A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
595–603
MAGNETICALLY CONTROLLED GROWING RODS FOR THE
TREATMENT OF EOS: EXPERIENCE FROM A SINGLE CENTER
AND XPS SURFACE ANALYSIS OF THE RODS
MAGNETNO VODENE RASTO^E PALICE ZA ZDRAVLJENJE
ZGODNJIH SKOLIOZ: IZKU[NJE ENEGA CENTRA IN XPS
ANALIZE POVR[INE PALIC
Alja` Mer~un
1,2
, Robert Ko{ak
3
, Monika Jenko
3,4
, Janez Kova~
5
, Miha Vodi~ar
1,2*
1
Department for Orthopedic Surgery, University Medical Center Ljubljana, Zalo{ka cesta 9, 1000 Ljubljana, Slovenia
2
Medical Faculty, University of Ljubljana, Korytkova cesta 2,1000 Ljubljana, Slovenia
3
MD Medicina, Bohori~eva ulica 5, 1000 Ljubljana, Slovenia
4
MD-RI Institute for Materials Research in Medicine, Bohori~eva 5, 1000 Ljubljana, Slovenia
5
Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
Prejem rokopisa – received: 2022-07-16; sprejem za objavo – accepted for publication: 2022-09-22
doi:10.17222/mit.2022.565
The treatment of early-onset scoliosis (EOS) remains one of the biggest challenges in paediatric orthopaedics. Magnetically
controlled growing rods (MCGRs) have increased in popularity compared to traditional growing rods (TGRs), providing curve
correction, spinal growth and a reduction of the associated surgical trauma. Between May 2015 and July 2022, 24 patients with
EOS were treated with an MCGR system using a standardized implantation procedure. An ultrasonography- or radiogra-
phy-controlled distraction of 3 mm every 3 months was performed. Whole spine radiographs were taken pre-operatively,
post-operatively, and in six month interval. The Cobb angle, T1-S1 height, and growth were measured. All the patients had a
dual-rod construct implantation. The mean age of the surgical patients was 8 years (6–11), and the mean follow up was
39 months (2–84). The etiology of the EOS was syndromic in six patients, congenital in two, idiopathic in three and
neuromuscular in 12. One patient had a conversion from TGR, and one patient had a concomitant resection of hemivertebra. The
mean preoperative Cobb angle was 69° (30–108°), postoperative was 38° (16–66°), and 38° (9–69°) at final follow-up. The
mean pre-operative T1–S1 length was 289 mm, increasing to 326 mm post-operatively, and 353 mm at the final follow-up. The
mean spinal growth was 64 mm (26–110 mm). Two retrieved rods were examined using X-ray photoelectron spectroscopy
(XPS). A surface analytical technique to determine the surface chemistry after exposure of the rods in the body. The MCGR sys-
tem represents a safe and less invasive option for the treatment of EOS.
Keywords: magnetically controlled growing rods (MCGRs), early-onset scoliosis (EOS), growth guidance, spine deformity,
XPS
Zdravljenje zgodnjih skolioz ostaja med najzhtevnej{imi izzivi otro{ke ortopedije. Magnetno vodene rasto~e palice (MVRP) v
zadnjem ~asu vse bolj zamenjujejo tradicionalne rasto~e palice (TRP), saj omogo~ajo rast hrbtenice ob ustrezni korekciji krivine
in zmanj{anju {tevila kirur{kih posegov. Med majem 2015 in julijem 2022 je bilo z MVRP zdravljenih 24 pacientov z zgodnjo
skoliozo. Vzpostavljen je bil standardiziran protokol za implantacijo ter distrakcijo pod ultrazvo~no ali rentgensko kontrolo za
3 mm vsake 3 mesece. Rentgenski posnetki celotne hrbtenice so bili narejeni predoperativno, pooperativno in nato vsakih
6 mesecev. Merjene vrednosti so bile Cobbov kot, razdalja T1-S1 in rast hrbtenice. Vsi pacienti v seriji so imeli vstavljene
MVRP obojestransko. Povpre~na starost pacientov je bila 8 let (6-11 let), s povpre~nim sledenjem 39 mesecev (2–84 mesecev).
Etiologija skolioze je bila pri 6 pacientih sindromska, pri 2 pacientih kongenitalna, idiopatska pri 3 pacientih in pri 12 pacientih
nevromi{i~na. Pri enem pacientu je bila napravljena menjava iz TGR, en pacient je imel napravljeno dodatno resekcijo
hemivertebre. Povpre~ni predoperativni Cobbov kot je bil 69° (30–108°), pooperativni 38° (16–66°) ter 38° (9–69°) pri zadnjem
merjenju. Povpre~na predoperativna razdalja med T1 in S1 je bila 289 mm, 326 mm neposredno po operaciji ter 353 mm pri
zadnjem merjenju. Povpre~na rast je bila 64 mm (26 mm-110 mm). Dve palici po revizijskih operacijah sta bili raziskani s
povr{insko analitsko tehniko rentgenske fotoelektronske spektroskopije (XPS) z namenom ugotoviti kemi~no sestavo povr{ine
po izpostavi v telesu. Sistem MVRP predstavlja varno in manj invazivno mo`nost zdravljenja zgodnjih skolioz.
Klju~ne besede: magnetno vodene rasto~e palice, zgodnja skolioza, vodenje rasti, deformacija hrbtenice, XPS
1 INTRODUCTION
Magnetically controlled growing rods (MCGRs)
were developed to reduce the number of surgeries, the
concomitant morbidity and complications related to con-
ventional growing-rod treatment. While treatment with
traditional growing rods (TGRs) consists of an acute
scoliosis correction and repetitive re-operations (every
6–12 months) for growth guidance and deformity main-
tenance, a MCGR treatment can achieve the same goals
without repetitive surgeries.
1
Spinal growth enables the
development of the thoracic cavity and prevents thoracic
insufficiency syndrome (TIS), as well as cardiac, renal,
and neural axis anomalies.
2–5
Currently, only one MCGR system is available on the
market. The rod is made of a titanium alloy and contains
an enlarged part called 'the actuator,' which houses the
internal magnet and the distraction portion of the rod
Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603 595
UDK 616-089.23:616.711 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 56(5)595(2022)
*Corresponding author's e-mail:
miha.vodicar@kclj.si (Miha Vodi~ar)

(Figure 1). There are two types of rods: the standard and
the offset rod. They differ in the position of the actuator,
so that the standard rod distracts cephalad and the offset
rod distracts caudally. As the external magnet affects the
internal magnet, the internal magnet rotates and causes
the rotation of the lead screw and the inner portion of the
rod, causing the distraction. Rods can be lengthened with
a manual distractor (used only during surgery to test the
functionality of the rod) and with an external remote
control (ERC) (Figure 2). Once the rods are implanted,
an external magnet is used to locate the inner magnet,
hence determining the optimal position for the ERC. The
rod has a maximum extension of 48 mm. The number of
distractions and the timing of the distractions are decided
upon by the treating physician, based on the protocols
used, the patients’ deformity, and the condition. Distrac-
tions are performed in an outpatient setting, without the
need for anaesthesia, analgesia, or sedation.
6–8
MCGRs can be used on patients from the age of 2;
however, the general recommendation is to try other
measures first and wait with spinal instrumentation, pos-
sibly until the age of 7. At this age, firm fixation to the
spine should be achievable. Patients with early-onset
scoliosis (EOS) generally progress in their condition, and
need treatment to enable good lung and heart function.
Most of the patients have secondary scoliosis.
2,9
The MCGR was approved for clinical use in 2009,
and was improved two time, in 2010 and 2012. The im-
provements dealt with the stability of the implant to pre-
vent unwanted breaks or shortenings of the rods.
10
Our
institution began implanting the MCGR in 2015. We cur-
rently have 24 patients under our care. The purpose of
this paper is to present our experience with the MCGR,
to report our results, and present the results of an XPS
chemical analysis of the surface of two rods (Ti6Al4V
alloy) after exposure in the body and compare them with
literature data. The XPS analytical method providing
specific information on surface chemistry was applied
since we expected mainly changes in the surface region
of the rods and not in the bulk.
2 EXPERIMANTAL PART
2.1 Materials and methods
Twenty-four patients were treated with MCGR (The
MAGEC System, NuVasive inc., USA) at a single uni-
versity hospital paediatrics orthopaedics unit from May
2015 until July 2022. Indications for operative treatment
were congenital, syndromic, or neuromuscular progres-
sive EOS. All surgeries were performed by the same
team of two attendant surgeons. The analyses consisted
of pre-operative, post-operative, and the latest spine ra-
diographs. We determined the size of the deformity
(Cobb angle)
11
and the length of the spine (T1–S1
length). Magnetically guided spinal growth was averaged
for the T1–S1 length difference within the initial
post-operative and final follow-up period. Overall, the
A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
596 Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603
Figure 3: Pre-operative AP radiographs of patient with EOS
Figure 1: Illustration of MAGEC rod
Figure 2: External Remote Controller (ERC)

spinal growth (summary of intraoperative distraction and
magnetically guided growth) was averaged for the T1-S1
length difference between the pre-operative and final fol-
low-up period. We regularly monitored and treated ad-
verse events.
All the procedures were performed under total intra-
venous general anaesthesia (TIVA) in a prone position.
The surgery consisted of a double midline approach, at
the cranial and caudal portion of the deformity. Muscles
were prepared and the spine was exposed. Fixation was
primarily established with transpedicular screws. In
cases with increased thoracic kyphosis, sublaminar bands
were used on the most cranial levels to prevent further
kyphosis of the proximal unfixed spine. The levels of fix-
ation were individually determined given the type of de-
formity. In non-ambulatory patients, fixation to the pel-
vis was also considered an option. All patients had a
dual-rod implantation. We aimed to implant a standard
and an offset rod, and where that was anatomically im-
possible, two rods distracting in the same direction were
used. The size and shape of the rods were customized ac-
cording to the patient’s height and spinal deformity. All
the rods were tested for function with a manual distractor
before the implantation. A subfascial tunnel was made
and rods were inserted from the proximal to the distal
end of the fixation. Deformity correction to a possible
degree was performed using standard techniques (de-ro-
tation, translation, distraction/compression) and the rods
were firmly fixed to the anchors. Patients were hospital-
ized until in-patient lung function, wound closure, and
analgesia management were needed.
According to the surgeons’ protocol, the rods were
evaluated and distracted every three months by 3 mm.
For the distraction, patients were positioned prone, with
their chest and abdomen supported by a pillow. Patients
that cannot lie prone were distracted in lateral decubitus,
one side at a time. The internal rod magnets were identi-
fied using a hand-held magnet. A hand-held magnetic
ERC was placed over the internal magnet and 3 mm of
distraction was performed. We always distracted the rod
on the concave side of the deformity first. The distraction
was primarily controlled by ultrasonography, and a fol-
low up X-ray every 6 months. After the recommendation
of a follow-up X-ray at every 6 months, ultrasonography
was abandoned, and in case of doubt, X-ray was per-
formed sooner.
The X-ray photoelectron spectroscopy (XPS) analy-
sis of the chemical composition of the surface was car-
ried out on a PHI-TFA XPS spectrometer from Physical
Electronics Inc equipped with Al-monochromatic source
emitting photons with an energy of 1486.6 eV. The ana-
lyzed area was 0.4 mm in diameter. The surface compo-
sition was quantified from the XPS peak intensities by
considering the relative sensitivity factors provided by
the instrument manufacturer.
19
To analyze distribution of
elements in the sub-surface region up to 100 nm deep the
XPS depth profiling was performed in combination with
ion sputtering. The Ar ions with an energy of 3 keV were
used. The velocity of the ion sputtering was estimated to
be 2 nm/min, calibrated on a Ni/Cr multilayer structure
of known thickness. This velocity can be different for
other materials like a Ti6Al4V alloy by ± 30 %. We pre-
sented the XPS elemental depth profiles as a function of
depth to give a rough estimate of the analysed depth of
the surface region. The sensitivity of the XPS method is
about 0.2 at.%.
Two MAGEC rod samples were analysed in detail by
XPS: Ti6Al4V-1 sample and Ti6Al4V-2 sample. The
samples were produced in different series and extracted
from patients after applications. Every sample was ana-
lysed on the surface and at a depth of about 100 nm. XPS
depth profiles of the elements Ti, Al, V, O and C were re-
corded in the surface region from the surface to a depth
of 100 nm to follow depth distribution of the elements.
3 RESULTS
Seven patients were male, and seventeen were fe-
male. All the patients had dual-rod construct implanta-
tion, and in patient No. 1 a pre-existing TGR was ex-
changed with a MGCR. The mean age of the patients
during surgery was 8 years (5–11 years), and the mean
follow up period was 39 months (2–84 months). The
aetiology of scoliosis was syndromic in six patients, con-
genital in two patients, idiopathic in 3, while the remain-
ing 12 patients had neuromuscular aetiology.
A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603 597
Figure 4: Post-operative AP and lateral radiographs of the same pa-
tient with EOS

Table 1: Patient characteristics
Patient characteristics Mean (range)
Age (years) 8(5 −11)
Gender
7 males
17 females
Aetiology
13 neuromuscular
6 syndromic
2 congenital
3 idiopathic
Primary surgery 23
Exchange surgery 1
Follow-up (months) 39 (2−84)
Number of levels 14 (10−17)
Patient No. 1 had a broken actuator 4 years after sur-
gery, and had a rod exchange 55 months after the initial
implantation. Patient No. 5 had growing rods exchanged
because of an inability to distract. The underlying reason
was not found, even after further analysis. Patient No. 10
had a congenital kyphoscoliosis and additional resection
of hemivertebra L1 performed during the same proce-
dure. Patient No. 11 had a revision surgery 2 months af-
ter the initial procedure due to proximal junctional
kyphosis (PJK) with three levels extension of fixation
and kyphosis correction. Patient No. 12 had rods im-
planted upside down, due to anatomical conditions.
Lengthening of this patient was uneventful. Patient No.
14 had a subcutaneously contained cerebrospinal fluid
leak after the initial surgery, later a revision procedure to
shorten the rods cranially due to pain and cutaneous fis-
tula formation, and then another revision procedure with
sublaminar bands placement cranially due to PJK. Pa-
tient No. 16 had a revision procedure to remove the
screw that was causing local inflammation and wound
dehiscence. This patient also had implantation of
sublaminar bands at the two most cranial levels due to
increased kyphosis during initial surgery. Due to repeti-
tive wound dehiscence and sinus tract formation one
growing rod was explanted. Half of the patients had
screw placement in two cranial and two caudal vertebra,
and two patients had additional screw placement on one
side (cranial and caudal respectively) for construct
strengthening. Nine patients had fixation extended to the
ileum. The mean number of levels included in the con-
struct is 14 (10–17).
A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
598 Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603
Table 2: Results of 24 patients treated for early-onset scoliosis by magnetically controlled growing rods
Patient
No.
Curve convexity
(*C-shaped ex-
tending to pel-
vis)
Follow up
(month)
Preop.
Cobb
angle
Postop.
Cobb
angle
Last
Cobb
angle
Preop
T1-S1
distance
(mm)
Postop
T1-S1
distance
(mm)
Last
T1-S1
distance
(mm)
Magnetic
distraction
(mm)
Spinal
growth
(mm)
1 left* 84 53 51 51 337 350 352 30 43
2 right* 77 81 48 56 294 345 370 49 100
3 left* 83 72 NA 44 296 303 339 45 52
4 right* 66 88 48 43 NA 437 471 34 NA
5 left* 73 48 21 29 306 320 343 42 56
6 left* 63 86 55 65 242 286 322 46 90
7 left* 55 48 29 33 325 355 378 47 77
8 left* 54 96 60 54 257 298 336 57 98
9 left (s-shaped) 51 76 33 38 313 340 342 12 39
10
right* (hemi-
vertebra L1)
41 74 39 35 230 245 242 59 74
11 right* 39 63 42 37 298 302 328 26 30
12 left* 39 70 54 52 306 328 330 17 39
13 right* 38 100 66 67 NA 354 354 10 NA
14 left* 38 103 41 40 221 312 312 42 110
15 left* 37 54 30 32 290 303 310 40 53
16 left* 33 73 40 40 292 331 331 20 59
17 left* 22 79 30 24 235 329 343 14 108
18 right* 14 30 31 9 288 319 330 11 42
19 left* 11 54 27 16 293 311 NA 0 NA
20 left* 6 41 20 16 338 364 364 0 26
21
lumbar right,
thoracic left*
5 108 41 40 341 338 339 1 -2
22 left* 4 58 31 31 272 301 303 2 31
23 left* 4 45 30 30 303 323 323 0 20
24
lumbar left, tho-
racic right*
2 na 16 17 NA 370 371 1 NA
NA – no measurement available

3.1 XPS surface analysis of two MAGEC rod’s
3.1.1 Sample Ti6Al4V-1
Table 3 and Figure 5 show the chemical composition
of the sample Ti6Al4V-1 on surface and at depth of 100
nm. Figure 6a shows an XPS spectrum from the surface
of this sample. The sample Ti6Al4V-1 contains on the
surface mainly O and C, which are related to a presence
of Al/Ti-oxide and/or surface contamination. Other ele-
ments present on the surface of the Ti6Al4V-1 sample
were Ti, Al, N, Si, Ca, Fe and Zr. Elements S and Zn
were detected in trace amounts. V was not detected on
the surface at a concentration larger than 0.2 at.%, which
is the sensitivity of the XPS method.
After removing a 100-nm-thick layer, an accurate
analyses of the chemical composition was performed
again. Figure 6b shows an XPS spectrum from a depth
of 100 nm into this sample. At a depth of 100 nm the ele-
ments O, Ti, Al, and C were detected. In addition, N, V,
Zr and Fe were also detected at a depth of 100 nm to a
smaller extent (1–2 at.%).
An XPS depth profile of the sub-surface region of the
Ti6Al4V-1 sample is shown in Figure 7. It can be seen
that at depth of 100 nm a high concentration of O is still
present. This is probably related to the Al oxide, since
the Al 2p spectrum is mainly at 74 eV related to the Al
3+
oxidation state.
19
The Ti 2p spectrum at a depth of 100
nm is centered at 454 eV, which suggests the Ti-metallic
state.
19
Also, the ratio between Ti and Al seen in Figure 7
A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603 599
Figure 6: a) XPS spectrum obtained on the surface of the sample Ti6Al4V-1, b) XPS spectrum obtained at depth of 100 nm of the sample Ti6Al4V-1
Figure 5: Chemical composition of sample Ti6Al4V -1 in at.%, on surface and at depth of 100 nm
Table 3: Chemical composition of sample Ti6Al4V-1 in at.% on surface and at a depth of 100 nm
Depth (nm) C O Ti Al V N Si Ca Fe Zn Zr S
Surface 57.4 29.3 1.7 1.5 4.7 2.7 1.2 0.4 0.5 0.2 0.5
Depth of 100 nm 9.1 39.5 27.4 18.7 1.5 1.6 0.4 0.6 1.2

indicates an enrichment of Al oxide in the 100-nm-thick
layer with respect to Ti, as one would expect for the
Ti6Al4V alloy, and should be much higher.
3.1.2 Sample Ti6Al4V-2
Table 4 and Figure 8 show the chemical composition
of the sample Ti6Al4V-2 on the surface and at a depth of
100 nm. Figure 9a shows an XPS spectrum from the
surface of this sample. XPS analyses on sample
Ti6Al4V-2 were performed in a similar manner as an-
other sample. On the surface, mainly O and C are pres-
ent, which are related to the Ti oxide and/or surface con-
tamination. Other elements present on the surface of the
TiAl sample were Ti, Al, N, Si, Ca, and Fe. Elements Zr,
S, Zn were not detected as was the case for sample
TiAlV. V was not detected on the surface at a concentra-
tion larger than 0.2 at.%, which is the sensitivity of the
XPS method.
After removing a 100-nm-thick layer, an accurate
analyses of the chemical composition was performed
again. Figure 9b shows an XPS spectrum from a depth
of 100 nm in this sample. At a depth of 100 nm the ele-
ments O, Ti, Al, and C were detected. In addition, also
elements of V, N, Si, Ca and Fe were detected at a depth
of 100 nm.
An XPS depth profile of sample Ti6Al4V-2 is shown
in Figure 10. It can be seen that at a depth of 100 nm a
high concentration of O is still present. This is probably
related to the Ti/Al oxide, since the Ti 2p spectrum is at
depth of 100 nm mainly at 458.6 eV, which suggests the
Ti
4+
oxidation state in a TiO
2
-like compound.
19
The Al 2p
spectrum is mainly at 74 eV related with the Al
3+
oxida-
tion state.
19
This means that both metallic elements, Ti
and Al, are involved in the oxide layer, which is the dom-
inant phase at a depth of 100 nm. The ratio between Ti
and Al seen in Figure 10 is high (about 9) indicating a
Ti-rich compound like Ti6Al4V.
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600 Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603
Figure 7: XPS depth profile of sample Ti6Al4V-1
Figure 8: Chemical composition of sample Ti6Al4V-2 in at.% on the surface and at a depth of 100 nm
Table 4: Chemical composition of sample Ti6Al4V-2 in at.% on the surface and at a depth of 100 nm
Depth C O Ti Al V N Si Ca Fe
Surface 60.7 26.2 1.5 6.0 4.3 1.0 0.4
Depth of 100 nm 7.8 53.4 30.6 3.5 0.8 0.9 1.6 0.4 1.0

4 DISCUSSION
The aim of the MCGR treatment is to partially cor-
rect the spinal deformity, and maintain the correction
while allowing the spine to grow and hence, allowing the
chest to grow and develop.
12
In our case series, the aver-
age correction of deformity achieved during surgery was
31 degrees of Cobb angle, resulting in average residual
curves of fewer than 50 degrees. The curves did not dete-
riorate during follow-up, nor were improved. While the
initial distraction during surgery was large (37 mm),
gradual spinal growth was maintained during outpatient
MCGR distractions (45 mm in 24 months, on average).
This average, however, does not reflect reality because a
larger number of patients have a shorter follow-up time.
Strict adherence to the protocol should yield 12-mm of
spinal growth per patient per year. These results are in
accordance with the existing literature.
4,13
Distraction strategies vary among surgeons and insti-
tutions. Current decision making is left to the surgeon’s
choice and the patient’s needs. Protocols differ from
monthly lesser distractions to three-monthly "as much as
possible" distractions.
14
Our protocol is based on the
knowledge that maturing spines grow approximately
10 mm per year; therefore, distractions of 3 mm every
three months are performed in all our patients. Further
research is needed to standardize distraction strategies.
1,4
Good fixation is crucial for a beneficial outcome. In
this aspect, we added additional fixation (screws at more
than two levels, iliac screws, or sub-laminar bands) for
patients with inactivity osteoporosis or poor pri-
mary-screw purchase during surgery. We performed fu-
sion of the fixed levels and have not had a screw con-
struct stability related complication. Pull out, however,
was described in 11.8 % in the literature.
15
Adverse events included a cerebrospinal fluid (CSF)
leak in one patient, a wound-closure problem due to
screw-head pressure in one patient, requiring the removal
of one rod, PJK in two patients, failure of the magnet
mechanism in one patient and a rod mechanism break in
one patient. The CSF leak was conservatively treated,
while other adverse events required revision surgery. Pre-
vious literature reports a 44 % complication rate and a
33 % unplanned revision rate. Our current series needed
fewer revisions, although the reported series had a larger
number of patients with single-rod implantation, but with
a higher failure rate. Based on this data, avoidance of
single-rod implantation is recommended.
15
Another
study also found better coronal deformity correction and
A. MER^UN et al.: MAGNETICALLY CONTROLLED GROWING RODS FOR THE TREATMENT OF EOS: ...
Materiali in tehnologije / Materials and technology 56 (2022) 5, 595–603 601
Figure 12: XPS depth profile of the sample Ti6Al4V-2
Figure 9: a) XPS spectrum obtained on the surface of the sample Ti6Al4V-2, b) XPS spectrum obtained at depth of 100 nm of the sample
Ti6Al4V-2

greater spinal growth with the dual-rod compared to the
single-rod surgery.
16
Planned or unplanned rod exchanges presented metal
debris on the tissues surrounding the rod. Care was taken
and serum metal-ion concentrations were measured with
a significant increase in titanium and vanadium levels.
Currently, it is believed that metalosis comes from the
actuator, releasing the ion debris during the distraction
process. So far, no clinical adverse correlation has been
published; however, careful follow-up is needed and in-
dependent analyses of explanted rods are suggested.
17
The spine length increases less with every subsequent
distraction. This is a phenomenon called ‘the law of di-
minishing returns,’ and has not been explained in full. It
is probably multifactorial, but for now it is believed that
it is probably connected to the strength of the lengthen-
ing mechanism.
18
The completion of growth is a sign of lengthening
cessation. These patients are referred to as MCGR grad-
uates. The manufacturer released a new recommendation
to explant all the implanted devices after the completion
of treatment; however, it is still unknown whether defini-
tive fusion is needed for patients with idiopathic EOS for
curves under 50 degrees.
1
In our case series, four patients
had achieved full skeletal maturity. Some patients are
scheduled for definitive fusion, while others (parents) do
not consent to another surgical procedure, mostly due to
the risk of medical complications.
4.1 XPS analysis of MAGEC rods Ti6Al4V-1 and
Ti6Al4V-2
XPS analyses on the surface and at a depth of 100 nm
show that the oxide is the main phase in this sub-surface
region. On the sample Ti6Al4V-1 the oxide consists of
mainly Al oxide, which is present in the metallic Ti ma-
trix. A smaller number of Al atoms are also detected in
the metallic state.
On the Ti6Al4V-2 sample the oxide is mainly from
the Ti-rich phase with smaller amount of Al oxide re-
sembling the Ti6Al4V alloy composition. On the surface
and in the sub-surface region of the Ti6Al4V-1 sample,
elements N, Si, Ca, S, Zn, Fe and Zr were also detected
in smaller concentrations. On the surface and in the
sub-surface region of the Ti6Al4V-2 sample the elements
N, Si, Ca, and Fe were detected. We should note that no
V was detected on the surface of the rods, but it appears
in the subsurface region at depth larger than 10 nm.
The differences between the samples Ti6Al4V-1 and
Ti6Al4V-2 are the following:
• On the Ti6Al4V-1 the main oxide phase is Al oxide
(Al
2
O
3
-like) embedded in the Ti-Al metallic matrix.
Also, the elements Zr, S, Zn were present.
• On the Ti6Al4V-2 the main phase is Ti oxide
(TiO
2
-like) with a small portion of Al oxide.
On both samples, the elements N, Ca, Si and Fe were
detected in addition to expected elements like Ti, Al, V,
O and C. Differences in the chemical composition and
the presence of Ti oxide and Al oxide show that the sur-
faces of the Ti6Al4V rods during exposure in the body
might be due to different reactions of the individual pa-
tients to implanted rods. Another possibility for the dif-
ferent chemical composition of the surface of the rods
may be the different positions of the XPS analyses with
respect to a specific placement of the rod with respect to
the magnetic element. Unfortunately, from the XPS sur-
face analyses of the exposed rods extracted from the two
patients we cannot conclude in a statistically significant
way on the detailed surface modifications in the body.
With the XPS method it was not possible to estimate
the total thickness of the oxide layer, since only the
subsurface layer of thickness 100 nm was analyzed. It is
evident that a complete oxide layer is thicker than
100 nm on both samples. It can be speculated that during
manufacturing some surface modifications of the
Ti6Al4V alloys were performed including the Zr-O,
Zn-O, Al-O, Fe-O or Si-O materials.
5 CONCLUSIONS
The MCGR system presents a relatively safe alterna-
tive for EOS treatment. It enables partial deformity cor-
rection, allows for spinal growth, and prevents deformity
deterioration and TIS. Further research is needed to de-
termine and unify distraction strategies and final treat-
ment. Chemical analyses of surface composition of rods
exposed in the body for two patients show the formation
of the TiO
2
/Al
2
O
3
oxide phases in the surface region.
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