MATERIALE PLASTICE 50 No. 3 2013 http:www.revmaterialeplastice.ro 307Short Term Results in Uncemented Ceramicized Metal Total [628585]

MATERIALE PLASTICE ♦ 50♦ No. 3 ♦ 2013 http://www.revmaterialeplastice.ro 307Short Term Results in Uncemented Ceramicized Metal Total
Hip Prosthesis
RADU RADULESCU1,2, ADRIAN BADILA2*, ROBERT MANOLESCU2, IOAN JAPIE2, SILVIA TERINTE2,
DAN NICOLAE PADURARU1,2, ALEXANDRA BOLOCAN1,2
1University of Medicine and Pharmacy “Carol Davila”, 37 Dionisie Lupu Street, Bucharest, Romania
2Bucharest University Hospital, 169 Splaiul Independenței, 050098, Bucharest, ROmania
The objective of our study was to assess the “in vivo” wear of cross linked polyethylene in contact with
different materials surfaces. Thus, we compared the polyethylene acetabular cups wear when they functionin a couple with ceramicized metal heads (zirconium oxide) with those in a couple with cobalt chromium
metal heads, in total hip arthroplasties. The polyethylene wear was quantified by digital measurements on
standardised digital front and lateral view X-rays and the differences were statistically analysed.
Keywords: ceramicized metal, polyethylene, hip prosthesis
* email: [anonimizat]; Tel.: +40 0722 516 470In the case of total hip replacement prostheses, the
friction between the 2 surfaces – the acetabular cup and
the femoral head – leads in time to the wear of these parts
and to the formation of microparticles. Microparticleformation depends on multiple factors – the materials that
the parts are made of (cobalt chromium alloy,
polyethylene, ceramicized metal etc), the geometry of theprosthetic components, their more or less correctly
performed implantation, the forces and mechanical
stresses that they are submitted to etc. The sizes of thesemicroparticles are very small, 90% being under 10 μm, with
an average diameter ranging from 0.3 to 0.5 μm [1]. On
the other hand, the number of particles present in the
prosthetic chamber and in the adjacent spaces ranges
from billions to trillions [2]. These microparticlesaccumulate in the prosthetic chamber and determine a
foreign body type of response from the host, such as
inflammatory reactions. The intensity of the inflammatoryresponse depends on the sizes of the microparticles and
their composition, but most of all on their number. The
cells involved in the processes are macrophages (thatmigrate in order to phagocytate microparticles), as well
as fibroblasts and osteoclasts. The response of the host
organism involves local release of numerous enzymes,cytokines, mediators and growth factors. The local
inflammatory reaction leads to osteolysis and, in time, to
the mobilization of the prosthesis components(loosening), which makes necessary its removal and
replacement with another one, with optimal intraosseous
fixation.
The search for an optimal friction torque, which would
generate fewer microparticles and thus ensures a longer
use of arthroplastic implants represents an ongoingconcern for biomaterial researchers, orthopaedic
specialists and manufacturing companies. The most
recent material to enter the array of arthroplastictherapeutic techniques is ceramicized metal – zirconia,
which is used in hip and knee replacements, in
combination with cross-linked polyethylene.
Experimental part
Our objective was to compare the polyethylene wear
of ceramicized metal heads on polyethylene cups withthat of cobalt chromium metal heads on polyethylene cups
in total hip arthroplasties.
Material and methods
48 subjects with primary osteoarthritis of the hip were
included in a prospective study: in the first group, consistingof 24 cases, we performed total hip replacement with
uncemented prosthesis with ceramicized friction torque
(zirconium – zirconium oxide)/ polyethylene, while in thesecond group, also consisting of 24 subjects , uncemented
prostheses with a standard metal head (cobalt chromium)
on polyethylene cups were implanted. Selection forinclusion in one or the other of the two groups was
randomized, based on the last digit of the patient’s Social
Security number: if the digit was even, the patient wasincluded in the first group, and if it was odd, he was selected
for the second one. In Group 1 the average age was 41.6
years (range: 25 – 63) and the distribution based on genderwas 14 women / 10 men, while in Group 2 – the mean age
was 43.4 years (range: 27 – 65) and the gender based
distribution was 15 females / 9 males. Average follow-upperiod was 2.1 years (range: 37 months – 14 months). The
Harris Hip Score was determined before surgery, at one, 2
and 3 years after surgery. Standardised digital antero-posterior and lateral view hip X-rays were obtained
immediately after surgery, 6 months after surgery and each
year after that. Digital measurements were performed inorder to quantify the linear wear between two radiological
examinations.
Results and discussions
At the end of the study period, data from 19 subjects in
Group 1 were available and from 17 patients belonging toGroup 2. The Harris Score increased in Group 1 from a
preoperative 54.71 +/- 5.61 to 94.32+/-3.86 at the final
check-up, and in Group 2 from 53.46 +/- 6.37 to 91.65 +/- 4.36. The difference between the Harris Hip Scores in the
two Groups at final check-ups was not statistically
significant (p>0.1). The linear wear 1 year postoperativewas 0.02 mm in Group 1 (range: 0 – 0.05) and 0.07 mm in
Group 2 (range: 0 – 0.15) (statistically significant difference,
p<0.05), while at 2 years after surgery the linear wear

MATERIALE PLASTICE ♦ 50♦ No. 3 ♦ 2013 http://www.revmaterialeplastice.ro 308
Fig. 1. Heads with ceramicized metal layer on femoral stems
Fig. 2. Metallic femoral heads with a layer of ceramicized metalFig. 3. Zirconia / polyethylene friction couple (metallic femoral
head with a zirconia layer in an acetabular cup – the metal back
was cut-off in order to visualize the polyethylene cup inside it)
was 0.07 (range: 0 – 0.11) in Group 1 and 0.18 mm for
Group 2 (range: 0 – 0.25) (statistically significant difference,p<0.05).
Zirconia is a ceramic compound consisting of zirconium
dioxide (ZrO
2). Zirconium is a strong transition metal, with
an atomic number of 40 and atomic mass of 91.224. It is
one of the most biocompatible metals available (titanium,
zirconium, vanadium and niobium). The biocompatibilityof these metals is ensured by their resistance to corrosion,
and by the fact that they have no evident role in the living
world.
Hip prostheses with a ceramicized metal/ polyethylene
friction torque have a layer of zirconia (brand name –
oxinium – Smith & Nephew Inc, 1450 Brooks Road,Memphis, TN 38116, USA) on the surface of the metal
femoral head (fig. 1). The metallic component of oxinium
consists in 97.5% zirconium and 2.5% niobium (a metalwith high biocompatibility as well). This layer is obtained
by saturating the superficial zirconium metallic layer with
oxygen at a very high temperature, until it becomes a layerof zirconia – ceramic material. This layer is very thin – 5
nm, but it is very strongly fixed to the underlying metal, as
it is not applied to, but an integral part of the prosthetichead (fig. 2). This prosthetic head is covered by 3 layers:
the superficial ceramic layer (ceramicized metal), an
intermediate layer rich in oxygen, and the deep, non-oxygenated layer. In the intermediate metallic layer, the
hardness of the material diminishes progressively, ensuring
a systematic transition from the hardness of the superficialceramic material to the metallic core, maintaining its
elasticity.
The theoretical advantages of ceramicized metal are:- higher mechanical resistance and hardness than
cobalt-chromium alloys (theoretically it erodes and formsmicroparticles slower, it is not frail and not prone to
catastrophic fractures – like usual alumina ceramic);
– smoother surface with superior lubrication – the surface
is hydrophilic (it forms fewer polyethylene microparticles
through abrasion); the friction coefficient of zirconia/polyethylene is approximately half of that of cobalt-
chromium alloy/ polyethylene (fig. 3);
– it contains zirconium and niobium, metals found at the
top of the biocompatibility scale (they do not determine
hypersensitivity reactions like those inflicted by chromium
or cobalt);
– allows the manufacturing of femoral heads with a wide
range of sized necks (fig. 4) (which is also possible in the
case of standard cobalt-chromium alloy metallic heads,but not in the case of alumina type ceramic/ aluminium
oxide heads, due to the danger of breakage).
Compared to ceramic- alumina type total hip prostheses
there is another advantage as well – the polyethylene cups
can be manufactured in different constructive variants –
with an anti-luxation ring, semi-retentive or retentive (whichis not possible for alumina cups, due to the frailty of the
material) (fig.5).
In order to verify if these in vitro demonstrated
advantages have an in vivo correspondent, we attempted
to prospectively compare ceramicized metal/polyethylene
friction torque prostheses with those with cobalt-chromiumalloy/polyethylene. We used clinical criteria quantified by
the Harris Hip Score – the presence of pain and its
characteristics, patient’s ability to perform usual activities(walking, climbing stairs, ability to sit, presence of limping,
need for support – crutch or stick etc.) and hip mobility. Its
values range from 0 to 100 points. Depending on theirnumerical values, the results are considered as low (<70
Fig. 4. Prosthetic femoral component with metallic heads (with
ceramicized metal layer) of different sizes and different necks
lengths

MATERIALE PLASTICE ♦ 50♦ No. 3 ♦ 2013 http://www.revmaterialeplastice.ro 309points), satisfactory (70-79 points), good (80-89 points) or
excellent (over 90 points). Short-term results were
excellent in both groups.
In terms of clinical results, there are no statistically
significant differences between the two types of friction
torques.
In order to determine the wear of the polyethylene cup,
we used digital measurements on Dicom type images,
performed under standard conditions, on the same non-
portable radiological machine, for all patients. Thesemeasurements showed a more intense wear of the
polyethylene cups in a torque with cobalt-chromium alloy.
The differences are not statistically significant. A faster wearimplies a more accelerated production of polyethylene
microparticles, a more intense inflammatory response from
the host tissues, osteolysis and mobilization of theprosthesis in time. It is worth mentioning that, up to the
final radiological check-up, there were no periprosthetic
osteolysis areas and no reinterventions required. Furtherfollow-up of the groups will allow us to see if there is a
correlation between the accelerated production of
microparticles demonstrated by radiological findings andthe development, in time, of osteolytic areas.
Another issue we should consider is that of
hypersensitivity reactions determined by some of themetals used for arthroplastic or osteosythesis implants.
Metals most frequently associated with this type of
reactions include nickel, cobalt, chromium and beryllium,in this order. The incidence of sensititivity to metals among
the general population is approximately 10% – 15%, with
the majority of hypersensitivity reactions being determinedby nickel (approximately 14%) [4]. When interacting with
biological systems, metals suffer a corrosive process. As aresult of this, metallic ions are released, which can spread
in the entire organism, determining remote lesions or form
compounds in combination with proteins, which can actas allergens, triggering an immune response from the host.
The reactions determined by orthopaedic implants are,
generally, of type-IV delayed-type hypersensitivity (DTH)[5]. The antigen (the metal contained in the metal-protein
compounds) activates sensitized T lymphocytes, which
release cytokines and determine the recruitment andactivation of macrophages [5].
Ceramicized metal hip prostheses contain only
zirconium and niobium, metals with high biocompatibility,while standard prostheses contain cobalt, chromium and
very small quantities of nickel. In our series there were no
cases of hypersensitivity reactions to metal reported; apossible track for future research can refer to skin reaction
testing for the metals contained in the prosthesis, prior to
its implantation.
Conclusions
The clinical results obtained with the two types of
prostheses (ceramicized metal head/ cross-linked
polyethylene cup and cobalt chromium alloy head/ high
molecular weight polyethylene cup) overlap, nostatistically significant differences between them being
reported.
The rate of polyethylene wear is significantly higher in
the cases with cobalt chromium alloy/ high molecular
weight polyethylene compared to those with ceramicized
metal / cross-linked polyethylene.
References
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Manuscript received: 20.05.2013Fig. 5. Total hip prosthesis with ceramicized metal layer on the
metal heads and polyethylene cup (the metal back was removed)