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Minimally invasive techniques for spinal surgery are becoming more widespread as improved technologies are developed. Stabilization plays an important role in fracture treatment, but appropriate instrumentation systems for endoscopic circumstances are lacking. Therefore a new thoracoscopically implantable stabilization system for thoracolumbar fracture treatment was developed and its biomechanical in vitro properties were compared. In a biomechanical in vitro study, burst fracture stabilization was simulated and anterior short fixation devices were tested under load with pure moments to evaluate the biomechanical stabilizing characteristics of the new system in comparison with a currently available system. With interbody graft and fixation the new system demonstrated higher stabilizing effects in flexion/extension and lateral bending and restored axial stability beyond the intact spine, as well as having comparable or improved effects compared with the current system. Because of this biomechanical characterization a clinical trial is warranted; the usefulness of the new system has already been demonstrated in 45 patients in our department and more than 300 cases in a multicenter study which is currently under way. [ABSTRACT FROM AUTHOR]

Whether injuries to the alar ligaments could be responsible for complaints of patients having whiplash injury in the upper cervical spine is still controversially discussed. It is known that these ligaments protect the upper cervical spine against excessive lateral bending and axial rotation movements. The objective of the present in vitro study was therefore to examine whether the alar ligaments or any other structures of the cervical spine are damaged in side collisions. In a specially designed acceleration apparatus, six human osteoligamentous cervical spine specimens were subjected to incremental 90° side collisions from the right (1 g, 2 g, 3 g, etc.) until structural failure occurred. A damped pivot table accounted for the passive movements of the trunk during collision, and a dummy head (4.5 kg) ensured almost physiological loading of the specimens. For quantification of functional injuries, the three-dimensional flexibility of the specimens was tested in a spine tester before and after each acceleration. In all six specimens, structural failure always occurred in the lower cervical spine and always affected the facet joint capsules and the intervertebral discs. In four specimens, this damage occurred during the 2 g collision, while in the other two it occurred during the 3 g and 4 g collision, respectively. The flexibility mainly increased in the lower cervical spine (especially in lateral bending to both sides) and, to a minor extent, in axial rotation. In vitro low-speed side collisions caused functional and structural injury to discoligamentous structures of the lower cervical spine, but did not damage the alar ligaments. Since the effects of muscle forces were not taken into account, the present in vitro study reflects a worst-case scenario. Injury thresholds should therefore not be transferred to reality. [ABSTRACT FROM AUTHOR]

The biomechanics of whiplash is often studied using cadaveric cervical spine specimens. One of the most important points in this kind of study is to create realistic loading conditions. The aim of the present project therefore was to develop an acceleration apparatus, which allows the study of whiplash with human cadaveric cervical spine specimens under as realistic loading conditions as possible.The new acceleration apparatus mainly consisted of a sled, a pneumatic acceleration unit and a railtrack and offered several unique features to create more realistic loading conditions. Among these features, the possibility to simulate the passive movements of the trunk is of capital importance. In this new apparatus, first, the general feasibility of whiplash experiments was studied, second, the reproducibility of the impacts was quantified and third, the effect of simulated movements of the trunk on accelerations and loads was examined.In the new acceleration apparatus various types of collisions could reproducibly be simulated. Simulated passive movements of the trunk strongly influenced the loading pattern of the neck. Without pivoting a steep increase of all loading parameters could be observed. This increase was less pronounced if pivoting was allowed.In conclusion, biomechanical aspects of whiplash could reproducibly be examined in the new acceleration apparatus. Due to its significant effects on the loading of the neck, pivoting of the trunk should always be taken into account in future experiments on the biomechanics of whiplash in which isolated cervical spine specimens are used. [Copyright &y& Elsevier]

Introduction. Nonsteroidal antirheumatics (NSAR; NSAID) are often used in patients with fractured bones for analgetic reasons. This animal experiment was performed to determine the influence of NSAR on the process of fracture healing. As an alternative, tramadol, the centrally acting analgetic without peripheral effects, was included in this experiment. Materials and methods. Wistar rats were operated on by a transverse osteotomy of the proximal tibia of the left leg. The fracture was stabilized by intramedullary nailing (healing period 21 days). All drugs were applied orally twice a day. The animals were divided into four groups with 10 rats each: Group 1 was treated with placebo (P), group 2 with tramadol (T; 20 mg/kg body weight/day), group 3 with diclofenac sodium (DS; 5 mg/kg bw/day) for 7 days followed by 14 days of placebo, group 4 with diclofenac sodium (DL; 5 mg/kgbw/day) over 21 days. On day 21 the rats were killed, and each leg was examined by X-ray, then the tibia was examined by CT scan, three-point bending, and histology. Results. The results of CT and three-point bending showed that rats treated by diclofenac presented with delayed fracture healing compared with those treated by placebo or tramadol. Bone density in CT was highest in group 1 (mean 611.4±50.1 mg/ml), followed by group 2 (mean 542.5±29.5 mg/ml). Groups 3 (mean 411±34.0 mg/ml; p=0.006) and 4 (mean 395.2±15.4 mg/ml; p=0.009) were significantly lower. The stability of the bones, as measured by the breaking force (Fmax), was highest in group 1 (mean 45.8±19.0 N), followed by group 2 (mean 39.0±7.9 N; NS); group 3 (mean 20.6±7.8 N; p=0.01) was significantly lower than the placebo animals, followed by group 4 (mean 26.5±8.3 N; p=0.03). Similar results were shown for bending stiffness: group 1 (mean 1404.6±611.4 Nmm/mm), group 2 (mean 1033.2±232.1 Nmm/mm; NS), group 3 (mean 564.2±457 Nmm/mm; p=0.045), and group 4 (mean 494.8±340.2 Nmm/mm; p=0.028). There were no significant differences between groups 1 and 2 and between groups 3 and 4, respectively. Diclofenac serum levels on day 21 in rats with long-term diclofenac application (mean 301.4±83.3 ng/ml) were comparable to those in humans. Conclusion. Oral application of diclofenac significantly delayed fracture healing in rats. This effect might be comparable to other NSAR and fracture healing in humans. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the influence of microstructural parameters, such as porosity and osteon dimensions, on strength. Therefore, the predictive value of bone mineral density (BMD) measured by quantitative computed tomography (QCT) for intracortical porosity and other microstructural parameters, as well as for strength of cortical bone biopsies, was investigated. Femoral cortical bone specimens from the middiaphysis of 23 patients were harvested during total hip replacement while drilling a hole (dia. 4.5 mm) for the relief of the intramedullary pressure. In vitro structural parameters assessed in histological sections as well as BMD determined by quantitative computed tomography were correlated with yield stress, and elastic modulus assessed by a compression test of the same specimens. Significant correlations were found between BMD and all mechanical parameters (elastic modulus: r = 0.69, p < 0.005; yield stress: r = 0.64, p < 0.005). Significant correlations between most structural parameters assessed by histology and yield stress were discovered. Structural parameters related to pore dimensions revealed higher correlation coefficients with yield stress (r = −0.69 for average pore diameter and r = −0.62 for fraction of porous structures, p < 0.005) than parameters related to osteons (r = 0.60 for osteon density and average osteonal area, p < 0.005), whereas elastic modulus was predicted equally well by both types of parameters. Significant correlations were found between BMD and parameters related to porous structures (r = 0.85 for porosity, 0.80 for average pore area, and r = 0.79 for average pore diameter in polynomial regression, p < 0.005). Histologically assessed porosity correlated significantly with parameters describing porous structures and haversian canal dimensions. Our results indicate a relevance of osteon density and fraction of osteonal structures for the mechanical parameters of cortical bone. We consider the measurement of BMD by quantitative computed tomography to be helpful for the estimation of bone strength as well as for the prediction of intracortical porosity and parameters related to porous structures of cortical bone. [Copyright &y& Elsevier]