Revision of cemented acetabular components is most commonly performed
because of aseptic loosening with migration of the component. The most
challenging aspect of acetabular revision is the management of bone loss
compromising implant fixation and stability. The severity of bone loss can be
pronounced, as a result of asymptomatic osteolysis and stress-shielding, prior
to migration of cementless components. This bone loss is a common condition
that is expected to become more common in the future.
The prevalence of revision hip arthroplasty is 18% in the United States and
8% in the Swedish registry. The indications for acetabular revision include
symptomatic aseptic loosening, failure of fixation, infection, wear,
osteolysis, and instability. Revision may be indicated for an asymptomatic
patient who has progressive osteolysis, severe wear, or bone loss that could
compromise a future reconstruction. Contraindications for revision of the
acetabular component include severe bone loss precluding allograft fixation or
implant fixation, uncontrolled infection, or medical comorbidities that
preclude surgery.
Several options, including both nonbiologic and biologic fixation, are
available for acetabular revision. Nonbiologic fixation refers to any method
of reconstruction that achieves stability of the acetabular component through
a mechanical construct without the need for osseointegration between the
acetabular shell and the host bone. Biologic fixation refers to any surgical
option that requires direct contact with host bone and osseointegration into
the acetabular shell in order to provide long-term fixation. Nonbiologic
fixation options include cementing of a polyethylene cup, use of a superior
structural allograft and a cemented polyethylene cup with or without an
antiprotrusio cage, impaction grafting with or without an antiprotrusio cage,
and application of a total acetabular allograft. Biologic fixation options
include use of a hemispherical uncemented cup at the anatomic hip center or a
high hip center (>2 cm superior to the native hip center), a jumbo cup (66
to 80 mm), an oblong cup, an uncemented hemispherical cup supported by
structural allograft, and a modular cementless implant system.
As the outcomes of acetabular revision have been better with cementless
fixation than they have been with cement fixation, cementless fixation has
become the preferred method for the majority of acetabular revisions.
Templeton et al.1
and Gaffey et al.2
reported no cases of aseptic loosening of uncemented Harris-Galante-I
components used for revisions of cemented components, whereas cemented
revision acetabular components had a 14% rate of revision for aseptic
loosening and a 33% prevalence of radiographic evidence of aseptic
loosening1,2.
Della Valle et al., in a study of the experience with cementless acetabular
revision at the Rush University Medical Center, found aseptic loosening in two
of 138 patients followed for a mean of fifteen years, with revision (for any
reason) reported in nineteen of the 138
patients3. In a
study of the results of cementless revisions performed by Harris, Hallstrom et
al. reported a rate of aseptic loosening of 11% (thirteen of 122) and a rate
of revision because of aseptic loosening of 4% (five of
122)4.
Reliable and durable fixation of cementless acetabular components requires
intimate contact between the implant and viable bone as well as mechanical
stability (motion of less than 40 to 50 µm). Bone loss can compromise both
of these prerequisites for successful use of cementless implants. The amount
of host bone required to provide durable fixation is not known. Although it is
difficult to measure the amount of bone supporting an implant, most surgeons
believe that 50% to 60% is necessary. This value was derived from the
literature and is a measure of the coverage of the acetabular component in the
coronal plane as seen on an anteroposterior radiograph. However, the support
of an implant is geometrically more complex than can be determined on a
two-dimensional radiograph alone. The location of the remaining supportive
bone probably has a more important role in providing durable fixation than
does the quantity of bone. Finally, the percentage of bone necessary to
support the implant probably decreases as the implant size increases because
of the increased surface area.
Inherent Stability
Although there are reports of the successful use of uncemented cups in
revision surgery without the achievement of an initial
press-fit1,3,
we believe that it is necessary to achieve inherent stability of the implant.
Trial components are used to accomplish this goal and to assess the remaining
bone stock properly. A trial implant can have full inherent stability, partial
inherent stability, or no inherent stability. A trial component with full
inherent stability will not be displaced by pushing on its rim or by trial
reduction. A trial component with partial inherent stability will maintain its
position while the inserter is removed, but it will be displaced by loading of
its rim and by trial reduction. Finally, when a trial component has no
inherent stability, support by host bone is inadequate to maintain placement
of the component in the desired location once the inserter is removed.
AAOS Classification
The AAOS (American Academy of Orthopaedic Surgeons) classification of bone
defects, described by D'Antonio et
al.5,6,
identifies the pattern and location of bone loss but does not quantify the
defect. The bone loss is classified as contained, segmental, combined
contained and segmental, pelvic discontinuity, and ankylosis. This is the most
commonly used classification in the literature.
Paprosky Classification
The classification system that we use is based on the severity of bone loss
and the ability to obtain cementless fixation for a given bone loss
pattern7. The key to
the classification is determining the ability of the remaining host bone to
provide initial stability to a hemispherical cementless acetabular component
until ingrowth occurs. Intraoperative decisions are based on the findings when
trial components are used. The amount of rim that remains determines the
stability of the trial implant and is one of the variables that identifies the
type of acetabular defect. A Type-I defect has an undistorted rim; a Type-II
defect, a distorted but intact rim with adequate remaining bone to support a
hemispherical cementless implant; and a Type-III defect, a non-supportive
rim.
Radiographic Correlation
Preoperative findings on the anteroposterior radiograph of the pelvis are
used to predict the type of defect and allow the surgeon to plan for the
acetabular reconstruction accordingly. The four criteria that are important to
assess on the preoperative radiograph include: (1) superior migration of the
hip center, (2) ischial osteolysis, (3) teardrop osteolysis, and (4) position
of the implant relative to the Kohler line.
Superior migration of the hip center represents bone loss in the acetabular
dome involving the anterior and posterior columns. Superior and medial
migration indicates a greater involvement of the anterior column. Superior and
lateral migration indicates a greater involvement of the posterior column. The
amount of superior migration is measured as the distance in millimeters
(adjusted for magnification) relative to the superior obturator line.
Ischial osteolysis indicates bone loss from the inferior aspect of the
posterior column, including the posterior wall. The amount of ischial
osteolysis is quantified by measuring the distance from the most inferior
extent of the lytic area to the superior obturator line.
Teardrop osteolysis indicates bone loss from the inferior and medial aspect
of the acetabulum, including the inferior aspect of the anterior column, the
lateral aspect of the pubis, and the medial wall. Moderate osteolysis includes
partial destruction of the structure with maintenance of the medial limb of
the teardrop. Severe involvement means complete obliteration of the
teardrop.
Medial migration of the component relative to the Kohler line represents a
deficiency of the anterior column. The Kohler line is defined as a line
connecting the most lateral aspect of the pelvic brim and the most lateral
aspect of the obturator foramen on an anteroposterior radiograph of the
pelvis. The medial aspect of the implant is lateral to the Kohler line with
Grade-1 migration and medial to the line with Grade-3 migration. With Grade 2,
there is migration to the Kohler line or slight remodeling of the iliopubic
and ilioischial lines without a break in continuity.
Type-I Defect
With a Type-I defect, the acetabular rim is intact and supportive without
distortion (Fig. 1). The
acetabulum is hemispherical, and there may be small focal areas of contained
bone loss (cement anchor sites). The anterior and posterior columns are
intact. A hemispherical cementless implant is almost completely supported by
native bone and has full inherent stability.
The preoperative radiograph shows no migration of the component and no
evidence of osteolysis in the ischium or teardrop, and the Kohler line has not
been violated (the medialmost aspect of the component is lateral to the Kohler
line).
Type-II Defect
In a Type-II defect, the acetabulum is distorted but there is adequate host
bone to support a cementless acetabular component
(Fig. 2-A). The trial component
has full inherent stability. The distortion may be superior and lateral,
superior and medial, or directly medial. At least 50% of the surface area of
the component is in contact with host bone for potential ingrowth, and good
mechanical support can be provided entirely by host bone. The anterior and
posterior columns remain intact and supportive. The hip center can be elevated
as much as 1.5 cm to achieve superior contact and support.
On the preoperative radiograph of a Type-II defect, the superior migration
of the hip center is <3 cm from the superior obturator line and there is no
substantial osteolysis of the ischium or teardrop (ischial osteolysis
extending <7 mm distal to the obturator line).
Type-IIA defect: The pattern of bone loss is superior and medial,
allowing migration of the failed component into a cavitary defect medial to
the thinned intact superior rim. In the majority of patients, the defect is
treated with particulate allograft because the defect is contained. The
remaining superior rim provides a buttress for containment of the
allograft.
Type-IIB defect: Less than one-third of the circumference of the
superior rim is deficient, and the defect is not contained. The remaining
anterior and posterior rims and columns can support an implant. Allograft is
used to restore bone stock and not to support the implant. The defect is
segmental, and a femoral head allograft may be chosen. The majority of
reconstructions are done without grafting of the segmental defect.
Type-IIC defect: There is a medial wall defect and migration of
the acetabular component medial to the Kohler line
(Fig. 2-B). The rim of the
acetabulum is intact and will support a hemispherical component.
Reconstruction of these defects is similar to the treatment of protrusio
acetabuli in the setting of a primary arthroplasty. Sequentially larger
reamers are used until the acetabular rim is engaged. Particulate bone graft
can be placed medially in order to lateralize the hip center of rotation back
to its anatomic position.
Type-III Defect
The remaining acetabular rim in a Type-III defect will not provide adequate
initial component stability to achieve reliable biologic fixation
(Fig. 3-A). The trial implant
lacks full intrinsic stability. The use of structural allograft is an option
to restore the center of rotation to the proper anatomic location and to
provide mechanical stability for the implant.
Type-IIIA defect: There is adequate host bone in contact with the
ingrowth surface of the implant to obtain durable biologic fixation
(Fig. 3-B)—i.e., more
than 40% to 60% of the surface area of the cementless cup is in contact with
host bone. The trial component has partial inherent mechanical stability.
Support of the implant with a structural augment or allograft is necessary in
the short term to provide initial stability and thus allow ingrowth into the
areas of the implant that are in contact with the host bone. The defect
involves more than one-third but not more than one-half of the circumference
and usually is located between the 10 o'clock and 2 o'clock positions.
Preoperative radiographs show superior and lateral migration of the component
<3 cm above the obturator line (with adjustment for magnification). Ischial
lysis is mild to moderate, extending <15 mm inferior to the obturator line.
There is partial destruction of the teardrop, but the medial limb of the
teardrop usually is present. The component is at or lateral to the Kohler
line, and the ilioischial and iliopubic lines are intact.
Type-IIIB defect: Host bone is in contact with <40% of the
ingrowth surface of the implant. Inherent stability is not achievable with a
trial implant. The defect involves more than half of the circumference of the
rim, and it usually extends from the 9 o'clock to the 5 o'clock position
(Fig. 3-C). Patients with a
Type-IIIB defect are at high risk for occult pelvic discontinuity, and this
possibility must be ruled out at the time of reconstruction. Preoperative
radiographs show extensive ischial osteolysis (extending >15 mm distal to
the superior obturator line), complete destruction of the teardrop, migration
medial to the Kohler line, and migration >3 cm superior to the obturator
line. With a Type-IIIB defect, the failed acetabular component migrates
superiorly and medially, in contrast to the migration with the Type-IIIA
defect, which is superior and lateral.
Our algorithmic approach to revision of the acetabulum is shown in
Figure 4. We use a
posterolateral approach to the hip for all acetabular revisions. The initial
decision regarding how to proceed with the operation depends on the superior
migration of the hip center prior to the revision. If the hip center has not
migrated >3 cm above the superior obturator line, the surgeon determines
whether full inherent stability can be achieved with a trial component. If it
can, the defect is classified as Type I or Type II, and a hemispherical
cementless implant is utilized. If there is migration medial to the Kohler
line, the defect is classified as Type IIC and the rim will support the
hemispherical implant.
When the hip center has migrated >3 cm superior to the superior
obturator line or the surgeon is unable to achieve full inherent stability of
the hemispherical trial component, the defect is classified as Type III. If a
trial component has partial inherent stability, there is generally enough
contact with host bone to support ingrowth and therefore the defect is Type
IIIA. Type-IIIA defects usually have an oblong shape, but occasionally they
are spherical. If the defect is spherical, a jumbo cup may be appropriate.
With oblong remodeling of the host acetabulum, the options include a
structural distal femoral graft with a cementless hemispherical cup, a modular
trabecular metal augment with a hemispherical cup, or a high-hip-center
hemispherical cup. The former two options are appropriate when restoration of
an anatomic hip center is desired. With both the structural distal femoral
graft and the modular augment, the goal is to provide support to a
hemispherical implant that has partial inherent stability until there is
adequate supportive ingrowth into the cup. The advantages of a distal femoral
allograft are the good results that have been seen with longer follow-up and
the restoration of bone for future reconstruction if necessary. The potential
advantages of a modular cup-and-augment system include less stripping of the
ilium and less mobilization of the abductors, a technically easier and faster
procedure, and the fact that the augment does not have the potential for
resorption. The disadvantages of this method include its unknown long-term
durability, the potential for debris generation at the interface, the
potential for fatigue failure, and the inability to restore bone stock for
future revisions.
When the hemispherical trial component has no inherent stability, the
defect is classified as Type IIIB. When pelvic discontinuity has been ruled
out, the options for treatment of such defects include (1) nonbiologic
fixation with an impaction allograft supported with a cage or with a
structural allograft (an acetabular allograft or a distal femoral allograft)
supported with a cage and (2) biologic fixation with a modular trabecular
metal system or a custom triflanged implant.
In the presence of pelvic discontinuity, we determine intraoperatively
whether the discontinuity appears to be acute, with the potential for healing,
or chronic, without the potential for healing. If healing is possible, we use
a compression plate across the dissociation as well as one of the
reconstructive approaches described for a Type-IIIB defect above. When there
is no potential for healing, we distract the discontinuity and insert bone
graft into the defect. The initial stability of the structural graft or the
modular reconstruction is greatly enhanced by distraction (as opposed to
compression, with which there is little chance for the host bone to bring
about healing of the discontinuity).
General Principles
Preoperative planning based on the aforementioned classification system is
critical so that the appropriate grafting material, tools for implant removal,
and components are available at the time of surgery. If there has been
extensive medial migration, imaging (angiography or computed tomography
scanning with intravascular infusion of contrast medium) and possibly
intrapelvic mobilization of vascular structures should be considered.
The patient must be positioned carefully, with particular attention paid to
the orientation of the pelvis and torso relative to the floor, as internal
landmarks often are distorted in the setting of revision surgery. A
posterolateral approach is used. Extensile exposures often are necessary, with
the incision extending toward the posterior superior iliac spine. The plane
between the iliotibial band and the underlying vastus lateralis and the
abductors (often scarred to the iliotibial band) is redeveloped. After the
borders of the gluteus medius and gluteus minimus have been identified, the
plane between the gluteus minimus and the capsule is identified and the
abductors are mobilized anteriorly. We do not routinely expose the sciatic
nerve unless dissection through heterotopic ossification is necessary. A
posterior capsular flap is developed off of the greater trochanter
subperiosteally and is extended to the superior aspect of the acetabulum and
then continued distally along the proximal part of the femur in a
subperiosteal fashion. Intraoperative evaluations (a cell count and analysis
of frozen sections) are done to rule out infection. We assume that a white
blood-cell count of <3000/µL (3.0 × 109/L) indicates
the absence of infection and a count of >10,000/µL (10.0 ×
109/L) indicates the presence of an infection. When the cell count
is between 3000 and 10,000, we base our decision on the C-reactive protein
level and on the findings of the analysis of frozen sections.
The posterior flap is retracted, and an anterior capsulectomy is done. If
the femoral component is to be retained, an anterior pouch is developed for
placement of the retained component during retraction. The superior aspect of
the ilium and the posterior column are dissected in the subperiosteal plane to
obtain the necessary exposure. An extended trochanteric osteotomy may be
needed, depending on the visualization and the anticipated reconstruction of
the femur. After the removal of the existing components, a systematic
débridement of granulation tissue and interface membrane is carried out
to assess the entire remaining acetabular bone stock and to rule out the
possibility of a pelvic discontinuity.
Type-IIC Defects
In the majority of Type-IIC defects, particulate graft is placed medially.
If the medial membrane is not a sufficient buttress for the particulate graft,
a femoral head cut into a wafer, with the diameter of the wafer greater than
the diameter of the medial bone defect, can be used as a buttress for the
particulate graft. Use of acetabular reamers in reverse impacts the cancellous
allograft medially and recreates the hemispherical shape of the socket. As
more cancellous allograft is added medially, the reamer begins to translate
laterally and to catch on the rim. The reamers (used in reverse) disengage
from the reamer drive shaft as they come into contact with the host bone rim.
At this point, sufficient graft has been placed medially.
Type-IIIA Defects
Distal Femoral Structural Allograft with an Uncemented Acetabular
Component
To optimize the outcome, an appropriate graft must be selected to match the
mechanical demands of the proposed reconstruction. We do not use a femoral
head allograft when the graft is to serve a structurally supportive role.
Instead, we employ a fresh-frozen distal femoral or proximal tibial allograft.
The trabecular patterns of the graft are oriented parallel to the direction of
load to optimize stress transfer. The graft is contoured to maximize the
contact surface area between it and the host bone, to optimize the chance of
union. The allograft should be fixed to the host bone with 6.5-mm screws
oriented parallel with one another in the direction of loading, without
interfering with placement or fixation of the component. If there is pelvic
discontinuity, fixation with a posterior column plate should be performed
before proceeding with the allografting. The fixation of the acetabular
component to the host bone-allograft reconstruction is separate from the
fixation of the allograft to the host bone.
The goal of acetabular reconstruction with the use of a structural
allograft is to obtain a stable construct with the hip center of rotation
positioned at the level of the native acetabulum. The desired hip center is
identified, and acetabular reamers are used to size and shape the acetabulum
for a hemispherical cementless implant. After it is ascertained that adequate
host bone is available to come into contact with the implant, a trial
component is placed to determine areas of contact, inherent stability, and the
location of segmental loss.
Preparation of the distal femoral allograft begins with trimming of the
epicondyles so that the medial-to-lateral dimension of the allograft matches
the diameter of the acetabular cavity. A female reamer that is about 1 to 2 mm
larger than the acetabular cavity is then used to ream the distal aspect of
the allograft in slight flexion, to avoid notching of the anterior cortex of
the graft and so that the reamed condyles will be directed into the acetabular
cavity. The metaphyseal portion of the allograft is then cut in the coronal
plane to create the shape of the number 7, with the anterior aspect of the
metadiaphyseal bone left in continuity with the distal condyles. The superior
aspect of the allograft (the anterior cortex) is generally approximately 5 to
6 cm in length.
The angle between the condyles and the anterior cortex on the posterior
aspect of the allograft is contoured with a burr to optimize the contact
between the allograft and the host ilium. If a ledge of bone is present
between the lateral margin of the ilium and the depth of the acetabular cavity
at the site of the defect, the allograft should be cut at a more acute angle.
This "tongue-in-groove" effect will provide tremendous stability
at the graft-host junction.
The superior limb of the allograft is contoured to the lateral aspect of
the ilium and is secured provisionally with Steinmann pins. It is important to
tap the allograft screw-holes, in order to minimize the risk of fracture,
before placing four parallel 6.5-mm cancellous screws with washers. The screws
should be oriented obliquely into the ilium in the direction of loading to
compress the graft against the remaining ilium. The acetabular cavity then can
be reamed to contour the portion of the graft that will be in contact with the
component. Smaller reamers initially are used, and then the reamers are
sequentially increased in size to obtain the dimensions of the desired
acetabular cavity. Care must be taken to prevent removal of additional host
bone or inadequate reaming of the allograft that can cause failure of contact
between the remaining host bone and the component. Remaining voids are filled
with particulate allograft, and a cementless cup is impacted into the newly
sculpted acetabular cavity and fixed with multiple screws for adjunctive
fixation (Figs. 5-A, 5-B, and
5-C).
Modular Trabecular Metal System
Treatment of a Type-IIIA defect with a modular trabecular metal system
begins with use of acetabular reamers to identify the desired location for the
cup placement and to determine the location of all remaining supportive host
bone (which is usually anterior-superior and posterior-inferior). Progressive
reaming is performed to engage the bone of the anterior and posterior columns
in order to achieve partial inherent stability of the trial acetabular
component. With the trial component in the appropriate amount of version and
abduction, the posterior-superior augment is placed against the host bone. The
augment can be placed in any position or orientation to improve the initial
stability, and the bone or the augment can be contoured with a barrel burr to
optimize the surface contact area. With the trial component in place, the
augment is secured to the host bone with screws. The augment is then packed
with bone graft, leaving the portion facing the cup exposed.
Polymethylmethacrylate cement is placed directly onto the trabecular metal
revision cup but only in the areas mating with the augment. The acetabular
component is then firmly impacted to achieve a press-fit against the host
bone. We recommend the placement of multiple screws for initial fixation. If
the liner is cemented, one should consider placing bone wax into the end of
the screws to facilitate removal if needed.
Type-IIIB Defects
Total Acetabular Transplant with a Cage
Acetabular reamers are used to size the acetabular cavity and to identify
the location of all remaining bone to support the allograft. The ledge of bone
on the superior aspect of the ilium that will abut against the allograft
should be identified. The acetabulum of the allograft is reamed on the back
table, with care taken not to weaken it by excessive reaming. A cage is sized
to the allograft prior to placement. The allograft hemi-pelvis is cut in a
curvilinear fashion from the greater sciatic notch to the anterior superior
iliac spine to maintain a portion of the ilium attached to the acetabulum. The
pubic and ischial portions of the allograft are cut distal to the confluence
of the acetabulum with enough length to accommodate the inferior defects. One
should avoid leaving excessive inferior bone on the allograft that prevents
optimal medialization of the inferior aspect of the graft as this can result
in vertical cup placement and lateralization of the hip center. Medialization
of the hip center is desired.
A female reamer, 1 to 2 mm larger than the acetabular reamer used to size
the acetabulum, can be used to mark and shape the medial aspect of the graft
to fit the defect. A groove is made in the superior aspect of the ilium of the
allograft to correspond to the ledge of bone along the superior aspect of the
native acetabulum. This tongue-and-groove junction provides a stable buttress
between the host and the allograft. A burr is used to debulk the inner table
of the ilium on the allograft and to maintain a shelf distally that will fill
the acetabular defect. The allograft should be press-fit and then secured with
Steinmann pins provisionally. It is then fixed with four 6.5-mm partially
threaded screws with washers directed obliquely into the ilium from both the
intra-articular and the lateral iliac aspects of the graft. A pelvic
reconstruction plate is then contoured to the posterior column, ideally with
three screws in the native ilium and ischium. It is recommended that a cage,
secured with cage-host bone screws as well as cage-allograft bone screws, be
used to protect all transplants. If possible, the inferior flange of the cage
is inserted into a slot in the ischium for fixation. A metal shell or a
polyethylene liner is then cemented into the cage-allograft composite, with
the surgeon avoiding the tendency to place the component in a vertical and/or
retroverted position.
Modular Trabecular Metal System
When a Type-IIIB defect is treated with a modular trabecular metal system,
the acetabular defect is sized with reamers in the desired location to find
the dimension of the cavity until two points of fixation are achieved
(anterior to posterior, anterior-inferior to posterior-inferior, or
posterior-superior to anterior-inferior). Augments are used to decrease
acetabular volume and to restore a rim to support a revision cup. The location
and orientation of the augments are highly variable, depending on the
bone-loss pattern. Augments are often placed on the medial aspect of the ilium
or they may be stacked. It is more common to use the augments with the wide
base placed laterally and the apex placed medially, which is the opposite of
how the augments are often used in Type-IIIA defects. The revision cup will
have direct contact with the augments, which will be necessary in order to
achieve a press-fit. As is done for a Type-IIIA defect, the augments are
initially secured to the host bone with the use of multiple screws. Portions
of the augments may need to be removed with a burr or a reamer in order to
optimize the surface area contact between them and the revision shell.
Particulate bone graft is then placed into any remaining cavities before the
hemispherical revision shell is impacted into place. As is done for a
Type-IIIA defect, the interfaces between the revision shell and the augments
are cemented. (These interfaces should be in compression.) Multiple screw
fixation is used through the revision shell.
Several authors have reported durable results at a minimum of ten years
following acetabular revision with the use of a hemispherical cementless
socket (Table I). Because of
these predictable clinical results, hemispherical cementless sockets are now
used for almost all Type-I and II acetabular defects. Type-IIIA acetabular
defects can be treated with a distal femoral allograft, a bilobed implant, or
a trabecular metal acetabular component with a superiorly placed trabecular
metal augment. The long-term clinical results of acetabular reconstruction
with the use of a trabecular metal system are currently unknown. However,
trabecular metal appears to allow extensive bone in-growth and is associated
with high initial frictional resistance.
The midterm results of revisions with bilobed acetabular components have
been disappointing. These implants were designed to lower the hip center of
rotation and to obtain fixation, both in the true acetabulum and in the ilium.
Chen et al. reported a 24% failure rate in thirty-seven hips followed for an
average of forty-one months
postoperatively8. In
contrast, the midterm results of revisions with a distal femoral allograft and
a hemispherical cementless acetabular component have been acceptable. After a
minimum of seven years and an average of ten years of follow-up of twenty-two
hips, the senior one of us (W.G.P.) found that seventeen hips were functioning
well without loosening and only four had been revised (at an average of 5.5
years postoperatively).
Treatment of Type-IIIB acetabular defects with an acetabular transplant and
a cemented acetabular component (without a cage) has had poor clinical
results. The senior one of us (W.G.P.) followed sixteen patients for a minimum
of eight years (average, ten years) and found that six hips were functioning
without loosening, six had been revised because of aseptic loosening at an
average of 2.9 years, and an additional four had radiographic evidence of
loosening. Because of these poor results following use of an unsupported
structural allograft, we began to use reconstruction cages. At two to eight
years following use of such a cage in forty-eight hips with a Type-III defect,
twenty hips were functioning without loosening, nine had been revised because
of aseptic loosening, and an additional nine had radiographic evidence of
loosening.
The poor clinical results observed after treatment of Type-IIIB defects
recently prompted us to use a trabecular metal acetabular component with one
or two augments in the majority of Type-IIIB cases. Modular trabecular metal
revision systems have not been used long enough for us to report follow-up
results at the present time; however, we are encouraged by the early
outcomes.
In conclusion, the increasing prevalence of arthroplasties and the younger
age and greater life expectancy of the patients who receive them promises a
continued need for solutions for patients requiring acetabular revision in the
face of severe bone loss. The algorithmic approach that we outlined allows the
surgeon to predict the findings in the operating room, plan the treatment of
expected bone loss patterns, and make appropriate judgments regarding the
reconstructive technique that will achieve the best possible results. Our
preference is to achieve cementless fixation when possible and to use
alternative solutions when initial stability cannot be obtained.
The authors did not receive grants or outside funding in support of their
research or preparation of this manuscript. One or more of the authors
received payments or other benefits or a commitment or agreement to provide
such benefits from a commercial entity (Zimmer). Zimmer has contributed to a
research fund un-related to this project.
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