B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
695–702
IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
REKONSTRUKCIJA VELIKIH ACETABULARNIH DEFEKTOV Z
METODO IMPAKTIRANJA KOSTNIH PRESADKOV
Bo{tjan Kocjan~i~
1
, Lovro Suhodol~an
1
, Klemen Avsec
1
, Matja` Godec
2
,
Barbara [etina Bati~
2
, ^rtomir Donik
2
, Monika Jenko
2
, Drago Dolinar
1
1
University Medical Centre Ljubljana, Department of Orthopedic Surgery, Zalo{ka cesta 9, 1000 Ljubljana, Slovenia,
2
Institute of Metals and Technology, Lepi pot 11, 1000 Ljubljana, Slovenia
dolinardrago@gmail.com
Prejem rokopisa – received: 2018-03-06; sprejem za objavo – accepted for publication: 2018-05-24
doi:10.17222/mit.2018.036
Revision surgery of the hip on the acetabular side is a challenge, especially in the presence of extensive bone loss. Although the
impaction allografting of morsellised bone combined with the cement fixation of acetabular implants is still commonly used in
revision hip surgery, it fails in most extensive acetabular defects. A series of twelve impaction allograft acetabular revisions is
presented. Eleven defects were combined, defined as cavitary and segmental. In one case, there was only medial bone loss, with
intact and supportive columns. Of the total number of revised hips, four needed to be re-revised and were considered failures,
while two of them suffered repeated dislocations. All failures were observed in the Paprosky type 3B group. Taking aseptic
loosening as an end-point, the overall reconstruction survival rate was 66.7 % at an average of 58.4 months. In patients with
uncontained segmental acetabular wall defects, we prefer the use of supplemental devices in order to close the peripheral defects
combined with a bone-impaction technique. The use of either an acetabular reconstruction ring or trabecular metal acetabular
components with augments in combination with impacted bone allografts initially offers a more stable construct, while the
impacted allografts are incorporated into the host bone. SEM, EBSD and AES analyses of the retrieved metal meshes and a new
one are also presented.
Keywords: large acetabular defects, impaction grafting, metal mesh, SEM, EDS, EBSD, AES
Revizija kol~ne endoproteze predstavlja kirur{ki izziv, zlasti ob prisotnosti obse`ne izgube kosti na acetabularni strani. ^eprav
se metoda impaktiranja kostnih presadkov v kombinaciji s cementiranimi acetabularnimi ~a{icami {e vedno pogosto uporablja
pri reviziji kol~ne endoproteze, ta odpove pri najbolj obse`nih acetabularnih defektih. Predstavljamo serijo dvanajstih revizij
acetabularnih komponent kol~ne endoproteze. Enajst acetabularnih defektov je bilo kombiniranih, opredeljenih kot kavitarni in
segmentni. V enem primeru je pri{lo zgolj do izgube kostnine medialno z nepo{kodovanim acetabularnim obodom. Od skup-
nega {tevila revidiranih kolkov je bilo {tiri potrebno ponovno operativno revidirati in {tejejo za neuspe{ni poskus zdravljenja s to
metodo, dva od teh sta imela ponavljajo~e izpahe. Vsi neuspe{ni poskusi zdravljenja spadajo po klasifikaciji v skupino Paprosky
tip 3B. Pri asepti~no omajanih rekonstrukcijah acetabularnih komponent kol~nih endoprotez je bilo skupno pre`ivetje rekon-
strukcij 66,7%vpo vpre~ju 58,4 meseca po operativnem posegu. Pri bolnikih z obse`nimi segmentnimi acetabularnimi defekti
dandanes raje uporabljamo druge rekunstruktivne metode. Uporaba bodisi acetabularnih rekonstrukcijskih obro~ev ali trabeku-
larnih kovinskih acetabularnih komponent v kombinaciji s kostnimi presadki nudi bolj stabilen konstrukt, s konstantnej{imi in
bolj{imi klini~nimi rezultati. Predstavljene so tudi SEM-EDS, SEM-EBSD in AES analize dopolnilnih kovinskih pripomo~kov,
odstranjenih pri revizijski operaciji in novih mre`ic iz nerjavnega jekla AISI 316L.
Klju~ne besede: veliki acetabularni defekti, impaktiranje kostnih presadkov, kovinska mre`ica, SEM, EDS, EBSD, AES
1 INTRODUCTION
A total hip arthroplasty (THA) ranks as one of the
most successful operations yet devised.
1
As the number
of THA increases and the indications for hip replacement
widen, the number of failures continues to rise. Projec-
tion models predict an increase in demand for revision
arthroplasties over the next two decades. The prevalence
of revision hip arthroplasty is 18 % in the United States
and8%intheSwedish registry.
2,3
Substantial bone loss
after THA presents a challenge in reconstruction, as nu-
merous patients have more than one failed revision
surgery of serious cavitary and segmental acetabular
defects. The indications for acetabular revision include
symptomatic aseptic loosening with migration of the
component, failure of the fixation, infection, wear, oste-
olysis, and instability. Progressive osteolysis in an
asymptomatic patient and severe wear or bone loss that
could compromise a future reconstruction represents
relative indications.
3
Revision surgery of the hip on the
acetabular side is a challenge, especially in the presence
of extensive bone stock loss. The goals of revision sur-
gery on the acetabular side are to provide an initial
support for the cup, the restoration of the anatomic hip
center and leg length, to provide conditions for long-term
durability, and to restore bone stock for future revisions.
4
Various reconstruction techniques for extensive ace-
tabular bone defects including large jumbo uncemented
acetabular components, bilobed acetabular components,
the reconstruction with a high hip centre, a cemented or
cementless component revision with impaction grafting,
reinforcement rings and cages, and structural bone allo-
grafts as well as impaction bone grafting are described
by several authors.
3,5–14
The impaction allografting of
morsellised bone combined with the cement fixation of
Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702 695
UDK 620.1:617.3:616.718.16:615.477.2 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(6)695(2018)

acetabular implants is commonly used in revision hip
surgery because it offers the opportunity for restoration
and regeneration of bone stock. Furthermore, it allows
the creation of an anatomic, biomechanical natural center
of rotation.
15
Although initial studies have shown good
results, other studies have identified potential problems
with this technique.
15,16–20
Long-term survival rates for
massive acetabular deficiencies have been reported bet-
ween 72 % and 94 %. Nevertheless, impaction grafting
in most extensive acetabular defects (Paprosky 3A and
B, AAOS III) is controversial and always requires the
use of supplemental devices such as metal mesh fixed to
the iliac bone to transform non-contained into contained
deficiencies.
12,15,21
The paper presents short- to mid-term results for the
use of original impaction bone grafting with a metal
mesh in order to reconstruct extensive acetabular defects.
The results of the failure analyses of the metal mesh,
using scanning electron microscopy (SEM), electron-
backscattered diffraction (EBSD), Auger electron spec-
troscopy (AES) and X-ray photoelectron spectroscopy
(XPS) methods are also included.
2 METHODS
We have reviewed a consecutive series of twelve
impaction allograft acetabular revisions and studied the
clinical and radiological outcomes to identify the factors
associated with the failure of reconstruction. Between
February 2010 and November 2012, twelve impaction
allograft reconstructions of the acetabulum were per-
formed, of these seven were 2 female and 5 were male
patients. The average age of the patients at operation was
68.7 years (range 49.6 to 84.4). Pre- and post-operative
radiological and clinical data of the twelve hips were
available for review. The reason for revision was aseptic
loosening in ten hips and septic loosening in two hips. In
ten patients (83.3%) an isolated acetabular revision was
undertaken, and in two (16.7%) both components were
revised.
Surgeries were performed according to the principles
established by Schreurs et al. and Slooff et al. with Exe-
ter X-change revision instrumentation (Stryker How-
medica Osteonics, Allendale, New Jersey) under epidural
hypotensive anesthesia and through a posterolateral
approach.
16,17
The acetabulum and femur were widely
exposed, obtaining complete visualization of the aceta-
bular limits and its anterior, superior, and posterior
segmental defects. All implants, polymethylmethacrylate
(PMMA), granulation tissue and interface were removed
completely and the transverse ligament or the inferior
teardrop was identified. These landmarks allowed the
reconstruction of the center of rotation in an anatomic
position. The specific requirements for the metal mesh
were determined by inserting a trial cup at the transverse
ligament level. Pre- and peri-operatively, all the patients
were screened for infection using blood tests, bone scans
and intra-operative cultures. Cemented polyethylene
acetabular components were used. The allograft bone
was obtained from our own bone bank, where femoral
heads were deep-frozen after harvesting. The donor
selection conformed to the guidelines of the Musculo-
sceletal Council of the American Association of Tissue
Banks.
22
Before impaction the allograft bone was thawed
at room temperature and prepared by hand with a ron-
geur and bone mill to produce bone chips of approx-
imately 0.7 cm to 1 cm in diameter. All the cartilage was
removed first. The acetabular host bone was reamed until
a bleeding bone bed was created. If necessary, small drill
holes were made for revascularization of the host bone.
The bone graft was forcefully impacted until a solid new
bone bed was created using Stryker impaction instru-
mentation (Stryker Howmedica Osteonics). The aceta-
bular components were cemented with Palacos® cement
containing gentamicin (Heraeus Medical) using a pres-
surizing technique recommended by the manufacturer in
order to produce a cement mantle at least 2 mm thick.
Metal meshes (Stryker Howmedica Osteonics) were used
in all the presented cases. The acetabular metal mesh
was 0.38 mm thick and had 2-mm perforations. The
caudal rim of the component was positioned at the level
of the transverse ligament. That mesh was trimmed and
shaped according to the segmental deficiency. Once
placed in position, it was fixed to the iliac bone with
several bicortical screws using 15–20 mm interval in bet-
ween in order to get a stable fixation of the metal mesh.
The rehabilitation protocol included early mobilization
and ambulation with a walker and toe-touch weight
bearing on the operated side for 45 d. After that the
patients were encouraged to progressive weight bear as
tolerated until they were free of walking assistance
(range, 45–110 d).
We evaluated the patients clinically and radiologi-
cally. Radiostereometry analysis x-rays were taken at
(15, 45, 90 and 180) d postoperatively and then yearly. A
clinical assessment was made with a Harris Hip Score.
We classified the acetabular bone deficiencies radiogra-
phically based on the pre-operative radiograph as well as
intraoperative findings using the American Academy of
Orthopaedic Surgeons (AAOS) classification and the
Paprosky classification.
Eleven defects were combined (Paprosky Type 3,
AAOS III), defined as cavitary and segmental. In four
cases there were segmental defects with non-supportive
columns and superolateral migration (Paprosky type 3A)
and in seven cases extensive segmental acetabular
defects with superomedial migration were noted (Pap-
rosky type 3B). In one case, there was only medial bone
loss, with intact and supportive columns (Paprosky 2C,
AAOS II). We excluded cases with pelvic discontinuity,
septic failures, cases where the acetabular component
was retained, and cases where major structural grafts,
augments, or reinforcement cages were utilized. Clinical
failure was defined as the need for further acetabular
B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
696 Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702

revision, regardless of the etiology. Radiographic failure
was defined as the progression of radiolucent lines in the
three acetabular areas or migration greater than 5 mm.
The samples of retrieved and new metal meshes
(stainless steel AISI 316L) were prepared using a Jeol
IB-09010CP ion cross-section polisher which produces
pristine cross-sections of samples and creates a mirrored
surface. The CP uses an argon beam to mill the cross-
sections and polish the material.
The microstructures of the samples were investigated
using a JEOL JSM 6500F field-emission scanning elec-
tron microscope (SEM) equipped with a HKL Nordlys II
electron-backscatter diffraction (EBSD) camera using
Channel 5 software. Individual diffraction patterns were
obtained together with mapping of the area of the inte-
rest. The instrument was operated at 15 kV and approxi-
mately 2-nA current for the EBSD analysis, with a tilting
angle of 70°. The instrument is equipped with EDS
technique of Oxford instruments for chemical analysis.
The instrument has both secondary-electron (SE) and
backscattered-electron (BE) imaging modes for morpho-
logical analyses of the samples. For the SE or BE
imaging, the instrument was operated with an accele-
ration of 15 kV at a current of approximately 0.5 nA.
The vacuum was maintained below 1·10
–6
mbar.
The Auger electron spectroscopy (FE-AES) instru-
ment used in this study was a Thermo Scientific Micro-
lab 310-F spectrometer, equipped with a thermally
assisted Schottky field-emission electron gun (FEG) that
provides a stable electron beam in the accelerating
voltage range 0.5–25 kV, and a spherical-sector electron
kinetic energy analyzer. The spectra were usually
acquired with a constant retarding ratio (CRR) of 4,
which provides an energy resolution that is 0.5% of the
pass energy. The parameters used in the AES analysis
included a 10-keV primary electron beam at a current of
1 nA, an angle of incidence of 0°, and an Auger emission
angle of 30°. AES depth profiling was performed by
argon-ion sputtering at 3 keV and scanning the ion beam
overa2mm×2mmarea. The sputtering rate was about
0.7 nm/min. The instrument is also equipped with an
X-ray source (Mg, Al dual anode), which in combination
with the electron-energy analyzer, allows for an XPS
surface chemical analysis to be made in the same instru-
ment. The XPS measurements were performed using
non-monochromatic Al–K
 radiation (1486.6 eV) with
an anode voltage of 12.5 kV and an emission current of
16 mA. For the XPS depth profiling, a 3-keV Ar-ion
beam scanned overa4mm×5mmarea was used, and
this corresponded to a 0.1 nm/min sputtering rate.
3 RESULTS AND DISCUSSION
The minimal post-operative follow-up period was 40
months and the maximum was 73 months, with a mean
average of 58 months. Of the 12 revised hips, four
needed to be re-revised and were considered failures, 2
of them suffered repeated dislocations. All failures were
observed in the Paprosky type 3B group (4 out of 7).
Taking aseptic loosening as an end-point, the overall
reconstruction survival rate was 66.7 % at an average of
58 months (40–73 months). An average of 2.3 femoral
heads were used per case (range 1–4) to reconstruct the
acetabular defects. The average time of revision pro-
cedure was 225.8 min (170–360 min), and the average
blood loss was 1467 mL (600–2500 mL). A successful
clinical result at the last follow up (HHS over 70, stable
implant) was observed in eight patients, where the
average HHS for all patients at 24 months was 75.6, and
in the successful group at last follow up the average HHS
was 78.6. The average fleion of the operated hip at the
last follow up was 84.2° (Table 1). During the last
examination six out of eight successfully treated patients
walked without any aid, while two were using crutches.
B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702 697
Table 1: Details of epidemiology and results
No
Age
(years)
Diagnosis AAOS Paprosky
Followup
(mts)
HHS
(24 months)
HHS
(at followup)
Revision
(months)
observations
1 74,8 AL IB 2C 67 79 79
2 84,4 AL III 3B 41 69 69 27
repetitive luxations, mesh
failure, reoperation
3 69,8 AL III 3B 40 82 84
4 68,1 AL III 3A 64 84 85
5 49,6 AL III 3B 73 73 71 47
breakage of reconstruction,
reoperation
6 82,4 AL III 3B 52 82 76
7 72,8 AL III 3A 52 75 79
8 54,7 AL III 3B 68 79 78
9 73,3 SL III 3B 64 59 58 39
infection, debridement,
retention
10 57,5 AL III 3B 48 69 67 32
repetitive luxations,
reoperation
11 64,8 AL III 3A 57 81 83
12 72,3 SL III 3A 70 77 76
AL, aseptic loosening; SL, septic loosening; HHS, AAOS, Academy of Orthopedic Surgeons

One patient had an acute deep haematogenous infec-
tion of the revised hip after an infection of the urinary
tract without radiographic signs of loosening or migrat-
ion 39 m postoperatively. The patient was treated with
surgical debridement, component retention, and
antibiotic therapy suppression, and showed no signs of
loosening 64 m after the initial reconstruction. Two of
the patients presented with a positive post-operative
Trendelenburg test. One patient also had a transient palsy
of the sciatic nerve; no other major problems were noted.
The length of the leg was restored completely in 10
patients. In two patients who had a pre-operative short-
ening of 5 cm, the remaining shortening was 1 cm.
In the following section one typical case of a success-
ful reconstruction and two examples of failed reconstruc-
tions with impaction allografting will be presented.
Case 1: A preoperative radiograph of a patient
showing a loose Muller reinforcement ring of the right
hip (Figures 1a, 1b). Moderate segmental and cavitary
acetabular deficiency (AAOS type III, Paprosky type 3A)
was successfully reconstructed with impaction
allografting (Figures 1c, 1d). Figure 1c shows an
immediate post-op radiograph, Figure 1d shows a stable
situation of the reconstruction at latest follow-up (70 m
postop).
Case 2: A patient that suffered failure of Paprosky 3B
acetabular reconstruction (extensive posterior and mo-
derate medial wall deficiency) 39 m after impaction
grafting. Figure 2a shows a good and successful
reconstruction with the Exeter method at follow-up.
Later on, the breakage of the reconstruction was caused
by hip dislocation, which occurred during the spinal
decompression surgery (Figure 2b). A bent mesh and
pulled screws of the posterior acetabulum reconstruction
were noted. Massive segmental deficiency was re-recon-
structed with a Burch-Schneider reinforcement cage
(Zimmer) (Figure 3c).
Case 3: A patient who had multiple reconstructions
of combined extensive segmental and cavitary deficiency
of the right acetabulum (Paprosky 3B, AAOS III). After
complete breakage of Burch-Schneider Reinforcement
Cage (Zimmer)(Figures 3a, 3b), impaction allografting
B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
698 Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702
Figure 1: X-ray images of a successful reconstruction with the impaction allografting technique
Figure 3: X-ray images of a failed re-revision with the Exeter technique. Mesh breakage after 27 months. Further re-reconstructed with
Trabecular Metal™ Acetabular Revision System (Zimmer).
Figure 2: X-ray images of an unsuccessful reconstruction with metal mesh and impaction bone grafting in a segmental acetabular defect

using the Exeter technique was employed (Figure 3c).The
mesh reconstruction failed after 27 m (Figure 3d) and
was further re-reconstructed with Trabecular Metal™
Acetabular Revision System (Zimmer) (Figure 3e).
3.1 SEM, EDS and EBSD
The microstructures of the retrieved and new metal
meshes are shown in Figure 4. Channelling contrast
from differently oriented grains can be seen from the
backscattered-electron image, with twin grains present,
as well as some inclusions. The EDS analysis (Table 2),
performed over a larger area, corresponds well to the
composition of the AISI 316 L stainless steel, as can be
seen from Table 2. The inclusions present are mostly
oxides. No porosity was observed in the images.
Table 2: EDS analyses of fractured metal mesh and new metal mesh
(w/%)
Element Si Cr Mn Fe Ni Mo
Fractured metalmesh 0.5 17.8 2.4 61.7 14.6 3.0
New metal mesh 0.5 17.9 2 61.6 14.4 3.5
An additional EBSD analysis was performed to char-
acterise the crystal structure and grains of the new and
the retrieved mesh. The analysis showed an austenitic
(fcc) crystal structure, with no prevalent texture. The
B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702 699
Figure 6: a) AES spectra, taken on retrieved metal mesh (AISI 316L),
b) AES depth profile of the same metal mesh
Figure 4: a) BE image of cross-section microstructures of retrieved
and b) new metal mesh
Figure 5: EBSD analysis of the metal mesh: a) orientation map of the
new mesh, b) grain reconstruction of the new mesh, CSL  3 grain
boundaries are shown in red, c) orientation map of the retrieved mesh,
d) grain reconstruction of the new mesh, CSL 3 grain boundaries are
shown in red

images in Figures 5a and 5c show the orientation
mapping of the new and retrieved mesh, while 5b and 5d
show the grain reconstruction, with  3 grain boundaries
shown in red color. The retrieved mesh shows a slightly
higher percentage of twin boundaries, with 65 % of the
total grain-boundary length corresponding to twins;
while the new mesh has about 60 % of twin boundaries.
The twinning in the austenitic stainless steel is due to
fatigue and plastic deformation. The grain sizes are
similar in both cases.
3.2 AES and XPS
AES and XPS surface analysis confirm the presence
of a thin, passive Cr
2
O
3
film contaminated by carbon.
The thin oxide films on the surfaces of the fractured
AISI 316 L austenitic stainless-steel mesh retrieved and
new were analyzed by AES. Figures 6b and 7b show the
AES depth profiles of a thin oxide film on the AISI 316
L stainless steel of the retrieved and new metal meshes.
Figure 8 represents the XPS depth profile of the mesh
after 27 m use in patients with all possible species on the
stainless-steel surface. The film on the surface shows a
very thin oxide layer with predominantly C, O and from
the kationic fraction Cr as Cr
2
O
3
. The present cationic
fractions shown in Figure 8 are also Fe and Cr in
metallic form, but this is not due to the non-uniform
passive film, but the thickness is so small that we can
observe the matrix below the oxide layer.
Since AES and XPS are surface-sensitive techniques
we can measure the thicknesses of the thin oxide films.
We calculated on both the retrieved and new metal
meshes an about 2-nm-thick oxide film.
4 CONCLUSIONS
The management of Type 3A or 3B defects of the
acetabulum according to Paprosky is one of the most
challenging aspects of revision hip arthroplasty. Due to
the fact that many of these patients have a long life ex-
pectancy it is of fundamental importance to re-establish
the bone sub layer of the acetabulum and also to re-
establish the rotation center of the hip as much as
possible back to its anatomic place. Different operative
methods can be used to achieve this goal, but none has a
good long-term survival of the implant.
Although managing this kind of revision hip surgery
using the impaction allografting of morsellised bone
combined with metal meshes and cemented fixation
showed promising survival rates at the beginning, longer
follow up studies have identified potential problems,
especially when treating extensive segmental acetabular
defects.
15–20
Our series found an unacceptably high rate of failure
of impaction grafting for acetabular revision. The ma-
jority of patients (11 of 12) analyzed in our study had
large, combined, uncontained defects of acetabulum with
non-supportive columns. In our series a 57 % failure rate
was noted in the subgroup with large, uncontained, seg-
B. KOCJAN^I^ et al.: IMPACTION GRAFTING OF LARGE ACETABULAR DEFECTS
700 Materiali in tehnologije / Materials and technology 52 (2018) 6, 695–702
Figure 8: XPS depth profile of retrieved metal mesh (27 month)
Figure 7: a) AES spectra, taken on new metal mesh (AISI 316L), b)
AES depth profile of the same metal mesh

mental defects with major medial bone loss (Paprosky
3B), and none in the moderate combined acetabular bone
loss (Paprosky 3A type group). Our study confirmed
good-to-excellent survival rates and clinical results when
using the impaction allografting of morsellised bone
with metal meshes in Paprosky type 2C and type 3A
segmental defects of the acetabular wall. Furthermore,
when using this technique in the uncontained extensive
segmental acetabular wall defects (Paprosky type 3B),
the survival rates of the construct fall significantly.
Our findings are similar to the study of van Haarens
and Buttaros, as we consider extreme segmental defects
combined with major medial wall defects (Paprosky type
3B) a contra-indication for the use of metal mesh with
impaction bone grafting. A possible explanation for the
relatively high failure rates may include micro movement
leading to mechanical instability and graft resorption
followed by stainless-steel fatigue resulting in mesh
rupture and migration.
12,15
Another important factor is the
quality of the host bone that is usually significantly more
affected in extreme acetabular defects. Good bone qual-
ity is of major importance for adequate graft incorpora-
tion, which is essential for the survival of the construct.
12
Furthermore, our explanation for the observed insta-
bility and repeated dislocation in two of our patients
would be that thick bone grafting allows for greater sub-
sidence of cemented acetabulum. Additionally, it is
sometimes advisable to make more soft-tissue tension in
these types of revision procedures in order to achieve
better stability of the implant that can lead to excessive
leg lengthening and puts adjacent neurovascular struc-
tures at risk.
The latter is especially the case with the sciatic nerve,
since the operative management of great posterior
acetabular wall defects requires its relatively large
exposure in order to properly fix the metal mesh. Exten-
sive exposure often means close contact with the sciatic
fossa and visualization of the nerve. Taking this into con-
sideration, we believe that only one transient palsy was a
very successful result in our clinical setting.
Recently, in patients with uncontained segmental
acetabular wall defects we prefer to use supplemental
devices to close the peripheral defects combined with the
bone-impaction technique.
The use of either an acetabular reconstruction ring or
trabecular metal acetabular components with augments
in combination with impacted-bone allografts initially
offers a more stable construct, while the impacted allo-
grafts are incorporated into the host bone.
23
We believe that a metal mesh fixed to the ilium com-
bined with impacted allografts and a cemented cup has
its primary role in the contained cavitary and moderate-
size uncontained cavitary acetabular defects (AAOS type
I and II, Paprosky type 2 and 3A), where high survival
rates were reported.
15–18
On the other hand, we found
worryingly high failure rates with this reconstruction
technique in cases with large segmental defects, which
concurs with authors who have identified the same
potential problem.
15,19
The limitations of our study include a small patient
cohort, but taking into account also the published data in
the literature we can conclude that in the selected revi-
sion cases with moderate acetabular wall defects the
impaction grafting technique combined with metal
meshes is good and provides a biological restoration of
the bone stock. In revisions with extensive acetabular
bone defect the same technique carries with it a high risk
of failure.
15–20
SEM and EBSD analyses showed an austenitic
microstructure with numerous twin grains due to fatigue
and plastic deformation. AES and XPS surface analyses
of the retrieved and new metal mesh confirm the pre-
sence of a thin passive Cr
2
O
3
film contaminated by C
with an estimated thickness of 2 nm.
24
Acknowledgments
This work was carried out within the framework of
Department of Orthopaedic Surgery University Medical
Centre Ljubljana, with no extra funding. The failure
analysis of the meshes were carried out at the Institute of
Metals and Technology, financially supported by
Slovenian Research Agency ARRS-0206-0132.
Ethics statement
The article does not contain any studies with human
participants or animals performed by any of the authors.
Informed consent was obtained from all the individual
participants included in the study.
Conflict of interest
The authors declare that they have no conflict of
interest.
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