We performed a retrospective review of the records of all patients
with a unilateral Crowe type-IV dislocation of the hip who had undergone a
total hip arthroplasty at our institution between July 1988 and December 1996.
This study was approved by our institutional committee for clinical research,
and informed consent was obtained from the patients participating in the
study.
Sixty-two patients met the criteria for inclusion. One patient had died
from unrelated causes, two patients had emigrated, and three others could not
be located, leaving fifty-six patients available for the study. Follow-up of
all patients consisted of a clinical examination, at which radiographs were
made and the Harris hip score and limb lengths were assessed by a surgeon who
had not been involved in the index surgery. All patients also underwent a
detailed clinical neurological examination focusing on sciatic nerve function.
Electromyography and nerve conduction velocity studies were not routinely
done.
The duration of follow-up averaged twelve years and three months (range,
seven years to fifteen years and five months). There were forty-seven women
and nine men. The mean age at the time of the surgery was 35.4 years (range,
twenty-two to fifty-five years). The hip with the Crowe type-IV dislocation
was on the right side in twenty-nine patients and on the left side in
twenty-seven. The mean Harris hip score before the surgery was 63.6 points
(range, 43 to 79 points). The contralateral hip appeared normal in forty
patients and was dysplastic in sixteen (Crowe type I in seven patients, type
II in four, and type III in five). In the subgroup with bilateral dysplasia,
all five type-III hips were treated with a total hip arthroplasty (four of
which were performed prior to the total hip arthroplasty for the Crowe type-IV
hip and one of which was done after it) and two of the type-II hips were
treated with an osteotomy of the innominate bone.
Preoperative Planning
A scanogram including the hips, knees, and ankles was made to measure the
preoperative limb-length discrepancy and to estimate the amount of lengthening
required7.
Anteroposterior and lateral radiographs of the femur were made to assess the
severity of coxa valga and femoral anteversion, the position of the greater
trochanter, and the size of the medullary canal. Templates were used to
estimate the size of the prosthetic components. The native hip socket was
evaluated for suitability for augmentation with structural bone graft and/or
medialization of the cup. The goal was to equalize the limb lengths. We
attempted to place the acetabular component in the anatomical position if the
contralateral hip was normal. If the contralateral hip was also dysplastic,
the cup was placed symmetrical to the planned final position of the
contralateral hip.
Iliofemoral Distraction
When the estimated amount of lengthening required exceeded 4 cm,
iliofemoral distraction was done prior to the total hip arthroplasty. The pins
were placed in the iliac crest and the distal part of the ipsilateral femur
(Fig. 1). The technique has
been described in detail in a previous
publication7. All
patients were admitted to the hospital for the distraction, which was 2.0 to
2.5 cm on the first day and 0.2 cm per day thereafter. The pin sites were
cared for meticulously. Any loose pins were immediately removed to avoid
infection. At the time of the total hip arthroplasty, the pins were removed
after anesthesia had been induced, the pin tracks were débrided, and an
antibiotic solution (0.5 mL of 16 mg/mL gentamicin solution) was injected into
each pin track.
Surgical Approach
A lateral Hardinge
approach8 was used
in twelve patients in whom the anatomy of the proximal part of the femur was
relatively normal. A direct lateral approach through a trochanteric osteotomy
was used in forty-three patients who had trochanteric overgrowth. A direct
lateral approach with a proximal femoral osteotomy was used in one patient in
whom the proximal part of the femur was curved. The femoral head and neck was
cut at a level just proximal to the lesser trochanter to facilitate correction
of the anteversion.
Acetabular Reconstruction
The joint capsule was excised as completely as possible. The soft tissue
and any bone overgrowth obstructing the true acetabulum were removed. The
anterior and posterior borders of the innominate bone were identified to
assess the three-dimensional structure of the bone stock. The location of the
best bone stock in which to place the prosthetic cup was marked. The
acetabulum was prepared with osteotomes to accommodate the smallest reamer (38
mm). It was then enlarged and deepened to the largest possible size without
breaching the anterior or posterior border of the innominate bone. In hips
with a very shallow acetabulum, the medial wall of the acetabulum was
deliberately perforated to create a hole of up to 1 cm in diameter without
damaging the periosteum of the inner table. The acetabular cup was implanted
with use of a press-fit technique. Additional screws were used to fix the cup
as necessary. The excised femoral head was used as structural bone graft to
augment the acetabulum in forty-seven patients with <70% coverage of the
cup by native
bone9.
Femoral Reconstruction
The femoral canal was reamed with use of the patella for orientation. When
the femur appeared to be relatively normal, the medial proximal inner cortex
at the calcar area was shaped with a burr to allow press-fitting of a regular
stem of an adequate size. In patients who had a straight and narrow
hypoplastic proximal part of the femur, cerclage wires were passed around the
proximal part of the femur and a 2-cm longitudinal split was made in the
proximal part of the femur with an osteotome. The prosthetic stem was
inserted, and the wires were tightened to allow adequate expansion of the
proximal femoral canal without uncontrolled fracture. Bone graft was then
inserted into the gap created by the split. The psoas tendon, fascia lata, and
adductor longus tendon were released when necessary. The trochanteric
osteotomy site was repaired with wires, with the abductor muscles under
adequate tension. All stems were commercially available stock items. A 26-mm
cobalt-chromium femoral head was used in all patients.
Postoperative Care
Muscle-strengthening exercises and walking with crutches were started three
days after the surgery. Full weight-bearing was allowed and gait-training was
begun at six weeks after the surgery when the patient had not required a bone
graft and at twelve weeks when the patient had received a structural bone
graft.
The limb-length discrepancy before the surgery averaged 4.9 cm
(range, 2.5 to 7.0 cm). Iliofemoral distraction was used for the forty-eight
patients in whom the discrepancy was >4.0 cm. The distraction period ranged
from eight to seventeen days, and a mean of 4.5 cm (range, 3.0 to 5.5 cm) of
length was obtained. There were no pin-track infections. However, the iliac
pins loosened in six patients and were removed. The distraction procedure was
terminated before the planned distraction was completed in those patients, who
lost an average of 1.7 cm (range, 1 to 2.5 cm) of distraction length. They
underwent the total hip arthroplasty on the day after the external fixator was
removed. None of the femoral pins loosened.
The acetabular cups included seven Dual Geometry microstructured shells,
twenty-nine Omnifit PSL microstructured cups, thirteen Omnifit PSL HA
(hydroxyapatite-coated) cups, and seven Secur-Fit HA cups (all manufactured by
Osteonics, Allendale, New Jersey). The diameter of the cup was 40 mm in four
patients, 42 mm in eleven, 44 mm in seventeen, 46 mm in nine, 48 mm in seven,
50 mm in five, and 52 mm in three. The thickness of the polyethylene insert
ranged from 5.8 to 10.3 mm. Twenty-nine Omnifit microstructured, thirteen
Omnifit PSL HA, and fourteen Secur-Fit HA femoral components (all Osteonics)
were used. All of the femoral heads were cobalt-chromium and 26 mm in
diameter.
The operative time for the total hip arthroplasty averaged 105 minutes
(range, sixty-five to 210 minutes). The mean estimated blood loss (including
postoperative drainage) was 760 mL (range, 250 to 1200 mL).
The limb length increased an average of 4.6 cm (range, 2.5 to 6.0 cm) after
the total hip arthroplasty compared with the preoperative limb length (Figs.
2-A,
2-B,
2-C,
2-D). The limb-length
inequality at the time of the latest follow-up ranged from 0 to 2.0 cm
(average, 0.3 cm). There was no overlengthening on the side of the index
surgery. The mean Harris hip score improved from 63.6 points preoperatively to
90.2 ± 6.7 points (range, 77 to 100 points) at the time of the latest
follow-up. No patient needed crutches or a cane for walking, and none required
a shoe-lift.
There were no dislocations of the total hip prosthesis and no superficial
or deep infections. Three patients sustained a fracture of the proximal part
of the femur during placement of the implant, and these fractures were treated
with cerclage wires without additional problems. Wires used to fix the
trochanteric osteotomy site broke in five patients. The osteotomy site united
in three of those patients, and it did not unite in the other two. All five
patients were asymptomatic, and no additional surgery was needed. In one
patient, who had had a discectomy for the treatment of a protruded
intervertebral disc five years before the total hip arthroplasty, an L5
radiculopathy developed after the arthroplasty. This neurological complication
resolved eleven months later without surgery.
At the time of the latest follow-up, osteolysis around the acetabular
component was noted in nine hips (16%). Eight Omnifit PSL HA components were
considered to be loose, and five of them were revised. Twenty-one hips (38%)
had erosive scalloping around the stem, mainly in
Gruen10 zones 1 and
7. There was no intramedullary osteolysis of the femur, and no stem was
considered to be loose.
Survivorship
At the time of follow-up, at a minimum of seven years after the
arthroplasty, no femoral stem had been revised. However, nine cups had been
revised, four because of polyethylene wear. The four patients with
polyethylene wear had moderate-to-severe pain and proximal migration of the
head in the cup. Two of the four cups had a 40-mm diameter with a 5.8-mm
polyethylene thickness, and the other two had a 42-mm diameter with a 6.8-mm
polyethylene thickness. The other five revisions were done because of cup
loosening. Of note, all of the loose cups were Omnifit PSL HA components,
which is a hydroxyapatite-coated smooth-surfaced hemispheric cup. These cups
were associated with moderate-to-severe pain, in addition to which broken
fixation screws and migration of the cup were noted on the radiographs.
The results of Kaplan-Meier survival analysis of the cups are shown in
Figure 3. The seven-year,
ten-year, and twelve-year survival rates for the cups (all kinds) were 91.3%
(95% confidence interval, 87.4% to 95.2%), 79.0% (95% confidence interval,
73.8% to 84.2%), and 77.2% (95% confidence interval, 70.8% to 83.6%),
respectively. However, the seven-year and ten-year survival rates for the
Omnifit PSL HA cups were 78.6% (95% confidence interval, 67.7% to 89.5%) and
64.3% (95% confidence interval, 52.3% to 76.3%), which were markedly worse
than the rates for the other cups (Dual Geometry, microstructured Omnifit PSL,
and Secur-Fit HA cups), which had ten-year and twelve-year survival rates of
93.8% (95% confidence interval, 88.5% to 99.4%) and 87.5% (95% confidence
interval, 79.7% to 95.3%) (p < 0.05).
A cementless microstructured cup (Omnifit PSL) with morselized allograft
was used for all of the revisions. The femoral stem was not revised in any
hip. Osteolytic areas around the components were débrided, and bone
graft was placed in the defects. Because the anatomy had been corrected during
the index total hip arthroplasties, the revisions were not technically
difficult. The cups implanted during the revisions were, on the average, 6.6
mm (range, 4 to 14 mm) larger than the original cups.
In patients with a unilateral Crowe type-IV high dislocation, the
severe limb-length inequality results in a marked limp that, because of the
uneven knee height, cannot be corrected even with a large
shoe-lift11.
Restoring the normal hip center would be ideal in these patients, but it is
technically difficult. Recent clinical studies have shown excellent results
when good primary stability was achieved and the hip joint center had been
properly
restored12.
The rate of nerve palsy is high after total hip arthroplasty in patients
with hip dysplasia, and this has been commonly attributed to stretching of the
nerves during
lengthening13.
However, in a 1999 report on eight nerve palsies following 508 total hip
arthroplasties, Eggli et al. indicated that the palsies were not related to
the amount of lengthening per se but to the difficulty (the so-called struggle
factor) of the
surgery14. There
were no clinically evident femoral or sciatic nerve palsies in our series; the
only neurological complication was a radiculopathy attributable to preexisting
perineural fibrosis. However, because perioperative electromyograms and nerve
conduction studies were not done in our study, it is possible that we missed
subclinical sciatic nerve dysfunction.
The standard technique used to reduce the hip has been femoral shortening,
through either a midtrochanteric or, more often, a subtrochanteric resection
osteotomy. The technique of preoperative iliofemoral distraction that we
described allows hip reduction without sacrificing femoral length. It further
stretches the surrounding soft tissues, making an extensive soft-tissue
release unnecessary and the surgery correspondingly easier.
The main disadvantages of the iliofemoral distraction technique are the
need for the iliofemoral external fixator to be in place for approximately two
weeks and the potential for infection at the site of the total hip
arthroplasty due to the fixation pins. We concede that the fixator is
uncomfortable, but it is no worse than any other lower-extremity external
fixator and it is certainly justifiable considering its benefits. We are
deeply concerned about the possibility of infection. The pins are placed away
from the surgical field for the total hip arthroplasty. Meticulous pin-site
care is mandatory, and the pins are checked daily for stability. Any loose
pins are removed immediately. Local wound débridement and application
of antibiotics further decrease the chances of
infection15,16.
In our experience, a stable, clean pin track does not usually become infected
in two weeks, and there were no hip infections in this series.
Dysplastic hips have a shallow acetabulum with a short anteroposterior
diameter, and this limits the size of the cup and therefore the thickness of
the polyethylene insert. In this series, four of the fifty-six cups were
revised because of polyethylene wear. It should be noted that all of the
femoral heads were 26 mm in diameter and the polyethylene was conventional,
not highly cross-linked. Since 1997, we have switched to using 22-mm heads and
highly cross-linked polyethylene inserts with the expectation that they will
perform better.
Five of the thirteen Omnifit PSL HA cups were revised because of loosening.
This particular design is prone to early failure secondary to delamination of
the
hydroxyapatite17,18.
No other type of cup loosened.
The 100% rate of survival of the femoral stems at a minimum of seven years
is noteworthy. There was no varus migration of a stem, no subsidence of >5
mm, and no radiolucent line in Gruen zone 2 or 6. The three fractures of the
proximal part of the femur during stem insertion all occurred early in the
series, before we prophylactically split the femur when needed. The fractures
were treated with cerclage wires, and long-term stability was not affected.
All of the stems were commercial off-the-shelf standard designs. The abnormal
anatomy of the proximal part of the femur was managed with trochanteric
osteotomy, transfemoral osteotomy, longitudinal femoral splitting, reshaping
of the canal, or bone graft as the situation dictated. Although we do not use
modular femoral stems because of cost considerations, they are available and
their use may allow the surgeon to avoid splitting the femur.
Dearborn and Harris reported that revision hip surgery for patients with
developmental dysplasia of the hip is more difficult than is a standard
revision19.
However, in our nine revisions, the defects were readily treated with
morselized allograft and a larger cup, and overall we did not find the
revisions to be more difficult than a standard revision. This is likely due to
the restoration of the normal anatomy during the index total hip procedure.
?