With use of the institutional databases at three centers (the University of
Iowa Hospitals and Clinics in Iowa City, Iowa; Iowa Methodist Medical Center
in Des Moines, Iowa; and the Mayo Clinic in Rochester, Minnesota), we
identified all patients undergoing revision hip arthroplasty, in which a
tripolar constrained acetabular liner was cemented into a well-fixed and
well-positioned cementless acetabular component. Between December 1, 1988, and
October 30, 2000, thirty-one constrained liners (Osteonics, Allendale, New
Jersey) were cemented into thirty patients with fixed cementless acetabular
shells. There were fifteen women and fifteen men with a mean age of 72.1 years
(range, thirty-one to ninety-one years) at the time of the arthroplasty. At
all three institutions, the clinical and radiographic data on all arthroplasty
patients were collected prospectively. The mean duration of follow-up was 3.9
years (range, two to 12.7 years) for both clinical and radiographic follow-up
in the living patients. All patients were followed clinically for a minimum of
two years or until death. Four patients had died from causes unrelated to the
hip surgery by the time of the final follow-up. No patient was lost to
follow-up.
The surgical approach for the index operation was anterolateral (seventeen
hips), posterolateral (twelve hips), or transtrochanteric (two hips). A
constrained tripolar liner (Osteonics) was cemented into a secure acetabular
shell in all hips (Fig. 1). The
acetabular shells were Harris-Galante-I components (Zimmer, Warsaw, Indiana)
in fourteen hips, Trilogy prostheses (Zimmer) in seven hips, Harris-Galante-II
components (Zimmer) in five hips, PSL cups (Osteonics) in three hips, a PCA
(porous-coated anatomic) prosthesis (Howmedica, Rutherford, New Jersey) in one
hip, and a Duraloc TriSpike shell (DePuy, Warsaw, Indiana) in one hip. The
mean size of the shells was 58 mm in diameter (range, 52 to 80 mm).
The liners were 2 to 4 mm smaller than the retained cup to allow for an
adequate cement mantle. Cups were retained only if they could accommodate the
smallest available constrained liner, which was 50 mm. This ensured that the
liner could be contained in the shell with an adequate cement mantle and
without leaving the liner proud of the shell. The Osteonics constrained liner
with an outer diameter of 50 to 56 mm accommodates only a 22-mm femoral head.
When the diameter of the liner was =56 mm, we used fixed or modular heads
with a diameter of 28 mm. When the metal capturing ring could be removed from
the liner, we used the groove for cement interdigitation at the periphery of
the liner. In all but the first five liners, we scored the polyethylene to a
depth of 1 or 2 mm in a spiderweb pattern, depending on the liner thickness,
to add lever-out and torsional strength to the cement liner construct. If the
shell had no holes, it was scored in the same pattern with a metal cutting
burr. The cement was pressurized in the shell, and the liner was introduced
with the cement in a doughy state with the extended lip of approximately
10° to 15° placed in a position to optimize hip stability; that is, if
the acetabular shell was fixed in 50° of abduction, the extended lip of
the liner was placed laterally, and, if the shell was in neutral version, the
extended lip was placed posteriorly. At the discretion of the treating
surgeon, antibiotic powder (gentamicin or tobramycin) was mixed with the
cement and was used to treat eleven hips. Antibiotics were not used in the
cement for the other twenty hips.
At the time of the index surgery, the acetabular and femoral components
were evaluated for orientation and stability. The orientation of the
acetabular component was determined to be adequate (between 35° to 50°
of abduction and 0° to 15° of anteversion) in all hips. The stability
of the hip was tested by moving the hip in all directions. A constrained liner
was used if instability occurred within the functional range of motion
(flexion of 90°, adduction of 20°, abduction of 30°, and rotation
of 15° each) and was not thought to be related to component
malpositioning. The indication for the use of the constrained liner was
recurrent instability in sixteen hips (three of which had no functioning
abductor muscles noted at the time of surgery) and instability during revision
arthroplasty in fifteen hips. Nine of the latter hips had no or grossly
insufficient abductor muscles at the time of the index procedure. The patients
had a mean of 2.7 previous hip operations (range, one to seven
operations).
Ten femoral components were found to be loose or malpositioned and were
revised. Six had been inserted without cement and four, with cement. Other
procedures carried out at the time of the index operation included a femoral
head exchange (twenty-two hips), trochanteric advancement (three hips), and
acetabular cancellous bone-grafting (two hips).
The clinical outcome was assessed with use of the Harris hip
score6. Serial
anteroposterior pelvic and lateral radiographs of the involved hip were
reviewed to evaluate the position of the prosthesis and to assess for signs of
loosening and osteolysis. Radiolucencies around the acetabular shell were
evaluated in the three zones of DeLee and
Charnley7 at the
time of the index surgery and at the final follow-up evaluation to determine
whether there was any progression. Acetabular migration was evaluated with use
of the technique of Massin et
al.8. Femoral
loosening was evaluated with use of the criteria of Harris et
al.6,9
and Engh et al.10.
Lytic areas of >0.5 cm2 in the pelvic bones were considered to
represent periacetabular osteolysis.
Liner Revisions
Two revisions in which a constrained liner had been used failed. The first
failure occurred four months postoperatively in a patient who underwent the
procedure because of recurrent dislocation. She had previously undergone a
complex revision with a proximal femoral tumor prosthesis. At the time of the
index revision, the constrained liner was cemented proud and subsequently
dissociated from the cement four months postoperatively. A second liner was
cemented deeper into the shell, and the patient had no additional problems
prior to her death ten months later (Figs.
2-A, 2-B,
2-C, 2-D).
The second failure involved a patient with a seizure disorder. She was
first seen with clicking in the hip soon after having a seizure. A radiograph
revealed that the locking ring was fractured. A second constrained liner was
cemented into the shell, and the patient had no further dislocations during
the seven years that she was followed after the revision
(Figs. 3-A and 3-B). The only
other reoperation in this group of patients was in a hip with a periprosthetic
fracture at the tip of the femoral stem, which was treated successfully with
open reduction and internal fixation.
The mean Harris hip scores in the living patients improved significantly
from 53.1 points (range, 27.2 to 89 points) preoperatively to 80.8 points
(range, 27.2 to 100 points) at the latest follow-up examination (p <
0.0001). Of the twenty-seven hips in the twenty-six living patients,
twenty-one hips (77.8%) in twenty patients were pain free at the latest
follow-up visit and six hips (22.2%) in six patients were causing mild pain,
which did not affect the patients' activity. Five of the twenty-six patients
reported that they were able to walk unlimited distances. Eight patients with
nine hips could walk at least five blocks, eight patients walked less than
five blocks, and five patients were restricted to indoor activity only.
Eighteen patients used one or two canes when they walked, three patients used
a walker, and five patients (six hips) walked without aids.
Radiographic Findings
No progressive acetabular radiolucency was detected around any acetabular
component. In the latest follow-up radiographs of the twenty-seven hips in the
living patients, nonprogressive radiolucent lines were noted around one
acetabular zone in two hips, around two zones in three hips, and around three
zones in four hips. The radiolucent lines in all of these hips had been
present prior to the index operation. None of the hips had pelvic
osteolysis.
As hips with cementless fixation of the acetabular component have been
followed over a longer term, two clinical scenarios are becoming common:
recurrent instability following primary or revision hip replacement in hips
with secure cementless acetabular components and intraoperative instability
during revision hip surgery for the treatment of acetabular wear and
osteolysis or femoral loosening with secure acetabular components.
In such situations, the surgeon can remove the secure component and replace
it with a new one that is compatible with his or her preferred design of
constrained liner, or the surgeon can cement a constraining liner into the
well-fixed acetabular shell. The latter option avoids the potential for bone
loss associated with removal of a well-fixed acetabular shell and does not
disrupt a secure bone-prosthesis
interface11,12.
We began using this approach in a limited number of hips fourteen years ago
and have used it more frequently over the last five years as we have gained
confidence with the procedure. More recently, mechanical studies have
demonstrated the superior interface strengths between the shell and the
polyethylene liner when adequate scoring of the shell liner is performed and
when adequate cement mantles are achieved around the
liners13,14.
There are several clinical reports on cementing polyethylene liners into
metal-backed
shells15,16.
Successful use of this construct with another constraining device was reported
with a minimum one-year follow-up interval in a small series of
patients17.
In the present two to twelve-year follow-up study of thirty-one hips, only
one liner-cement interface and only one other constraining liner mechanism
failed. These results are comparable with those in series in which the
tripolar constraining liner was used as a modular cementless acetabular liner
with a compatible shell in a similar group of
patients4,5.
Currently, our indications for cementing a tripolar constraining liner into
a secure cementless acetabular shell include a relatively well-positioned
shell (30° to 55° of abduction with a range of version of =5°
of retroversion to 20° of anteversion) and a relatively inactive patient.
In addition, a liner corresponding to a 50-mm Osteonics shell, the smallest
liner available, must be able to be contained in the shell with an adequate
cement mantle and without leaving the liner proud of the shell. We place a
trial liner in the secure shell to be sure that we can achieve 2 mm of cement
mantle and a liner that is fully captured within the shell. We prefer to use
an older style liner so that the metal capturing ring can be removed. This
provides a groove for cement interdigitation at the periphery of the liner.
Furthermore, we would prefer that the manufacturer make constrained liners
designed for use with cement; i.e., with grooves for cement interdigitation
and nubs to prevent bottoming out of the liners.
At a mean of 3.9 years, we found that this approach to the treatment of
recurrent hip instability and intraoperative hip instability in relatively
low-demand patients has provided encouraging results. The long-term durability
of this construct still must be determined.