nitinol and Scoliosis

Biomechanical analysis of scoliosis instrumentation using superelastic Nickel-titanium shape memory (SNT) rods.. To compare SNT with conventional Titanium (Ti) and Cobalt-chrome (Co-Cr) rods. A clinical trial has documented comparable efficacy between two adolescent idiopathic scoliosis (AIS) cohorts instrumented using SNT versus conventional Ti rods. The shape memory and superelasticity of the SNT rod are thought to allow easy rod insertion, progressive curve correction, and correction from spinal tissue relaxation, but study is yet to be done to assess the effects of the shape memory and superelasticity.. Instrumentations of AIS patients from the clinical trial were computationally simulated using SNT, Ti and Co-Cr rods (5.5 or 6 mm; 30°, 50° or 60° sagittal contouring angles; 0°, 25° or 50° coronal over-contouring angles). Curve correction, its improvement from stress relaxation in the spine, and loads in the instrumentation constructs were computed and compared.. The simulated main thoracic Cobb angles (MT) and thoracic kyphosis with the SNT rods were 4°-7° higher and 1°-2° lower than the Ti and Co-Cr rods, respectively. Bone-implant forces with Ti and Co-Cr rods were higher than the SNT rods by 84% and 130% at 18 °C and 35% and 65% at 37 °C, respectively (p < 0.001). Further corrections of the MT from the simulated stress relaxation in the spine were 4°-8° with the SNT rods versus 2°-5° with the Ti and Co-Cr rods (p < 0.001).. This study concurs with clinical observation that the SNT rods are easier to insert and can result in similar correction to the conventional rods. The SNT rods allow significantly lower bone-implant forces and have the ability to take advantage of post-instrumentation correction as the tissues relax.

Topics: Adolescent; Alloys; Biomechanical Phenomena; Child; Chromium Alloys; Computer Simulation; Female; Humans; Male; Prostheses and Implants; Prosthesis Design; Scoliosis; Spinal Fusion; Titanium; Treatment Outcome; Young Adult

We looked at long-term follow-up of spine stapling with Nitinol Staples. This was a cohort of all adolescent idiopathic scoliosis (AIS) patients with curves at high risk to progress based on curve magnitude, premenarchal status in all females, failure of brace treatment, and skeletal immaturity.. This is a single surgeon retrospective review of consecutive AIS patients treated with Nitinol staples for progressive scoliosis. Fourteen patients, 16 curves from 2005 to 2008 were eligible. Minimum curve for stapling was 30 degrees. Standard preoperative, intraoperative, and postoperative data were collected. All patients were followed for a minimum of 36 months and to skeletal maturity. Three groups were: improved (group 1), correction of any amount; minimal progression (group 2), progression ≤10 degrees; and failure (group 3), ≥10 degrees of progression.. A total of 13 thoracic curves and 2 compensatory lumbar curves met the inclusion criteria (94%). Average follow-up was 61 months. The mean preoperative main thoracic curve was 35 degrees. All but 1 patients progressed at least 9 degrees in a brace prior to stapling. Females were all premenarchal, 10 patients were Risser 0 and 3 Risser 1. The average number of vertebrae stapled per curve was 6. Group 1 included 6 curves (40%). Group 2, 5 curves (33%). Group 3, 4 curves (27%). Three patients went on to uncomplicated fusion. Final curve measurement at the end of follow-up or before fusion (P=0.0037), curve progression (P≤0.001), and percentage of coronal correction on first postoperative standing radiograph (P=0.042) were the significant differences between groups 1+2 (successful) versus group 3 (failures). In total, 73% of this group either progressed ≤10 degrees or improved.. This is the first study that follows AIS patients treated with spine stapling to skeletal maturity. Staples likely changed natural history in some of our patients. Initial percentage of correction on first standing postoperative PA x-rays was the only predictor of success. Stapling was safe without any long-term complications.. Level III-retrospective study.

Topics: Adolescent; Aftercare; Alloys; Bone Development; Child; Disease Progression; Female; Humans; Lumbar Vertebrae; Male; Radiography; Reoperation; Retrospective Studies; Scoliosis; Spinal Fusion; Surgical Stapling; Thoracic Vertebrae; Time Factors; Treatment Outcome

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).. 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.. 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.. 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.. The volume wear rate of LSZ-4D device was found to be 12.5 mm per year from which 5 mm³ 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.. 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.

Topics: Adolescent; Alloys; Biocompatible Materials; Child; Chromium Alloys; Device Removal; Female; Friction; Humans; Male; Materials Testing; Microscopy, Electron, Scanning; Orthopedic Fixation Devices; Prostheses and Implants; Prosthesis Design; Scoliosis; Surface Properties; Titanium

NiTinol shape memory alloy is characterized by its malleability at low temperatures and its ability to return to a preconfigured shape above its activation temperature. This process can be utilized to assist in scoliosis correction. The goal of this retrospective study was to evaluate the clinical and radiographic results of intraoperative use of shape memory alloy rod in the correction of scoliosis. From May 2002 to September 2006, 38 scoliosis patients (ranging from 50° to 120°; 22 cases over 70°) who underwent shape memory alloy-assisted correction in our institute were reviewed. During the operation, a shape memory alloy rod served as a temporary correction tool. Following correction, the rod was replaced by a rigid rod. The mean blood loss at surgery was 680 ± 584 ml; the mean operative time was 278 ± 62 min. The major Cobb angle improved from an average 78.4° preoperatively to 24.3° postoperatively (total percent correction 71.4%). In 16 patients with a major curve <70° and flexibility of 52.7%, the deformity improved from 58.4° preoperatively to 12.3° postoperatively (percent correction, 78.9%). In 22 patients with a major curve >70° and flexibility of 25.6%, the deformity improved from 94.1° preoperatively to 30.1° postoperatively (percent correction, 68.1%). Only one case had a deep infection. There were no neurologic, vascular or correction-related complications such as screw pullout or metal fracture. The study shows that the intraoperative use of a shape memory rod is a safe and effective method to correct scoliosis.

Topics: Adolescent; Adult; Alloys; Child; Female; Humans; Internal Fixators; Lumbar Vertebrae; Male; Radiography; Retrospective Studies; Scoliosis; Spinal Fusion; Thoracic Vertebrae; Treatment Outcome

Single- or dual-shape memory metal (nitinol) rods were used to create spinal deformity in a mini-pig model.. To determine the practicality of employing nitinol rods for clinical spinal deformity correction using an animal deformity creation model.. Nitinol rods can, theoretically, be approximated to curved spines when cooled/malleable, achieving spinal deformity correction on warming and returning to their original (straight) shape. Square cross-sectional rods may allow transverse plane correction. Single-rod constructs could achieve greater deformity correction clinically, whereas dual rods provide lower implant failure risk. The clinical feasibility and potential effectiveness of single versus dual nitinol rod constructs in creating spinal deformity in an animal model was studied.. Twenty mature mini-pigs were grouped: single rod with screws locked to the rod, single rod with screws unlocked, dual rods--locked, dual rods--unlocked. Square nitinol rods (80° manufactured curvature) were cooled (-20°C), straightened, placed into multilevel square-headed pedicle screws and warmed (40°C). Serial radiographs followed deformity creation over 12 weeks. Single versus dual rods, locked versus unlocked rods were compared (P<0.01). Computed tomography showed screw placement and fusion (none attempted). Preoperative and 12-week postoperative serum nickel levels were compared (P<0.05).. Scoliotic deformities were created immediately in single and dual rod groups (28°±8°, 26°±7°; P=0.59); locked and unlocked groups (24°±7°, 30°±6°; P=0.08). At final follow-up, there was no difference between single and dual rods (31°±11°, 28°±10°; P=0.58); unlocked rods and locked rods were 34.9°±9.4° and 25.0°±8.1° (P=0.02). No implant failure occurred, however, the aggressive rod contour led to vertebral endplate fractures. Serum nickel 12 weeks post rod placement were unchanged from preop levels (5.1±0.6 μg/L, 4.7±0.2 μg/L, P=0.10).. Nitinol rods, reliable in creating spinal deformity in an animal model, could potentially straighten deformed spines. Square rods, facilitated by markedly reduced stiffness when cooled, have the potential to predictably perform axial plane correction.

Topics: Alloys; Animals; Bone Nails; Bone Screws; Female; Male; Models, Animal; Orthopedic Procedures; Reproducibility of Results; Scoliosis; Spine; Swine; Swine, Miniature; Temperature; Tomography, X-Ray Computed

An in vitro immature bovine study of thoracic spine fixation using shape memory alloy for minimally invasive adolescent scoliosis treatment.. The purpose of this study was to detect differences in thoracic spine range of motion due to the placement of spinal staples manufactured from a common shape memory alloy.. Scoliosis surgery attempts to both correct the existing deformity and prevent further curve progression. The gold standard in surgical treatment of scoliosis is posterior instrumentation and fusion using pedicle screws or hooks. Fusionless techniques generally use less invasive procedures than fusion methods. One such technique, anterior stapling of the vertebrae, theoretically enables preservation of growth, motion, and spinal function. However, the degree of stability afforded by this method has not been reported.. Eight immature bovine specimens (T4-T9) were used in this study. Nitinol staples were cooled to below the transition temperature and placed on the spine such that they spanned the disc space. The specimen was then heated above the critical temperature and the staple tines engaged the vertebral endplates. A common flexibility protocol was used to determine the ranges of motion (ROM) in flexion-extension, lateral bending, and axial rotation. The intact spine and 4 construct variants (combinations of staple type and placement) were evaluated using this testing protocol. ANOVA statistics with post hoc testing was used to discern statistical differences.. Not all staple variants were able to achieve significant reductions with respect to the intact condition. ROM was significantly restricted in axial rotation and lateral bending with the introduction of staple instrumentation. Further, there seemed to be a mechanical equivalence between a single double-prong staple and 2 single-prong staples. Our data indicate that staple fixation does not result in consistently elevated adjacent segment motion.. Our results imply that staples are able to significantly restrict motion while not achieving motion reductions that one would achieve with fusion-promoting instrumentation. The choice between double- and single-prong staples remains a matter of preference. Neither staple variant provided a mechanical advantage. The single-prong staple did allow more control in the placement of the staple over the disc space. The addition of an anterior staple significantly reduced the overall flexion-extension ROM.

Topics: Alloys; Animals; Biomechanical Phenomena; Cattle; Internal Fixators; Minimally Invasive Surgical Procedures; Models, Animal; Orthopedic Procedures; Range of Motion, Articular; Scoliosis; Surgical Fixation Devices; Surgical Stapling; Thoracic Vertebrae

Retrospective review.. To report the feasibility, safety, and utility of vertebral body stapling without fusion as an alternative treatment for adolescent idiopathic scoliosis.. The success rate of brace treatment of adolescent idiopathic scoliosis ranges from 50% to 82%. However, poor self-image and brace compliance are issues for the patient. An alternative method of treatment such as a motion-preserving vertebral body stapling to provide curve stability would be desirable.. We retrospectively reviewed 21 patients (27 curves) with adolescent idiopathic scoliosis treated with vertebral body stapling. Patients were immature as defined by Risser sign or=6 degrees or beyond 50 degrees was considered a failure of treatment. Of these 10 patients, 6 (60%) remained stable or improved and 4 (40%) progressed. One of 10 (10%) in the stapling group had progressed beyond 50 degrees and went on to fusion. Six patients required stapling of a second curve, three as part of the primary surgery, and three as a second stage, because a second untreated curve progressed. The results need to be considered with caution, as the follow-up is still short.. The data demonstrate that vertebral body stapling for the treatment of scoliosis in the adolescent was feasible and safe in this group of 21 patients. In the short-term, stapling appears to have utility in stabilizing curves of progressive adolescent idiopathic scoliosis.

Topics: Adolescent; Alloys; Child; Feasibility Studies; Female; Follow-Up Studies; Humans; Male; Orthopedic Procedures; Reproducibility of Results; Retrospective Studies; Scoliosis; Spine; Treatment Outcome

Nitinol, a shape memory alloy, is flexible at low temperatures but retains its original shape when heated. This offers interesting possibilities for scoliosis correction. Of the shape memory alloys, nitinol is the most promising medically because of biocompatibility and the ability to control transition temperature. In vivo: Six goats with experimental scoliosis were instrumented with 6-mm nitinol rods. The rods were transformed, and the scoliosis corrected, in the awakened goats by 450-kHz radio frequency induction heating. The curves averaged 41 degrees before instrumentation, 33 degrees after instrumentation, and 11 degrees after rod transformation. The animals tolerated the heating without discomfort, neurologic injury, or evidence of thermal injury to the tissues or the spinal cord. In vitro: Nitinol rods were tested under both constant deflection and constant loading conditions and plotted temperature versus either force or displacement. The 6-mm rod generated forces of 200 N. The 9-mm rod generated up to 500 N. We safely coupled shape memory alloy transformation to the spine and corrected an experimental spinal deformity in awake animals. The forces generated can be estimated by the rod's curvature and temperature. The use of shape memory alloys allows continuous neurologic monitoring during awake correction, true rotational correction by rod torsion, and the potential option of periodic correction to take advantage of spinal viscoelasticity and the potential of true rotational correction by rod torsion.

Topics: Alloys; Animals; Biomechanical Phenomena; Goats; Materials Testing; Orthopedic Fixation Devices; Radiography; Scoliosis; Spine; Temperature

Nitinol, a metal alloy which is able to remember (and return to with slight heating) the shape it had before it was deformed, is demonstrated to be useful in the Harrington rod treatment of scoliosis. A bent nitinol rod can return to its original straight length, applying both axial and lateral forces to the spine during the operation of postoperatively by means of external heating. A research program using simulated spinal forces in a test fixture and implantation in a cadaver was undertaken to show the feasibility of modifying the existing procedure.

Topics: Adult; Alloys; Elasticity; Female; Humans; Nickel; Scoliosis; Stainless Steel; Temperature; Titanium; Traction