Shigenori Kawabata

Imaging of neural conduction block by neuromagnetic recording

OBJECTIVE For the clinical application of neuromagnetic recordings in neural conduction block, the patterns of magnetic fields in the region should be clarified. Using an experimental in vitro model, the spatiotemporal course of the neuromagnetic fields at the site of complete conduction block was examined. Additionally, the magnetic compound action fields (CAFs) and electric compound action potentials (CAPs) were compared and correlated. METHODS In a chamber containing Ringers solution, 10 isolated sciatic nerves of rabbits were electrically stimulated. Both evoked CAPs and CAFs were measured before and after the ligation of the nerve. The sequential positions of the current dipoles and the location of the conduction block were estimated by the least-squares search. RESULTS The magnetic contour maps of the CAFs showed a characteristic quadrupolar pattern propagating along the nerve. The peak of the leading magnetic field ceased and disappeared at the position of the nerve ligation, while the trailing magnetic field became attenuated before reaching that position. The positions of the conduction blocks were localized by magnetic recordings within a difference of 2mm. CONCLUSIONS The neuromagnetic recordings could visualize the change of the magnetic fields at the site of the complete conduction block and closely localize that position. SIGNIFICANCE The neural conduction block was visualized and localized by neuromagnetic recordings.

Middle-Term Results of a Prospective Comparative Study of Anterior Decompression With Fusion and Posterior Decompression With Laminoplasty for the Treatment of Cervical Spondylotic Myelopathy

Study Design. A clinical prospective study. Objective. To assess whether clinical and radiologic outcomes differ between anterior decompression and fusion (ADF) and laminoplasty (LAMP) in the treatment of cervical spondylotic myelopathy (CSM). Summary of Background Data. No reports to date have accurately and prospectively compared middle-term clinical outcomes after anterior and posterior decompression for CSM. Methods. We prospectively performed LAMP (n = 50) in 1996, 1998, 2000, and 2002, and ADF (n = 45) in 1997, 1999, 2001, and 2003. The Japanese Orthopedic Association (JOA) score, recovery rate, and each item of the JOA score were evaluated. For radiographic evaluation, the lordotic angle and range of motion (ROM) at C2–C7 and residual anterior compression to the spinal cord (ACS) after LAMP on magnetic resonance imaging were investigated. Results. Eighty-six patients (ADF n = 39; LAMP n = 47) could be followed for more than 5 years (follow-up rate 91.5%). Demographics were similar between the two groups. The mean JOA score and recovery rate in the ADF group were superior to those in the LAMP group from 2-year data collected after surgery. However, LAMP was safer and less invasive than ADF with respect to physical status and complications in the perioperative period. For individual items of the JOA score, the ADF group showed significantly more improvement of upper extremity motor function than the LAMP group (P < 0.05). There was a significant difference in maintenance of the lordotic angle in the ADF group compared with the LAMP group despite no difference in ROM. The LAMP group was divided into two subgroups: (1) LAMP(+) (n = 16) comprising patients who had ACS at 2 years after surgery, and (2) LAMP(–) (n = 31) comprising patients without ACS. Recovery rate differed significantly between the LAMP(+) and LAMP(−) groups despite there being no difference between the LAMP(−) and ADF groups. Conclusion. The recovery rate of the JOA score in the ADF group was better than that in the LAMP group. The clinical outcomes after LAMP could be influenced by ACS.

A genome-wide association study identifies susceptibility loci for ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common spinal disorder among the elderly that causes myelopathy and radiculopathy. To identify genetic factors for OPLL, we performed a genome-wide association study (GWAS) in ∼8,000 individuals followed by a replication study using an additional ∼7,000 individuals. We identified six susceptibility loci for OPLL: 20p12.3 (rs2423294: P = 1.10 × 10−13), 8q23.1 (rs374810: P = 1.88 × 10−13), 12p11.22 (rs1979679: P = 4.34 × 10−12), 12p12.2 (rs11045000: P = 2.95 × 10−11), 8q23.3 (rs13279799: P = 1.28 × 10−10) and 6p21.1 (rs927485: P = 9.40 × 10−9). Analyses of gene expression in and around the loci suggested that several genes are involved in OPLL etiology through membranous and/or endochondral ossification processes. Our results bring new insight to the etiology of OPLL.

S3-4. New alarm point of transcranial electrical stimulation motor evoked potentials for intraoperative spinal cord monitoring. A prospective multicenter study of the Spinal Cord Monitoring Working Group of the Japanese Society for Spine Surgery and Related Research (JSSR)

Transcranial electrical stimulation motor evoked potentials (TcMEPs) became the gold standard for intraoperative spinal cord monitoring. However there is no definite alarm point of TcMEPs due to a lack of multicenter study. Thus we set 70% decrease of amplitude as the alarm point of TcMEPs from the experience of our 48 true positive cases from 2007 to 2009. 959 cases of spinal deformity, spinal cord tumor and ossification of the posterior longitudinal ligament (OPLL) were included in this prospective multicenter study from our 18 institutes related to the Japanese Society for Spine Surgery and Related Research monitoring working group from 2010 to 2012. There were only two false negative cases which were intramedullary spinal cord tumor. This new alarm criterion provided higher sensitivity (95%) and specificity (91.1%) for intraoperative spinal cord monitoring and good accuracy except for intramedullary spinal cord tumor. This study is the first prospective multicenter research to investigate the alarm point of TcMEPs. We recommend the alarm point to be a 70% decrease of amplitude for routine spinal cord monitoring, especially in surgery for spinal deformity, OPLL and extramedullary spinal cord tumor.

Long-term outcomes of surgical treatment for tethered cord syndrome.

Surgical outcomes for tethered spinal cord syndrome (TCS) associated with low-lying conus medullaris were evaluated. We investigated the long-term results of untethering the spinal cord and dural plasty in surgical patients with a wide age range. Improvement of bladder dysfunction and suppression of leg deformity progression were noted in two pediatric patients. However, severe urinary dysfunction generally remained postoperatively. Adult patients commonly showed low back or leg pain as clinical manifestations. In seven adult patients, urinary dysfunction also improved. Neurologic findings and urinary deficits showed a favorable improvement mostly in adult TCS in comparison with natal or juvenile onset of TCS. A short duration from onset to surgery and cranial movement of the conus medullaris as assessed by postoperative magnetic resonance imaging were factors indicating a favorable prognosis.

Hybrid grafting using bone marrow aspirate combined with porous β-tricalcium phosphate and trephine bone for lumbar posterolateral spinal fusion: a prospective, comparative study versus local bone grafting.

Study Design. A prospective, comparative study. Objective. We developed a hybrid graft (HBG) of porous &bgr;-tricalcium phosphate ceramics/percutaneously harvested bone sticks/autologous bone marrow aspirate for lumbar posterolateral fusion (PLF). The aim of this study was to investigate the efficacy of the HBG as a substitute for conventional corticocancellous iliac autografts. Summary of Background Data. Iliac crest bone graft (ICBG) has been traditionally used as the golden standard for lumbar spinal fusion. The significant complication rate associated with harvesting corticocancellous ICBG, however, has encouraged development of alternative graft substitutes. Methods. From September 2005, 61 consecutive patients underwent decompressive laminotomy and 1-level instrumented PLF. Each patient in this study had the constructs of the HBG placed on 1 side of the intertransverse process gutter. An autologous local bone graft (LBG) harvested during decompressive laminotomy was placed on the other side as a control. Radiographic evaluation was performed at 6 months, 1 year after surgery, and subsequently on an annual basis. The fusion statuses on either side of vertebra were compared. Results. The flexion-extension motion in the dynamic x-rays at the target level decreased over time. Only 1 case exhibited over 5° of angular motion 2 years after surgery. In the evaluation of fusion status, the fusion rate for the HBG side (68.9% at 6 months, 83.6% at 1 year, 93.5% at 2 years) was higher than that for the LBG side (49.2% at 6 months, 75.4% at 1 year, 89.1% at 2 years) with a significant difference at 6 months after surgery. No significant complications at the donor site were found postoperatively. Conclusion. The HBG promoted posterolateral spinal fusion without significant donor site morbidity. Because of its efficacy and safety, this hybrid construct seems promising as an alternative to conventional iliac bone grafts for lumbar spinal fusion.

Novel cell seeding system into a porous scaffold using a modified low-pressure method to enhance cell seeding efficiency and bone formation.

The efficient seeding of cells into porous scaffolds is important in bone tissue engineering techniques. To enhance efficiency, we modified the previously reported cell seeding techniques using low-pressure conditions. In this study, the effects of low pressure on bone marrow-derived stromal cells (BMSCs) of rats and the usefulness of the modified technique were assessed. There was no significant difference found in the proliferative and osteogenic capabilities among various low-pressure (50–760 mmHg, 1–10 min) conditions. To analyze the efficacies of the cell seeding techniques, BMSCs suspended in the plasma of rats were seeded into porous β-tricalcium phosphate (β-TCP) blocks by the following three procedures: 1) spontaneous penetration of cell suspension under atmospheric pressure (SP); 2) spontaneous penetration and subsequent low pressure treatment (SPSL), the conventional technique; and 3) spontaneous penetration under low pressure conditions (SPUL), the modified technique. Subsequently, these BMSCs/β-TCP composites were used for the analysis of cell seeding efficiency or in vivo bone formation capability. Both the number of BMSCs seeded into β-TCP blocks and the amount of bone formation of the SPUL group were significantly higher than those of the other groups. The SPUL method with a simple technique permits high cell seeding efficiency and is useful for bone tissue engineering using BMSCs and porous scaffolds.

Three dimensionally configured SQUID vector gradiometers for biomagnetic measurement

We proposed a composite superconducting quantum interference devices (SQUIDs) gradiometer with an axial-type gradiometric pick-up coil and two planar-type gradiometric pick-up coils. Three gradiometers are built into a single module in orthogonal position to each other and the pick-up coils of two planar-type gradiometers are concentric. Therefore, the sensor can detect magnetic fields elicited by action currents in a living body as a quasi three-dimensional vector at a specific point. The outward form of the sensors is identical to our conventional axial-type gradiometric SQUID magnetometer. Therefore, the new sensor can be mounted on our conventional sensor array without large modification. We applied the new sensors to the SQUID magnetometer system for the spinal cord evoked magnetic fields and successfully measured the magnetic fields from the spinal cords from small animals.

Visualization of Conductive Spinal Cord Activity Using a Biomagnetometer

Study Design. The authors measured conductive cervical spinal cord evoked magnetic fields (SCEFs) after thoracic spinal cord stimulation in cats and visualized spinal cord activities. Objective. To evaluate the usefulness of magnetic field measurement. Summary of Background Data. Magnetic field measurement has several theoretical advantages compared with electric potential measurement. Although biomagnetometers for the brain and heart are already on the market and are widely used, methods for magnetic field measurement of the spinal cord have not been established. Method. Cervical laminectomy was performed on adult cats under anesthesia and the dural tube was exposed. Electrical stimuli were applied to the lower thoracic spinal cord by a catheter epidural electrode. SCEFs were recorded using a biomagnetometer specially designed for recording spinal cord action potentials. SCEFs were measured at 35 different points over the cervical spine and isomagnetic field maps of SCEFs were constructed. Thereafter, the spinal cord was transected completely at C5 and SCEFs were measured again. Results. The detected SCEFs showed a clear biphasic configuration. The first deflection of the magnetic fields from the left side was directed outward, but the right-side deflection was directed inward. The second deflection showed reversed polarity. The isomagnetic field maps of SCEFs clearly demonstrated the quadrupolar pattern and propagated at a conduction velocity of 80–120 m/s. After spinal cord transection, the propagation of SCEFs stopped at the transection site, and the SCEFs could not be obtained above the site. Conclusions. The authors concluded that magnetic field measurement is useful for evaluation of spinal cord function. Moreover, it was apparent that SCEFs could indicate conduction block in the spinal cord.

A 75-ch SQUID Biomagnetometer System for Human Cervical Spinal Cord Evoked Field

A 75-ch SQUID biomagnetometer system for the measurement of the cervical spinal cord evoked magnetic field (SCEF) was developed for the purpose of the noninvasive functional diagnosis of the spinal cord. The sensor array has 25 SQUID vector sensors arranged along the cylindrical surface to fit to the shape of the subjects neck. The magnetic fields, not only in the direction radial to the subjects body surface but also in the tangential direction, are observed in the area of 80 mm times 90 mm at one time. The dewar has a unique shape with a cylindrical main body and a protrusion from its side surface. The sensor array is installed in the protruded part. This design is optimized to detect magnetic signals at the back of the neck of the subject sitting in a reclining position. We applied the developed SQUID system to the cervical SCEF measurement of normal subjects who were given electric pulse stimulation to their median nerves at the wrists. The evoked magnetic signals were successfully detected at the cervixes of all subjects. A characteristic pattern of transition of the SCEF distribution was observed as a reproducible result and the signal components propagating along the spinal cord were found in the time varying SCEF distribution. We expect that the investigation of the propagating signal components would help to establish a noninvasive functional diagnosis of the spinal cord.