Ken Wakabayashi

Mechanism of Intervertebral Disc Degeneration Caused by Nicotine in Rabbits to Explicate Intervertebral Disc Disorders Caused by Smoking

Study Design. The effects of nicotine on intervertebral discs in rabbits were studied experimentally. Objectives. To investigate the effects of nicotine on the vascular buds in rabbits for elucidating the mechanism of nicotine-induced vertebral disc degeneration. Background data. Several groups have suggested that cigarette smoking is associated with low back pain, but the exact mechanism is not yet fully understood. Methods. The pump was filled with a diluted nicotine solution, then implanted under the skin of rabbits for 8 weeks. This model was designed to maintain blood nicotine concentration at approximately 110 ng/mL. Rabbits receiving physiologic saline were used as control animals. Results. Nicotine treatment resulted in necrosis and hyalinization of the nucleus pulposus in all rabbits. The anulus fibrosus showed a disturbance of the pattern of overlapping laminae with and without clefts and separation. These resulted in changes indicative of stenosis of vascular buds and perivascular calcification. Nicotine treatment resulted in hypertrophy of vascular walls, necrotic changes in endothelial cells, and narrowing of the vascular lumen. Nicotine treatment resulted in delineation of vascular buds in the vicinity of the vertebral endplate and a reduction of their numbers. However, the control animals showed a dense vascular network. The number of vascular buds decreased in nicotine treatment. Conclusion. The authors believe that both reduction in the density of vascular buds and narrowing of the vascular lumen result in decreased oxygen tension, leading to decreased synthesis of proteoglycan and collagen, thus facilitating degeneration of the disc.

Penetration of a screw into the thoracic aorta in anterior spinal instrumentation. A case report.

With recent advances in spine surgery, spinal instrumentation has allowed the introduction of varied new devices and techniques, expanding its potentials. Yet this has also led to the incidence of unexpected complications. The current article reports on a serious case the authors recently experienced, in which a screw used for the instrumentation of the thoracic vertebra penetrated the aorta.

Allografting intervertebral discs in dogs : a possible clinical application

Study Design A lumbar disc is a tissue that is often a cause of low back pain. We conducted experimental allografting of intervertebral discs in dogs. Objectives To evaluate the clinical potential for allografting of intervertebral disc. Summary of Background Data There have been few reports on the allografting of intervertebral discs. The allografting of discs frozen at -196 C has never been documented. In the present experiments, we studied the effect of freezing at -80 C and -196 C on disc allografts to 25 hybrid adult dogs. Methods A vertebral disc was obtained from donor dogs with parts of the adjoining vertebral bodies to serve as the allograft disc unit. After soaking in 10% dimethyl sulfoxide at 4 C, the allograft discs were frozen and stored at either -80 C or -196 C. After storage for approximately 4 weeks, they were transplanted peritoneally into the recipient lumbar vertebrae and fixed using plates and screws to preserve mobility of the grafted disc. At the same time, cells from allograft discs were incubated to examine their ability to synthesize proteoglycan and collagen. Radiologic examination of the changes after surgery in the intervertebral space was followed serially. Results Radiographs revealed a complete bone union of the vertebral bodies at 5 months and gradual narrowing of the intervertebral space beginning at 6 months. Histologically, the anulus fibrosus was well preserved, especially in disc units stored at -196 C. Cellular synthetic activity was seriously diminished. Conclusions Our results indicate that allograft of intervertebral discs has clinical potential because it can serve as a dynamic disc spacer for a certain period of time, but its long-term merits and demerits have to be established.

Clinical values of intraoperative ultrasonography for spinal tumors.

Intraoperative ultrasonography was conducted in 52 cases of spinal tumor, at 7.5 MHz, mainly by means of linear scanning, to evaluate its clinical usefulnes. The procedure was effectively applied in such clinical purposes as: 1) locating the tumor, 2) deciding the resectability of intramedullary tumors, 3) deciding the site for intraspinal biopsy or shunt tube insertion, 4) deciding the site for intraspinal biopsy or shunt tume insertion, 4) establishing the topical relationship between the spinal cord and the tumor, and 5) diferentiating neurilemoma from meningioma. Of 10 patients with intramedullary tumors, 5 (50%) were removed, because extirpation was possible when the spinal cord and the tumor were well demarcated on the ultrasonogram. Intratumorous cysts were found to exist in 73% of neurilemoma and 14% of meningioma cases, enabling the differential diagnosis between the two tumors. Intraoperative ultrasonography is an uninvasive method to reveal intradural and extradural conditins and thus constitutes a valuable diagnostic means to ensure safe and precise spinal surgery.

Differences on intraoperative ultrasonography between meningioma and neurilemmoma

Abstract We examined the differences on intraoperative ultrasonography between 17 cases of meningioma and 29 of neurilemmoma, the common intradural extramedullary tumors. In meningiomas, cysts were rarely seen (in 12.5 %, P < 0.01 %) and echogenicity was high (in 82.3 %, P < 0.01 %). In neurilemmoma, many cysts were seen (72.5 %) and low echoes tended to be more common (72.4 %, P < 0.01 %). In the neurilemmomas with high or isoechogenicity, Antoni A types, histologically rich in collagen fibres, predominanted.

Evaluation of hydroxyapatite-coated screws for lumbar spine fixation in dogs

To evaluate the firmness of fixation of hydroxyapatite(HA)-coated screws used for spinal fixation, research has been done to measure the force required to pull out such screws. However, despite its importance, no research has been done to evaluate the twisting force necessary to loosen the screw. With regard to the twisting force, we evaluated the effects of HA coating on securing titanium alloy screws to canine lumbar vertebrae. Bonding of HA-coated (HA) screws and titanium alloy (Diapason; D) screws to the bone was examined serially over a period of 24 weeks by measuring the torque required to loosen the screws after a period of fixation and by histological examination of the screw-bone interface. Twelve screws (six screws of each type) were used in each of seven mongrel dogs, on each side of the lumbar vertebrae (L1–L6). The torque required to loosen D screws 6 weeks after insertion was three times higher than that used at time 0. With the HA scew, the torque at 2 and 6 weeks was four and six times higher, respectively, than that at time 0. Eight weeks after insertion, the torque for the HA screw was 2.3 times greater than that for the D screw (P<0.01). Histological examination showed direct binding of HA to the bone early after insertion. Our results indicate that HA screws are firmly fixed in bone within a short period after insertion into the vertebra. In the clinical setting, the use of HA screws for spinal fixation may produce stable spine fixation within a short period after operation.

Rigix plate system for anterior fixation of thoracolumbar vertebrae.

Only a few plate systems are available for anterior fixation of thoracolumbar vertebrae because of the difficulty in fastening a screw and a plate together. If the fixation is inadequate, the screws will become loose. The Rigix plate system consists of screws made of titanium alloy and a plate made of pure titanium. All screws used for internal fixation are screwed into the plate. This system permits the use of anchor screws, which facilitate exertion of force to compress the vertebral bodies together or to distract them from each other. In this study, Rigix plates were used in 24 patients (20 with burst fractures and 4 with metastatic tumors). In the 20 patients with fracture, internal fixation with a graft and a Rigix plate was performed after anterior decompression. In the four patients with malignant tumors, total spondylectomy was performed anteriorly and posteriorly, followed by implantation of a vertebral prosthesis, and then internal fixation with a Rigix plate combined posterior instrumentation with Diapson (Stryker Co., Tokyo, Japan) pedicular screws. Bone union was achieved in all patients. Neither breakage of instruments nor loosening of connections occurred in any case. In patients treated for bone metastases, the reconstructed spinal structure was able to be maintained for a long period. Of the screws used, five (5%) were not able to remain fixed as intended because they were inserted at inappropriate angles into the plate, but the fixation itself was excellent. Because of the low profile, ease of manipulation (mean instrumentation time was 25 min), and compatibility with magnetic resonance imaging, the Rigix plate is useful for anterior fixation of thoracolumbar vertebrae.

Cryopreserved intervertebral disc allografts in dogs: Chronological changes in 3-year period after transplantation

To explore the potential clinical applications of allografting cryopreserved intervertebral discs, we employed the technique in 10 donor and 20 recipient mongrel adult dogs. The intervertebral disc was excised en bloc, along with portions of the adjoining vertebral bodies, from the donor dogs. These “units” were soaked with 10% dimethyl sulfoxide and cryopreserved at −80°C for 8 weeks or at −196°C for 3 weeks. The unit was implanted at the L4/L5 or L5/L6 level in the recipient animal. Synostosis between the donor and recipient vertebral bodies was completed within 6 months of surgery. Radiologically, the intervertebral spaces within the transplanted unit were well preserved. The spaces were still maintained at 12 months, despite radiological manifestations of slight degeneration, with no marked changes being observed from the condition at 6 months. At 36 months, the unit showed marked morphological changes, including narrowing of the intervertebral spaces, but the upper and lower bodies had not yet fused. Cell incubation indicated a profound decrease in the cellular activity of the transplanted disc. Our findings suggested that the cryopreserved and transplanted intervertebral disc maintained mobility for at least 36 months. The techniques employed and results of the present study may contribute to further exploration of the clinical applicability of cryopreserved allografts.

Evaluation of cylindrical interbody fusion devices in canine lumbar spine : Comparison of fixation stiffness in devices with and without hydroxyapatite coating

To establish intervertebral body fusion without the use of autogenous bone grafts, we tested special titanium cylindrical devices. The firmness of fixation of devices coated with hydroxyapatite (HA) (HA-D) or not coated (Ti-D) was compared in nine mongrel dogs. General anesthesia, was compared in nine mongrel dogs. General anesthesia, was conducted and the devices were implanted in the same animal through the peritoneum in two adjacent intervertebral spaces (between L3 and L6). The follow-up period was 2–72 weeks, and two animals at a time were evaluated at different periods during follow-up (groups I–IV). In each group, the entire lumbar segment of L3-7 was removed en bloc and examined histologically and radiologically with soft X-ray. In Group II (the earliest group), radiographs of the HA-D showed bone growth converging into the perforations of the device, indicating a firm bond between HA-D and vertebral bodies. No such bone growth was observed in the Ti-D. Histologically, the HA-D showed an intimate bond between the new osseous tissue and HA as early as in group I. In group III, marked ingrowth of bone was noted with both types of devices, although it was more marked with HA-D than Ti-D. Fibrous gaps between the metal and bone were present in Ti-D throughout the study period of 72 weeks. The HA-D allowed a firm bond between HA and ingrowth of ample amounts of bone inside the perforations, as well as a strong bond between HA and the vertebral bodies. When the HA-D was used for interbody fixation, early stable interbody fixation was achieved, indication that the hydroxyapatite-coated cylindrical device may be suitable for interbody fixation without the need for a bone autograft.