Abstract Background. Growth guidance sliding treatment devices such as Shilla (Medtronic, USA) or LSZ-4D (Conmet, Russia) used for the treatment of scoliosis in children who have high growth ...potential have unlocked fixtures allowing rods to slide during growth of the spine which avoids periodical extensions. However, the probability of clinical complications associated with metallosis after the implantation of such devices is poorly understood. The content of metal ions in the blood and tissues of pediatric patients treated for scoliosis using fusionless growth guidance sliding instrumentation, have not yet been investigated. Purpose. The aim of this study was to measure the content of metal ions in blood and tissues surrounding implanted growth guidance sliding LSZ-4D devices made of titanium alloy (Ti6Al4V) and to identify the incidence of metallosis associated clinical complications in some patients with these devices. Study design. One center case-control retrospective study. Patients sample. Study group included 25 patients with high growth potential (3 males, 22 females, average age at primary surgery for scoliosis treatment is 11.4±1.2 years old) who had sliding growth guidance instrumentation LSZ-4D (Conmet, Moscow, Russia) implanted on 13 (range 10-16) spine levels for 6±2 years. The LSZ-4D device was made from titanium alloy Ti6Al4V and consisted of two rectangular section rods and fixture elements. Locked fixtures were used on one spinal level, while the others were unlocked (sliding). The control group consisted of 13 patients (12 females and 1 male, 11±1.2 years old) without any implanted devices. Outcome measures. The content of Ti, Al and V metal ions in the whole blood and tissues around the implanted device was measured. Incidence of metallosis associated complications in the study group were recorded. Methods. Metal ion content was measured by ICP-MC on quadrupolar Nexion 300D (Perkin Elmer, USA). Results. 5 of 25 patients in the study group developed metallosis associated complications (two sinuses and three seromas in the lumbar part of the spine). Revisions were carried out in two of these patients. 90% of patients in the study group had increased content of Ti and V ions in the blood (2.8 and 4 times respectively). Median content of Ti ions in soft tissues adjacent to implanted sliding device was more than 1,500 fold higher compared with the control group. These levels are much higher than previously reported for spinal instrumentation. Conclusion. Increased content of Ti and V ions in the blood and especially in tissues around the titanium growth guidance sliding device LSZ-4D accompanied by clinical manifestations (seromas and sinuses) indicate the importance of improving of wear resistance of such instrumentation with the coatings and the necessity to exchange sliding instrumentation once the child is fully grown.
Background
To compare the biomechanical stability of a novel, C-shaped nickel–titanium shape memory alloy (SMA) implant (C-clip) with traditional cerclage wiring in the fixation of a Vancouver B1 ...(VB1) periprosthetic femoral fracture (PFF).
Methods
In total, 18 synthetic femoral fracture models were constructed to obtain unstable VB1 fracture with an oblique fracture line 8 cm below the lesser trochanter. For each model, the distal portion was repaired using a 10-hole locking plate and four distal bi-cortical screws. The proximal portion was repaired using either three, threaded cerclage wirings or three, novel C-shaped implants. Specimens underwent biomechanical testing using axial compression, torsional and four-point bending tests. Each test was performed on three specimens.
Results
The C-clip was statistically significantly stronger (i.e., stiffer) than cerclage wiring in the three biomechanical tests. For axial compression, medians (ranges) were 39 (39–41) and 35 (35–35) N/mm, for the C-clip and cerclage wiring, respectively. For torsion, medians (ranges) were, 0.44 (0.44–0.45) and 0.30 (0.30–0.33) N/mm for the C-clip and cerclage wiring, respectively. For the four-point bending test, medians (ranges) were 39 (39–41) and 28 (28–31) N/mm; for the C-clip and cerclage wiring, respectively.
Conclusion
Results from this small study show that the novel, C-shaped SMA appears to be biomechanically superior to traditional cerclage wiring in terms of stiffness, axial compression, torsion and four-point bending, and may be a valuable alternative in the repair of VB1 PFF. Further research is necessary to support these results.
A complex influence of various structural parameters (including an increased dislocation density, size of Ni-rich (Ni4Ti3 and Ni3Ti2) particles, and volume fraction of Ti-rich (Ti4Ni2Ox) particles as ...well as content of Ni in the alloy) on the strain-controlled fatigue behaviour of NiTi alloy has been studied in this work. It was revealed that in low-cycle conditions (εa≥2%) strain-controlled fatigue resistance of NiTi alloy may be improved by the creation of a microstructure which increases the part of deformation that is realized by martensitic mechanism. This part is suggested to be estimated by measuring (εcr) parameter, defined as the maximal strain which sample can completely recover after unloading and heating to the temperature higher than Af. A modified Coffin–Manson equation is suggested to describe and predict the strain-controlled fatigue behaviour in the range of high strain amplitudes (εa≥2%), where εcr0.2 serves as one of the coefficients, while another coefficient may be deducted from the empirical relation based on the bending test measurements. No correlation between NiTi alloy strain-controlled fatigue resistance and εcr0.2 parameter was observed for the high-cycle conditions (εa≤1.5%). In this case NiTi alloy performance may be improved by nanosize Ni-rich particles precipitation, creation of increased dislocation density or decreasing of the Ti4Ni2Ox volume fraction.
The static and cyclic mechanical behavior of samples of composite material with a matrix made of silicone rubber or low-pressure polyethylene reinforced with fibers of titanium nickelide with a ...martensitic structure has been investigated. It is shown that such composite materials have high deformation cycle resistance.
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 wear ...resistance of alloys Nitinol, Ti, and cobalt chromium (CoCr).
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. To do that, wear resistance of Nitinol, Ti, and CoCr was compared.
SUMMARY OF BACKGROUND DATA.There are 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 (6 × 4 mm) rods and 40 ± 8 fixture elements (20 ± 4 hooks and 20 ± 4 clips) retrieved from 3 patients (implantation period, 3.5–5.8 yr). 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°C ± 1°C.
RESULTS.The volume wear rate of LSZ-4D device was found to be 12.5 mm per year from which 5 mm per year is the wear debris of the rod and 7.5 mm per year is the contribution of fixtures. Wear resistance of Nitinol is 100 times higher than that of Ti and comparable with that of CoCr.
CONCLUSION.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.Level of Evidence5
The influence of the TiN and DLC coatings deposition on the wear resistance of Nitinol – Ti6Al4V friction pair for the potential application in fusionless sliding spinal implants for the scoliosis ...correction was studied in this work. Wear tests were carried out using pin-on-disc scheme in diluted calf serum. It was found that the deposition of TiN or DLC only on titanium component of the Nitinol – Ti6Al4V friction combination can significantly improve it’s wear performance. Deposition of TiN or DLC coating on both components was found not to be effective due to delamination or wearing through of the coatings.
Untypical corrosion damage including erosions combined with the build-up of titanium oxide as a corrosion product on the surface of explanted Nitinol spinal rods in the areas where it was in contact ...with titanium pedicle screw head is reported. It was suggested that Nitinol rods might have inferior fretting corrosion resistance compared with that made of titanium or CoCr.
Fretting corrosion of Nitinol spinal rods with titanium (Ti6Al4V) pedicle screws were tested in-vitro by conducting a series of potentiostatic measurements of the peak-to-peak values of fretting corrosion current under bending in a 10% solution of calf serum in PBS. The test included Nitinol rods locked in titanium pedicle screws of different designs. Performance of commercially available titanium (Ti6Al4V) and CoCr spinal rods was also investigated for a comparison. Corrosion damage observed after the in-vitro tests was studied using SEM and EDAX analysis and was compared with patterns on Nitinol rods retrieved 12months after initial surgery. Metal ions level was measured in the test media after in-vitro experiments and in the blood and tissues of the patients who had the rods explanted.
The results of this study revealed that Nitinol spinal rods locked in Ti pedicle screws are susceptible to fretting corrosion demonstrating higher fretting corrosion current compared with commercially used Ti6Al4V and CoCr rods. On the surface of Nitinol rods after in-vitro tests and on those retrieved from the patients similar corrosion patterns were observed. Improved resistance to fretting corrosion was observed with Nitinol rods in the in-vitro tests where pedicle screws were used with a stiffer locking mechanism. Since the development of the localized corrosion damage might increase the risk of premature fatigue failure of the rods and result in leaching of Ni ions, it is concluded that Nitinol rods should not be used in conjunction with Ti pedicle screws without special protection especially where the design provides a high degree of mobility to the rods.
•Erosions and built-up of Ti oxide on explanted Nitinol spinal rods are observed.•The damage is localized in the area where rods were in contact with Ti pedicle screw.•Nitinol has lower resistance to fretting corrosion compared with Ti6Al4V and CoCr.•Corrosion patterns on explanted and laboratory tested Nitinol rods are similar.•Nitinol rods performance improves in pedicle screws with stiffer locking mechanism.
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