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Classical finite element (FE) models can estimate vertebral stiffness and strength with much lower computational costs than [micro]FE analyses, but the accuracy of these models rely on calibrated material properties that are not necessarily consistent with experimental results, In general, trabecular bone material properties are scaled with computer tomography (CT) density alone, without accounting for local variations in anisotropy or micro-architecture. Moreover, the cortex is often omitted or assigned with a constant thickness. In this work, voxel FE models, as well as surface-based homogenized FE models with topologically-conformed geometry and assigned with experimentally validated properties for bone, were developed from a series of 12 specimens tested up to failure. The effects of changing from a digital mesh to a smooth mesh, including a cortex of variable thickness and/or including heterogeneous trabecular fabric, were investigated. In each case, FE predictions of vertebral stiffness and strength were compared with the experimental gold-standard, and changes in elastic strain energy density and damage distributions were reported. The results showed that a smooth mesh effectively removed zones of artificial damage locations occurring in the ragged edges of the digital mesh. Adding an explicit cortex stiffened and strengthened the models, unloading the trabecular centrum while increasing the correlations to experimental stiffness and strength. Further addition of heterogeneous fabric improved the correlations to stiffness ([R.sup.2] = 0.72) and strength ([R.sup.2] = 0.89) and moved the damage locations closer to the vertebral endplates, following the local trabecular orientations. B was furthermore demonstrated that predictions of vertebral stiffness and strength of homogenized FE models with topologically-conformed cortical shell and heterogeneous trabecular fabric correlated well with experimental measurements, after assigning purely experimental data for bone without further calibration of material laws at the macroscale of bone. This study successfully demonstrated the limitations of current classical FE methods and provided valuable insights into the damage mechanisms of vertebral bodies. [DOI: 10.1115/1.3212097]

Background: Various surgical techniques to treat posterolateral knee instability have been described. To date, the recommended treatment is an anatomical form of reconstruction, in which the 3 key structures of the posterolateral corner are addressed: the lateral collateral ligament, the popliteofibular ligament, and the popliteus tendon. Hypothesis: Two methods of surgical reconstruction will restore posterolateral knee instability, in terms of static laxity as well as dynamic 6 degrees of freedom kinematics, to statistically significant levels compared with the intact state. Study Design: Controlled laboratory study. Methods: Two surgical techniques (A and B) were used to reconstruct the posterolateral structures in 10 cadaveric knees. Static tests were performed on the intact, sectioned, and reconstructed knees at 30° and 90° of flexion for anterior-posterior laxity and external rotational laxity, as well as at 0° and 30° of flexion for varus laxity; dynamic 6 degrees of freedom kinematic testing, through a path of motion from 90° of flexion to full extension, was also performed. Results: For the static varus tests, external rotation and varus laxity were significantly increased after the posterolateral structures were cut. Both reconstruction techniques restored external rotation and varus laxity to levels not significantly different from the intact state. For technique B, dynamic testing did not show any significant difference for all degrees of freedom kinematics compared with the intact state. However, for technique A, a significant internal tibial rotation was observed throughout the entire path of motion from 0° to 90° of knee flexion. Conclusions: Both surgical techniques for anatomical posterolateral corner reconstruction showed good results in the static laxity tests. The anatomical reconstruction of all structures, including the popliteus tendon, resulted in ah abnormal internal tibial rotation during dynamic testing. Keywords: posterolateral knee; knee reconstructions; popliteus complex; knee kinematics, Injuries to the posterolateral corner of the knee can easily be missed on knee examination, although their identification is important clinically, as they may cause posterolateral rotatory instability of the [...]

The variety of experimental setups used during in vitro testing of distal radius fracture treatments impairs interstudy comparison and might lead to contradictory results. Setups particularly differ with respect to their boundary conditions, but the influence on the experimental outcome is unknown. The aim of this biomechanical study was to investigate the effects of 2 common boundary conditions on the biomechanical properties of an extra-articular distal radius fracture treated using volar plate osteosynthesis. Uniaxial compression tests were performed on 10 synthetic radii that were randomized into a proximally constrained group (ProxConst) or proximally movable group (ProxMove). The load was applied distally through a ball joint to enable distal fragment rotation. A significantly larger (ProxConst vs ProxMove) stiffness (671.6 ± 118.9 N⋅mm-1 vs 259.6 ± 49.4 N⋅mm-1), elastic limit (186.2 ± 24.4 N vs 75.4 ± 20.2 N), and failure load (504.9 ± 142.5 N vs 200.7 ± 49.0 N) were found for the ProxConst group. The residual tilt did not differ significantly between the 2 groups. We concluded that the boundary conditions have a profound impact on the experimental outcome and should be considered more carefully in both study design and interstudy comparison. [ABSTRACT FROM AUTHOR]

Purpose: Vertebral augmentation is an established treatment for patients with pathological vertebral compression fractures. These procedures typically employ a PMMA-based bone cement, which possesses a high compressive stiffness. Because of the increased risk of subsequent fractures after vertebral augmentations, there is a desire for reducing this stiffness. The goal of our study was to examine the influence of adding isotonic saline on the biomechanical properties of PMMA vertebroplasty cement.Methods: A PMMA-based vertebroplasty cement was prepared according to the manufacturer's recommendations after which isotonic saline was mixed into the cement at 10, 20, and 30% (volume:volume). Testing bodies were cast, and compression and bending tests were performed. Fracture surfaces were studied using SEM. Measurements of injectability, setting temperature, and radioopacity were also performed.Results: The addition of saline solution (of up to vol-30%) led to a pronounced reduction in the compression modulus of the cement from 3409 ± 312 to 1131 ± 127 MPa. In parallel, maximal compression strength was reduced from 86 ± 4 to 33 ± 3 MPa and bending strength from 40 ± 4 to 24 ± 3 MPa. The differences regarding injectability, setting temperature, and radioopacity were small and probably of no clinical relevance.Conclusions: The compressive stiffness of PMMA-based vertebroplasty cement can be reduced to almost a third by the addition of saline. The probable explanation is an increase in microporosity. Future simulator experiments will show whether the achieved reduction in stiffness is large enough to reduce the rate of subsequent vertebral fractures. [ABSTRACT FROM AUTHOR]