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Biomedical subjects

Masashi Neo

Publications and source records attributed to Masashi Neo.

At least 19 recordsLinked to original sources
PubMed2007

Flexion myelopathy of the thoracic spine. Case report.

The authors report a rare case of surgically treated symptomatic thoracic kyphosis caused by dynamic compression in an elderly man. Myelopathy due to thoracic kyphosis has been reported in patients with congenital kyphosis, Scheuermann dorsal kyphosis, and Cushing disease, but to the authors' knowledge this is the first report of dynamic kyphosis in an elderly person. This otherwise healthy 84-year-old man presented with a 2-year history of progressive difficulty in walking and bilateral leg dysesthesia. Despite several cervical and lumbar surgeries, his symptoms gradually worsened. A radiological examination revealed severe thoracic kyphosis, with a lateral Cobb angle of 59 degrees from T-2 to T-12. On a dynamic computed tomography (CT) myelogram, severe thoracic spinal cord draping and stretching on flexion was demonstrated. On extension, however, imaging studies failed to show draping or stretching. Posterior corrective fusion was performed with instrumentation from T-2 to T-9. Postoperative CT myelography demonstrated no significant spinal cord compression with restoration of the cerebrospinal fluid space anterior to the spinal cord, and the successful correction of the kyphosis to 44 degrees. The patient's neurological sequelae gradually resolved throughout 6 months of follow up.

Aged, 80 and over↗
PubMed2006

Pore throat size and connectivity determine bone and tissue ingrowth into porous implants: three-dimensional micro-CT based structural analyses of porous bioactive titanium implants.

A porous structure comprises pores and pore throats with a complex three-dimensional (3D) network structure, and many investigators have described the relationship between average pore size and the amount of bone ingrowth. However, the influence of network structure or pore throats for tissue ingrowth has rarely been discussed. Four types of bioactive porous titanium implants with different pore sizes and porosities (6mm in diameter and 15 mm long) were analyzed using specific algorithms for 3D analysis of interconnectivity based on a micro focus X-ray computed tomography system. In vivo histomorphometric analysis was performed using the very same implants implanted into the femoral condyles of male rabbits for 6 and 12 weeks. This matching study revealed that more poorly differentiated pores tended to have narrow pore throats, especially in their shorter routes to the outside. In addition, for assessment of the entire implant, we proposed new two indices that represent the degree of bone and tissue ingrowth into an implant by considering the effect of narrow pore throats. Data obtained suggest that this sort of novel analysis is useful for evaluating bone and tissue ingrowth into porous biomaterials.

Algorithms↗
PubMed2006

Comparison of the anatomical risk for vertebral artery injury associated with the C2-pedicle screw and atlantoaxial transarticular screw.

STUDY DESIGN: We evaluated the trajectories of atlantoaxial transarticular and C2-pedicle screws in 3 dimensions using computerized tomography. OBJECTIVE: To compare the anatomic risk for vertebral artery injury associated with C2-pedicle and atlantoaxial transarticular screws. SUMMARY OF BACKGROUND DATA: The atlantoaxial fixation technique using C1-lateral mass screws combined with C2-pedicle screws is considered a safer technique for preventing vertebral artery injury than atlantoaxial transarticular fixation. However, few reports have compared the anatomic risk of vertebral artery injury associated with C2-pedicle screws with that of transarticular screws. METHODS: A total of 62 consecutive patients with cervical lesions were evaluated using 3-dimensional images reconstructed by a computer-assisted navigation system. We compared the maximum possible diameters of the atlantoaxial transarticular screw and C2-pedicle screw trajectories, and examined whether the maximum possible diameters were limited by the height or width of the bony structure in screw trajectories < or = 4 mm in diameter. RESULTS: Mean maximum possible diameters did not differ significantly between the trajectories of 124 atlantoaxial transarticular and 124 C2-pedicle screws. In screw trajectories < or = 4 mm in diameter, 57.1% of transarticular screw trajectories were limited by the height of the bony structure, and all pedicle screw trajectories were limited by the width. CONCLUSIONS: C2-pedicle screw placement has nearly the same anatomic risk of vertebral artery injury as transarticular screw placement. Preoperative 3-dimensional evaluation may be useful for choosing the best surgical technique.

Adult↗
PubMed2006

Accelerated degradation and improved bone-bonding ability of hydroxyapatite ceramics by the addition of glass.

Dense hydroxyapatite (HA) ceramics are useful bone substitutes, but they degrade minimally. One solution is to incorporate degradable materials in the HA. In this study, we manufactured glass-containing HA and investigated whether the degradability and bone-bonding ability of the HA were improved. The glass-containing HA was manufactured from a mixture of HA powder and 1.0 wt% glass powder. The control HA was manufactured from pure HA powder. In vitro degradability was evaluated by soaking in physiological saline, and a rabbit model was used to evaluate in vivo degradability and bone-bonding ability. Detaching tests were performed for all removed samples to quantify bone-bonding ability of each type of HA. The glass-containing HA showed higher degradability than the control HA, both in vitro and in vivo. The detaching failure load of the glass-containing HA was rapidly elevated after implantation and was higher than that of the control HA. Our results suggest that the dissolution of the added glass made the glass-containing HA degradable and that the detaching failure load of the glass-containing HA was elevated by reinforcement of the mechanical locking at the roughened interface. Incorporation of glass additives into HA can be concluded to be a good candidate for producing a bone substitute that can partially degrade and bond to bone firmly and rapidly.

Absorbable Implants↗
PubMed2006

Osteoinductive porous titanium implants: effect of sodium removal by dilute HCl treatment.

In a previous study, we observed that chemically and thermally treated plasma-sprayed porous titanium possesses intrinsic osteoinductivity and that bone formation occurs after 12 months in the muscles of beagle dogs. The aim of this study was to optimize the surface treatment and to accelerate the osteoinductivity. Previous studies have reported that sodium removal converts the sodium titanate layer on the surface of an alkali-treated titanium plate into a more bioactive titania layer. In this study, we developed a dilute hydrochloric acid (HCl) treatment for porous titanium, which removed sodium from the complexly shaped porous structure more effectively than conventional hot water treatment. Three types of surface treatments were applied: (a) alkali and heat treatment (AH treatment); (b) alkali, hot water, and heat treatment (Water-AH treatment); and (c) alkali, dilute HCl, hot water, and heat treatment (HCl-AH treatment). The osteoinductivity of the materials implanted in the back muscles of adult beagle dogs was examined at 3, 6, and 12 months. The HCl-AH-treated porous bioactive titanium implant had the highest osteoinductivity, with induction of a large amount of bone formation within 3 months. The dilute HCl treatment was considered to give both chemical (titania formation and sodium removal) and topographic (etching) effects on the titanium surface, although we cannot determine which is the predominant factor. Nevertheless, adding the dilute HCl treatment to the conventional chemical and thermal treatments is a promising candidate for advanced surface treatment of porous titanium implants.

Animals↗
PubMed2006

Long-term follow-up study of bioactive bone cement in canine total hip arthroplasty.

We report a long-term study of bioactive bone cement (BABC) in a canine total hip arthroplasty (THA) at follow-up of 8 years. Previous studies have shown excellent biomechanical and histological results at follow-up of 6, 12, and 24 months. In the present study, THA was performed in a beagle dog using BABC consisting of an apatite- and wollastonite-containing glass ceramic (AW-GC) powder and SiO2 powder as the filler and a bisphenol-a-glycidyl methacrylate (Bis-GMA) based resin as the organic matrix. Histological examination showed direct bonding between BABC and bone without any intervening soft tissue layer at the BABC-bone interface. A reactive layer, through which BABC bonded to the bone, was observed thicker at 8 years than it was at 24 weeks. No adverse effects of BABC were observed. BABC maintained the high bioactivity and direct bonding to bone in a canine THA at follow-up of 8 years.

Animals↗
PubMed2006

Spinous process plate fixation as a salvage operation for failed anterior cervical fusion. Technical note.

The purpose of this retrospective review was to demonstrate the effectiveness of simple spinous process plate fixation as a salvage operation for failed anterior cervical fusion (ACF). In this technique, the spinous processes are securely sandwiched between a pair of plates with thorns, which are squeezed together by tightening screws that extend through the plates. The authors salvaged six failed ACFs (nonunion of bone graft, plate migration, or bone graft dislodgment) by conducting this fixation without bone grafting, or with an anterior or posterior local bone graft only. Anterior bone union was attained within 6 months in all cases. This technique is easy to perform and probably provides more mechanical strength than does conventional spinous process wiring, resulting in prompt fusion without the need for a new massive bone graft. This technique is a practical option in salvage operations for failed ACF.

Adult↗
PubMed2006

Delayed postoperative spinal epidural hematoma causing tetraplegia. Case report.

The authors describe a case of postoperative spinal epidural hematoma (PSEH) that developed in a patient 9 days after he underwent laminoplasty. A PSEH is a rare but critical complication of spinal surgery that usually occurs within a few days of the procedure. The authors draw attention to the possibility of delayed PSEH and its triggering mechanism. In this case, a 59-year-old man with no history of bleeding disorder underwent cervical laminoplasty for mild myelopathy. On the 7th postoperative day computed tomography demonstrated no abnormal findings in the operative field. On the 9th postoperative day, while straining to defecate, the patient suddenly felt neck and shoulder pain, and tetraplegia rapidly developed. Magnetic resonance imaging demonstrated a huge epidural hematoma. The clot was evacuated during emergency revision surgery, during which the arterial bleeding from a split muscle wall was confirmed. The postoperative course after the revision surgery was uneventful and the patient had none of the previous symptoms 1 year later. A PSEH causing paralysis can occur even more than a week after surgery. The possibility of a delayed-onset PSEH should be kept in mind, and prompt diagnosis should be made when a patient presents with paresis or paralysis after an operation. The authors recommend advising patients that for a while after surgery they avoid strenuous activity.

Cervical Vertebrae↗
PubMed2005

The clinical risk of vertebral artery injury from cervical pedicle screws inserted in degenerative vertebrae.

STUDY DESIGN: Postoperative outcomes of cervical pedicle screw (CPS) placement were evaluated. The screws were inserted in degenerative vertebrae using anatomic landmarks. OBJECTIVE: To evaluate the risks of this procedure caused by misplacements and subsequent complications. SUMMARY OF BACKGROUND DATA: The CPS gives superior vertebral fixation but risks causing vertebral artery and spinal cord injury. However, few clinical reports have been published concerning CPS misplacement and subsequent complications. Therefore, the risk of this procedure is still unclear. METHODS: There were 18 consecutive patients, who submitted to CPS fixation of degenerative vertebrae C2-C6, evaluated using computerized tomography (CT). In 5 of 9 patients in whom the screw critically violated the transverse foramen, viability of the vertebral artery was evaluated using multi-detector row CT angiography. RESULTS: There were no intraoperative vertebral artery or spinal cord injuries and no serious postoperative complications. A total of 86 screws were inserted, and 25 (29%) breached the pedicle cortex. Of them, 84% deviated laterally and violated the transverse foramen. There were 13 screws (15%) that deviated more than 2 mm. However, multi-detector row CT angiography showed the continuity of the vertebral artery in all cases. CONCLUSIONS: The deviation rate of CPS placement using anatomic landmarks was higher than anticipated, although no serious complications were encountered. Refinement of the technique (e.g., using a computer-assisted navigation system) is strongly recommended.

Adult↗
PubMed2005

In vivo evaluation of a porous hydroxyapatite/poly-DL-lactide composite for use as a bone substitute.

We investigated the biocompatibility, osteoconductivity, and biodegradability of a porous composite of hydroxyapatite (HA) and poly-DL-lactide (PDLLA) implanted into rabbit femoral condyles and compared it with porous HA. Six weeks after implantation, the HA/PDLLA was covered with bone and contacted the bone directly. The amount of newly formed bone in the pores was similar in both materials during the examined period. The newly formed bone in the HA/PDLLA tended to increase over 26 weeks, but that in the HA did not show a significant increase after 12 weeks. By 26 weeks, remodeling of the newly formed bone in the pores was seen and bone marrow tissue was found in the pores of the HA/PDLLA. The porous HA/PDLLA was resorbed much faster than the porous HA. Porous HA/PDLLA was resorbed continuously through bone formation and remodeling. Conversely, porous HA was scarcely resorbed throughout the period. HA/PDLLA is thought to be degraded almost completely after about 1 year, and in this study, porous HA/PDLLA showed excellent osteoconductivity and faster resorption than HA. Therefore, HA/PDLLA might be a desirable material for bone substitutes.

Animals↗
PubMed2005

A 5-7 year in vivo study of high-strength hydroxyapatite/poly(L-lactide) composite rods for the internal fixation of bone fractures.

The biocompatibility and biodegradation of hydroxyapatite (HA)/poly(L-lactide) (PLLA) composite bone implant rods were studied using two types of HA particles as reinforcing fillers, uncalcined-HA (u-HA) or calcined-HA (c-HA). Composite rods of u-HA/PLLA and c-HA/PLLA were implanted into the distal femurs of 25 rabbits. Four of these rabbits lived for more than 5 years after implantation, with one living for 7 years 4 months. Samples were retrieved after the rabbits died naturally and specimens were examined by light microscopy and scanning electron microscopy (SEM). For u-HA/PLLA, the shrinkage of the rods progressed further after 4 years, and some were almost completely resorbed. We could not find traces of the rod in some sections from more than 6 years. Remodeled bone encircled the residual material, and trabecular bone bonded directly to the rod was found toward the center. For u-HA/PLLA 30%, results were similar to u-HA/PLLA 40%, and the cross-sectional area had decreased by 4.0% at over 7 years. Most of the PLLA had been released from the rods. Neither obvious osteolytic nor osteoarthritic changes were found after 4 years.

Animals↗
PubMed2005

A safe screw trajectory for atlantoaxial transarticular fixation achieved using an aiming device.

STUDY DESIGN: A retrospective evaluation and characterization of the trajectory of atlantoaxial transarticular screws inserted using an aiming device. OBJECTIVES: To confirm that the screws were inserted through the safest trajectory, which is through the most dorsal and medial part of the isthmus of C2, and to characterize the trajectory on lateral radiograms by comparison with historical controls. SUMMARY OF BACKGROUND DATA: Posterior atlantoaxial transarticular screw fixation entails the potential risk of vertebral artery (VA) injury, which may be lethal. Although much literature recommends that the screws should be inserted aiming at the anterior arch of C1, the authors considered that the safest screw path is via the most dorsal and medial part of the isthmus regardless of the C1 anterior arch, and have used an original aiming device to achieve this trajectory. METHODS: Forty-three consecutive patients who submitted to atlantoaxial transarticular screw fixation using the aiming device were evaluated for screw position using computed tomography (CT) and lateral radiogram. The medialization index (the distance between the screw and the cortex of the spinal canal of C2 on axial CT) and the dorsalization index (the thickness of the bone remaining dorsal to the screw at the isthmus of C2 on sagittal reconstruction CT) were measured. Further, three parameters on the lateral radiograms of these patients were compared with those in the literature and those of our previous cases performed without the aiming device. RESULTS: Neither VA injury nor violation of the spinal canal was encountered, although 12 high-riding VAs were included in this series. The mean medialization index was 0.21 mm, and the indexes of 86.3% of the screws were zero. The mean dorsalization index was 0.36 mm, and the indexes of 76.8% of the screws were zero. These results demonstrated that most of the screws were inserted as aimed, proving the usefulness of the aiming device. The trajectory of these screws on lateral radiograms was characterized by significantly less bone thickness dorsal to the screw at the isthmus compared with the two control groups. As a result, more screws were pointed above the anterior arch of C1. CONCLUSIONS: The atlantoaxial transarticular screw was inserted safely as aimed by using the aiming device. The trajectory was characterized by less bone thickness dorsal to the screw on lateral radiogram, which should be a new intraoperative landmark for screw insertion, in place of the anterior arch of C1.

Adult↗
PubMed2004

Transpedicular screw placement evaluated by axial computed tomography of the cervical pedicle.

STUDY DESIGN: We evaluated the trajectory of transpedicular screws in the cervical spine using axial computed tomography (CT). OBJECTIVES: To provide a safe transpedicular screw trajectory by measuring the dimensions of the cervical pedicle and evaluating the entrance points and the insertion angles of transpedicular screws. SUMMARY OF BACKGROUND DATA: The morphology of the cervical pedicle has been studied, but few in vivo CT-based studies of pedicle dimensions and transpedicular screw placement in the cervical spine have been reported. METHODS: The dimensions of the pedicles (C3-C7) were determined in 30 patients with cervical spinal lesions from CT images. The space available for transpedicular screws (SAS) was defined as the distance between two parallel lines tangential to the spinal canal and the transverse foramen, respectively. SAS was evaluated at 25 degrees and 50 degrees insertion angles. RESULTS: SAS at a 25 degrees insertion angle (SAS-25) ranged from 4.7 to 5.4 mm. SAS at 50 degrees (SAS-50) ranged from 6.1 to 6.6 mm. SAS-25 and SAS-50 were significantly different. Four-millimeter-diameter screws would fit in all 120 C3-C6 vertebrae studied at 50 degrees, but 20 (17%) would not fit at 25 degrees. CONCLUSIONS: Axial CT measurements should facilitate transpedicular screw fixation in the cervical spine. We believe that the screw insertion angle should be close to 50 degrees, which is the mean pedicle transverse angle from C3-C6. The entry point of the pedicle screw should be located as laterally as possible in the posterior surface of the lateral mass.

Adult↗
PubMed2004

Detection of a dural defect by cinematic magnetic resonance imaging and its selective closure as a treatment for a spinal extradural arachnoid cyst.

STUDY DESIGN: We document a giant spinal extradural arachnoid cyst treated by selective closure of the dural defect. It was diagnosed using cinematic magnetic resonance imaging (cine-MRI). OBJECTIVE: To demonstrate the effectiveness of selective closure of the dural defect as a treatment for a spinal extradural arachnoid cyst. SUMMARY OF BACKGROUND DATA: The standard treatment for a spinal extradural arachnoid cyst is total resection of the cyst wall, if possible, and the closure of the communication site, if any, between the cyst and the subarachnoid space, after an extensive laminectomy. To our knowledge, selective closure of the dural defect through minimal laminotomy with little cyst resection has not been reported. METHODS: A 29-year-old woman presented with right leg muscle weakness and was diagnosed with an extradural arachnoid cyst ranging from spinal regions T11 to L3 using MRI. Myelography demonstrated that the cyst communicated with the subarachnoid space. Cine-MRI showed a pulsating flow voiding on the left side of level L1, suggesting the location of the communication site. Fenestration of the T12-L1 region was performed, preserving the spinous processes and the facet joints. A small dural rent was found on the left side of level L1. This was closed using small clips. RESULTS: MRI 12 days later demonstrated that the cyst had shrunk dramatically. It had disappeared completely by 4 months. The patient's muscle weakness improved gradually, and she was almost complaint-free 6 months after the operation. CONCLUSIONS: Selective closure of the dural defect based on cine-MRI will be useful for treating extradural arachnoid cysts.

Adult↗
PubMed2004

Osteoinduction of porous bioactive titanium metal.

This is the first report of bone induction in a non-osseous site by titanium metal, which has long been recognized as a non-bioactive material. After undergoing specific chemical and thermal treatments, porous bioactive titanium induced bone formation without the need of additional osteogenic cells or osteoinductive agents. Four types of titanium implants were implanted in the dorsal muscles of mature beagle dogs, and were examined histologically after periods of 3 and 12 months. Chemically and thermally treated titanium, as well as pure titanium, was implanted either as porous blocks or as fibre mesh cylinders. Bone formation was found only in the chemically and thermally treated porous block implants removed after 12 months. The present study shows that even a non-soluble metal that contains no calcium or phosphorus can be an osteoinductive material when treated to form an appropriate macrostructure and microstructure. This finding may elucidate the nature of osteoinduction, and lead to the advent of epochal osteoinductive biomaterials for tissue regeneration.

Animals↗
PubMed2004

In vivo absorption of porous apatite- and wollastonite-containing glass-ceramic.

The behavior of porous apatite- and wollastonite-containing glass-ceramic (AW) in the bone marrow cavity was investigated. Cylinders of porous AW (4 mm in diameter and 20 mm long, mean porosity of 70% and mean pore diameter of 200 microm) were implanted into the bone marrow cavity of rabbit femurs, and analyzed by chronological radiograms and by scanning electron microscopy one, three, six, and 12 months later. The pores of porous AW are interconnected and homogeneously distributed, and its compressive strength is nearly equal to that of human cancellous bone. Bone formed in the pores at the center of the material by one month and bonded to the material directly. The volume of newly formed bone in the material pores reached a peak at three months, and decreased gradually after six months. The trabecular structures of AW were gradually remodeled by newly formed bone, while AW-bone bonding was maintained during bone remodeling and material absorption. AW was absorbed continuously, and at six and 12 months the residual material corresponded to about 64 and 30% of the starting material, respectively. Porous AW may therefore be useful as an absorbable bone substitute.

Absorbable Implants↗
PubMed2003

Atlantoaxial transarticular screw fixation for a high-riding vertebral artery.

STUDY DESIGN: The feasibility of inserting a screw for the narrow isthmus with a high-riding vertebral artery was evaluated in patients subjected to posterior atlantoaxial transarticular screw fixation. OBJECTIVE: To demonstrate the feasibility of inserting bilateral screws and obtaining a stable atlantoaxial complex for patients with a high-riding vertebral artery. SUMMARY OF BACKGROUND DATA: Posterior atlantoaxial transarticular screw fixation entails the potential risk of vertebral artery injury, which may be lethal. The risk is much higher for the narrow isthmus caused by a high-riding vertebral artery, and many authors recommend that the procedure should be abandoned if the isthmus is too narrow. On the other hand, bilateral screw fixation is stronger than unilateral screw fixation. METHODS: For this study 27 consecutive patients who submitted to atlantoaxial transarticular screw fixation were evaluated before surgery for the position of the vertebral artery grooves using computed tomography (CT) reconstruction. Seven of the patients were defined as having a unilateral high-riding vertebral artery. For these patients, bilateral screw insertion through the most posterior and medial part of the isthmus was performed. RESULTS: No massive bleeding or major complications were encountered in any patients with a high-riding vertebral artery. Postoperative computed tomography reconstruction demonstrated that five of the screws cleared the vertebral artery groove successfully, and two slightly breached it. No screws penetrated into the vertebral artery groove. CONCLUSIONS: It is possible to insert a screw safely, even into the narrow isthmus with a high-riding vertebral artery, if the surgeon realizes where the screw should be inserted and has the requisite insertion technique. Bilateral screw fixation should provide a high fusion rate.

Adolescent↗