Titanium Constructs Research Articles

Blood titanium levels in patients with large and sliding titanium implants

BackgroundTitanium, which is known to be a highly biologically inert element, is one of the most commonly used metals in orthopaedic implants. While cobalt and chromium blood metal ion testing is routinely used in the clinical monitoring of patients with metal-on-metal hip implants, much less is known about the levels of titanium in patients with other implant types. The aim of this study was to better understand the normal ranges of blood titanium levels in patients implanted with large and sliding titanium constructs by comparison with reference levels from conventional titanium hips.MethodsThis study examined data collected from 136 patients. Over a period of 24 months, whole blood samples were collected from 41 patients implanted with large titanium implants: long (range 15 to 30 cm) spine rods with a sliding mechanism (“spine rods”, n = 18), long bone tumour implants (“tumour implants”, n = 13) and 3D-printed customised massive acetabular defect implants (“massive acetabular implants”, n = 10). This data was compared with standard, uncemented primary titanium hip implants (“standard hips”, 15 cm long) (n = 95). Clinical, imaging and blood titanium levels data were collected for all patients and compared statistically between the different groups.ResultsThe median (range) of blood titanium levels of the standard hip, spine rods, femoral tumour implants and massive acetabular implants were 1.2 ppb (0.6–4.9), 9.7 ppb (4.0–25.4), 2.6 ppb (0.4–104.4) and 5.7 ppb (1.6–31.5) respectively. Spine rods and massive acetabular implants had significantly greater blood titanium levels compared to the standard hips group (p < 0.001).ConclusionThis study showed that titanium orthopaedic implants that are large and/or have a sliding mechanism have higher blood titanium levels compared to well-functioning, conventionally sized titanium hips. Reassuringly, the increased levels did not appear to induce adverse metal reactions. This study provides useful baseline data for future studies aimed at assessing blood titanium levels as a biomarker for implant function.

Porous Titanium by Additive Manufacturing: A Focus on Surfaces for Bone Integration

Additive manufacturing (AM) is gaining increasing interest for realization of customized porous titanium constructs for biomedical applications and, in particular, for bone substitution. As first, the present review gives a short introduction on the techniques used for additive manufacturing of Ti/Ti-Alloys (Direct Energy Deposition—DED, Selective Laser Melting—SLM and Electron Beam Melting—EBM) and on the main bulk properties of additively manufactured titanium porous structures. Then, it discusses the main advancements in surface modifications of additively manufactured titanium constructs for bone contact applications. Even if specific surface modifications of constructs from AM are currently not widely explored, it is a critical open issue for application in biomedical implants. Some thermal, chemical, electrochemical, and hydrothermal treatments as well as different coatings are here described. The main aim of these treatments is the development of surface micro/nano textures, specific ion release, and addition of bioactivity to induce bone bonding and antibacterial activity. Physicochemical characterizations, in vitro bioactivity tests, protein absorption, in vitro (cellular/bacterial) and in vivo tests reported in the literature for bare and surface modified AM Ti-based constructs are here reviewed. Future perspectives for development of innovative additively manufactured titanium implants are also discussed.

Nitinol Memory Rods Versus Titanium Rods: A Biomechanical Comparison of Posterior Spinal Instrumentation in a Synthetic Corpectomy Model.

Study Design:Biomechanical investigation.Objective:To compare the biomechanical performance of nitinol memory metal rods and titanium rods when used as posterior spinal instrumentation in a synthetic model.Methods:Biomechanical testing was performed using ultra-high-molecular-weight polyethylene blocks. Nineteen spinal constructs were created to allow comparison of 5.5-mm nitinol rods with 5.5-mm titanium rods. Static compression and rotational testing were performed on an Instron 8874 and Instron 4202 at 37°C to simulate body temperature.Results:The average titanium construct stiffness under static compression or bending was 47.2 ± 9.1 N/mm while nitinol’s stiffness averaged 48.9 ± 12.4 N/mm (P = .83). During axial rotation testing, the nitinol rod system showed no torsional stiffness difference from the titanium system: 0.95 ± 0.03 Nm/deg versus 0.96 ± 0.17 Nm/deg, respectively (P = 0.91). There was a statistically significant difference between the average torsional yield point for the titanium constructs (14.4 ± 1.6 Nm/deg) and nitinol constructs (21.3 ± 0.8 Nm/deg) (P = .004). The torsional toughness of the nitinol constructs was also statistically greater than the titanium rods: 473 GN/m3 versus 784 GN/m3 (P = .0006). There was no statistically significant difference between the nitinol group sustaining a higher number of fatigue cycles until failure and the titanium group (181 660 cycles vs 64 104 cycles, respectively, P = .22).Conclusions:This study provides biomechanical evidence that nitinol rods used in a posterior construct are comparable to titanium rods with regard to compression and have increased torsional failure load and torsional toughness. While nitinol trended toward superior fatigue resistance, there was no significant difference in nitinol versus titanium construct fatigue resistance.

Chest wall reconstruction after tumor resection

Pediatric chest wall tumors are rare. Malignancies predominate of which sarcomas are the most common. Their resection and the subsequent reconstruction of the chest wall has been a surgical challenge since Dr. Frederick W. Parham published his first comprehensive account on the subject in 1898. Chest wall reconstruction is age, site and pathology dependent, must preserve long term function and cosmesis, must accommodate future growth and development, and must not be a hindrance to adjuvant radiotherapy. Bony reconstruction can be relatively simple or complex involving combinations of synthetic meshes, bioprosthetic materials, steel or titanium constructs, autografts, homografts and porcine or bovine xenografts. Soft tissue coverage can be achieved with direct closure, skin grafts, local advancement flaps, pedicled or free myocutaneous or osseomyocutaneous flaps or a combination of these. Complications to be avoided include scoliosis, pain and activity restriction, restrictive pulmonary deficits and interference with adjuvant radiotherapy which may result in tumor recurrence. Advances in cancer therapy have improved short- and long-term survival but significant functional and cosmetic challenges remain particularly for large chest wall defects in the very young. The future may lie with absorbable semi-rigid meshes, biointegratable acellular homografts and xenografts, demineralized bone matrices and bone marrow stromal cells, the patient's own lab-grown stem-cell based vascularized osseomyocutaneous chest wall grafts or the obsolescence of surgical resection altogether in the age of targeted anti-tumor and immune based therapy.

The Biomechanical Study of the Bioabsorbable Plates in Finger Fracture Fixation

Objectives: Plates and screws have been proven to be a strong construct for the treatment of finger fractures as it allows for immediate postoperative mobilization. However, plates made in metal can be high in profile and may lead to both adjacent tendons and soft tissue irritation. Meanwhile bioabsorbable plates and screws have the advantage of being more conforming and low in profile. Yet there are concerns on its biomechanical strength. This study aims to explore the biomechanical strength of bioabsorbable construct by comparing with its titanium counterpart. Materials and Methods: Fifty-four simulated bone models of hand with a transverse osteotomy were used to simulate a finger fracture. A control group of 18 bone models (group 0) were fixed with a standard 4-hole, 1.5-mm titanium straight plates. A second set of 18 bone models (group 1) were fixed by 1.5-mm bioabsorbable mesh plate which was fashioned to cover half of the circumference of the bone. For the remaining set of 18 bone models, similar fixation was employed using the bioabsorbable plates except that it covered two-third instead of half of the circumference of the bone. All bone models were mounted to the Servo-hydraulic MTS 858 Bionix testing machine for biomechanical testing. Six bone models from each group were tested for maximum bending force, maximum torsional force, and fatigue property. The fatigue property was to simulate the load that the fixation construct would encounter over a 6 weeks period, ie, a period that allows the bone to heal with callous. It was set at 100 000 cycles at a displacement rate of 1 mm/s. Results: The average maximum bending force for group 0, group 1, and group 2 were 67.0 ± 10.2 N, 40.8 ± 15.0 N, and 43.3 ± 15.0 N, respectively. There was a significance between the metal and both the bioabsorbable groups with P &lt; .001. For the average maximum torsional force, group 0 was 0.66 ± 0.06 Nm, group 1 was 0.27 ± 0.06 Nm and group 2 was 0.32 ± 0.07 Nm. A significance difference between the metal and both the bioabsorbable groups was noted at P &lt; .001. For the fatigue tests, all constructs, except 2 in group 1, were able to withstand 1 000 000 cycles. The subsequent force to failure of both the bioabsorbable constructs were only 10% of the titanium constructs (6.8 N vs 67.6 N) of which the P was &lt;.001. No significant difference was noted in maximum bending strength, maximum torsion force, and fatigue stress between the 2 groups of bioabsorbable constructs. Conclusion: The biomechanical strength of the bioabsorbable plates is inferior to the titanium plates. Yet as the requirement of finger fracture fixation is mainly to provide a stable environment for finger mobilization, the fatigue property of a construct appears to be more important. Thus, the strength of bioabsorbable plate and screw construct may still be strong enough to allow the fracture to heal.

Mechanical Construct Characteristics Predisposing to Non-union After Locked Lateral Plating of Distal Femur Fractures.

To identify discrete construct characteristics related to overall construct rigidity that may be independent predictors of nonunion after lateral locked plate (LLP) fixation of distal femur fractures. Retrospective case-control study. Three level-1 urban trauma centers. Two hundred and seventy-one supracondylar femoral fractures treated with LLP at 3 affiliated level 1 urban trauma centers between August 2004 and December 2010. Nonunion was defined as a secondary procedure for poor healing. Construct variables included: (1) combined plate design and material variable, (2) Plate length, (3) # screws proximal to fracture, (4) total screw density (TSD), (5) proximal screw density (PSD), (6) presence of a screw crossing the main fracture, and (7) rigidity score multivariable analysis was performed using logistic regression to identify independent risk factors for nonunion. LLP fixation. Nonunion. Nonunion rate was 13.3% (n = 36). There was a significant association between plate design/material and nonunion with 41% of stainless constructs and 10% of titanium constructs resulting in a nonunion (P < 0.001). Rigidity scores reached significance (P = 0.001) with constructs resulting in a nonunion having higher scores. No significant univariate differences with respect to number of proximal screws, plate length, total screw density, or proximal screw density were observed between healed fractures and those with nonunion. Results of the multivariate analysis confirmed that the primary significant independent predictor of nonunion was plate design/material (odds ratio, 6.8; 95% CI, 2.9-16.1; P < 0.001). When treating distal femur fractures with LLP, combined plate design and material variable has a highly significant influence on the risk of nonunion independent of any other construct variable. Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

From Bench to Bedside: How Stiff is Too Stiff? Far-cortical Locking or Dynamic Locked Plating May Obviate the Question.

From Bench to Bedside: How Stiff is Too Stiff? Far-cortical Locking or Dynamic Locked Plating May Obviate the Question.

In Vitro Comparison of Dynesys, PEEK, and Titanium Constructs in the Lumbar Spine.

Introduction. Pedicle based posterior dynamic stabilization systems aim to stabilize the pathologic spine while also allowing sufficient motion to mitigate adjacent level effects. Two flexible constructs that have been proposed to act in such a manner, the Dynesys Dynamic Stabilization System and PEEK rod, have yet to be directly compared in vitro to a rigid Titanium rod. Methods. Human lumbar specimens were tested in flexion extension, lateral bending, and axial torsion to evaluate the following conditions at L4-L5: Intact, Dynesys, PEEK rod, Titanium rod, and Destabilized. Intervertebral range of motion, interpedicular travel, and interpedicular displacement metrics were evaluated from 3rd-cycle data using an optoelectric tracking system. Results. Statistically significant decreases in ROM compared to Intact and Destabilized conditions were detected for the instrumented conditions during flexion extension and lateral bending. AT ROM was significantly less than Destabilized but not the Intact condition. Similar trends were found for interpedicular displacement in all modes of loading; however, interpedicular travel trends were less consistent. More importantly, no metrics under any mode of loading revealed significant differences between Dynesys, PEEK, and Titanium. Conclusion. The results of this study support previous findings that Dynesys and PEEK constructs behave similarly to a Titanium rod in vitro.

PEEK rod systems for the spine

Traditional materials for the spine such as titanium and stainless steel have produced satisfying long-term fusion rates, mainly due to their strength and stiffness. However, although fixation with titanium rods leads to high fusion rates, increased stiffness of titanium constructs may also contribute to stress shielding and adjacent segment degeneration. Dynamic and flexible materials such as the Dynesys system allow better stress distribution to all of the spinal columns, but increase the rate of complications including screw loosening, infection, back and leg pain, and endplate vertebral fracture. Semi-rigid instrumentation systems using rods made from synthetic polymers such as the polyetheretherketone (PEEK) have been recently introduced as an alternative biomaterial for the spine. PEEK is a fully biocompatible and inert semi-crystalline thermoplastic polymer with minimal toxicity; it has a modulus of elasticity between that of cortical and cancellous bone, and significantly lower than titanium. However, there are very few clinical studies with small sample size and short-term follow-up using PEEK rod-pedicle screw spinal instrumentation systems. Additionally, their results are conflicting. To enhance the literature, this review discusses the effect of this medical for the spine and summarizes the results of the most important related series.

Comparative Analysis of the Oxygen Supply and Viability of Human Osteoblasts in Three-Dimensional Titanium Scaffolds Produced by Laser-Beam or Electron-Beam Melting.

Synthetic materials for bone replacement must ensure a sufficient mechanical stability and an adequate cell proliferation within the structures. Hereby, titanium materials are suitable for producing patient-individual porous bone scaffolds by using generative techniques. In this in vitro study, the viability of human osteoblasts was investigated in porous 3D Ti6Al4V scaffolds, which were produced by electron-beam (EBM) or laser-beam melting (LBM). For each examination, two cylindrical scaffolds (30 mm × 10 mm in size, 700 µm × 700 µm macropores) were placed on each other and seeded with cells. The oxygen consumption and the acidification in the center of the structures were investigated by means of microsensors. Additionally, the synthesis of pro-collagen type 1 was analyzed. On the LBM titanium scaffolds, vital bone cells were detected in the center and in the periphery after 8 days of cultivation. In the EBM titanium constructs, however, vital cells were only visible in the center. During the cultivation period, the cells increasingly produced procollagen type 1 in both scaffolds. In comparison to the periphery, the oxygen content in the center of the scaffolds slightly decreased. Furthermore, a slight acidification of the medium was detectable. Compared to LBM, the EBM titanium scaffolds showed a less favorable behavior with regard to cell seeding.

Aseptic Loosening of Pedicle Screw As a Result of Metal Wear Debris in a Pediatric Patient

This is a case report. To report a case of soft-tissue reaction to wear debris and osteolysis around a pedicle screw after posterior spine fusion in a pediatric patient. Posterior spine fusion with instrumentation is a standard procedure for stabilization and curve correction in patients with scoliosis. Late operative site pain accounts for the highest frequency of reoperation. Debris accumulation for steel and titanium constructs occurs at the pedicle screw-rod junction. Cellular reaction to metal wear may be responsible for osteolysis and aseptic loosening around spinal implants. A 14-year-old male patient with neurofibromatosis and right thoracic scoliosis of 50° underwent posterior spine fusion from T2 to T10. The postoperative course was complicated by continuous pain, and imaging studies demonstrated hardware failure, requiring a revision and subsequent development of a perihilar opacity of unknown origin. Further studies demonstrated hypermobility with adjacent soft-tissue reactivity and inflammation surrounding the right T5 transpedicle screw. After hardware removal, the patient's recovery was uneventful. Six months later, a repeated computed tomographic scan demonstrated resolution of the previously described soft-tissue mass and a satisfactory fusion of the thoracic spine. Metal wear debris can form in pediatric patients during the healing process after spinal fusions or when pseudarthrosis is present. Clinically, this manifests as back pain with a possible aseptic inflammatory abscess. Hardware removal can achieve resolution of symptoms and regression of inflammation.

Loss of apical vertebral derotation in adolescent idiopathic scoliosis: 2-year follow-up using multi-planar reconstruction computed tomography

The objective of this study was to evaluate 2years post-surgical loss of three-dimensional correction in adolescent idiopathic scoliosis (AIS) patients using multi-planar reconstruction computed tomography (CT). Twenty-seven AIS patients treated by segmental pedicle screw (PS) constructs were included in this study. Correction in the axial plane was evaluated using the "relative apical vertebral rotation angle" (rAVR), defined as the difference between the axial rotation angles of the upper instrumented vertebra and the apical vertebra on reconstructed axial CT images. The Cobb angle of the main curve and apical vertebral translation was measured to evaluate the coronal correction. Thoracic kyphosis was also measured for the evaluation of sagittal profile. Measurements were performed before surgery, and 1week and 2years after surgery. The relationships between the correction losses and skeletal maturity, and variety of spinal constructs were also evaluated. The mean preoperative Cobb angle of the major curve was 59.1°±11.2° before and 13.0°±7.2° immediately after surgery. Two years later, the mean Cobb angle had increased significantly, to 15.5°±7.8°, with a mean correction loss of 2.5°±1.5° (p<0.001). The mean preoperative rAVR of 28.5°±8.4° was corrected to 15.8°±7.8° after surgery. It had increased significantly to 18.5±8.4 by 2years after surgery, with a mean correction loss of 2.7°±1.0° (p<0.001). The mean correction losses for both the Cobb angle and rAVR were significantly greater in the skeletally immature patients. The significant correlations were recognized between the correction losses and the proportion of multi-axial screws, and the materials of constructs. Statistically significant loss of correction in the Cobb angle and apical vertebral axial rotation angle (AVR) were recognized 2years after surgery using PS constructs. The correction losses, especially AVR, were more evident in the skeletally immature patients, and in patients treated with more multi-axial screws and with titanium constructs rather than with stainless constructs.

Osteoinductive hydroxyapatite-coated titanium implants

Previous studies have shown that heterotopic induction of bone formation by calcium phosphate-based macroporous constructs is set into motion by the geometry of the implanted substrata, i.e. a sequence of repetitive concavities assembled within the macroporous spaces. The aim of this study was to construct osteoinductive titanium implants that per se, and without the exogenous application of the osteogenic soluble molecular signals of the transforming growth factor-β supergene family, would initiate the induction of bone formation. To generate intrinsically osteoinductive titanium implants for translation in clinical contexts, titanium grade Ti-6A1-4V cylinders of 15 mm in length and 3.85 mm in diameter, with or without concavities, were plasma sprayed with crystalline hydroxyapatite resulting in a uniform layer of 30 μm in thickness. Before coating, experimental titanium implants were prepared with a sequence of 36 repetitive concavities 1600 μm in diameter and 800 μm in depth, spaced a distance of 1000 μm apart. Mandibular molars and premolars were extracted to prepare edentulous mandibular ridges for later implantation. Planar and geometric hydroxyapatite-coated titanium constructs were implanted in the left and right edentulized hemi-mandibles, respectively, after a healing period of 7–8 months, 3 per hemi-mandible. Three planar and three geometric implants were implanted in the left and right tibiae, respectively; additionally, planar and geometric constructs were also inserted in the rectus abdominis muscle. Six animals were euthanized at 30 and 90 days after implantation; one animal had to be euthanized 5 days after surgery and the remaining animal was euthanized 31 months after implantation. Undecalcified longitudinal sections were precision-sawed, ground and polished to 40–60 μm; all sections were stained with a modified Goldner’s trichrome. Undecalcified specimen block preparation was performed using the EXAKT precision cutting and grinding system. Histomorphometric analyses of bone in contact (BIC) showed that on day 30 there was no difference between the geometric vs. planar control implants; on day 90, the ratio of BIC to surface within the geometric implants was greater than on the standard planar implants in both mandibular and tibial sites; 31 months after implantation, selected concavities cut into the geometric implants harvested from the rectus abdominis muscle showed the spontaneous induction of bone formation with mineralized bone surfaced by osteoid seams. These data in non-human primates indicate that geometrically-constructed plasma-sprayed titanium implants are per se osteogenic, the concavities providing a unique microenvironment to initiate bone differentiation by induction.

Novel titanium constructs for chest wall reconstruction in children

PurposeWe have previously reported the use of the vertical expandable prosthetic titanium rib (VEPTR) for treatment of thoracic dystrophy. This report describes our experience with this device and other novel titanium constructs for chest wall reconstruction. MethodsThis is a retrospective chart review of all children and adolescents undergoing chest wall reconstruction with titanium constructs between December 2005 and May 2010. ResultsSix patients have undergone chest wall reconstruction with VEPTR or other titanium constructs. Four had chest wall resection for primary malignancy, 1 had metastatic chest wall tumor resection, and 1 had congenital chest wall deformity. There were no immediate complications, and all patients have exhibited excellent respiratory function with no scoliosis. ConclusionsChest wall reconstruction after tumor resection or for primary chest wall deformities can be effectively accomplished with VEPTR and other customized titanium constructs. Goals should be durable protection of intrathoracic organs and preservation of thoracic volume and function throughout growth. Careful preoperative evaluation and patient-specific planning are important aspects of successful reconstruction.

Single cycle to failure in torsion of three standard and five locking plate constructs

The biomechanical properties of standard plates and recently designed locking plates were compared in torsion. We hypothesized that titanium (Ti) constructs would have the greatest deformation, and String of Pearls (SOP) constructs the greatest strength and stiffness. Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP, Ti LC-DCP, locking compression plate (LCP), 10 mm and 11 mm Advanced Locking Plate System (ALPS) 10 and 11, SOP and Fixin plates were applied to a validated bone model simulating a bridging osteosynthesis. Yield torque (strength), yield angle (deformation) and stiffness were compared using one-way ANOVA with post hoc Tukey (p <0.05). The ALPS 11 constructs had significantly greater elastic deformation than all constructs except for the ALPS 10. There were not any differences in strength observed except for the ALPS 10 constructs, which was less than that for the SOP, LCP, DCP and ALPS 11 constructs. No differences in construct torsional stiffness were observed with the SS LC-DCP, DCP, LCP and SOP constructs; however all had greater stiffness than all remaining constructs. The ALPS 10 construct had lower stiffness than all constructs. Modulus of elasticity of Ti explains the higher deformation and lower stiffness of these systems, with similar results for the Fixin due to its lower section modulus compared to all other plates. The SOP and standard constructs had surprisingly similar biomechanical properties in torsion. The rationale for selecting these implants for fracture repair likely needs to be based upon their differing biomechanical properties inherent to the diverse implant systems.

Single cycle to failure in bending of three standard and five locking plates and plate constructs

To evaluate the biomechanical properties of standard and locking plates in bending. We hypothesised that titanium (Ti) constructs would have the greatest deformation and that String of Pearl (SOP) constructs would have the greatest strength and stiffness, and would behave differently compared to plates alone. Dynamic compression plates (DCP), stainless steel (SS) limited contact (LC)-DCP®, Ti LC-DCP, locking compression plates (LCP), 10 mm and 11 mm advanced locking plate system (ALPS 10 / 11), SOP and Fixin plates were evaluated individually and as constructs applied to a validated bone model simulating a bridging osteosynthesis. Bending stiffness and strength were compared using one-way ANOVA with post hoc Tukey, and unpaired t-test (p <0.05). The SOP plates had significantly greater stiffness than all other plates; Ti LC-DCP, ALPS 10 and Fixin plates had significantly lower stiffness than all other plates. The SOP constructs had the highest mean bending stiffness, and strength that was significantly different from only the Ti LC-DCP, ALPS 10 and Fixin constructs. The ALPS 10 constructs had the lowest mean bending stiffness, and strength that was significantly different from only ALPS 11 and SOP constructs. Comparison of bending structural stiffness of plates versus constructs showed a significant difference in all plate pairs except for the DCP and ALPS 10. Due to differing plate construct properties inherent to these diverse implant systems, identical approaches to fracture management and plate application cannot be applied.

Biomechanics of polyaryletherketone rod composites and titanium rods for posterior lumbosacral instrumentation

Object Interest is increasing in the development of polyaryletherketone (PAEK) implants for posterior lumbar fusion. Due to their inherent physical properties, including radiolucency and the ability to customize stiffness with carbon fiber reinforcement, they may be more advantageous than traditional instrumentation materials. Customization of these materials may allow for the development of a system that is stiff enough to promote fusion, yet flexible enough to avoid instrumentation failure. To understand the feasibility of using such materials in posterior lumbosacral instrumentation, biomechanical performances were compared in pure moment and combined loadings between two different PAEK composite rods and titanium rods. Methods Four human cadaver L3–S1 segments were subjected to pure moment and combined (compressionflexion and compression-extension) loadings as intact specimens, and after L-4 laminectomy with complete L4–5 facetectomy. Pedicle screw/rod fixation constructs were placed from L-4 to S-1, and retested with titanium, pure poly(aryl-ether-ether-ketone) (PEEK), and carbon fiber reinforced PEEK (CFRP) rods. Reflective markers were fixed to each spinal segment. The range of motion data for the L3–S1 column and L4–5 surgical level were obtained using a digital 6-camera system. Four prewired strain gauges were glued to each rod at the level of the L-4 screw and were placed 90° apart along the axial plane of the rod to record local strain data in the combined loading mode. Biomechanical data were analyzed using the ANOVA techniques. Results In pure moment, when compared with intact specimens, each rod material similarly restricted motion in each mode of bending, except axial rotation (p &lt; 0.05). When compared with postfacetectomy specimens, each rod material similarly restricted motion (p &lt; 0.05) in all bending modes. In combined loading, rod stiffness was similar for each material. Rod strain was the least in the titanium construct, intermediate in the CFRP construct, and maximal in the pure PEEK construct. Conclusions Pure PEEK and CFRP rods confer equal stiffness and resistance to motion in lumbosacral instrumentation when compared with titanium constructs in single-cycle loading. The carbon fiber reinforcement reduces strain when compared with pure PEEK in single-cycle loading. These biomechanical responses, combined with its radiolucency, suggest that the CFRP may have an advantage over both titanium and pure PEEK rods as a material for use in posterior lumbosacral instrumentation. Benchtop fatigue testing of the CFRP constructs is needed for further examination of their responses under multicycle loading.

Engineering a Titanium and Polycaprolactone Construct for a Biocompatible Interface Between the Body and Artificial Limb

Intraosseous transcutaneous amputation prostheses may be able to overcome the problems that stem from the nonuniform distribution of pressure seen in the conventional stump-socket prosthetic replacement devices. Transcutaneous devices have had limited success in amputees. By optimizing the attachment of the skin to the prosthetic, intraosseous transcutaneous amputation prostheses may become clinically viable options. This report details studies evaluating the development of a modified titanium construct with a specially machined surface to increase the adherence of tissue as well as scaffold. A computer-aided biology tool was used to fabricate polycaprolactone (PCL) scaffolds with a specific three-dimensional architecture. To extrude the PCL, it was dissolved in acetic acid to produce a 70% PCL liquid. A scaffold with a porosity of >50% was fabricated to have a tensile strength similar to skin. The presence of a specially machined surface greatly increased the adhesion of the PCL scaffold to the titanium constructs. When the 70% PCL was properly neutralized by heating at 55 degrees C and washing in 90% ethanol (EtOH), there was only a decrease (10%) in the viability of cells seeded onto the PCL constructs when compared with the cells in culture. The antibacterial properties of titanium dioxide anatase, silver nanoparticles, and chlorhexidine diacetate mixed in either type I collagen or hyaluronic acid (HA) were assessed. The addition of 1% (w/w) chlorhexidine diacetate in HA resulted in a 71% decrease in bacteria seen in nontreated HA. These results show promise in developing a novel engineered titanium and PCL construct that promotes effective adhesion between the titanium-skin interface.

Titanium Versus Stainless Steel for Anterior Spinal Fusions

In vitro biomechanical evaluation of rod stress during physiologic loading of anterior scoliosis instrumentation. To determine effects of material properties and rod diameter on rod stresses in anterior scoliosis instrumentation. Relationships between instrumentation dimensions, materials, and potential rod failure in anterior scoliosis instrumentation remain unclear. Eighteen immature bovine spines were randomized to 3 groups: 1) 4.0-mm stainless steel, 2) 5.0-mm stainless steel, and 3) 4.75-mm titanium alloy. Spines underwent physiologic tests in flexion-extension, lateral bending, and torsion. Rod surface strains were converted to rod stress and normalized to each material's yield stress. Construct stiffness and the normalized rod stresses were compared with a one-way ANOVA (P < 0.05). The 4.0-mm steel and 4.75-mm titanium construct stiffness was similar across all tests. The 5.0-mm steel system was significantly stiffer than 4.0-mm steel (lateral bending/torsion) and 4.75-mm titanium (torsion/flexion) constructs. Rod surface stress was significantly lower for the 4.75-mm titanium rod compared with 4.0-mm and 5.0-mm steel rods for all tests. The percentage of yield stress was lowest for the 4.75-mm Ti rod for all tests due to titanium's greater yield stress. This suggests the 4.75-mm rod has a lower fatigue failure risk than either steel construct.

The Effects of Rod Contouring on Spinal Construct Fatigue Strength

In vitro fatigue loading using a corpectomy model outfitted with posterior pedicle screw instrumentation. The purpose of this study was to detect differences in fatigue resistance of titanium and stainless steel spinal constructs that use rods contoured using a French Bender, and to compare differences in fatigue resistance of contoured and straight titanium rods. Instrumentation failure is generally thought to be caused by fatigue or cyclic loading. Intraoperative contouring of the posterior rods is almost always required to match the native kyphotic (thoracic) or lordotic (cervical or lumbar) spinal curvature. How bending these rods affects their overall fatigue resistance is not well described. In addition, changes in fatigue resistance may be a function of material type. Spinal constructs were evaluated using the ASTM F1717-01 model. Two different titanium-based rods (Ti6AL4V and CpTi) and two different steel-based rods (Orthinox and 316L stainless steel) were evaluated in this study (n = 6 for each group). Rods were contoured at two points using a French Bender and were rigidly coupled to polyaxial pedicle screws within UHMWPE vertebral bodies. Constructs were cycled at a load ratio of 10 between a minimum and maximum loading regime of -250 N/-25 N and -700 N/-70 N at a frequency of 4 Hz. Estimated maximum nominal stresses at various points of interest in the spinal constructs were calculated using beam theory. Effects of the rod material, load, and stress on the number of cycles to failure were analyzed using Cox proportional hazards regression. All of the spinal constructs with contoured CpTi rods and contoured Ti6Al4V rods failed at one of the bends in the rods. Almost all of the spinal constructs with straight CpTi rods and straight Ti6Al4V rods failed where the blocker screw fastens the rod to the coupler of the polyaxial screw head. Contoured titanium constructs demonstrated significantly lower fatigue life than contoured 316L constructs. Contouring tended to lower the fatigue life of both the Ti6Al4V and CpTi constructs. Intraoperative rod contouring using a French Bender significantly reduces the fatigue life of titanium spinal constructs.