To The Editor:
We read with great interest "Dislodgment of Polyethylene
Liners in First and Second-Generation Harris-Galante Acetabular
Components. A Report of Eighteen Cases" (2001;83:553-9),
by Della Valle et al. One of the shortcomings of this otherwise
informative article was that the authors were unable to provide
a denominator; that is, they could not report on the prevalence
of this complication. We used the Harris-Galante first and second-generation acetabular
components extensively in the 1980s and early 1990s1-4. In a recent review of our joint
replacement registry, we identified 560 Harris-Galante-I cups implanted
in primary or revision total hip arthroplasty with a minimum follow-up
of seven years and found that four (0.7%) of them had dissociation
of the acetabular liner. We also identified 476 Harris-Galante-II cups
implanted in primary or revision total hip arthroplasty with the
same minimum follow-up and found that six (1.3%) had dissociation
of the liner. The wear rate of the liner in patients with this complication
is of considerable interest to us. For the ten patients who had
dissociation of the liner, the mean wear rate was 0.23 mm/yr
compared with a mean wear rate of 0.13 mm/yr for the patients
without this complication. Thus, liners that had dissociation had
almost twice the rate of polyethylene wear as those that did not. When
the head of the femoral component is eccentrically located within
the acetabular liner, the shell-liner interface is exposed to large
torsional moments, increasing the propensity for dissociation through
overload of the capture mechanism used in both the first and second-generation
components. These torsional moments would be exacerbated by an elevated
liner or a skirted femoral head, which are more prone to impingement,
if the head is eccentrically situated in the liner. Once dislodgment
has occurred, a revision of the acetabular component is necessary because
of the damage caused to the metal shell by fretting of the shell against
the femoral head. In the presence of a well-fixed bone-ingrown acetabular
component, this revision can be a difficult procedure fraught with potential
major complications. In addition, severe metallosis is always a
risk. We believe that the risk of dislodgment can be reduced by
early intervention when there is evidence of accelerated polyethylene
wear. Performing a liner exchange early and restoring the superimposition
of the center of the acetabular component on the center of the femoral
head can dramatically reduce eccentric torsional loads. Liner exchange
is relatively simple, and major complications can be avoided. If the
capture mechanism is damaged, the new polyethylene liner can be cemented
into the existing shell.
Therefore, we strongly advocate regular follow-up examinations
of all patients who have undergone total hip arthroplasty. In the
setting of accelerated polyethylene wear, even if the patient is asymptomatic,
strong consideration should be given to liner exchange in these
modular components. By implementing this practice, the prevalence
of liner dissociation and the potentially severe complications associated
with it can be substantially reduced.
A.G. Della Valle, P.S. Ruzo, S. Li, P. Pellicci, T.P.
Sculco, and E.A. Salvati reply:
We thank our distinguished colleagues for their thoughtful comments.
They are correct in stating that we were unable to determine the
prevalence of dislodgment, and we acknowledge the prevalence that
they report. However, in our experience, the dislodgments are occurring
with increasing frequency, suggesting that data from their joint replacement
registry may understate the true prevalence unless they have up-to-date
follow-up data for all of their patients, which is unlikely.
We agree that progressive wear increases the eccentric loads
on the liner. However, the mean wear rate (0.17 mm/yr)
in our eighteen dissociated liners was not substantially different
from the mean wear rate (0.13 mm/yr) in their patients
without this complication, suggesting that excessive wear is not
a necessary prerequisite for liner dislodgment.
Again, we thank our colleagues for their comments, which are
particularly important as they have the longest experience with
this acetabular component. The senior author, Jorge O. Galante,
deserves particular credit for his outstanding contribution to the
development and clinical application of titanium fiber mesh, which
has endured the test of time. Nonetheless, the locking mechanism
between the liner and the metallic shell appears to be at an increased
risk of failure with longer periods of follow-up.