Effects of neurectomy and tenotomy on the bone mineral density and strength of tibiae.

The right hindlimbs of 5 or 6-week old Wistar male rats were sciatic/femoral neurectomized, tenotomized or sham operated. The rats were sacrificed 2 weeks after the surgery and the tibiae were removed. pQCT measurement was performed on total, cortical, and trabecular bone separately at different regions. Reduction of the bone mineral density by unloading was observed more significantly at metaphysis than at diaphysis due to histological heterogeneity between metaphysis and diaphysis; metaphysis is rich in trabecular bone and diaphysis is abundant in cortical bone. Trabecular bone might be more sensitive to unloading because the reduction rate of volumetric bone mineral density in trabecular bone was approximately 10 times and 3 times larger than that of cortical bone in both neurectomy and tenotomy rats, respectively, Unloading also reduced the cross-sectional area and stress strain index at metaphysis.

In vivo evaluation of the bond strength of adhesive 4-META/MMA-TBB bone cement under weight-bearing conditions.

In order to minimize the problems associated with implant fixation using acrylic bone cement, we studied a new adhesive bone cement that consists of 4-methacryloyloxyethyl trimellitate anhydryde (4-META) and methylmethacrylate (MMA) as monomers, tri-n-butylborane (TBB) as an initiator, and PMMA powder (4-META/MMA-TBB cement). It shows remarkable adhesive properties to metal and bone in vitro. The purpose of this study was to evaluate the strength of the bond of the cement to both metal and bone in vivo under weight-bearing conditions. Metal prostheses were implanted in the right femora of 12 rabbits using either adhesive 4-META/MMA-TBB cement or the conventional PMMA cement, as the control, for fixation. After 4 and 12 weeks, both femora were excised and the same operations were performed in the left femora in vitro. Eighteen femora were sectioned for the mechanical assessment of the bone-cement and cement-implant interfaces. 4-META/MMA-TBB cement had a significantly higher interfacial shear strength than the conventional PMMA cement: 201 N and 90 N, on average, for the implant-cement interface (p<0.01); and 138 N and 89 N, on average, for the bone-cement interface (p<0.01), at 12 weeks. The present results suggest the efficacy of 4-META/MMA-TBB cement in providing greater fixation of implants to bone and promise a firmer intramedullary fixation than the control conventional PMMA cement.

[Monitoring of the spinal cord function using evoked spinal cord potentials].

Monitoring of the spinal cord function by evoked spinal cord potentials (ESP) has come to be used widely with the establishment of a safe technique using an epidural electrode and the great improvement in medical electronic devices. According to other investigations ESP has been recorded through an electrode placed in the posterior epidural space, it is well known that residual ESP can be actually recorded after transection of the posterior half of the spinal cord and that ESP shows no change after a small transection of the anterior column. If ESP originating from the anterior half of the spinal cord is recorded, it is very useful for monitoring during anterior decompression surgery for myelopathy such as ossification of the posterior longitudinal ligament and cervical spondylosis. The purpose of this report is to analyse ESP originating from the anterior half of the spinal cord experimentally and further investigate the ESP monitoring clinically. Sixty cats were used in this study. ESP recording principally consisted of stimulation to the spinal cord at the level of thoracic or lumbar region and recording of ESP with a monopolar electrode placed in the cervical epidural space. Changes in the ESP after transection and compression of the spinal cord were analysed. Anterior vertebrectomy and laminectomy at C2 and C6 were performed for the purpose of placing an electrode correctly and facilitating transection or compression of the spinal cord. Recording electrodes were placed on both the anterior and posterior surfaces of the dura mater at C2. As the result of this study, it is apparent that there exists the ESP originating from the anterior half of the spinal cord. Such ESPs are more accurately recorded through an anterior placed electrode rather than through that placed posteriorly.