Analysis of Retrieved Growth Guidance Sliding LSZ-4D Devices for Early Onset Scoliosis and Investigation of the Use of Nitinol Rods for This System

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DOI: 10.1097/BRS.0000000000000660

Analysis of retrieved growth guidance sliding LSZ-4D devices for early

onset scoliosis and investigation of the use of Nitinol rods for this system

Elena Lukina1,2

, MSc, Mikhail Kollerov2, PhD, Jay Meswania

3, PhD, David Wertheim

1, PhD,

Peter Mason1, PhD, Paul Wagstaff

1, MSc, Aleksandr Laka

4, PhD, Hilali Noordeen FRCS (Tr

& Orth)5, Wai Weng Yoon FRCS (Tr & Orth)

5, Gordon Blunn

3 PhD

1 – Kingston University London, UK

[email protected] and [email protected] 104 Roehampton Vale, SW15 3RX

2 – “MATI”-RSTU, Russia

3 – University College London, UK

4 – Russian University of Peoples’ Friendship, Moscow, Russia

5 – Royal National Orthopedics Hospital, UK

Corresponding author:

Elena Lukina

e-mail: [email protected] [email protected]

Tel. +44(0)7895545709 and +79162266225

Address for correspondence and reprints:

4 GREENWOOD ROAD

KT70DY

THAMES DITTON

UK

mailto:[email protected]





The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA-approved for

this indication and is/are not commercially available in the United States. No funds were

received in support of this work. Relevant financial activities outside the submitted work:

board membership, consultancy, payment for development of educational presentations,

employment, grants, payment for lectures, stocks, travel/accommodations/meeting expenses.

Study Design. Analysis of volumetric wear loss of retrieved growth guidance sliding devices

LSZ-4D for treatment of early onset scoliosis and laboratory in-vitro wear test for

comparison of Nitinol, Ti and CoCr alloys wear resistance.

Objective. To evaluate quantitatively the amount of wear debris from the sliding LSZ-4D

device and to investigate the potential of using Nitinol for replacing Ti alloys in spinal

instrumentation. In order to do that, wear resistance of Nitinol, Ti and CoCr was compared.

Summary of Background Data. There is little data regarding the amount of wear debris

associated with growth guidance sliding devices for patients with early onset scoliosis and the

wear resistance of superelastic Nitinol compared with Ti and CoCr.

Methods. Volumetric wear loss was measured on LSZ-4D devices made from titanium alloy

Ti6Al4V and each consisted of 2 rectangular section (6x4 mm) rods and 40±8 fixture

elements (20±4 hooks and 20±4 clips) retrieved from 3 patients (implantation period 3.5-5.8

years). Images of wear scars were taken on Bruker interferometer microscope and

incorporated into MATLAB software. Wear resistance of Nitinol, Ti and CoCr was studied

using reciprocation pin-on-disk wear test in bovine serum at 37±1OC.

Results. The volume wear rate of LSZ-4D device was found to be 12.5 mm3 per year from

which 5mm3 per year is the rods wear debris and 7.5 mm

3 per year is the contribution of

fixtures. Wear resistance of Nitinol is 100 times higher compared to Ti and comparable to

that of CoCr.


Conclusions. Application of wear resistant coatings on Ti components in growth guidance

sliding devices for the treatment of early onset scoliosis will be useful. High wear resistance

of Nitinol combined with its superelastic and shape memory properties could make

application of Nitinol rods for spinal instrumentation beneficial.

Key words: early onset scoliosis, wear, retrievals, growth guidance system, Nitinol, Implant

Level of Evidence: 5

Volumetric wear loss of retrieved growth guidance sliding devices LSZ-4D for early onset

scoliosis treatment made from Ti6Al4V was measured to be 12.5 mm3 per year. A laboratory

study using pin-on-disk wear test revealed wear resistance of Nitinol to be 100 times superior

to that of Ti and comparable to CoCr.

Key points:

The volume wear rate measured for the retrieved LSZ-4D growth guidance device

made of titanium alloy Ti6Al4V was found to be 12.5 mm3 per year from which 5mm

3 per

year is the rods wear debris and 7.5 mm3 per year is the contribution of fixtures;

In-vitro pin-on-disk wear test study have revealed that wear resistance of Nitinol

tested against titanium alloy Ti6Al4V in the simulated body environment is 100 times higher

compared to titanium alloy Ti6Al4V and comparable to that of Cobalt Chromium alloy;

Application of wear resistant coatings on Ti components in growth guidance sliding

devices for treatment of early onset scoliosis will be useful. High wear resistance of Nitinol


combined with its superelastic and shape memory properties could make application of

Nitinol rods for spinal instrumentation beneficial.

INTRODUCTION

Surgery for early onset scoliosis (EOS) requires fusion-less instrumentation as early fusion

may result in complications such as trunk shortening, pulmonary dysfunction and overloading

of the spine [1]. There are number of fusion-less instrumentation for EOS treatment that is

commonly used now. These include vertical expandable prosthetic titanium rib (VEPTR)

instrumentation [2], non-invasive growth guidance devices including magnetically extendable

growing rods [3] or sliding systems Shilla or LSZ-4D instrumentation [4-5] and invasively

(mechanically) extendable growing rods [6]. However, due to the absence of fusion

movement of rods against fixtures is possible and may result in undesirable wear debris

formation. This process is likely to be more pronounced for growth guidance sliding devices

where rods are able to slide in unlocked fixtures as the child is growing.

While absolute amounts of wear debris produced by joint prostheses such as total hip, knee

and spinal disk replacements (THP, TKP, TDP), which have a high range of motion, are

extensively covered in literature [7-8], there is limited information on quantitative values of

volumetric wear of spinal implants used for EOS.

Titanium alloys (Ti) are biocompatible; however they have lower wear resistance compared

to cobalt chromium (CoCr) and stainless steel (SS) [9].

Wear debris generated during articulation of total metal-on-metal hip prosthesis made of

CoCr is one of the main reasons for the failure of these implants [10]. Release of CoCr wear

debris and ions leads to tissue necrosis, pseudotumors and hypersensivity [11-12]. Polymer-

on-metal hip implants which include CoCr and polyethylene components also suffer from

aseptic loosening and osteolysis as a result of polyethylene wear debris [13]. Attempt to


introduce knee implants with titanium on polyethylene friction pair was made in late 1980s.

However, these prostheses were withdrawn from the market because of the problems

associated with excessive Ti wear [14].

Prominent wear scars on Ti and SS spinal scoliosis instrumentation were reported by

Villarraga et al. [15]. Wang et al. revealed high concentrations of Ti in tissues collected from

areas near pedicle screw-rod junction [16]. In addition, titanium wear debris produced by

spinal implants has been reported to cause inflammation and osteolysis [17-19]. In contrast,

Singh et al. [20] estimated the wear loss of the Shilla growth guidance device (Medtronic,

USA) made of SS is less than 1 mm3 per year.

Nitinol, an alloy with Shape Memory effect could be another promising material for rods in

scoliosis instrumentation [21-24]. It has an ability to return to it’s preconfigured shape at

body temperature and has been used in scoliosis correction. It has the potential benefit of a

more gradual and sustained correction [24]. However, wear resistance of Nitinol in biological

environment is poorly understood, especially in combination with Ti which is the main

material used for fixtures.

The purpose of current work was to measure volume wear loss of retrieved LSZ-4D devices

made of titanium alloy Ti6Al4V. The second purpose was to investigate the potential of using

Nitinol for replacing Ti alloys in spinal instrumentation. In order to do that, we used a pin-on-

disk test to compare wear resistance of Nitinol, Ti and CoCr.

MATERIALS AND METHODS

Description of retrieved growth guidance sliding LSZ instrumentation and patient’s

sample

Growth guidance sliding LSZ-4D device (Conmet, Russia) for EOS scoliosis treatment was

retrieved from 3 patients (1 male, 2 female) undergoing routine final definitive fusion surgery

following skeletal maturity. The LSZ-4D sliding device consists of two rectangular cross-


section 6x4 mm rods and fixture units. Locked fixtures are normally located on one spinal

level while unlocked fixtures are used at distal and proximal ends of the device thus enabling

sliding while spine is growing (fig.1A). Each fixture unit contains a clip and a hook (fig.1B).

All components are made of titanium alloy Ti6Al4V.

In total six rods and sixty fixture units (60 hooks and 60 clips) were analyzed from 3 patients.

The components were implanted for periods for between 3.5 and 5.8 years (average: 4.3

years). None of these patients had any clinical complications. Clinical information for all

retrieved devices is given in Table 1.

Volume wear loss of LSZ-4D sliding device components was measured by taking images of

wear scars using a Bruker interferometer microscope. The interferometry data was then

incorporated into MATLAB software (The MathWorks Inc., Natick, MA, USA). The system

then calculates the displaced volume in parallel planes with 1 pixel spacing lines along the

length of the groove. The median height over 20 pixels is calculated at the end of each line.

Using linear interpolation, the volumes under the lines are calculated and summed over the

length of the groove. In case one edge of the groove was worn out, the system also allowed

the volume to be calculated with respect to the mean of a region; in this mode the user could

select the top surface and the displaced volume beneath is computed taking into account the

tilting of the image. Following processing with MATLAB, 3D visualizations were performed

using Amira v5.4 (Visualization Sciences Group, Germany).

Photos of wear grooves on rods (fig. 2A), clips (fig. 2C) and hooks (fig. 2E) and their

corresponding interferometry images reconstructed in MATLAB followed by 3D

visualizations (fig. 2B, D and F respectively) are presented in figure 2.

This volumetric wear loss measurement was validated in the in-vitro test where the wear of

test components were measured volumetrically using the method described above and related


to the loss of material measured gravimetrically. The difference in measurements was less

than 5%.

Scanning electron microscopy (SEM) was used to examine the wear scars on these devices

(EVO 50, Carl ZEISS).

Wear particles were extracted from tissues adjacent to the implanted LSZ-4D device in the

lumbar part of the spine during routine final definitive fusion surgery. Particles were digested

in papain and proteinase K according to ISO 17853:11 [26]. The particles size and shape was

determined by analyzing SEM images taken at 30,000 magnification using ImagePro3

software (Nexis, Russia). Chemical composition of particles was analysed using energy

dispersive x-ray analysis (EDAX).

In-vitro pin-on-disk wear test

In-vitro wear tests were conducted using a pin-on-disk set up (fig.3A and B) according to

ASTM G99-05(2010) [27] at 37±1OC with 1 Hz frequency of reciprocating sliding

movement. Diluted bovine serum was used as a lubricant according ISO 18192-1:2011 [28].

The load on the pins was 10N which provided contact stresses of approximately 3 MPa which

was the calculated stress level based on literature data on bending moments encountered by

spinal rods during various functional activities [29]. The amplitude of reciprocation

movement was 6 mm.

Pins were made of titanium alloy Ti-5.8wt.% Al-3.9wt.%V (Ti6Al4V); Ti-55.8 wt.%Ni

(Nitinol), and Co-27wt.%Cr-5wt.%Mo, low carbon (CoCr alloy). All disks were made of

titanium alloy Ti6Al4V.

The pins were 5.5 mm in diameter, and were rounded to 20 mm radius. The discs measured

40 mm in diameter and 5mm in height. The temperature of shape recovery of Nitinol

measured according ASTM 2082-06 [30] was Af=37±1OC. Surfaces of the pins and discs

were ground and polished to the roughness of Ra 0.04±0.01µm. Volume wear loss (∆V) of


both counter-parts separately was determined after 0.05, 0.2, 0.5 and 0.85 million cycles as

∆V=∆m/ρ, where ∆m – weight loss gravimetrically measured, g and ρ – density of the

material, g/mm3. Number of tests for each condition n=3. Wear scars were analyzed using

SEM. Wear particles were isolated from the bovine serum according to ISO 17853:11 [26]

and analysed using SEM and EDAX.

The Mann-Whitney U test was used to determine if there was statistically significant

difference in the size of wear particles digested from tissues adjacent to the implanted LSZ-

4D device and those digested from the bovine serum after in-vitro wear tests. A p value of

less than 0.05 was defined as statistically significant. This test was run after Kolmogorov-

Smirnov test revealed that the wear particle’s size significantly deviated from a normal

distribution. Statistical analysis was performed with SPSS 22.0 software (IBM Corp., USA).

RESULTS

Analysis of retrievals

Wear

The whole assemble of LSZ-4D sliding device analyzed from each of three patients included

2 rods and 40±8 fixture elements (20±4 hooks and 20±4 clips).

Analysis of wear regions on the retrieved rods revealed larger scars on distal and proximal

parts of rods and minor wear in the central region near the spine level with locked screw. The

average width of scars was 10±2 mm.

Wear of the hooks and clips was also observed to be uneven. Only 17 of 60 examined clips

and 18 of 60 examined hooks were severely damaged with deep grooves while the rest had

minor scratches with no measurable volume wear. Severely damaged fixture elements were

located on distal or proximal part of rods. None of the patient’s devices was seen to be any


more or less worn than the others. The examples of most heavily damaged clip, hook and

distal part of rods are shown on Figure 2.

The average volume wear rate for the whole LSZ-4D sliding device assuming a linear wear

rate was 12.5±1.5mm3 per year with individual contributions from rods, hooks and clips

being 5±1.2mm3, 3±1mm

3 and

4.5±1.5mm

3 per year respectively (fig.4).

Analysis of wear scars and particles

SEM analysis of wear scars on retrieved rods, hooks and clips of LSZ-4D device revealed

deep abrasive grooves and adhesion deposits of titanium (fig. 5A) indicating abrasive and

adhesion mechanisms of Ti6Al4V alloy wear damage.

The average size of wear particles (fig. 5B) digested from tissues surrounding implanted

LSZ-4D device was 0.46µm (range from 0.09 to 1.59µm). Average aspect ratio was 1.2-1.5

and they were classified as round to oval according to ISO 17853:2011 [26]. The size

distribution of particles is given in Figure 5C where it can be seen that approximately 50% of

particles have a size less than 0.4 µm.

EDAX analysis of wear particles chemical composition demonstrated typical profiles of

Ti6Al4V alloy with titanium and aluminum (fig. 5D). Oxygen peaks make it possible to

assume oxidation of titanium wear particles within the biological environment. Gold and

palladium peaks appear from the nanosize coating deposited on particles for EDAX analysis.

In-Vitro pin-on-disk wear test

Wear

Figure 6A and B demonstrates volume wear loss of Ti6Al4V, Nitinol and CoCr pins tested

against titanium disks. Wear loss of Ti6Al4V pins was 33±2mm3 after 0.5 million cycles

which is at least 100 times more compared to Nitinol and CoCr pins which were measured to


be 0.15±0.02 and 0.1±0.01 mm3 respectively after 0.5 million cycles (fig.6B). Nevertheless,

wear resistance of disk counter-parts (fig. 6C) made of Ti6Al4V did not demonstrate much

difference regardless of pin material and was measured to be 37±3, 25±2 and 20±2 mm3 after

0.5 million cycles when tested against Ti6Al4V, Nitinol and CoCr pins respectively.

Analysis of wear scars and particles

Ti6Al4V- Ti6Al4V friction combination

SEM analysis of wear scars on pins and disks made of Ti6Al4V alloy (fig.7A) revealed

abrasive and adhesion mechanisms of Ti6Al4V alloy wear damage similar to that observed

on the retrievals of LSZ-4D devices (fig.5A).

SEM micrographs of wear particles collected after 0.5 million cycles for Ti6Al4V-Ti6Al4V

combination, their size distribution and EDAX chemical composition are given in Figure

7B,C,D. The average particle size was 0.45µm (range from 0.13 to 1.6 µm). Their shape was

round to oval, similar to that collected from patient’s tissues (average aspect ratio was 1.3-

1.6). Approximately 70% of particles had size less than 0.4 µm. EDAX analysis of the

particles revealed the presence of titanium, aluminum and vanadium. There was no

statistically significant difference in the size of wear particles digested from tissues adjacent

to the implanted LSZ-4D device and those collected after in-vitro wear test (p=0.57).

Nitinol-Ti6Al4V friction combination

Mild abrasive grooves and deposits of the titanium counter-part were seen over the entire

surface of the Nitinol pins (fig.8A). The roughness of wear scars on Nitinol was 0.170.05

Ra.

SEM micrographs of wear particles collected after 0.5 million cycles for Nitinol-Ti6Al4V

combination and their size distribution are given in Figure 8B,C. The average size of the wear

particles was 0.3µm (range from 0.10 to 1.97 µm) with a round shape (average aspect ratio


was 1.2-1.4). Approximately 70% of particles were less than 0.4 µm. EDAX analysis of

particles revealed no traces of Ni (fig. 8D).

Discussion

The volume wear rate measured for the retrieved components of LSZ-4D growth guidance

device made of titanium alloy Ti6Al4V was found to be 12.5 mm3 per year with 5mm

3 and

7.5 mm3 per year contributed from rods and fixtures. We measured wear rate on three devices

which had typical size and depth of wear scars normally observed during routine operations

to replace the sliding mechanism with a spinal fusion devices. The absolute values of wear

rate will depend on the design of the device, fixtures density and patient activity. Wear loss

values observed in our study are greater compared to the Shilla growth-guidance device made

of SS. The latter is reported to have 0.78 mm3 per year [20], which can be explained by the

higher wear resistance of SS compared with titanium and the difference in fixtures density.

However wear rate measured in the current work for LSZ-4D devices, is similar to values

(15-26 mm3 per year) reported for metal-on-metal THR made of CoCr alloys which are

known for their superior wear resistance [7,31-32]. In hip replacements this amount of metal

debris although composed of CoCr, often leads to adverse biological reactions, bone

resorption and implant failure. Taking into account the poor wear resistance of titanium

alloys and the size of the wear scars on the rods the range of motion in sliding growth

guidance devices may be much lower compared to THR articulations. Patients with

implanted LSZ-4D devices analysed in this study developed no clinical complications or

device loosening. However, in other cases seromas, fistulas and inflammation of the tissues

adjacent to the device was observed after LSZ-4D instrumentation implantation, which may

be caused by the metal wear debris. Work is now in progress to estimate the occurrence and

severity of these complications. Retrieved spinal instrumentation made of more wear resistant

SS has been reported to have corrosion damage in addition to wear scars [15]. Therefore,


using of spinal instrumentation made of titanium with additional wear resistant coatings to

limit the release of metal debris may be beneficial.

This work has shown that over 50% of wear particles retrieved from tissues surrounding

LSZ-4D devices were less than 400 nm. This is similar to the size described for metal

particles from THR which is reported to be 0.02-0.8 μm for CoCr and from 0.04-0.9 μm for

Ti [33]. The larger size of wear particles observed for Shilla devices [20] might be possibly

explained by using laser scattering methodology for measuring particles size where the effect

of particle agglomeration is unclear.

Results of in-vitro pin-on-disk test in this work revealed that the wear resistance of Nitinol is

comparable to that of CoCr with a volume wear rate is 100 times less compared to Ti6Al4V.

Similar performance of Nitinol was observed by Li [34] and can be explained by superelastic

deformation of Nitinol asperities thus reducing contact stresses and abrasive wear [35-36].

Comparison of wear scars on retrieved LSZ-4D device components and titanium pins and

disks in in-vitro test reveals similar abrasive and adhesive wear damage mechanisms. The

size and shape of wear particles retrieved from tissues adjacent to the implanted LSZ-4D

device and those digested from bovine serum after the laboratory wear test are also similar,

which makes it possible to assume that in-vitro test adequately simulates reciprocating

translation movement of rods against fixtures.

The wear rate of titanium pins in Ti6Al4V-Ti6Al4V friction combination being 33±2mm3 per

0.5 million cycles corresponds approximately to wear debris produced by two rods of LSZ

device after 6.5 years of implantation. Volume wear loss of Nitinol pins after 0.5 million

cycles was measured to be 0.15 mm3, which is relatively low for 6 years of implantation. It

may be concluded that the high wear resistance of Nitinol rods combined with their

superelastic and shape memory properties could be beneficial for the application in spinal

instrumentation. Nevertheless, further in-vitro wear tests of assembled devices incorporating


Nitinol rods are needed in order to evaluate the volume of wear debris generated by specific

device which will take into account the device design, lubrication and edge effects.

Limitations of the study:

Only 3 retrieved implants have been investigated in our study. Nevertheless, it was shown

that the in-vitro wear tests are able to replicate wear damage mechanisms seen on retrievals

and the shape and size of wear particles isolated from tissues adjacent to LSZ-4D implants

was similar to those isolated from the in- vitro tests. This made it possible to compare the

wear performance of Nitinol, which might be a prospective material for spinal

instrumentation with metal materials which are currently used. However, further in vitro and

in-vivo testing of Nitinol is necessary for its safe application.

Conclusions

This paper investigates the wear of sliding titanium devices to treat early onset scoliosis in

adolescent patients. We showed the average volumetric wear rate for the retrieved LSZ-4D

growth guidance device made of titanium alloy (Ti6Al4V) was in total 12.5 mm3 per year. Of

this, the rods contributed 5mm3 per year with the fixtures contributing 7.5 mm

3 per year. We

used an in-vitro pin-on-disk wear test to investigate the wear resistance of Nitinol tested

against titanium alloy in a simulated body environment. We showed that Nitinol wear loss

was 100 times lower compared with titanium alloy Ti6Al4V and comparable to that of Cobalt

Chromium alloy. The wear mechanism and the size and shape of wear particles after in-vitro

tests was similar to wear patterns identified from retrieved titanium components and to the

wear debris isolated from tissues adjacent to these implants.

References:


1. Karol LA, Johnston C, Mladenov K et al. Pulmonary function following early

thoracic fusion in non-neuromuscular scoliosis. The Journal of Bone & Joint Surgery

2008;90(6):1272-1281.

2. Campbell Jr, R. M. (2013) VEPTR: past experience and the future of VEPTR

principles. European Spine Journal 2013; 22(2): 106-117.

3. Akbarnia BA, Cheung K, Noordeen H et al. Next Generation of Growth-Sparing

Techniques: Preliminary Clinical Results of a Magnetically Controlled Growing Rod

in 14 Patients With Early-Onset Scoliosis. Spine 2013;38(8):665-670.

4. McCarthy RE, Luhmann S, Lenke L et al. The Shilla Growth Guidance Technique for

Early-Onset Spinal Deformities at 2-Year Follow-Up: A Preliminary Report. J.

Pediatr. Orthop. 2014;34:1-7.

5. Sampiev MT, Laka AA, Zagorodniy NV et al. The application of growth-guidance

LSZ device for infantile and adolescent scoliosis treatment. Russian Medical Journal

2013;5:24-28.

6. Thompson, G. H., Akbarnia, B. A., & Campbell Jr, R. M. (2007). Growing rod

techniques in early-onset scoliosis. Journal of Pediatric Orthopaedics 2007; 27(3):

354-361.

7. Lord JK, Langton DJ, Nargol AV, et al. Volumetric wear assessment of failed metal-

on-metal hip resurfacing prostheses. Wear 2011, 272:79-87.

8. Lee JL, Billi F, Sangiorgio SN, et al. Wear of an experimental metal-on-metal

artificial disc for the lumbar spine. Spine 2008; 3: 597-606.


9. McKellop H, Rostlund R, Ebramzadeh E, et al. Wear of titanium 6-4 alloy in

laboratory tests and in retrieved human joint replacements. In: Brunette D, ed.

Titanium in medicine: material science, surface science, engineering.Berlin: Springer;

2001: 747-770.

10. Fabi, D., Levine, B., Paprosky, W., Della Valle, C., Sporer, S., Klein, G.&

Hartzband, M. Metal-on-metal total hip arthroplasty: causes and high incidence of

early failure. Orthopedics, 2012; 35(7): e1009-16.

11. Ollivere, B., Darrah, C., Barker, T., Nolan, J., & Porteous, M. J. Early clinical failure

of the Birmingham metal-on-metal hip resurfacing is associated with metallosis and

soft-tissue necrosis. Journal of Bone & Joint Surgery, British Volume 2009; 91(8):

1025-1030.

12. Mahendra, G., Pandit, H., Kliskey, K., Murray, D., Gill, H. S., & Athanasou, N.

Necrotic and inflammatory changes in metal-on-metal resurfacing hip arthroplasties:

relation to implant failure and pseudotumor formation. Acta orthopaedica 2009;

80(6): 653-659.

13. Hallan, G., Lie, S. A., & Havelin, L. I. High wear rates and extensive osteolysis in 3

types of uncemented total hip arthroplasty: a review of the PCA, the Harris Galante

and the Profile/Tri-Lock Plus arthroplasties with a minimum of 12 years median

follow-up in 96 hips. Acta orthopaedica 2006; 77(4): 575-584.

14. Schroeder, H. P., Smith, D. C., Gross, A. E., Pilliar, R. M., Kandel, R. A.,

Chernecky, R., & Lugowski, S. J. Titanemia from total knee arthroplasty: a case

resulting from a failed patellar component. The Journal of arthroplasty 1996;

11(5):620-625.

15. Villarraga ML, Cripton PA, TetiSD, et al Wear and corrosion in retrieved

thoracolumbar posterior fixation. Spine 2006;31:2454-2462.


16. Wang J, Warren D, Harvinder S, et al Metal debris from titanium spinal implants.

Spine 1999;24:899-903.

17. Hallab NJ, Cunningham BW, Jacobs JJ. Spinal implant debris-induced osteolysis.

Spine 2003;28(suppl):125–38.

18. Cunningham BW, Orbegoso CM, Dmitriev AE, et al. The effect of spinal

instrumentation particulate wear debris: an in vivo rabbit model and applied clinical

study of retrieved instrumentation cases. Spine J 2003;3:19–32.

19. Mochida Y, Bauer TW, Nitto H, et al. Influence of stability and mechanical properties

of a spinal fixation device on production of wear debris particles in vivo. J Biomed

Mater Res 2000;53:193–8.

20. Singh V, Simpson J, Rawlinson J, et al Growth Guidance system for early-onset

scoliosis. Spine 2013;38:1546-1553.

21. Yoshihara H. Rods in spinal surgery: a review of the literature Spine J 2013: In press.

22. Kollerov, M., Lukina, E., Gusev, D., Mason, P., & Wagstaff, P. (2013). Impact of

material structure on the fatigue behaviour of NiTi leading to a modified Coffin–

Manson equation. Materials Science and Engineering: A 2013; 585: 356-362.

23. Otsuka C, Wayman M. Shape Memory Materials, Cambridge: Cambridge University

Press, 1998.

24. Cheung K, Kuong E, Samartzis D, et al. Assessing the Safety and Efficacy of a Novel

Superelastic Rod in Comparison to Conventional Titanium Rod for Scoliosis Curve

Correction. Paper presented at: 18th

International Meeting on advanced spinal

techniques. 2011; Copenhagen.


25. Lenke, L. G., Betz, R. R., Harms, J., Bridwell, K. H., Clements, D. H., Lowe, T. G., &

Blanke, K. Adolescent idiopathic scoliosis a new classification to determine extent of

spinal arthrodesis. The Journal of Bone & Joint Surgery 2001; 83(8): 1169-1181.

26. ISO 17853:2011 Wear of implant materials – Polymer and metal wear particles –

Isolation and characterization 11.040.40: Implants for surgery, Prosthetics and

Orthotics. Geneva, Switzerland: International Organization for Standardization, 2008.

27. ASTM G99-05(2010) Standard Test Method for Wear Testing with a Pin-on-Disk

Apparatus.Section Three – Corrosion of metals; Wear and Erosion. West

Conshohocken, PA:ASTM International, 2010.

28. ISO 18192-1:2011 Implants for surgery -- Wear of total intervertebral spinal disc

prostheses -- Part 1: Loading and displacement parameters for wear testing and

corresponding environmental conditions for test. Implants for surgery, Prosthetics

and Orthotics. Geneva, Switzerland: International Organization for Standardization,

2011.

29. Rohlmann A, Graichen F, Bergmann G. Loads on an Internal spinal fixation device

during physical therapy. J Bone Joint Surg Am 2002;82:44-52.

30. ASTM 2082-06 Standard Test Method for Determination of Transformation

Temperature of Nickel-Titanium Shape Memory Alloys by Bend and Free

Recovery.Section Thirteen - Medical and Surgical Materials and Devices. West

Conshohocken, PA:ASTM International, 2006.

31. Morlock MM, Bishop N, Zustin J et al. Modes of implant failure after hip resurfacing:

morphological and wear analysis of 267 retrieval specimens. J. Bone Joint Surg. Am.

2008;90 (Suppl. 3):89–95.


32. Witzleb W, Hanisch U, Ziegler J et al. In vivo wear rate of the Birmingham hip

resurfacing arthroplasty: a review of 10 retrieved components. J.Arthroplasty

2009;24(6):951–956.

33. Doorn PF, CampbellPA, Worrall J. Metal wear particle characterization from metal

on metal total hip replacements: transmission electron microscopy study of

periprosthetic tissues and isolated particles. J Biomed Mat Res 1998:103-111.

34. Li DY. A new type of wear-resistant material: pseudo-elastic TiNi alloy. Wear

1998;221:116-123.

35. Qian L, Zhou Z, Sun Q. The role of phase transition in the fretting behavior of NiTi

shape memory alloy. Wear 2005;259:309-318.

36. Yan W. Theoretical investigation of wear-resistance mechanism of superelastic shape

memory alloy NiTi. Materials Science and Engineering: A. 2006;427: 348-355.

Figure 1. (A) Illustration of LSZ-4D sliding growth guidance device. Locked fixture is used

on one spinal level. Unlocked fixtures are used at distal and proximal end of the device

enabling sliding and continued spinal growth; (B) Assembled fixture unit consisting of clip

and hook.


Figure 2. Photos of wear grooves on LSZ-4D sliding device components (rods (A), clips (C)

and hooks (E)) and their corresponding images (B, D and F) taken using Bruker

interferometry microscope and reconstructed in MATLAB followed by 3D visualisations

performed using Amira software.

Figure 3. Photo (A) and scheme (B) of pin-on-disk wear test for the in-vitro evaluation of

wear resistance of metal materials used in the manufacture of spinal implants.


Figure 4. Average volume wear for retrieved components of LSZ-4D device made of titanium

alloy Ti6Al4V. The whole device analyzed from each patient included 2 rods and 40±8

fixture elements (20±4 hooks and 20±4 clips).


Figure 5. (A) SEM micrograph of the wear scar on LSZ-4D device retrieved hook revealing

abrasive and adhesion mechanisms of wear damage; (B) SEM micrograph of wear particles

enzymatically digested from retrieved tissues. (C) Particle size distribution calculated using

SEM micrographs (D) The chemical composition of typical wear particles measured by

EDAX analysis.


Figure 6. (A) Volume wear loss of Ti6Al4V, Nitinol and CoCr pins tested against Ti6Al4V

disks in-vitro pin-on-disk; (B) detailed comparison revealed that volume wear loss of Nitinol

pins is comparable to that of CoCr; (C) volume wear loss of titanium disks counter-parts

remains high regardless of the pin material.


Figure 7. (A) SEM micrograph of Ti6Al4V pin wear scar after pin-on-disk test of Ti6Al4V-

Ti6Al4V combination revealing abrasive/adhesion mechanisms of wear damage similar to

that seen on retrievals; (B) SEM micrograph of wear particles collected after 0.5 million

cycles; (C) Particle size distribution (D) The chemical composition of wear particles.

Figure 8. (A) SEM micrograph of Nitinol pin wear scar after pin-on-disk test of Nitinol-

Ti6Al4V combination revealing mild abrasive wear and adhesion of titanium counter-part;

(B) SEM micrograph of wear particles; (C) Particle size distribution (D) The chemical

composition of wear particles revealed no traces of Ni.


Table 1 Clinical information for all retrieved LSZ-4D sliding devices

Implant Age at

implantation

Gender Scoliosis

type* and

degree

Level of

device

implantation

Implan

tation

time

(years)

Number of device

elements

rods fixtures

clips hooks

LSZ-4D(1) 11 Female IBN,

76

T2/L4 5.8 2 24 24

LSZ-4D(2) 12 Female IIAN,

63

T4/L2 3.5 2 20 20

LSZ-4D(3) 10 Male IAN,

66

T2/T12 3.5 2 16 16

*Lenke classification [25]

Analysis of Retrieved Growth Guidance Sliding LSZ-4D Devices for Early Onset Scoliosis and Investigation of the Use of Nitinol Rods for This System

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