Wear Evaluation Following Clinical use of Retrieved Polyethylene Mobile Inserts in Rotaglide Total Knee Replacement with a Combined Qualitative and Quantitative Topographic Method
Anastasios P Nikolaides1*, Fares Sayegh2, Athanasios Tsakonas3 and Apostolos J Polyzoides4
1 Senior Orthopaedic and Trauma Specialist, University of Birmingham, UK
2 Professor in Trauma and Orthopaedics, Aristotle University of Thessaloniki, Greece
3Retired Consultant Orthopaedics and Trauma Surgeon, Hippokratio General Hospital, Greece
4 Retired Consultant Orthopaedics and Trauma Surgeon, Solihull Hospital, UK
Submission: September 18, 2018;Published: October 12, 2018
*Corresponding author: Anastasios P Nikolaides, Senior Orthopaedic and Trauma Specialist, Honorary Senior Lecturer University of Birmingham, Heart of England NHS Foundation Trust, Heartlands Hospital, Bordesley Green East, B9 5SS, Birmingham.
How to cite this article: Anastasios P Nikolaides, Fares Sayegh, Athanasios Tsakonas, Apostolos J Polyzoides. Wear Evaluation Following Clinical use
of Retrieved Polyethylene Mobile Inserts in Rotaglide Total Knee Replacement with a Combined Qualitative and Quantitative Topographic Method. Ortho
& Rheum Open Access J 2018; 13(1): 555853. DOI: 10.19080/OROAJ.2018.13.555853.
Background: The Rotaglide Total Knee System was introduced into clinical practice in 1988. It was the first condylar Total Knee Endoprosthesis with a highly conforming mobile polyethylene insert which rotates and glides on top of a highly polished tibial component, thus theoretically reducing wear
Materials and Methods:We studied the wear of 17 retrieved Rotaglide mobile polyethylene inserts bearings. In all cases The Posterior Cruciate Ligament was preserved. The mean time of in vivo use was 8 years (3 months to 15.6 years). To measure the PE, wear we used a new method of evaluation, by calculating the percentage of contact surface with signs of specific mode of wear.
Results:Thinner inserts showed moderate to severe wear after 9.5 years. In 51–85% of the total upper surface delamination dominates, but plastic deformation and pitting to a much extend are also present. Little wear of burnishing type and abrasions develop after 5.5 years mainly in the posterior condyles and in the thin inserts is accompanied by fracture and loss of material. In all bearings, there is no significant backside wear. 18% of the backside surface had no wear, 42% showed some abrasions and scattered areas of burnishing and the remaining 40% is dominated by pitting inside areas of burnishing.
Conclusion: Delamination predominantly, combined with polyethylene fracture of the thinner inserts is the main wear pattern of the upper articular surface. In all inserts, there was no significant backside wear.
Keywords: Rotaglide Total Knee Arthroplasty; Polyethylene wear; Mobile insert
Polyethylene wear remains one of the major contributors of failure in Total Knee Arthroplasty [1,2]. It affects either the upper articulating with the femoral component surface of the insert, or the backside surface articulating with the tibial component. Although upper surface wear is predominant [3-5], backside wear has also been responsible for accumulation of wear debris in the synovial fluid [6,7]. Polyethylene wear particles in turn trigger an inflammatory granulomatous response with accumulation of macrophages and the release by them of cytokines. The result is osteolysis and aseptic loosening of the implants [8,9]. Recent studies have not shown any difference in the concentration of wear particles in the synovial fluid in fixed or mobile inserts . However fixed bearing is linked to
increased backside wear when the articulating upper surface is more conforming, compared to flatter contact surface .
The Rotaglide Total Knee Arthroplasty was introduced into clinical practice in 1988. It was the first Total knee implant which used a mobile polyethylene fully conforming insert which glided and slide on top of a highly polished tibial component Although there are several reports in the literature regarding long term clinical results of this prosthesis [12-19], to our knowledge there are no studies describing wear patterns of its fully conforming mobile PE insert. Evaluation of wear on the retrieved Polyethylene inserts in knee prostheses has generated a great amount of work since the beginning of the eighties, because these observations have led to a better understanding of the wear mechanisms. A general review of the literature regarding the methods used for
wear evaluation shows that most of the studies are based upon
a system of gradation as described by Hood in 1983 . They
define 7 different modes of wear, a 4-point severity scale, and 10
different zones to obtain a total score reflecting the total wear
and the different modes involved.
This method has been improved to include an estimation
of the surface of worn areas, expressed in area (mm2) or as
a percentage of the articulating surface . More recently,
enhancement of resolution of commercial cameras and use of
commercial software has led to an easier work . Backside
wear of fixed inserts has also been evaluated, mainly by similar
methods  with adaptation due to the necessity of evaluating
gross deformation in the screw holes of the tibial tray, or by
methods involving coordinate measurement machines (CMM)
, since unworn backside surfaces are generally plan. CMM
methods have not been extensively used  for evaluating
wear of articulating surfaces of retrieved implants, because
they need knowledge of the unworn surface of a similar or even
better the same implant. CMM methods are powerful when used
to evaluate wear on implants tested in knee wear simulators,
as demonstrated by Muratoglu  who used in conjunction
a gravimetric method to demonstrate how true wear can be
separated from creep in the CMM results. For the purposes of
this project, a review of the scientific literature has been made
to collect typical photographs of the different types of wear,
according to the definitions used by Hood  and adopted by
many other authors.
Seventeen retrieved tibial inserts of Rotaglide total knee
prostheses were collected, sterilized and submitted for wear
evaluation. The implantation time varies from 2 years to 15.6
years (mean = 8.7 years, standard deviation = 4.5 years). In all
cases the Posterior Cruciate Ligament was preserved (Table 1).
For all the inserts except one, the anatomical side (left or right)
of implantation is unknown and cannot be deduced from the
reference code, as the Rotaglide PE insert is totally symmetrical
to be indifferently implanted on a left or on a right knee. Four (4)
inserts were retrieved because of early sepsis (from 2 years to 5
years) and were totally unworn. From the remaining 13 inserts,
12 were broken: 10 were broken in 2 parts (9 with breakage of
one of the two bearing surfaces, 1 with breakage in the middle),
the other 2 were broken in 3 parts (breakage of the two bearing
surfaces). Unfortunately, from theses 12 broken inserts, only 6
were complete, the other 6 presented at least one missing part
that had not been delivered to the lab.
For each insert, capture of the images of the frontside and
backside was made by a digital camera (Nikon Coolpix 5400,
5 Megapixels). The digital zoom was avoided in order not to
compromise resolution. Flash light was avoided as it reflects
too much on the polyethylene surface. However, digital cameras
have generally no problem with ambient light. A ruler was
positioned in the same focal plane as the wear surface, to be
used as calibration reference for the computation of absolute
wear areas if needed.
Overview: The observation of the 17 implants revealed that
they can be classified in four different groups, according to
their general aspect and macroscopic degree of wear:
Group A: The implants are macroscopically not worn and
are not broken. They correspond to the implants that were
retrieved for sepsis.
Group B: The implants have low wear, and they have at least
one broken condyle.
Group C:The implants have moderate wear, and they have at
least one broken condyle.
Group D: The implants are totally worn. In this case they can
be unbroken or have at least one broken part.
This very simple classification according to the general
aspect is very easy to operate, and the four isolated groups
are rather consistent. Table 2 presents the available data of
individual implants, when they are grouped according to the
above classification. “Thickness” refers to the nominal thickness
of the implanted PE inserts, and corresponds to the one given
in the manufacturer’s catalogue. This information was provided
by the surgeons who retrieved the implants. In the column “broken condyle”, “1” indicates that only one condyle is broken,
and the other is intact; and “1+” indicates one broken condyle
and the other in bad condition. “Middle” indicates that the
insert is broken in two parts, along an anteroposterior line,
passing through the plane of symmetry of the insert. Inside each
group, the appearance of PE inserts is rather consistent, and
the difference between the four groups is evident. This can be
appreciated by studying 4 of the inserts one related to a specific
group (Figures 1-4).
The results of this classification reveal the following: In
group A, are gathered 4 inserts retrieved for early sepsis, and
of different thickness, from 9.5 to 14.5mm. This is supposed
to give an indication about the normal distribution between
the implanted inserts, as the sepsis is not related to a specific
characteristic of the implant. The time in service varies from 2
years to 5 years (mean 3.48 years). The traces of wear are very
slight, and very difficult to photograph because of light reflection
on the polyethylene.
Group B gathers 4 inserts that have low wear but have a
broken condyle. Except the case of sample n °17 which has
prematurely failed after 2 years, (valgus, broken lateral condyle),
the time in service varies from 5.5 years to 9.6 years (mean
6.23 years). In this group, only inserts of 7mm and 9.5mm
thickness are present. This may suggest that such thin inserts
are overstressed in the bearing surfaces, above the fatigue limit
of the polyethylene. Group C gathers 5 inserts that are more
worn that group B, because they have survived more under the
stresses that tend to break the condyles. The time in service
varies from 9.8 to 12 years (mean 10.78 years). Just like group
B, only inserts of 7mm and 9.5mm thickness are represented.
In two occasions, the inserts have the two condyles broken. The
appearance of the inserts reveals also gross deformation or
delamination of the posterior aspect of the surviving condyles.
Group D gathers 4 inserts that exhibit severe wear, mainly
delamination that leads to the fracture of the upper surface and
material removal. The time in service varies from 11.0 to 15.6
years (mean 13.90 years). Two of the inserts have a broken
condyle and the other is in bad condition, one exhibiting a
longitudinal fracture after wear of the anterior aspect. These
3 broken inserts have thickness of 7 to 9.5mm. The only insert
which is unbroken has a thickness of 17mm, which seems to
prevent from overstressed leading to fractures.
From these results and assuming the examined PE inserts are
representative of the population of retrieved Rotaglide inserts, it
may be deduced that the main reasons for retrieval before 10 years in service, is either early sepsis, or fracture of at least one
condyle. In this case, and even with up to 10 years in service, the
wear remains moderate. The fracture of the condyle(s) mainly
happens with thin PE inserts, 7 mm or 9.5 mm thick. Such thin
inserts can occasionally survive until 15 years without fracture
of the condyles but exhibit severe wear. The same type of wear
can also be seen on thicker inserts; these latter ones having the
advantage of being apparently prevented from condyle fractures
due to the thickness of polyethylene in this sensible zone.
The qualitative characterization of wear lies upon the
definitions of Hood  and Cornwall . Seven different types
of wear have been described and documented by these authors:
a. Delamination is a subsurface laminate mechanism of
degradation characterized by a visual opacity as the crack
(or craze) propagates through the material beneath and
approximately parallel to the surface. Delamination is a
b. Pitting is characterized by small defects observed on
the articular surface. Pitting is also thought to be a fatiguerelated
phenomenon; however, it has not been established
whether the pit initiation is a surface or subsurface
c. Abrasion is characterized by a tufted appearance
usually caused by high friction articulation as the polymer
bearing surface comes into direct contact with bone or bone
cement. Macroscopically, abraded areas appear significantly
rougher than the original machined polymer surface.
Microscopically, tearing of the polymer is clear.
d. Scratching usually occurs in the direction of articulation
and is often associated with third body wear or surface
irregularities. Microscopically, scratching is a combination
of deformation and removal of material.
e. Burnishing is a micro polishing mechanism causing the
bearing surface to appear smoother than the original surface.
It is not known whether this process is associated with the
removal of fine particulate debris or a surface heating effect
leading to viscous flow.
f. Deformation involves the permanent depression of the
polymeric bearing material without material removal.
g. Embedded debris is usually identified as bone and
bone cement fragments on the polymeric bearing surface.
Metallic beads from porous coating removal and debris from
metal-on-metal contact are third bodies that adversely affect
h. An additional mechanism, Failure, is included to
describe areas of completely removed bearing surface
leading to contact between the femoral condyle and the
metal backing of either the tibial plateau or the patellar
In the group A, the bearing surfaces appear very lightly
worn. Some scratches are visible, as well as burnishing, which
is defined as the removal of the original surface finish. This
kind of wear can also be seen at the backside, the burnishing
/ scratching areas appearing at the periphery, and rather on
the posterior aspect. Note that the original surface finish of the
backside and upper surface are different: backside shows marks
of machining while upper surface does not.
PE no wear & not broken. Burnishing areas of the backside
cannot be seen on the actual photographs, because of the
reflection of the light on the polyethylene. Contours of sample
n °1 have been depicted and copied to the other samples, after
adjustment to the correct scale and eventual rotation. It generally
fits rather well, showing that this system could be imported to
more worn implants, to superpose the shape of the presumed
PE low wear & broken condyle. Sample 17 which presents a
broken condyle after 2 years in service shows that the fractures
initiates from the backside, after a gross delamination of the
posterior side of the lateral condyle. The other 3 inserts do not
show such gross delamination, but plastic deformation at the
backside near the fracture. The front side reveals only slight
scratching oriented according to the movement of the femoral
part against the polyethylene bearing surface.
PE moderate wear & broken condyle. The initiation of the
fracture of the condyles is mainly located on the front side, after
gross delamination of the surface. The traces of wear are much
more visible than in the previous group. Zones of delamination,
plastic deformation, larges scratches can be seen. In sample n °9,
embedded debris can be suspected.
PE totally worn. All types of wear are represented and cover
almost the totality of the implant surface. Gross delamination is
predominant, with removal of large parts of the surface. Plastic
deformation is also present on large areas; the polyethylene is
mainly pushed to the periphery. Sample n °8 has been extensively
characterized and can be examined for the different types of
wear, by opening the PE totally worn.doc. Note that this insert,
17 mm thick and extensively worn on the frontside, presents a
backside in good condition except the posterior edge of the two
condyles. On the contrary, the three other inserts of this group
exhibit large zones of delamination and plastic deformation on
The four groups exhibit different degrees of wear, showing
the evolution of degradation according the time in service.
It seems that fracture of the condyles is a phenomenon not
directly related to wear, as in group B fractures occurred without extensive wear. On the contrary, it seems to be related to
overstressed, probably due to the thickness of the polyethylene
in the bearing zone.
These results concern the evaluation of worn areas for two
Group A (inserts macroscopically not worn on the front side
and not broken, corresponding to retrieval for early sepsis) for
the backside because these inserts exhibit typical patterns that
can be easily depicted with low magnification. As the backside of
the implants is flat, the photographs generally show significant
light reflection, and cannot be directly exploited.
The different characteristic types of surfaces are the
1: the surface is intact, without scratches and the marks of
original machining are present.
2: the marks of original machining are still visible, but the
surface exhibits also some scratches.
2+: this is the evolution of the previous one, with attenuated
marks of machining and more visible scratches.
2++: marks of machining very attenuated and deep and
3: the surface is burnished, very well polished, without trace
of machining, and without or very attenuated scratches.
We can consider that the abrasive phenomenon concerns
mainly the transformation of type 1 areas into type 2, and then
type 2+ and 2++. On the contrary, as noted by Cornwall, the
topology of type 3 areas rather suggests a cold flow deformation.
The delimitation of the different types of areas was handmade
through a fine felt-tip marker, directly on the PE insert.
Pictures of these inserts were then captured (Nikon Coolpix 5.1
Megapixels) and treated with 2 specifics.
Software Packages: Adobe Photoshop for colouring the
different areas according to the type of wear, and Image J for
measuring in mm² the various worn surface areas. For each
insert, the surface areas corresponding to the different types of
wear have been computed and expressed as a percentage of the
total surface. The results are summarised in Table 3, Different
regions corresponding to the previous definitions have been
coloured from light grey for type 1, to dark grey for type 2++,
and pink for type 3. The characteristic shape of the burnished
regions can be noted, which appears at the periphery of the
inserts; for types 2, 2+ and 2++ the patterns of the scratches
cannot be represented, but their orientation suggests a rotation
of the insert relatively to the peg of the tibial tray.
In samples n °2 (3.1 years in service) Figure 5 and n °3 (5
years in service) Figure 6, surfaces of type 1 (marks of machining
visible, no scratches) have disappeared to the profit of surfaces
of type 2 (marks of machining disappearing, scratches). Type
3 surfaces (burnished: marks of machining not visible, no
scratches) are also more extended. On the oldest insert (n °3, 5
years in service) pitting appears in a region that was previously
burnished. Group D (insert totally worn) for the upper surface
in contact with the femoral elements. In this case, the different
types of wear can be depicted directly on the original pictures.
These pictures were treated with Adobe Photoshop for colouring
the different areas with the different types of wear, and Image J
for calculating the surface areas.
The definitions of the different types of wear used, are the
ones presented the previous reports and corresponding to
the common definitions given by the literature: delamination,
pitting, abrasion, scratching, burnishing, deformation, embedded
debris and failure. Additionally, delamination has been divided
in 2 sub-groups: slight delamination, which means that the
phenomenon is visible but has not removed material, and gross
delamination with removal of material from the surface. The
results can be seen in Table 4. Different regions corresponding
to the previous definitions have been coloured. For each insert,
the surface areas corresponding to the different types of wear
have been computed and expressed as a percentage of the total
In sample No 16 Figure 7 delamination is predominant;
either without removal of material or with, this latter case being
mostly associated to fracture. Plastic deformation, scratching
and pitting are also present to a lesser extent, especially in the
region that covers the slot dedicated to the metallic peg, where
the polyethylene is thin; and, at the posterior edge of the bearing
Polyethylene wear and the subsequent osteolysis and
loosening of Knee Arthroplasty implants remains an important
cause of failure . The extent of contact surface between
components and Polyethylene affects the degree of wear [28,29].
The high contact surface of the Rotaglide Knee prosthesis as
measured by Heim et al.  is the result of the high conformity
of femoral component – PE insert interface. The combination
of high conformity and the mobility of the insert reduces the
Anteroposterior sliding of the femoral condyles on the insert
thus reducing wear. The mobile insert also enhances a more
physiological movement of the knee since it can rotate and slide
on a highly polished metallic surface of the tibial component
[31,32]. The result is a better kinematic environment and
less constrain of the tibial component – bone interface .
The analysis of the wear of the retrieved inserts confirm this
partially. In our study another important parameter is evident
and involves the sterilisation of the inserts. Those who were
produced before 1995 were sterilised in air, a process which can
decrease their mechanical strength.
In our study such inserts showed the worst wear. It is also
remarkable the presence of slight or no backside wear depending
on the longevity of the inserts, a finding that is present in other
publications regarding mobile inserts . In 18% of total
backside surface there was no wear, in 42% scratching with
burnishing and in the remaining 20% pitting with burnishing
was noted. Moderate and severe wear of the upper articular
surface is noted in inserts with more than 9.5 years of function
and thickness of 7mm and 9.5mm. Delamination is the main
wear pattern of these inserts and affects 66% of the total contact
surface. Plastic deformation affects 9% and 1.5% shows pitting
and scratching. The remaining surface cannot be assessed due to
the fracture of the insert at the posterior condylar area and the
loss of material.
Mild scratching and burnishing wear are evident after 5.5
years. Such wear mode is like other retrieved mobile inserts
reported in previous studies [35-38] where PCL was also
preserved and different from other studies where PCL was
sacrificed . It should also be mentioned that the alignment
of scratches was rotational rather than longitudinal confirming
the in vivo rotational ability of the mobile insert to the upper
polished surface of the tibial component.
The analysis of 17 retrieved mobile polyethylene inserts in
Rotaglide Total Replacement with a mean in vivo function of 8
years (3 months to 15.6 years) demonstrates that delamination
is the main mode of wear affecting the upper articular surface.
Thin inserts with 7.5 and 9mm thickness were particularly
vulnerable. In these inserts wear is accompanied by fracture of
one or both posterior condyles and the loss of material. In all
inserts regardless of thickness, there was no significant backside
wear, which is mainly of burnishing and pitting type. Compliance
with ethical standards.