evaluation of radiolucent lines were performed according to previously
published criteria4.
All radiolucent zones measuring >3 mm in width were considered to represent
osteolysis. The locations of periacetabular radiolucencies were described
according to the system of DeLee and
Charnley5. The
distance proximal to the interteardrop line and the lateral distance from a
vertical line from the lateral edge of the teardrop were used as references to
determine vertical and horizontal displacement of the hip center. Migration of
=4 mm or an angular change of >5° was deemed to be evidence of
migration of the acetabular component. Linear head penetration was measured
with use of the computer-assisted methods of Livermore et
al.6. For patients
who underwent exchange of the acetabular liner, the final radiograph that had
been made before acetabular exchange was used to determine the femoral head
penetration before reoperation and thus the wear rate. Measurements of
position, linear wear, and osteolysis were performed as described in our
previous report1.
Acetabular bone deficiency at the time of the index operation was classified
according to both the American Academy of Orthopaedic Surgeons
(AAOS)7 and Tanzer
systems8. According
to the AAOS system, there were two stage-1, seven stage-2, and thirty-seven
stage-3 hips. According to the Tanzer system, there were two stage-I, five
stage-II, nineteen stage-IIIA, eighteen stage-IIIB, and two stage-IV hips.
For the twenty patients (twenty-two hips) with the acetabular shell still
in place who had calculation of the Harris hip score at the time of the latest
evaluation, the average score improved from 52 points preoperatively to 73
points (range, 44 to 98) at the time of the most recent follow-up. Seven hips
were rated as poor (Harris hip score, <70). Of these seven hips, four were
in four patients with femoral osteolysis associated with a loose femoral
component, two were in patients who were substantially compromised by chronic
low-back pain, and one was in a patient who had had a stroke and had markedly
reduced activity.
In the entire group of forty-six hips, five acetabular shells (10.9%) had
been re-revised because of aseptic loosening (two shells) or infection (three
shells). The two re-revisions that were performed because of aseptic loosening
had been done at sixty-nine and 121 months after the index revision. Both
shells had migrated medially into the pelvis. One shell, in addition to being
loose, demonstrated substantial periprosthetic osteolysis accompanied by a
continuous radiolucent line. The shell that was re-revised at sixty-nine
months after the index revision had been placed 42.5 mm proximal to the
interteardrop line in a hip with Paprosky grade-IIIB bone
stock9, and had had
little intrinsic stability at the time of the index revision. The shell that
was re-revised at 121 months had been placed 52 mm proximal to the
interteardrop line in a hip with Paprosky
grade-IIIA9 bone
stock. Neither of these shells had contact with the pubis. Seven additional
hips underwent isolated exchange of the polyethylene liner with retention of
the acetabular shell. Two of these seven exchanges were performed because of
liner wear. One other liner was exchanged to cross-linked polyethylene
incidentally at the time of bone-grafting for the treatment of a pubic stress
fracture. No osteolysis was evident radiographically around either the femoral
or the acetabular component. The four remaining liners were exchanged for a
cross-linked polyethylene liner incidentally at the time of femoral revision.
Of the twenty-three hips with a minimum of fifteen years of follow-up, four
had radiolucent lines in one acetabular
zone5, three had
radiolucent lines in two zones, and four had radiolucent lines in all three
zones. Of the four hips with radiolucent lines in all three zones, none had a
continuous radiolucent line and none had migration of the shell.
For the entire study group of forty-six hips, at an average of 16.8 years
after the index revision, Kaplan-Meier analysis revealed a survival rate of
93% with revision of the acetabular shell because of aseptic loosening as the
end point (Fig. 2), 89% with
revision of the shell for any reason as the end point, and 74% with repeat
acetabular surgery for any reason as the end point
(Fig. 3).
In the original cohort of forty-six hips, sixteen femoral components (35%)
had been revised by the time of the minimum fifteen-year follow-up;
specifically, three femoral components (6.5%) had been re-revised because of
infection, six (13%) had been re-revised because of femoral osteolysis, and
seven (15%) had been re-revised because of aseptic loosening without
osteolysis. The revisions that were performed because of osteolysis were done
at an average of nine years (range, 5.5 to 14.5 years) after the index
revision in hips with proximal osteolysis in Gruen zones 1, 2, and 7. The
seven revisions that were performed because of aseptic loosening were done at
an average of 11.7 years (range, 5.75 to 15.8 years) after the index
revision.
At the time of the final follow-up, Kaplan-Meier analysis revealed a
survival rate of 61% with revision or removal of either the femoral or the
acetabular component for any reason as the end point, 69.6% with aseptic
loosening of either the femoral or the acetabular component as the end point,
and 81.5% with reoperations of the acetabular component because of aseptic
failure (i.e., shell revision or liner revision) as the end point.
Dislocation occurred in five hips (10.9%) at an average of one year (range,
0.25 to four years) after the index revision. Four of the five hips with
dislocation had had a trochanteric advancement, whereas one had not. Two hips
with a single dislocation and two hips with recurrent dislocations were
successfully treated with closed reduction and bracing. The fifth hip was in a
patient who had a complex problem involving prior tuberculosis, a failed cup
arthroplasty, and a failed total hip replacement. The index revision was
followed by infection and recurrent dislocations. This patient eventually
required a resection arthroplasty to control the infection.
The femoral head penetration rate averaged 0.16 mm/yr (range, 0.027 to
0.287 mm/yr) among the twenty-two hips with radiographs at the minimum
fifteen-year follow-up, whereas the ten-year follow-up penetration rate had
averaged 0.17 mm/yr. No hip center changed by >3 mm as compared with the
position on the initial index postoperative radiograph in any of the hips that
were evaluated. The hip center in this group averaged 43.5 mm (range, 37 to 77
mm) proximal to the interteardrop line on the immediate preoperative
radiograph and 38.6 (range, 34 to 74 mm) at the time of the most recent
evaluation.
In the interval between the ten-year report and the present report, no new
osteolytic lesions developed and no radiographically evident progression of
the extant lesions occurred.
The cementless acetabular shell that was evaluated in the present study,
when placed at a high hip center, demonstrated good performance and a low rate
of mechanical, radiographic, or clinical loosening at an average of 16.8 years
follow-up, despite the severe bone loss that was present at the time of the
index revision in many cases.
Infection (prevalence, 6.5%) was the most common reason for removal of the
acetabular shell in our series. Dislocation occurred in five hips (10.9%),
four of which did not require additional surgery. Because of the historically
high rate of dislocation after revision hip surgery, we now routinely increase
the femoral head size (to >32 mm) at the time of revision for any reason,
not just acetabular failure. However, this is not always possible with a high
hip center because of the relative paucity of bone proximally in the ilium,
which may mandate the use of a smaller acetabular component. For this reason,
we advocate the use of a large acetabular component placed against host bone
whenever
possible10,11;
however, in cases of severe bone loss, a high hip center may be the preferred
reconstructive option.
The rate of femoral head penetration in the present series was higher than
the rates that have been reported by some investigators for polyethylene that
has been sterilized with gamma radiation in air. This raises the question that
placement at a high hip center may increase the wear rate of conventional
polyethylene. The hips in the present study were not generally placed lateral
to the original hip center, and trochanteric advancements were performed to
keep the joint-reaction forces low and to optimize hip biomechanics.
Independent of whether or not the high hip center is causally related to an
increase in wear of gamma-in-air-irradiated polyethylene or whether other
factors could be involved, we recommend the use of alternate bearing surfaces
for high hip center reconstructions. This would allow for the placement of a
more wear-resistant bearing surface (and preferably, if possible, one that
would allow for the use of a larger femoral head as well). Despite these
higher penetration rates, the prevalence of pelvic osteolysis was low and none
of our patients in this small group demonstrated progression of osteolytic
lesions during the interval from the ten to the fifteen-year follow-up as
judged on the basis of plain radiographs. We attribute the discrepancy between
a higher penetration rate (increased polyethylene wear) and the absence of new
or progressive osteolytic lesions to three possible explanations. First, the
higher penetration rate extended over the first decade with only a low
prevalence of osteolysis. Second, the activity levels of the patients were
likely reduced both by increasing age and by the effects of the revision hip
operations. Third, only plain radiographs were used to detect osteolysis, a
notably inaccurate method.
On the basis of our results and those of
others12-14,
we recommend and continue to use uncemented acetabular components, augmented
with multiple screws and placed at a high hip center, for acetabular revision
in selected patients with severe acetabular bone deficiency. ?