An in vitro study comparing limited to full cementation of polyethylene glenoid components
Glennie et al. Journal of Orthopaedic Surgery and Research
An in vitro study comparing limited to full cementation of polyethylene glenoid components
R. Andrew Glennie 1
Joshua W. Giles 0
James A. Johnson 0
George S. Athwal 0
Kenneth J. Faber 0
0 Division of Orthopedics, Western University , 268 Grosvenor St, London N6A 4L6, ON , Canada
1 Department of Orthopedics, Dalhousie University , Halifax, NS , Canada
Background: Glenoid component survival is critical to good long-term outcomes in total shoulder arthroplasty. Optimizing the fixation environment is paramount. The purpose of this study was to compare two glenoid cementing techniques for fixation in total shoulder arthroplasty. Methods: Sixteen cadaveric specimens were randomized to receive peg-only cementation (CPEG) or full back-side cementation (CBACK). Physiological cyclic loading was performed and implant displacement was recorded using an optical tracking system. The cement mantle was examined with micro-computed tomography before and after cyclic loading. Results: Significantly greater implant displacement away from the inferior portion of the glenoid was observed in the peg cementation group when compared to the fully cemented group during the physiological loading. The displacement was greatest at the beginning of the loading protocol and persisted at a diminished rate during the remainder of the loading protocol. Micro-CT scanning demonstrated that the cement mantle remained intact in both groups and that three specimens in the CBACK group demonstrated microfracturing in one area only. Discussion: Displacement of the CPEG implants away from the inferior subchondral bone may represent a suboptimal condition for long-term implant survival. Cement around the back of the implant is suggested to improve initial stability of all polyethylene glenoid implants. Clinical relevance: Full cementation provides greater implant stability when compared to limited cementation techniques for insertion of glenoid implants. Loading characteristics are more favorable when cement is placed along the entire back of the implant contacting the subchondral bone.
Glenoid component loosening is a common cause of
failed total shoulder arthroplasty (TSA) [1, 2]. Multiple
studies have identified factors associated with glenoid
component failure including glenohumeral mismatch,
glenohumeral instability, excessive glenoid reaming at
the time of surgery, cementing techniques,
malalignment of the glenoid component, and osteopenic host
bone [1, 3].
Although different methods of glenoid fixation are
available, clinical and biomechanical studies would
suggest that all polyethylene-cemented implants may have
better initial in vitro stability and superior mid- and
longterm clinical survivorship when compared to
metalbacked implants [4–7]. Polyethylene glenoid prostheses
can be broadly categorized as either “keeled” or “pegged.”
Currently, the cement mantle required for adequate initial
fixation and durable long-term survivorship of
polyethylene prostheses is not well established [8–12].
Little is known about the effect of various glenoid
cementation techniques in total shoulder arthroplasty. Several
recent publications examining the effect of pressurization
found improved cement interdigitation within cancellous
bone that theoretically creates a stronger initial bond
to the host bone that may enhance implant stability,
minimize radiolucent lines, and increase implant
survivorship [13–15]. In addition, Neer suggested that
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building up cement along the back of the implant
lead to poorer implant survival since there was higher
potential edge loading and therefore more opportunity
for cement fracturing and third body debris in the
joint potentially starting the cascade of osteolysis .
Others have observed higher implant failure rates
when the cancellous bone is exposed for cementation
and suggested that preservation of the subchondral
plate is critical for implant survival . When the
subchondral plate is preserved, there is little
opportunity for cement interdigitation with cancellous bone.
The purpose of this study was to compare the
microcomputed tomography (micro-CT) findings and
biomechanical characteristics of two cementation techniques
employed during subchondral plate-sparing glenoid
preparation. The null hypothesis is that both cementation
techniques will demonstrate no significant difference in cement
mantle changes on micro-CT and similar biomechanical
properties regardless of cementation technique.
Materials and methods
Sixteen unmatched cadaveric human shoulder
specimens were tested (ages 42–75). Each specimen was
imaged with radiographs to ensure there were no osseous
abnormalities that would prevent component
implantation. Seven scapulae were randomized to receive a
traditional fully cemented technique with cement around the
pegs and the back-side of the implant (CBACK) and
nine were randomized to a limited cementing technique
only around the implanted pegs (CPEG). Randomization
was carried out with a random number generator.
After each specimen was thawed and stripped of soft
tissues, the glenoid was prepared to accept a 46-mm
pegged prosthesis using the surgical technique provided
by the implant manufacturer (Anatomical™, Zimmer,
Warsaw, IN). Reaming to create a conforming surface
for the implants was performed in a manner that
preserved the deep cortical plate in all specimens. All
scapulae included in the study were size-matched to
accommodate a 46-mm implant. The humeral head was
simulated using an instrumented steel ball that
corresponded to the manufacturer’s recommended radius of
curvature mismatch. Third-generation cementation
technique was used as described by Reiss and Nyfeller [18, 19].
For the CBACK specimens, cement was injected (Simplex,
Stryker, NJ) into the glenoid peg holes and onto the
subchondral glenoid bone. Additional cement was intentionally
placed on the convex back surface of the component.
The cement was then pressurized and the implant
inserted. The limited cementation technique (CPEG)
injected and pressurized cement into the glenoid peg
holes with a syringe. No cement was applied to the
convex back surface of the implant or to the glenoid
face. Any excess cement that leaked from the peg
holes was removed from the back of the implant. In
both techniques, the excess cement was removed
beyond the margins of the polyethylene and the
component was pressed against the glenoid face with an
impaction device until the cement was fully cured.
Mechanical testing of micro-stability
Glenoid component deformation and differential
movement between the component and the adjacent bone
was measured using an optical tracking system (OptoTrak
Certus, NDI, Waterloo, ON). Two trackers were
necessary: a reference tracker was placed on the glenoid bone
remote from the implant and the second tracker was
placed on the inferior edge of the polyethylene implant. A
reference marker was placed on the bone adjacent to the
bone-implant interface in order to compensate for all
movement of the underlying bone that would otherwise
appear as component displacement when recorded by the
implant marker (Fig. 1). The optical tracking system was
calibrated and confirmed to have a resolution of 0.01 mm
and an accuracy of 0.1 mm prior to initiation of testing.
A sinusoidal cyclic loading protocol was used to
continuously load the construct with a 30 degree force vector
in the superior direction for a total of 10,000 repetitions at
1250 N. This testing regimen was chosen to simulate 5
high load activities (e.g., rising from a chair, walking with a
walker, turning a locked steering wheel, etc.) per day over
a 6-year period . Similar loading regimens have been
suggested previously . The force vector was achieved
using a pneumatic loading apparatus and applied to the
glenoid via a custom steel ball with a radius of curvature
equivalent to the implant manufacturer’s recommended
corresponding humeral head implant (Fig. 2).
Loading and optical tracking data were continuously
recorded using LabVIEW software (National Instruments,
Fig. 1 The optical tracker demonstrated on the inferior aspect of the
Fig. 2 The loading apparatus demonstrates a 30° loading vector
with two optical trackers. One optical tracker is attached to the
polyethylene and one is attached to the bone as a reference. The
scapula is potted within the cement box. There is masking tape over
the humeral ball to reduce potential reflection to the camera
Austin TX). Mean data at the 50th, 100th, 200th, 500th,
1000th, 5000th, and 10,000th cycle for each group was
compared using analysis of variance (ANOVA) in SPSS
(IBM, Armonk, NY).
CT-based radiological assessments
After specimen preparation and before loading, baseline
micro-computed tomography (micro-CT) scans were
obtained to evaluate the initial incorporation of cement
into the glenoid bone surface and in the peg holes. The
glenoid samples were imaged using the Locus Ultra
micro-CT scanner (General Electric, Fairfield, CT). The
scanner has an in-plane field of view of 140 mm in
diameter and an axial field of view of 96 mm in length.
The samples were imaged with an x-ray source voltage
of 120 kV and a current of 20 mA. In a scan time of less
than a minute, 1000 views were acquired. The data were
reconstructed into a three-dimensional (3-D) image
volume with an isotropic voxel size of 154 μm. After
completion of the complete loading protocol, the micro-CT
scanning was repeated. General Electric Health Care
MicroView™ (General Electric, Fairfield, CT) software
was used to quantitatively evaluate three-dimensional
images of the construct (Fig. 3).
Micro-CT images were evaluated in a random and
blinded order and data was recorded using a modified
scoring system that was based on the scoring system
previously described by Walch . An example of each
technique, both CBACK and CPEG, can be found in
Fig. 4. Average thickness of the cement mantle was
recorded for the CBACK components. Each component
was divided into eight different zones that corresponded
to positions on the medial surface of the glenoid
prosthesis (Fig. 5). A score of 0 was assigned if no
radiolucent lines were present within a zone and a score of 1
was assigned if radiolucent lines were present within the
zone. A radiolucent line was defined as a visible
radiolucency ≥1 mm comparing identical CT images pre- and
post-loading. The eight zones of the pre- and
postloading images were compared using chi-squared
analysis to determine whether any significant radiolucent
lines or cement fractures had developed. All eight zones
were carefully scrutinized in each specimen for any
evidence of microfracture.
One of the specimens from the CBACK group was
excluded due to inadvertent camera movement near the
beginning of the loading cycle. Therefore, the camera
could not visualize the tracker and the data was not
There was a significant difference in the
displacement of the polyethylene implant when comparing
CBACK and CPEG cementation techniques
dynamically (p = 0.03). Physiological loading displaced the
implant away from the inferior portion of the glenoid
(Fig. 6). The initial mean displacement of the CPEG
components at 50 cycles was 0.156 ± 0.038 mm
whereas mean displacement of CBACK components
was 0.055 ± 0.010 mm (p = 0.017). At 10,000 cycles,
the mean displacement of the CPEG components
increased to 0.255 ± 0.039 mm (p = 0.001). This data is
summarized in Table 1.
The CPEG implants had significant and progressive
displacement throughout the cyclic testing protocol
(Fig. 7). Using a Bonferroni correction for multiple
comparisons, the mean difference (0.017 mm) was
significant between 100 and 500 cycles (p = 0.019), as
well as the difference (0.03 mm) between 100 and
1000 cycles (p = 0.029). In contrast, there was no
significant difference in displacement of the CBACK
components throughout the protocol (p = 0.45). The
measured displacement occurred between the optical trackers
fixed to the inferior portion of the glenoid component and
the host glenoid bone.
In the 16 scapular specimens, there was no significant
change in appearance of the
polyethylene/cement/glenoid bone interface when comparing the eight zones of
interest (p = 0.14). Cement mantle thickness ranged
from 1.2 to 2.0 mm for all CBACK specimens. Cement
Fig. 3 Specimen 8 demonstrates slight change at the anterior portion of the cement mantle interface specifically comparing pre-loading and
post-loading CT images
mantle fracture was not observed in any specimen and
cement mantle defects observed after initial cementation
did not progress or change after the loading protocol.
Three CBACK specimens had 1-mm radiolucent lines at
sites 3, 5, and 8 (anterior position) of the subchondral
surface after loading. Specimen #3 demonstrated radiolucent
lines in zones 3 and 8. No significant changes were
observed at the superior, inferior, or posterior positions.
There were no changes to the bone under the cement
mantle indicative of bony compression or fracture. There
was no appreciable change in polyethylene shape when
comparing pre and post micro-CT scans (Table 2).
Establishing a cyclic loading protocol and method for
determining displacement of polyethylene components
in total shoulder arthroplasty can be valuable when
evaluating new designs [23–25]. We developed a testing
model that is capable of assessing displacement of
components dynamically during cyclic loading. Micro-CT
scans were useful to confirm that there was no gross
abnormality of the cement mantle prior to cyclic testing
and at the end of the protocol. The fact that there were
no cement mantle fractures was surprising to us, as we
theorized that the thin cement mantle would likely
fracture during cyclic loading.
The optical tracking during cyclic loading produced
several interesting findings related to glenoid component
displacement. Implants inserted with the CPEG
technique had an initial “setting in” of the component during
the first 1000 cycles and thereafter the rate of gradual
lift-off diminished but did not cease. This indicates that
there was ongoing displacement of the implant relative
to the glenoid bone that could represent an early mode
of failure with this technique.
Radiostereometric analysis (RSA) has been used to
measure in vivo implant displacement following total
hip and knee arthroplasty . Two displacement
patterns emerge; either the implant achieves solid initial
fixation after a brief period of “setting in” or the implant
continues to displace. The latter scenario is predictive of
catastrophic failure in polyethylene tibial components
Fig. 4 Examples of CPEG micro-CT scan on the left image and CBACK on the image to the right. The CPEG implant shows no cement along the
back of the component whereas the CBACK component shows cement extruding along the undersurface and side of the implant
Fig. 5 Glenoids were divided into eight zones of interest. The
superior peg lies in between zone 2 and 3. The central peg lies in
between zones 4 and 5 and the inferior pegs lie in zones 6 and 7
[27, 28]. A similar conclusion may possibly be drawn
here where significant initial movement of the CPEG
implant may be predictive of accelerated failure when
compared with the CBACK technique that demonstrated no
Fig. 6 Representation of the glenoid being loaded in a superior
direction and demonstrating lift-off as detected by the optical
trackers at the inferior portion of the subchondral bone
Table 1 Mean displacement measurements at different cyclic
loading points for both CPEG and CBACK implantation
The observation of implant displacement away from
the glenoid bone was not associated with failure and
overt loosening in our study as confirmed with the
micro-CT data. We are concerned that the initial
implant displacement persisted albeit at a diminished rate
during extended cyclical loading. It has been shown
previously that any tensile force or distraction at a bone
cement interface may impact upon long-term implant
survival . What we observed could represent a mode
of failure whereby synovial fluid accesses and egresses
from the space between the implant and host bone.
Many authors have stressed that the initial stability of
the implant may be a major determinant for long-term
survival [15, 9]. Our results indicated that implant
displacement away from the glenoid bone was not observed
with the CBACK cementing technique. This may
indicate better fixation and potentially improved
survivability. The presence of radiolucent lines however in 3 of
the 7 CBACK specimens, although not statistically
significant, is an interesting observation. Although the
loading mechanical properties were not affected in vitro,
over time, these radiolucent lines may generate
particulate debris that can initiate the cascade leading to
Movement of the inferior portion of the polyethylene
away from the glenoid subchondral bone as was
observed with limited cementation or the CPEG group
may be a suboptimal environment for long-term fixation
due to the gradual worsening lift-off and possible fluid
egress into the bone cement interface. Although the
initial displacement trend decreases after the first 1000
cycles, the implant continues to move relative to the
tracker on the bone and this trend may either continue
slowly or lead to eventual failure. The initial and
sustained stability observed with the CBACK components
throughout the loading protocol was superior and
warrants further in vivo investigation.
The major limitation of this work was using a loading
protocol that represented 5 high load activities per day.
This is the equivalent of 150 % body weight 5 times per
day for 6 years. The loading protocol may underestimate
Fig. 7 Graph demonstrates initial increase in displacement in CPEG implants with increasing cycles. This gradual increase in displacement
plateaus as the number of cycles increase. There is no appreciable difference in initial of final displacement with CBACK components
the actual loads the implant is subjected to during
normal day-to-day activities particularly if joint
replacements are performed in a younger population. If we
assumed double the number of high load activities then
our protocol would only represent cyclic loads that the
prosthesis is exposed to during a 3-year period.
Concerns that specimen degradation may occur during
testing precluded prolonging the cyclic loading portion of
the testing protocol. Specimen preparation took roughly
1 indicates the presence of new radiolucent line and 0 indicates no change
12 h in total in addition to the loading protocol. Future
study may need to focus on much higher numbers of
cycles and perhaps even loading specimens to failure with
cycling. An additional limitation with this study and
future studies using cyclic loading will be the ongoing
accuracy and the potential error of the cyclic loading data
with respect to the optical tracking system.
Total shoulder arthroplasty is an important
painrelieving operation and we must continue to develop
implants and optimize implantation techniques that
enhance implant survivorship. The lift-off or displacement
of the CPEG implants that was observed during the
dynamic testing protocol is concerning and may be
associated with glenoid loosening. Further in vitro and in vivo
testing and analysis are required to determine the
longterm survival of current cementing techniques.
The authors declare that they have no competing interests.
RAG, JWG, GSA, JAJ, and KJF have (1) made substantial contributions to
conception, design, and acquisition of data and analysis as well as
interpretation of data; (2) been involved in drafting the manuscript or
revising it critically for important intellectual content; (3) given final approval
of the version to be published; and (4) agreed to be accountable for all
aspects of the work in ensuring that questions related to the accuracy or
integrity of any part of the work are appropriately investigated and resolved.
All authors read and approved the final manuscript.
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