A 13-year follow-up study conducted by investigators
from the Netherlands showed that
total hip arthroplasty performed with an annealed,
crosslinked polyethylene insert resisted wear better over time
and had less osteolysis than using a conventional polyethylene insert.
The crosslinked [polyethylene] PE, even the
annealed version with some residual free radicals, maintained wear resistance
in the long term and produced less osteolysis, Bernd P. Grimm, PhD, said
during his presentation at the
12th EFORT Congress 2011. Now for us, the crosslinked PE
is the new standard and we can expect that maybe the highly crosslinked PE may
also perform well.
Grimm noted that researchers had theorized that using
crosslinked polyethylene may produce free radicals, which could lead to
accelerated wear or
High wear (3.3 mm) in conventional PE at
13-year follow-up and cyst formation in DeLee-Charnley zones half are
Images: Grimm BP
When we crosslink, we produce free radicals that
may cause oxidation which then may lead to accelerated wear and maybe again to
osteolysis or maybe damage such as rim fracture, Grimm said. There
is also the theory that crosslinked particle debris is of a different shape
smaller and maybe more frequent, and therefore, has higher
osteolytic potential. If so, some theorize that this may produce more
osteolysis despite less wear volume. But, maybe in the long term, wear
accelerates and we get higher osteolysis, Grimm said.
Prospective, randomized study
Grimm and colleagues conducted a prospective, randomized
study of 48 patients who underwent primary total hip arthroplasty (THA). Of the
31 patients available for review, 13 received Strykers first generation
PE material (Duration; Kalamazoo, Mich.) and 18 received a then considered
conventional PE that was gamma irradiated in air.
Average follow-up was 13 years. The researchers used the
Harris Hip score and anteroposterior (AP) and lateral radiographs to measure
outcomes. They analyzed wear with Roman version 1.70 and osteolysis using the
DeLee Charnley zones on AP and lateral radiographic views.
Low wear (0.6 mm) with the
crosslinked PE at 13-year follow-up was seen, and there are no signs of
osteolysis in this patient.
There was no statistical significance between groups
regarding age, gender, body mass index, stem and cup size, cup inclination or
preoperative and postoperative Harris Hip scores. Insert material was the only
variable, according to Grimm.
The crosslinked PE performed better with an annual wear
rate wear rate of 0.063 mm/year compared with 0.122 mm/year for the
conventional PE. The -48% reduction in wear for the crosslinked group was
comparable to the simulated prediction of -45%.
The wear reduction has increased with time so we
do not have accelerated wear, and we do not see an effective oxidation on the
wear rate, Grimm said.
One patient in the crosslinked group was above the
osteolysis threshold of greater than 0.01 mm/year compared with 10 patients in
the conventional group.
The investigators also found significantly less total
linear head penetration in the crosslinked group compared to the conventional
group (0.7 mm vs. 1.56 mm). The acetabular wear rate was also lower on
radiographic analysis in the crosslinked group compared to the conventional
group. by Renee Blisard
- Grimm B, Tonino A, Heyligers I. Long-term reduction of wear and
osteolysis with crosslinked PE? 13-year follow-up of a prospectively randomized
comparison with conventional PE. Presented at the 12th EFORT Congress 2011.
June 1-4. Copenhagen, Denmark.
- Bernd P. Grimm, PhD, can be reached at the AHORSE Research, Atrium
Medisch Centrum Parkstad, Department of Orthopedic Surgery, Heerlen, CX,
Netherlands; 49 (0)163 6 99 43 56; email: email@example.com.
- Disclosure: Grimm receives educational funding from and is a
paid consultant for Stryker. Heyligers is also a paid consultant for Stryker.
There is no doubt that we have made great strides in
addressing the issue of wear in total hip arthroplasty (THA). Introduction of
highly crosslinked polyethylene (XLPE) is perhaps one of the greatest
advancements in total joint arthroplasty. Although many issues regarding
alternative bearing surfaces (including XLPE) exist, the orthopedic community
unanimously embraces the notion that XLPE has reduced wear rate in patients
undergoing THA at least in the short to medium term.
The study by Grimm et al entitled, Long-term
reduction of wear and osteolysis with crosslinked PE. 13-years follow-up of a
prospectively randomized comparison with conventional PE, is taking a
step to assure us that XLPE performs well even in the longer term. In their
prospective study, Dr. Grimm and colleagues randomized 48 patients to receive
either Duration PE (what they call XLPE) or conventional PE. At 12.9 years
follow-up of the 31 patients that could be located, wear rate (measured using
Roman V1.70) was significantly (roughly 48%) less in the Duration group than
the conventional polyethylene. In addition, the incidence of periacetabular
osteolysis/cyst was much lower in the Duration group than the conventional PE.
Although a large number of their patients (>35%) were
lost to follow-up, which is almost inevitable with long-term studies, they were
able to demonstrate a difference in performance of Duration PE. The study,
however, carries a misleading title. The Duration PE that is being compared
with conventional PE is not however by any stretch of imagination
a highly crosslinked PE, which may explain why the wear rate for Duration is
still considerably higher than the current XLPE. The major difference between
the two PEs being compared in this study is that one was irradiated in an inert
gas (nitrogen) and annealed vs. the other PE that was irradiated in air. The
dose received were the same at 3MRad. I am sure the authors realize that the
current day XLPE receive in the order of 10 MRad irradiation.
Thus, the concern of the orthopedic community for
possible in vivo oxidation that they have also pointed out or potential for
fatigue fracture is not addressed by this study. Further, some will argue that
13 years is still an early time point when assessing wear of an
alternative bearing surfaces. Some would also raise issues with the
methods for measurement of wear that they have utilized.
Despite all of these shortcomings, the authors should be
applauded for conducting a level 1 study with a long term of follow-up.
Javad Parvizi, MD, FRCS
Orthopedics Today Editorial Board member
Disclosure: Parvizi is a consultant to
Zimmer, Smith & Nephew, Stryker and Biomet.