Mitsuru Takemoto

Bioactive Ti metal analogous to human cancellous bone: Fabrication by selective laser melting and chemical treatments

Selective laser melting (SLM) is a useful technique for preparing three-dimensional porous bodies with complicated internal structures directly from titanium (Ti) powders without any intermediate processing steps, with the products being expected to be useful as a bone substitute. In this study the necessary SLM processing conditions to obtain a dense product, such as the laser power, scanning speed, and hatching pattern, were investigated using a Ti powder of less than 45 μm particle size. The results show that a fully dense plate thinner than 1.8 mm was obtained when the laser power to scanning speed ratio was greater than 0.5 and the hatch spacing was less than the laser diameter, with a 30 μm thick powder layer. Porous Ti metals with structures analogous to human cancellous bone were fabricated and the compressive strength measured. The compressive strength was in the range 35-120 MPa when the porosity was in the range 75-55%. Porous Ti metals fabricated by SLM were heat-treated at 1300 °C for 1h in an argon gas atmosphere to smooth the surface. Such prepared specimens were subjected to NaOH, HCl, and heat treatment to provide bioactivity. Field emission scanning electron micrographs showed that fine networks of titanium oxide were formed over the whole surface of the porous body. These treated porous bodies formed bone-like apatite on their surfaces in a simulated body fluid within 3 days. In vivo studies showed that new bone penetrated into the pores and directly bonded to the walls within 12 weeks after implantation into the femur of Japanese white rabbits. The percentage bone affinity indices of the chemical- and heat-treated porous bodies were significantly higher than that of untreated implants.

Osteoinduction of porous Ti implants with a channel structure fabricated by selective laser melting.

Many studies have shown that certain biomaterials with specific porous structures can induce bone formation in non-osseous sites without the need for osteoinductive biomolecules, however, the mechanisms responsible for this phenomenon (intrinsic osteoinduction of biomaterials) remain unclear. In particular, to our knowledge the type of pore structure suitable for osteoinduction has not been reported in detail. In the present study we investigated the effects of interconnective pore size on osteoinductivity and the bone formation processes during osteoinduction. Selective laser melting was employed to fabricate porous Ti implants (diameter 3.3mm, length 15 mm) with a channel structure comprising four longitudinal square channels, representing pores, of different diagonal widths, 500, 600, 900, and 1200 μm (termed p500, p600, p900, and p1200, respectively). These were then subjected to chemical and heat treatments to induce bioactivity. Significant osteoinduction was observed in p500 and p600, with the highest observed osteoinduction occurring at 5mm from the end of the implants. A distance of 5mm probably provides a favorable balance between blood circulation and fluid movement. Thus, the simple architecture of the implants allowed effective investigation of the influence of the interconnective pore size on osteoinduction, as well as the relationship between bone quantity and its location for different pore sizes.

Vertebral artery injury during cervical spine surgery: a survey of more than 5600 operations.

Study Design. Retrospective survey. Objective. To clarify the present incidence and management of iatrogenic vertebral artery injury (VAI) during cervical spine surgery. Summary of Background Data. VAI is a rare complication of cervical spine surgery, but it may be catastrophic. Anterior cervical decompression (ACD) and posterior atlantoaxial transarticular screw fixation (Magerl fixation) have been the main causes, with reported incidences of 0.3% to 0.5% and 0% to 8.2%, respectively. Popular new surgical techniques, such as cervical pedicle screw or C1 lateral mass screw fixation, also entail the potential risk of VAI. Methods. A questionnaire was sent to our affiliated hospitals requesting information regarding iatrogenic VAI during cervical spine surgery. Results. Seven spine surgeon groups and 25 general orthopedist groups responded to the questionnaire, with a response rate of 89%. The overall incidence of VAI was 0.14% (8 cases among 5641 cervical spine surgeries). The incidence in anterior cervical decompression procedures was 0.18% and that in Magerl fixation was 1.3%. Inexperienced surgeons tended to commit VAI more frequently. One case of VAI during C1 lateral mass screw fixation was included, whereas there was no case of VAI caused by cervical pedicle screw fixation. In the case of “VAI in the screw hole,” hemostasis was obtained by tamponade or screw insertion, whereas “VAI in the open space” sometimes caused uncontrollable bleeding, in which embolization eventually stopped the bleeding. There were no deaths or apparent neurologic sequelae. Conclusion. The incidence of VAI during cervical spine surgery from this survey was similar to or slightly less than that in the literature. Tamponade was effective in many cases, but prompt consultation with an endovascular team is recommended if the bleeding is uncontrollable. Preoperative careful evaluation of the vertebral artery seems to be most important to prevent iatrogenic VAI and to avoid postoperative neurologic sequelae.

Effect of pore size on bone ingrowth into porous titanium implants fabricated by additive manufacturing: An in vivo experiment.

Selective laser melting (SLM) is an additive manufacturing technique with the ability to produce metallic scaffolds with accurately controlled pore size, porosity, and interconnectivity for orthopedic applications. However, the optimal pore structure of porous titanium manufactured by SLM remains unclear. In this study, we evaluated the effect of pore size with constant porosity on in vivo bone ingrowth in rabbits into porous titanium implants manufactured by SLM. Three porous titanium implants (with an intended porosity of 65% and pore sizes of 300, 600, and 900μm, designated the P300, P600, and P900 implants, respectively) were manufactured by SLM. A diamond lattice was adapted as the basic structure. Their porous structures were evaluated and verified using microfocus X-ray computed tomography. Their bone-implant fixation ability was evaluated by their implantation as porous-surfaced titanium plates into the cortical bone of the rabbit tibia. Bone ingrowth was evaluated by their implantation as cylindrical porous titanium implants into the cancellous bone of the rabbit femur for 2, 4, and 8weeks. The average pore sizes of the P300, P600, and P900 implants were 309, 632, and 956μm, respectively. The P600 implant demonstrated a significantly higher fixation ability at 2weeks than the other implants. After 4weeks, all models had sufficiently high fixation ability in a detaching test. Bone ingrowth into the P300 implant was lower than into the other implants at 4weeks. Because of its appropriate mechanical strength, high fixation ability, and rapid bone ingrowth, our results indicate that the pore structure of the P600 implant is a suitable porous structure for orthopedic implants manufactured by SLM.

Positively charged bioactive Ti metal prepared by simple chemical and heat treatments

A highly bioactive bone-bonding Ti metal was obtained when Ti metal was simply heat-treated after a common acid treatment. This bone-bonding property was ascribed to the formation of apatite on the Ti metal in a body environment. The formation of apatite on the Ti metal was induced neither by its surface roughness nor by the rutile phase precipitated on its surface, but by its positively charged surface. The surface of the Ti metal was positively charged because acid groups were adsorbed on titanium hydride formed on the Ti metal by the acid treatment, and remained even after the titanium hydride was transformed into titanium oxide by the subsequent heat treatment. These results provide a new principle based on a positively charged surface for obtaining bioactive materials.

Bone bonding bioactivity of Ti metal and Ti–Zr–Nb–Ta alloys with Ca ions incorporated on their surfaces by simple chemical and heat treatments

Ti15Zr4Nb4Ta and Ti29Nb13Ta4.6Zr, which do not contain the potentially cytotoxic elements V and Al, represent a new generation of alloys with improved corrosion resistance, mechanical properties, and cytocompatibility. Recently it has become possible for the apatite forming ability of these alloys to be ascertained by treatment with alkali, CaCl2, heat, and water (ACaHW). In order to confirm the actual in vivo bioactivity of commercially pure titanium (cp-Ti) and these alloys after subjecting them to ACaHW treatment at different temperatures, the bone bonding strength of implants made from these materials was evaluated. The failure load between implant and bone was measured for treated and untreated plates at 4, 8, 16, and 26 weeks after implantation in rabbit tibia. The untreated implants showed almost no bonding, whereas all treated implants showed successful bonding by 4 weeks, and the failure load subsequently increased with time. This suggests that a simple and economical ACaHW treatment could successfully be used to impart bone bonding bioactivity to Ti metal and Ti-Zr-Nb-Ta alloys in vivo. In particular, implants heat treated at 700 °C exhibited significantly greater bone bonding strength, as well as augmented in vitro apatite formation, in comparison with those treated at 600 °C. Thus, with this improved bioactive treatment process these advantageous Ti-Zr-Nb-Ta alloys can serve as useful candidates for orthopedic devices.

O-c2 Angle as a Predictor of Dyspnea and/or Dysphagia After Occipitocervical Fusion

Study Design. A retrospective clinical study. Objective. To confirm the impact of the O-C2 angle on dyspnea and dysphagia after posterior occipitocervical (O-C) fusion. Summary of Background Data. Dyspnea and dysphagia are complications of posterior O-C fusion with malalignment, and may be prolonged or occasionally serious. However, it is difficult to select a safe alignment during surgery, and no indicators of the appropriate alignment have been available to preclude these complications. Methods. The authors retrospectively reviewed 29 consecutive patients who had undergone O-C or occipitocervicothoracic fusion between 2003 and 2008. Data were analyzed for O-C2 angles on plain radiographs and the axial computed tomographic cross-sectional areas of the oropharynx just cranial to the epiglottis before and after surgery. The patients were grouped according to whether they developed postoperative dyspnea and/or dysphagia (group A) or not (group B). Results. After surgery, 4 patients complained of dysphagia, and 1 patient had dyspnea and dysphagia, although they had all undergone short O-C fusions. The difference in the O-C2 angle (dOC2A = postoperative O-C2 angle − preoperative O-C2 angle) and the percentage change in the cross-sectional area of the oropharynx (S) before and after surgery (% dS) were linearly correlated. Both dOC2A and % dS were significantly lower in group A than in group B. All patients with dOC2A of less than −10° showed % dS of less than −40%, and developed dyspnea and/or dysphagia after surgery. Conversely, no patients with positive dOC2A developed these complications. Conclusion. The O-C2 angle has considerable impact on dyspnea and/or dysphagia after O-C fusion. The O-C2 angle is easily measured during surgery and can be a practical index with which to avoid postoperative dyspnea and dysphagia.

A porous bioactive titanium implant for spinal interbody fusion: an experimental study using a canine model

OBJECT Porous biomaterials with adequate pore structure and appropriate mechanical properties are expected to provide a new generation of devices for spinal interbody fusion because of their potential to eliminate bone grafting. The purpose of this study was to evaluate the fusion characteristics of porous bioactive titanium implants using a canine anterior interbody fusion model. METHODS Porous titanium implants sintered with volatile spacer particles (porosity 50%, average pore size 303 microm, compressive strength 116.3 MPa) were subjected to chemical and thermal treatments that give a bioactive microporous titania layer on the titanium surface (BT implant). Ten adult female beagle dogs underwent anterior lumbar interbody fusion at L6-7 using either BT implants or nontreated (NT) implants, followed by posterior spinous process wiring and facet screw fixation. Radiographic evaluations were performed at 1, 2, and 3 months postoperatively using X-ray fluoroscopy. Animals were killed 3 months postoperatively, and fusion status was evaluated by manual palpation and histological examination. RESULTS Interbody fusion was confirmed in all five dogs in the BT group and three of five dogs in the NT group. Histological examination demonstrated a large amount of new bone formation with marrowlike tissue in the BT implants and primarily fibrous tissue formation in the NT implants. CONCLUSIONS Bioactive treatment effectively enhanced the fusion ability of the porous titanium implants. These findings, coupled with the appropriate mechanical properties in load-bearing conditions, indicate that these porous bioactive titanium implants represent a new generation of biomaterial for spinal interbody fusion.

Effect of indirect neural decompression through oblique lateral interbody fusion for degenerative lumbar disease.

Study Design. Prospective consecutive clinical study to assess the decompressive benefit and outcome of oblique lateral interbody fusion for lumbar degenerative diseases. Objective. To evaluate radiologically the effect of interbody distraction upon neural patency via an anterolateral retroperitoneal approach for the treatment of lumbar degenerative diseases. Summary of Background Data. Traditional treatment for symptomatic lumbar stenosis uses direct posterior decompression with or without fusion. Symptoms of radiculopathy and neurological claudication may also be alleviated indirectly through restoration of intervertebral and foraminal heights and correction of spinal alignment. Methods. Twenty-eight consecutive patients presenting with degenerative conditions that included concomitant lumbar stenosis underwent oblique lateral interbody fusion combined with percutaneous pedicle screw fixation at 52 lumbar levels without neuromonitoring. Magnetic resonance images were obtained successfully for 48 of 52 levels. The cross-sectional area of the thecal sac (CSA) was measured preoperatively and postoperatively on T2-weighted axial magnetic resonance images. Differences in CSA were compared, and the relationship between the ratio of CSA extension and that of the preoperative CSA was assessed. The change in disc height and segmental disc angle were measured. The relationships between CSA, disc height, segmental disc angle, and clinical results were assessed by correlational analysis. Results. Twenty-eight oblique lateral interbody fusions were performed successfully without neural complications. There was clinical improvement in all cases. The mean CSA increased from 99.6 mm2 preoperatively to 134.3 mm2 postoperatively (P < 0.001). The median CSA extension ratio was 30.2% and this correlated inversely with preoperative CSA. Disc height, segmental disc angle, and clinical results improved significantly. Multivariate regression analysis demonstrated that the preoperative CSA was the only independent factor that correlated inversely with the CSA extension ratio (corrected R2 = 0.361; P < 0.001). Conclusion. Spinal stenosis was resolved successfully by indirect decompression through a miniopen anterolateral retroperitoneal approach without the need for neuromonitoring. Level of Evidence: 3

Osteoinduction on acid and heat treated porous Ti metal samples in canine muscle.

Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600°C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro.