The effect of the investigated motion preservation device on the RoM of treated segments is in the range of other devices reported in the literature. Compared to the most implanted and investigated device, the Dynesys, the Elaspine has a less pronounced motion restricting effect in lateral bending and flexion/extension, while being less effective in limiting axial rotation. The pull-out force of the pedicle screws demonstrated anchorage comparable to other screw designs reported in the literature.
The medial periosteal hinge plays a key role in fractures of the head of the humerus, offering mechanical support during and after reduction and maintaining perfusion of the head by the vessels in the posteromedial periosteum. We have investigated the biomechanical properties of the medial periosteum in fractures of the proximal humerus using a standard model in 20 fresh-frozen cadaver specimens comparable in age, gender and bone mineral density. After creating the fracture, we displaced the humeral head medial or lateral to the shaft with controlled force until complete disruption of the posteromedial periosteum was recorded. As the quality of periosteum might be affected by age and bone quality, the results were correlated with the age and the local bone mineral density of the specimens measured with quantitative CT. Periosteal rupture started at a mean displacement of 2.96 mm (SD 2.92) with a mean load of 100.9 N (SD 47.1). The mean maximum load of 111.4 N (SD 42.5) was reached at a mean displacement of 4.9 mm (SD 4.2). The periosteum was completely ruptured at a mean displacement of 34.4 mm (SD 11.1). There was no significant difference in the mean distance to complete rupture for medial (mean 35.8 mm (SD 13.8)) or lateral (mean 33.0 mm (SD 8.2)) displacement (p = 0.589). The mean bone mineral density was 0.111 g/cm(3) (SD 0.035). A statistically significant but low correlation between bone mineral density and the maximum load uptake (r = 0.475, p = 0.034) was observed. This study showed that the posteromedial hinge is a mechanical structure capable of providing support for percutaneous reduction and stabilisation of a fracture by ligamentotaxis. Periosteal rupture started at a mean of about 3 mm and was completed by a mean displacement of just under 35 mm. The microvascular situation of the rupturing periosteum cannot be investigated with the current model.
Purpose Restoration of the anterior spinal profile and regular load-bearing is the main goal treating anterior spinal defects in case of fracture. Over the past years, development and clinical usage of cages for vertebral body replacement have increased rapidly. For an enhanced stabilization of rotationally unstable fractures, additional antero-lateral implants are common. The purpose of this study was the evaluation of the biomechanical behaviour of a recently modified, in situ distractible vertebral body replacement (VBR) combined with a newly developed antero-lateral polyaxial plate and/or pedicle screws and rods using a full corpectomy model as fracture simulation. Methods Twelve human spinal specimens (Th12-L4) were tested in a six-degree-of-freedom spine tester applying pure moments of 7.5 Nm to evaluate the stiffness of three different test instrumentations using a total corpectomy L2 model: (1) VBR ? antero-lateral plate; (2) VBR, antero-lateral plate ? pedicle screws and rods and (3) VBR ? pedicle screws and rods. Results In the presented total corpectomy defect model, only the combined antero-posterior instrumentation (VBR, antero-lateral plate ? pedicle screws and rods) could achieve higher stiffness in all three-movement planes than the intact specimen. In axial rotation, neither isolated anterior instrumentation (VBR ? antero-lateral plate) nor isolated posterior instrumentation (VBR ? pedicle screws and rods) could stabilize the total corpectomy compared to the intact state. Conclusions For rotationally unstable vertebral body fractures, only combined antero-posterior instrumentation could significantly decrease the range of motion (ROM) in all motion planes compared to the intact state.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.