on line editionThe innovation trap: modular neck in total hip arthroplasty
Review aRTicle
id
1 Department of 
Orthopaedics, Division 
of Surgery, University 
Medical Centre Maribor
2 Valdoltra Orthopaedic 
Hospital, Ankaran, 
Slovenia
Correspondence:
Samo K. Fokter,  
e: samo.fokter@guest.
arnes.si
Key words:
hip arthroplasty; 
modular neck 
fracture; titanium-
alloy; complications 
of arthroplasty; 
arthroplasty registries
Cite as:
Zdrav vestn. 2017;  
86: 115–26.
Received: 1. 9. 2016 
accepted: 16. 2. 2017
NeurobiologyReview article Zdrav vestn | March – april 2017 | volume 86
The innovation trap: modular neck in total 
hip arthroplasty
Samo K. Fokter,1 vesna levašič,2 Simon Kovač2
Abstract
Background: Innovations play a key role in the success of orthopeadic surgery. However, even minor 
modifications in the established concepts and designs may result in disasters. We face an endemic of 
modular femoral neck failures occurring in fully modular total hip arthroplasty (24 of approx.4000 
implanted), which has been popular in Slovenia for the last 20 years. Its most unfortunate conse-
quences challenge us to seriously address this problem. The aim of this report was to analyse the vol-
ume, and the causes of the problem, on the one hand, and to propose possible solutions, on the other.
Methods: The literature was searched for problems associated with Profemur Z fully-modular femo-
ral stem, made of titanium alloy (Ti6Al4V)or earlier versions with the same taper-cone design.The 
available hip arthroplasty registries were used to determine failure rates associated with the above 
mentioned design. The mechanisms of failure were studied in order to get in-depth understanding 
of this hip reconstruction device.
Results: Since 2010, several case reports on catastrophic modular femoral neck fractures of Pro-
femur Z have been published. In Slovenia the first case was described in 2012. The first two large 
series with modular femoral neck fractures were reported in 2016. The Australian Joint Replacement 
Registry was the first to discover elevated revision rates due to fractures of this hip reconstruction 
system. In 2010, the Agency for Medicinal Products and Medical Devices of the Republic of Slovenia 
(JAZMP) received the first 2 reports on Profemur Z modular neck complications, submitted by for-
eign institutions. The first Slovenian report dates back to 2012, and altogether 7 reports from Slovene 
hospitals had been received by December 2016. Corrosion at the neck-taper interface, where two 
equal or different materials are subject to constant wear in the presence of body fluids, was assumed 
to be responsible for the unacceptably high failure rates.
Conclusions: Manufacturers are responsible for producing and marketing safe devices. However, 
orthopaedic surgeons should carefully monitor all innovations for any adverse effects. JAZMP took 
appropriate measures only after receiving urgent field safety corrective notice from the manufacturer 
in 2015, stating that all lots of long modular necks made from cobalt-chromium alloy should be 
withdrawn. It should be noted here that the regulatory agency of the Republic of Slovenia was not 
receiving vigilance reports as appropriate, and was thus unaware of the dimension of this problem. A 
national arthroplasty registry would have most probably alerted the orthopaedic community to this 
questionable innovation earlier. Regulatory bodies should set up such a registry for the benefit of our 
patients as soon as possible.
Cite as: Zdrav Vestn. 2017; 86: 115–26.
on line edition Zdrav vestn | March – april 2017 | volume 86
NeuRobiology
Introduction
The primary goals of total hip ar-
throplasty (THA) include: pain reduc-
tion, range of motion improvement, and 
stability provision. Currently, we also 
aim to reach equal limb length and to 
restore the center of rotation. This goal 
is technically easier to achieve by using 
endoprostheses with modular necks, 
where the femoral component is com-
prised of two parts: the stem and the 
neck. The advantage of this design is 
that it allows the orthopaedic surgeon 
to choose intraoperatively the most suit-
able neck for the patient, independently 
of his or her stem size. In this manner, 
femoral offset and neck orientation can 
be adjusted more precisely. Important 
gender-specific anatomic differences ex-
ist regarding the femoral diameter, neck 
length and angle between the diaphysis 
and the neck (CCD angle) (1,2). Improp-
er biomechanical restoration after total 
hip arthroplasty could lead to limping 
and faster wear of the artificial joint. It 
has been shown that primary anatomic 
hip conditions could be restored in 50 % 
of patients using 8 versions of modular 
femoral necks (3).
Thanks to the above described ben-
efits, the popularity of modular femoral 
stems increased substantially over the 
last 30 years and they can now be found 
in the portfolio of practically all global 
producers of hip implants.
In the nineties, early modular femo-
ral stems GSP and later on, Anca-Fit 
(Cremascoli Ortho Company, Milan, 
Italy) with an oval Morse cone, which 
requires no additional screwing at cou-
pling, were increasingly used by the 
orthopaedic surgeons in Slovenia. The 
effective design provides good torsion-
al stability and simple intraoperative 
use  (4). The US Wright Medical Tech-
nology, Arlington, Tennessee, bought the 
Italian company in 2000. The company 
changed the design of the femoral stem 
but kept the original taper-cone and the 
material the GSP was made of, i.e. the ti-
tanium alloy (Ti6Al4V). The new prod-
uct Profemur Z, was placed on the mar-
ket in 2002. The longer variant (Profemur 
Z Revision), suitable for revision surgery 
with metaphyseal-diaphyseal femoral 
bone fixation, was introduced later on. 
Unlike some other models (Profemur E 
and Profemur L), both aforementioned 
models were available on the Slovenian 
market.
The taper-cone coupling between the 
femoral stem and modular neck is not 
ailment-free. It is subject to mechanical-
ly supported crevice corrosion, which is 
a combination of fretting corrosion and 
crevice corrosion, and may lead to failure 
of the modular neck (5). The first case re-
port on the Profemur Z modular femo-
ral neck failure was published in 2010, 
and the first case of the GSP modular 
femoral neck failure in Slovenia was re-
ported in 2012 (6,7). A doubled revision 
rate of fully modular THA due to dislo-
cation and aseptic loosening was docu-
mented by the Australian Orthopaedic 
Association National Joint Replacement 
Registry (AOANJRR) in 2010. After a 10-
year follow-up, the rate of revisions due 
to prosthesis fracture was higher with 
modular designs than with conventional 
models (1.3 % vs. 0.8 %) (8). Such sudden 
fracture of the modular femoral neck 
represents a catastrophic failure of the 
previously normally functioning THA. 
Also, it represents a most stressful expe-
rience for the patient, as it usually neces-
sitates a complete exchange of the femo-
ral component of the prosthesis (Figs. 1 
and 2).
The aim of this paper was to search 
the literature for information on prob-
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Figure 1: a Profemur Z 
implant femoral stem 
after explantation 
at the revision total 
hip arthroplasty. The 
fractured modular neck 
with a ceramic femoral 
head still attached.
lems arising from the use of Profemur 
Z, both in Slovenia and worldwide, in 
the period 2010–2016, and to propose 
solutions for earlier detection of similar 
complications associated with the use of 
“innovative” orthopaedic devices .
Methods
Using the keywords »modular neck 
failure«, »GSP«, »Anca Fit« and »Profe-
mur Z«, the PubMed, Scopus and Google 
Schoolar databases were searched for 
cases reported in the literature. From the 
collected articles, common characteris-
tics of patients were retrieved, focusing 
on the causes of this treatment compli-
cation. We obtained information on po-
tential complications of this fully modu-
lar primary total hip arthroplasty from 
all Slovenian hospitals.
We also reviewed the published re-
ports of national arthroplasty registries 
with emphasis on the fully modular 
prosthesis design. We examined the data 
provided by the Valdoltra Orthopaedic 
Hospital Arthroplasty Registry and the 
Library of Implants of Valdoltra  (9), as 
well as by the Public Agency for Me-
dicinal Products and Medical Devices of 
the Republic of Slovenia (JAZMP). We 
collected data related to incidents with 
medical devices of the manufacturer 
Wright Medical (from 2014 MicroPort 
Orthopedics Inc., USA) in Slovenia.
In addition, we reviewed The Manu-
facturer and User Facility Device Expe-
rience (MAUDE) database of the Food 
and Drug Administration (FDA), U.S.A., 
for the period 2000–2016 using the key-
words »Profemur« and »fracture« (10).
Results
Literature search
A total of 9 articles reporting modu-
lar neck fractures were found (6,7,11-17). 
In the first 8 articles, 13 patients (11 pa-
tients with Profemur Z and 2 patients 
with GSP, ) with modular femoral neck 
fracture were described (Table 1). All 
the patients were males who experi-
enced modular femoral neck fracture 
4.4 years after the primary THA (mean 
range 2–12 years). Their average body 
mass index (BMI) was 31.6 kg/m2 (range, 
26–39.3 kg/ m2). In all the patients, a long 
modular neck was implanted.
Pour et al. described fracture of 
7 necks in the group of 242 patients 
(277 hips) treated with fully modular 
Profemur E (170 endoprostheses) and 
Profemur Z (107 endoprostheses) THA 
in the period 2003–2009 with the av-
erage follow-up of 50 months  (17). In 
the Profemur E group, revision surgery 
was necessary in 15 (9 %) hips because 
of aseptic loosening. In the Profemur Z 
group, revision was required in 6 (6 %) 
hips because of fracture of the modu-
lar neck. Interestingly, only one (0.6 %) 
hip was revised because of modular 
neck fracture in the Profemur E group. 
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NeuRobiology
Figure 2: a fractured 
modular femoral neck. 
The distal part is still 
in the female part of 
the Morse taper of the 
femoral stem.
All fractures occurred in long modular 
necks (17).
Registry reports
According to the 2013 annual report 
of the Australian arthroplasty registry 
(AOANJRR) the proportion of revi-
sions of modular prostheses with the 
exchangeable neck compared to those 
with a single-piece (monoblock) femoral 
stem had been on a continuous increase 
over the previous 4 years. The cumula-
tive percentage of revisions during the 
10-year follow-up period was 6.4 % with 
monoblock stems and 10.8 % with mod-
ular stems. The Australian registry also 
found that the combination of a titani-
um-alloy stem and a cobalt-chromium 
alloy modular neck was associated with 
a higher revision rate than the combina-
tion of titanium-alloy femoral stem and 
a titanium-alloy modular neck (8).
In Europe, reports on fully modular 
stems are found in the arthroplasty reg-
istries of Italy, where they were initially 
manufactured by Cremascoli Ortho 
(Registries of Lombardy and Emilia Ro-
magna), as well as in Great Britain, Fin-
land, Lithuania, the Netherlands, Slova-
kia, France and Spain. On the initiative 
of Prof. Labek, the then Head of the Eu-
ropean arthroplasty registry, the Croa-
tian Institute for Public Health launched 
the project PARENT (PAtient REgis-
tries iNiTiative) involving a statistical 
analysis of the data retrieved from the 
registries ROLP (Registro Ortopedico 
Protesico Lombardo) from Lombardy, 
Italy, Great Britain, Finland, Lithuania, 
Slovakia, France and Slovenia (Valdol-
tra). A total of 41,694 femoral stems with 
modular necks were analyzed. The re-
sults of the analysis were presented at 
the congress of the European Associa-
tion of Orthopedics and Traumatology 
(EFORT) in Prague in 2015. The analysis 
did not confirm the conclusions of the 
Australian registry, except in Finland, 
which had the highest rate of revisions 
of modular femoral stems (i.e. 7.18 % at 
12 years) and 8 implant fractures in 543 
primary THAs.
In registry analyses it is particularly 
difficult to determine which part of the 
implant was broken, because most reg-
istries do not distinguish between these 
entities. The heading »implant fracture« 
therefore also encompasses breaks of the 
ceramic head of the older generation, 
which is a more frequent cause of the in-
cident than a modular neck fracture.
The Valdoltra survey was presented 
at the Valdoltra Orthopaedic Hospital 
Research Day in 2014. In a total of 1,057 
primary THAs using the Profemur Z 
modular femoral stems, 3 fractures of the 
modular neck occurred; all necks were 
made of a titanium alloy. The overall 
survival at 11.5 years, irrespective of the 
cause of the revision, was 94.5 % (± 3.1 % 
C.I.), which did not stand out compared 
with other types of primary THAs (18).
In 2010, JAZMP received 2 reports 
on the incident with the medical device 
Profemur long varus / valgus modular 
neck from abroad, whereas the first na-
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tional report on the modular neck frac-
ture was submitted in 2012. In 2013, two 
Slovenian hospitals reported on 3 modu-
lar neck fractures, in 2014, a report was 
received on the fracture of one modular 
neck, and in 2016, fractures of 2 modular 
necks made of cobalt-chromium alloy 
were reported. In August 2015, the autho-
rized representative of the manufacturer 
(MicroPort Orthopedics BV, Nether-
lands) informed JAZMP of the initiation 
of the recall for the long modular neck 
made of cobalt-chromium alloy because 
of fracture risk. In 2015, JAZMP was no-
tified that the medical device had been 
recalled. The fact that 2 vigilance cases 
were reported in 2016, clearly indicates 
that in 2015 the Slovenian distributor 
Mark Medical d.o.o., Sežana did not send 
the emergency recall notification issued 
by the manufacturer of the device to all 
hospitals in Slovenia, but only to those 
having the incriminated medical devices 
still in stock. At the request of JAZMP, in 
2016, the distributor informed about the 
recall the rest of Slovenian hospitals.
Tabela 1: objavljeni prikazi primerov zlomov izmenljivih vratov.
Author (year of 
publication) 
Age (years) Body mass 
index 
(kg/m2)
Time to 
failure 
(years)
Size of 
femoral 
component
Neck 
length and 
orientation
Articulation
wright et al. (2010) 49 39.3 4 4 long, varus 
anteverted
MoM
atwood et al. (2010) 30 29 2 Na long, straight coc
wilson et al. (2010) 62 25.6 2 5 long, 
retroverted
coc
Dangles and altstetter 
(2010)
63 Na (127,6 kg) 3.5 Na long, 
retroverted
MoM
Skendzel et al. (2010) 55 31.2 3,7 Na long, varus NP
67 34.6 3,4 Na long, varus NP
ellman and levine (2013) 59 29.6 5 3 long, varus MoM
vučajnk and Fokter (2012) 56 32 12 5 (gSP) long, straight coc
Fokter et al. (2016) 42 30 3.1 6 (gSP) long, straight MoP
54 33 2.3 6 long, straight coc
57 35 5.2 5 long, straight MoP
37 34 6 8 long, straight coc
51 26 4.8 5 long, straight coc
NA – not available; CoC – ceramic-on-ceramic; MoM – metal-on-metal; MoP – metal-on-polyethylene
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Table 2: Patients with modular femoral neck fractures treated in Slovenia
Case Gender BMI 
(kg/m2)
Time to 
revision 
years)
Acetabular 
component: 
manufacturer; model, 
diameter (mm), inlay
Femoral part: 
manufacturer; 
model, size
Neck: 
length, 
orientation, 
material
Head: 
diameter (mm), 
material, length in 
mm, (description)
1 M 30 3.1 co;
RcM 56, Poly
co;
gSP #6
long, 
straight, Ti
28, cocr,
+3.5 (l)
2 M 33 2.3 wMT;
eHS 54, cer
wMT;
Profemur Z #6
long,
varus, Ti
28, cer,
0 (M)
3 M 35 5.2 wMT;
eHS 54, Poly
wMT;
Profemur Z #5
long,
varus, Ti
28, cocr,
0 (M)
4 M 34 6 wMT,
eHS 52, cer
wMT;
Profemur Z #8
long, 
straight; Ti
28, cer,
0 (M)
5 M 26 4.8 wMT;
Procotyl l 52, cer
wMT;
Profemur Z #5
long, 
straight, Ti
36, cer,
0 (M)
6 F 39.4 7.8 wMT;
eHS 50, cer
wMT;
Profemur Z #6
long, 
straight; Ti
28, cer,
+3.5 (l)
7 M 30.3 4.5 biomet;
eternity 54, cer
wMT;
Profemur Z-R #6
Short, 
straight, Ti
36, cer,
+3.5 (l)
8 M 33.8 2.8 ZiM; allofit 52, 
X-Poly
wMT;
Profemur Z #5
long,
varus, Ti
36, cocr,
0 (M)
9 M 25.2 3.9 wMT;
eHS 52, cer
wMT;
Profemur Z #6
long,
varus, Ti
28, cer,
-3.5 (S)
10 F 31.9 8.8 wMT;
eHS 52, cer
wMT;
Profemur Z #3
long, 
straight, Ti
28, cer,
+3.5 (l)
11 M 32 12 co;
anca Fit 56, cer
co;
gSP #5
long, 
straight, Ti
28, cer,
+3.5 (l)
12 F 29.3 3.3 wMT;
Procotyl l 48, cer
wMT
Profemur Z #3
long, 
straight, Ti
32, cer,
-3.5 (S)
13 M 32.1 6.0 wMT;
eHS 56, Poly
wMT
Profemur Z #4
long,
varus, Ti
28, cer
0(M)
14 M 25.1 3.9 wMT
Procotyl l 56, Poly
wMT
Profemur Z #6
long,
varus, Ti
36, cer
+3.5(l)
15 M 29.2 5.9 wMT;
eHS 56, cer
wMT
Profemur Z #3
long,
varus, Ti
28, cer
+3.5 (l)
16 M 33.2 4.8 wMT;
eHS 56, Poly
wMT
Profemur Z #7
long,
retroverted, 
Ti
28, cer
-3.5 (S)
17 M 30.7 3.1 wMT;
Procotyl l 48, cer
wMT
Profemur Z #3
long,
varus cocr
32, cer
0 (M)
18 M 35.6 3.2 wMT;
Procotyl l 58, Poly
wMT
Profemur Z #4
long,
varus cocr
36, cer
-3,5 (S)
19 M 26 2.0 wMT;
Procotyl l 52, Poly
wMT
Profemur Z #5
long,
varus, cocr
32, cer
0 (M)
20 M 31 5.1 wMT,
Procotyl l 60, cer
wMT
Profemur Z #7
Dolgi,
retroverted, 
Ti
36, cer
0 (M)
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FDA MAUDE base
The FDA MAUDE database for the 
voluntary reporting of adverse events by 
the U.S.A. professionals, received at least 
41 reports on fractured THA modular 
necks during the period 2010–2016 (10).
Modular neck fractures in Slovenia
By the end of July 2016, a total of 24 
modular femoral neck fractures oc-
curring after THA had been reported 
in Slovenia: 9 were revised in the Celje 
General Hospital, 7 in the Maribor Uni-
versity Medical Center, 4 at the Ljubljana 
Department of Orthopedic Surgery, 3 in 
the Valdoltra Orthopaedic Hospital, and 
one in the Murska Sobota General Hos-
pital. According to the representative 
who marketed modular femoral stems 
in Slovenia, 3,244 Profemur Z modular 
necks were delivered from 2006 to the 
end of marketing, in 2015; for the older 
versions (GSP and Anca Fit) data were 
no longer available. Assuming that all 
those Profemur Z modular necks have 
actually been implanted, the percentage 
of modular neck fractures is 0.68 % (22 
fractures of the 3244 implanted prosthe-
ses). The figure is likely to represent the 
real rate of these events, because frac-
tures of the Profemur Z modular neck, 
which had been on the Slovenian market 
since 2003, never occurred later than 9 
years after the primary THA. Accord-
ing to the literature data, the majority of 
fractures occurred in males (21 out of 24 
cases). Most patients were overweight, 
with the average BMI 31.1 (25.1 to 39.4) 
kg/m2. In 23 cases, a long neck has been 
used; a short neck has been implanted 
only in one case. Most necks were made 
of the titanium alloy (21 modular necks) 
and only 3 necks were made of cobalt-
chromium (CoCr) alloy. Detailed data 
on patients and implants are summa-
rized in Table 2.
Discussion
The concept of interchangeable necks 
represents a useful solution for total hip 
arthroplasty in cases where anatomical 
conditions are not ideal, e.g in dysplas-
tic arthritis. Understandably, it was first 
used in revision arthroplasty and then 
also in younger arthroplasty patients 
with greater expectations for an active 
lifestyle after primary THA.
Modern uncemented hip endopros-
theses are mainly made of titanium al-
Case Gender BMI 
(kg/m2)
Time to 
revision 
years)
Acetabular 
component: 
manufacturer; model, 
diameter (mm), inlay
Femoral part: 
manufacturer; 
model, size
Neck: 
length, 
orientation, 
material
Head: 
diameter (mm), 
material, length in 
mm, (description)
21 M 31 6.9 wMT,
Procotyl l 56, Poly
wMT
Profemur Z #8
long,
varus, Ti
36, cer
+3.5 (l)
22 M Na Na wMT,
Na
wMT
Profemur Z #NP
long, Na, Ti Na
23 M Na Na wMT,
Na
wMT
Profemur Z #NP
long, Na, Ti Na
24 M Na Na wMT,
Na
wMT
Profemur Z #NP
long, Na, Ti Na
BMI–body mass index; CO–Cremascoli Ortho; WMT–Wright Medical Technology; ZIM – Zimmer; CoCr – cobalt-chrome alloy; Cer – 
Ceramic; Poly – polyethylene; X-Poly – cross-linked polyethylene; Ti–titanium alloy; NA – not available.
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loys. Titanium alloys are slightly less 
strong than cobalt alloys, but the modu-
lus of elasticity of the former is closer to 
the bone than the modulus of elasticity 
of cobalt alloy. Moreover, they are dis-
tinguished by a high level of bio-com-
patibility, and good corrosion resistance 
provided by the passive layer of titanium 
oxide on their surface. Endoprosthesis 
may be subject to various forms of cor-
rosion, such as crevice corrosion, and 
fretting, pitting and galvanic corrosion. 
The use of titanium alloys for the man-
ufacture of modular femoral necks was 
therefore a logical choice of many manu-
facturers. Unfortunately, it soon became 
clear that at the site of the contact be-
tween the femoral stem and the modular 
neck, an unexpected and rapid onset of 
corrosion may occur, resulting in frac-
ture of the neck despite the same ma-
terial used. Grupp et al. reported on 68 
modular titanium-alloy neck fractures 
in 5,000 necks implanted (1.4 %) occur-
ring on average 2 years after the implan-
tation of the Metha hip stem (Aesculap 
AG, Tuttlingen, Germany). The device 
was therefore removed from the mar-
ket  (19). The analysis of the fractured 
necks revealed micro cracks due to stress 
corrosion on the surface. At the modular 
neck-stem junction, fretting corrosion 
is followed by crevice and pitting corro-
sion: the modular neck is load-deflected 
and rubbed at the taper interface. This 
type of corrosion leads to continuous 
removal of the passive protective layer 
on the surface of titanium alloy. The au-
thors, therefore, recommended, that in 
patients with a high BMI, modular necks 
made of cobalt alloys should be used, 
because they are distiguished by better 
resistance to fretting corrosion, greater 
strength, higher modulus of elasticity, 
greater abrasion resistance and lower 
rate of crack propagation. Unfortunately, 
the combination of cobalt-chromium 
modular necks and titanium-alloy stems 
proved to be problematic. Femoral cal-
car erosion, pseudotumour formation 
and accelerated fretting corrosion have 
been reported (20,21). In addition, local 
toxicity of cobalt ions released by the ad-
ditional galvanic corrosion at the modu-
lar neck-stem junction of the Rejuvenate 
prosthesis (Stryker, USA) was respon-
sible for 86 % of revision operations re-
quired on average 4 years after primary 
THA  (22). Accelerated corrosion at the 
trunnion of a titanium-alloy stem and a 
modular neck made of cobalt-chromi-
um alloy may cause an even faster col-
lapse of otherwise stronger cobalt-chro-
mium necks. Menciere et al. reported on 
a collapse of modular cobalt-chromium 
neck, which occurred only 22 months af-
ter a THA with a Profemur L prosthesis, 
performed in a women with a low level 
of physical activity and a BMI of 28.7 kg/
m2 (23). Our first patient who sustained 
fracture of cobalt-chromium modular 
neck only 2 years after the implantation 
had only a minimally elevated BMI (26 
kg/m2). The manufacturer’s recommen-
dation to implant long modular necks 
made of cobalt-chromium alloy instead 
of titanium alloy was therefore com-
pletely inappropriate.
The analysis of modular neck frac-
tures pointed out that the complication 
was due to similar factors: corrosion at 
the modular neck-stem junction and 
overload of the modular neck, that un-
doubtedly accelerated the corrosion 
processes, causing larger bending of the 
neck in the taper. Thus it is not surprising 
that our patients who sustained modular 
neck fracture had increased BMI. In ad-
dition, a higher torque is known to ac-
celerate fracture, so the majority of the 
fractures occurred in THA using a long 
neck component. The bending moment 
with a long neck is 32 % higher than with 
a short neck  (14). A study published in 
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2017 found that in the patient with an 
implanted long modular neck a 30 % 
increase in body weight resulted in 2.45 
times greater load upon the site where 
the neck is locked on the femoral stem, 
as compared to the patient with an im-
planted short femoral stem (24). In our 
group of patients, fracture of the short 
modular neck occurred in one patient 
only, which is to some extent attributable 
to the use of a large femoral head (36 mm 
in diameter). Larger femoral heads exert 
greater stress on the implanted neck and 
may cause fractures of monobloc stems 
made of cobalt-chromium alloy (25).
The first to set up arthroplasty regis-
tries in Europe were the Nordic countries 
(Sweden, Finland, Norway, Denmark), in 
the eighties, followed by Hungary (1988), 
the Czech Republic (2001), Romania, 
Slovakia (2002), Austria, England and 
Wales (2003). Italy has two good re-
gional registries i.e. ROLP (Lombardy) 
and RIPO (Registro dell’implantologia 
Protesica Ortopedica, Emilia-Romagna), 
a national registry is still in the project 
phase. In Poland, Luxembourg and Cro-
atia national registries did not go beyond 
the project stage  (26). Slovenia belongs 
to a small group of European countries, 
including Bulgaria, Cyprus, Greece, Es-
tonia and Latvia, in which a functioning 
arthroplasty registry has not yet been es-
tablished.
The Arthroplasty Register of Slovenia 
(RES) is still in the deployment phase. It 
is aimed to monitor survival of implant-
ed hip and knee joint prostheses. It will 
thereby ensure quality control of arthro-
plasty and allow for earlier identification 
of poor-quality products and processes. 
This will reduce the cost of primary and, 
in particular, of revision hip and knee 
arthroplasties. The collected registry 
data will enable us to determine which 
implants are successful in the long term. 
A comparison with equal implants used 
in the countries with the established 
arthroplasty registries will thus be pos-
sible. By selecting better implants we will 
be able reduce the number of revision 
hip and knee arthtoplasties .
In order to standardize the data col-
lection process in the European Com-
mission PARENT project, coordinated 
by the Slovenian National Institute of 
Public Health (NIJZ), a »Questionnaire 
for device registries« was created. Under 
the PARENT project and in cooperation 
with the Valdoltra Hospital and NIJZ a 
hip arthroplasty RES database applica-
tion was developed. The largest propor-
tion of costs of the new database creation 
has already been covered. For the opera-
tion, the RES application will run on a 
server maintained by NJIZ; and data will 
be sent over the established secure con-
nections to all Slovenian hospitals. It is 
foreseen that database management will 
take place in the Valdoltra Hospital, an 
institution known for its 14-year experi-
ence in managing their hospital arthro-
plasty registry and for its active partici-
pation in designing the RES application. 
RES will be run by the Registry Com-
mittee and all the participant represen-
tatives of the major orthopedic institu-
tions, the Valdoltra Hospital, NIJZ, the 
Ministry of Health of the Republic of 
Slovenia, the Health Insurance Institute 
and the Slovenian Orthopaedic Associa-
tion involved in orthopaedic implantol-
ogy in Slovenia.
Until now, we have been dependent 
on the notifications received from for-
eign registries. The following is an ex-
ample we can learn from: in the U.S.A. 
the Articular Surface Replacement (ASR, 
DePuy) THA was implanted long af-
ter its use had been stopped in Sweden 
based on the first 329 registry reports . 
The registry detected an unacceptably 
high rate of early prosthesis loosening 
due to the ineffective design and inad-
on line edition Zdrav vestn | March – april 2017 | volume 86
NeuRobiology
equate material used. The revision hip 
arthroplasty rate in Sweden is one-half 
lower than in the U.S.A (3.2 % vs. 7.0 % in 
7 years) thanks to the data provided by 
the registry (27). In the States, a national 
register was created in 2010, but it does 
not yet include all hospitals in the coun-
try. In addition to the national registry, 
the Kaiser Permanente Implant Register 
and the local East Health Implant Regis-
ter have been established in the U.S.A., 
but they are owned by major health care 
companies.
The data of the Swedish registry can 
be translated into the Slovenian num-
bers as follows: for primary THAs a 
valid projection is from the current 
3,500 cases a year to 4,500 cases a year 
in 2050 and the estimated increase in 
the rate of revision operations (10–15 %) 
is from the currrent 440 to 560 in 2050.
(28) Assuming that each THA revision 
costs approx. 10,000  euros, excluding 
the costs of treatment-related social 
burden, let alone the patient’s suffering, 
one can easily calculate that a reduction 
in the number of THA revisions by 200 
interventions per year, as expected with 
the introduction of the national regis-
try, would save 2,000,000 EUR per year. 
This sum significantly exceeds the costs 
of maintaining the registry.
Conclusions
The Profemur endoprosthesis was 
designed as an innovative device, but 
because of the reported unanticipated 
fractures of modular femoral necks, 
it did not prove to be sufficiently safe. 
Unfortunately, shifting from titanium-
alloy modular necks to those made of 
cobalt-chrome alloy soon turned out to 
be a bad solution. The responsibility for 
producing and marketing safe products 
lies with the manufacturers or relevant 
institutions awarding certificates to 
producers. Doctors, however, must pay 
particular attention to potential adverse 
effects of newly introduced materials 
and designs of orthopedic implants. 
The history of orthopedics is criss-
crossed with bad innovations. In order 
to pinpoint them as soon as possible, 
arthroplasty registries were established 
in developed countries, and they are 
now being set up also in other areas of 
orthopedics.
The fact is that the Slovenian orthope-
dic community would have been much 
earlier alerted to the bad results of this 
problematic innovation, if a national ar-
throplasty registry had been established 
in Slovenia. Orthopaedic surgeons, who 
have been striving for this registry for 
many years, therefore request the re-
sponsible authorities to give full sup-
port to the establishment of a national 
arthroplasty register for the benefit of 
orthopedic patients in Slovenia.
Acknowledgements
The authors would like to thank Mar-
ko Kotnik, M.D., orthopaedic surgeon, 
Head of the Department of Orthopedics 
and Sports Injuries at the Celje General 
Hospital, primarius Slavko Kramberger, 
M.D., orthopaedic surgeon, Head of the 
Department of Orthopaedics at the Mur-
ska Sobota General Hospital, and Drago 
Dolinar, M.D., orthopaedic surgeon, 
Section A, the Department of Orthopae-
dic Surgery, Ljubljana, for the supplied 
data on modular neck fractures. Many 
thanks also go to Urška Ocvirk from the 
JAZMP Sector for medical devices for 
the data on vigilance cases relating to 
the Profemur Z endoprosthesis, and to 
the distributor of the THA models con-
sidered, for providing the number of the 
supplied modular necks.
on line editionThe innovation trap: modular neck in total hip arthroplasty
Review aRTicle
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