Four-genera of quasipositive knots

AbstractBy using a result of Rudolph concerning the four-genera of classical knots, we give an infinite family of knots which have arbitrary large gaps between the four-genera and the topological fourgenera

Discovery of a Strongly Lensed Galaxy at z=3.9 behind a z=0.83 Galaxy Cluster

We report the discovery and spectroscopic confirmation of three gravitationally-lensed images of a galaxy at z=3.9 in the background of a distant, rich cluster of galaxies at z=0.83, on the basis of observations with Faint Object Camera And Spectrograph (FOCAS) on the Subaru telescope. We construct a simple lens model of the cluster mass distribution based on Jee et al.'s weak lensing mass estimates from deep, high-resolution images by Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. The lens model can account simultaneously for the observed image configuration and the flux ratio of the closer pair located close to the critical curve. The parities of the three images are also consistent with the lensing hypothesis. Since this galaxy is apparently bright (i'_{AB} \sim 23.7) for its redshift due to the magnification, it serves as a good high redshift target on which we can make extensive and detailed studies based on multi-wavelength imaging and spectroscopy.Comment: 4 pages, 3 figures, 1 table, accepted for publication in PAS

Posterior cervical spine arthrodesis with laminar screws: a report of two cases

We performed fixation using laminar screws in 2 patients in whom lateral mass screws, pedicle screws or transarticular screws could not be inserted. One was a 56-year-old woman who had anterior atlantoaxial subluxation (AAS). When a guide wire was inserted using an imaging guide, the hole bled massively. We thought the re-insertion of a guide wire or screw would thus increase the risk of vascular injury, so we used laminar screws. The other case was an 18-year-old man who had a hangman fracture. Preoperative magnetic resonance angiography showed occlusion of the left vertebral artery. A laminar screw was inserted into the patent side (i.e., the right side of C2). Cervical pedicle screws are the most biomechanically stable screws. However, their use carries a high risk of neurovascular complications during screw insertion, because the cervical pedicle is small and is adjacent laterally to the vertebral artery, medially to the spinal cord, and vertically to the nerve roots. Lateral mass screws are also reported to involve a risk of neurovascular injuries. The laminar screw method was thus thought to be useful, since arterial injuries could thus be avoided and it could also be used as a salvage modality for the previous misinsertion.</p

Development of Dysphagia and Trismus Developed after C1-2 Posterior Fusion in Extended Position

Cervical misalignment after upper cervical fusion including the occipital bone may cause trismus or dysphagia, because the occipito-atlanto joint is associated with most of the flex and extended motion of the cervical spine. There are no reports of dysphagia and trismus after C1-2 fusion. The purpose of this paper is to demonstrate the potential risk of dysphagia and trismus even after upper cervical short fusion without the occipital bone. The patient was a 69-year-old man with myelopathy caused by os odontoideum and Klippel-Feil syndrome, who developed dysphagia and trismus immediately after C1-2 fusion and C3-6 laminoplasty. Radiographs and CT revealed that his neck posture was extended, but his symptoms still existed a week after surgery. The fixation angle was hyperextended 12 days after the first surgery. His symptoms disappeared immediately after revision surgery. The fixation in the neck-flexed position is thought to be the main cause of the patientʼs post-operative dysphagia and trismus. Dysphagia and trismus may occur even after short upper cervical fusion without the occipital bone or cervical fusion in the neck-extended position. The pre-operative cervical alignment and range of motion of each segment should be thoroughly evaluated

A Rare Course of Scoliosis Associated with Chiari Malformation and Syringomyelia

Spinal deformity is an important clinical manifestation of Chiari I malformation (CM-I) and syringomyelia. Here we report the result of an 8-year follow-up of a 13-year-old girl with severe scoliosis associated with Chiari malformation and a large syringomyelia. The patient presented at our hospital at the age of 13 with a 68° scoliosis. Magnetic resonance imaging showed Chiari malformation and a large syringomyelia. Neurosurgical treatment involved foramen magnum decompression and partial C1 laminectomy, but the scoliosis still progressed. We present the first case report of a rare course of scoliosis in a patient with CM-I and a large syringomyelia

Computer-assisted Minimally Invasive Posterior Lumbar Interbody Fusion without C-arm Fluoroscopy

Computer-assisted spinal surgery is becoming more common; however, this is the first technical report to describe the technique of minimally invasive spinal posterior lumbar interbody fusion (MIS-PLIF) without using C-arm fluoroscopy. The authors report 2 years of follow-up of a 49-year-old female patient with L4 degenerative spondylolisthesis. The patient suffered from low back pain and intermittent claudication for more than 6 years. The authors performed computer-assisted MIS-PLIF without C-arm fluoroscopy. Instead, O-arm® navigation, the use of which reduces radiation exposure to patients as well as others in the operating room, was employed. Surgery was successful, and correct lumbar alignment was maintained. She had neither neurological deficits nor low back pain at her 12-month final follow-up. In conclusion, computer-assisted MIS-PLIF without C-arm fluoroscopy is a useful technique that reduces radiation exposure to the surgeon and operating room staff

Spinal Metaplastic Meningioma with Osseous Differentiation in the Ventral Thoracic Spinal Canal

Ossified meningioma is classified histologically as a phenotype of metaplastic meningioma, and it is extremely rare. There are only 12 cases involving ossified spinal meningiomas in the literature. We present the case of a 61-year-old female with a primary tumor within the ventral spinal canal at T12. Although we performed a total tumor excision using an ultrasonic bone aspirator, a temporary deterioration of motor evoked potentials (MEPs) was observed during curettage with a Kerrison rongeur. The neurologic findings worsened immediately after surgery. Histologically, the tumor was diagnosed as a metaplastic meningioma with osseous differentiation. In order to avoid spinal cord injury, great care must be taken when removing an ossified meningioma located on the ventral spinal cord