Combined vertical and external rotational force in plantarflexion position produces posterior pilon fracture: A preliminary cadaveric study

BACKGROUND

Posterior pilon fracture is speculated to occur by a combination of rotation and axial load, which makes it different from rotational posterior malleolar fracture or pilon fracture, but is not validated in vitro. The aim of the current study is to investigate the injury mechanisms of posterior pilon fracture on cadaveric specimens.

METHODS

Eighteen cadaveric specimens were mounted to a loading device to undergo solitary vertical loading, solitary external rotational loading, and combined vertical and external rotational loading until failure, in initial position of plantarflexion with or without varus. The fracture characteristics were documented for each specimen.

RESULTS

Vertical loading force combined with external rotation force diversified the fracture types resulting in pilon fracture, tibial spiral fracture, rotational malleolar fracture, talar fracture or calcaneal fracture. Vertical violence combined with external rotational loading in position of 45° of plantarflexion and 0° of varus produced posterior pilon fracture in specimens No. 13 and 14.

CONCLUSION

Combination of vertical and external rotational force in plantarflexion position on cadaveric specimens produce posterior pilon fracture.

Change in the sub-sesamoid soft tissue thickness under different loading conditions

[Purpose] To measure the sub-sesamoid soft tissue thickness change from non-loading to self-weight loading conditions. [Participants and Methods] The study included 17 female participants for the study. A questionnaire was used to collect the demographic data and participant anamnesis, such as the presence of foot injuries and diabetes. The measured height and weight were used to calculate the body mass index. Participants were required to stand on an evaluation device from non-loading to 100% loading conditions to measure the sub-sesamoid soft tissue thickness. [Results] Significant differences were observed between the tibial and fibular sub-sesamoid soft tissue thicknesses under non-loading and all loading conditions. Significant soft tissue thinning was observed with a change from non-loading to 25% loading condition. However, no significant differences in the rate of change were observed between the tibial and fibular sub-sesamoid soft tissue thicknesses at 100% loading. [Conclusion] The sub-fibular sesamoid soft tissue was thicker than the sub-tibial sesamoid soft tissue in all loading conditions. The sub-sesamoid soft tissue thickness change was larger during initial loading stage than during the late loading stage, which may be normal in healthy females in their 20s.

[Development of a culture chamber for mechanical loading of adherent cells with large uniform strain]

Based on the current study of the influence of mechanical factors on cell behavior which relies heavily on experiments in vivo, a culture chamber with a large uniform strain area containing a linear motor-powered, up-to-20-Hz cell stretch loading device was developed to exert mechanical effects on cells. In this paper, using the strain uniformity as the target and the substrate thickness as the variable, the substrate bottom of the conventional incubation chamber is optimized by using finite element technique, and finally a new three-dimensional model of the incubation chamber with "M" type structure in the section is constructed, and the distribution of strain and displacement fields are detected by 3D-DIC to verify the numerical simulation results. The experimental results showed that the new cell culture chamber increased the accuracy and homogeneous area of strain loading by 49.13% to 52.45% compared with that before optimization. In addition, the morphological changes of tongue squamous carcinoma cells under the same strain and different loading times were initially studied using this novel culture chamber. In conclusion, the novel cell culture chamber constructed in this paper combines the advantages of previous techniques to deliver uniform and accurate strains for a wide range of cell mechanobiology studies.

T2 MR imaging vs. computational modeling of human articular cartilage tissue functionality

The detection of early stages of cartilage degeneration remains diagnostically challenging. One promising non-invasive approach is to functionally assess the tissue response to loading by serial magnetic resonance (MR) imaging in terms of T2 mapping under simultaneous mechanical loading. As yet, however, it is not clear which cartilage component contributes to the tissue functionality as assessed by quantitative T2 mapping. To this end, quantitative T2 maps of histologically intact cartilage samples (n=8) were generated using a clinical 3.0-T MR imaging system. Using displacement-controlled quasi-static indentation loading, serial T2 mapping was performed at three defined strain levels and loading-induced relative changes were determined in distinct regions-of-interest. Samples underwent conventional biomechanical testing (by unconfined compression) as well as histological assessment (by Mankin scoring) for reference purposes. Moreover, an anisotropic hyperelastic constitutive model of cartilage was implemented into a finite element (FE) code for cross-referencing. In efforts to simulate the evolution of compositional and structural intra-tissue changes under quasi-static loading, the indentation-induced changes in quantitative T2 maps were referenced to underlying changes in cartilage composition and structure. These changes were parameterized as cartilage fluid, proteoglycan and collagen content as well as collagen orientation. On a pixel-wise basis, each individual component correlation with T2 relaxation times was determined by Spearman's ρ_s and significant correlations were found between T2 relaxation times and all four tissue parameters for all indentation strain levels. Thus, the biological changes in functional MR Imaging parameters such as T2 can further be characterized to strengthen the scientific basis of functional MRI techniques with regards to their perspective clinical applications.

Functional in situ assessment of human articular cartilage using MRI: a whole-knee joint loading device

The response to loading of human articular cartilage as assessed by magnetic resonance imaging (MRI) remains to be defined in relation to histology and biomechanics. Therefore, an MRI-compatible whole-knee joint loading device for the functional in situ assessment of cartilage was developed and validated in this study. A formalin-fixed human knee was scanned by computed tomography in its native configuration and digitally processed to create femoral and tibial bone models. The bone models were covered by artificial femoral and tibial articular cartilage layers in their native configuration using cartilage-mimicking polyvinyl siloxane. A standardized defect of 8 mm diameter was created within the artificial cartilage layer at the central medial femoral condyle, into which native cartilage samples of similar dimensions were placed. After describing its design and specifications, the comprehensive validation of the device was performed using a hydraulic force gauge and digital electronic pressure-sensitive sensors. Displacement-controlled quasi-static uniaxial loading to 2.5 mm [Formula: see text] and 5.0 mm [Formula: see text] of the mobile tibia versus the immobile femur resulted in forces of [Formula: see text] N [Formula: see text] and [Formula: see text] N [Formula: see text] (on the entire joint) and local pressures of [Formula: see text] MPa [Formula: see text] and [Formula: see text] MPa [Formula: see text] (at the site of the cartilage sample). Upon confirming the MRI compatibility of the set-up, the response to loading of macroscopically intact human articular cartilage samples ([Formula: see text]) was assessed on a clinical 3.0-T MR imaging system using clinical standard proton-density turbo-spin echo sequences and T2-weighted multi-spin echo sequences. Serial imaging was performed at the unloaded state [Formula: see text] and at consecutive loading positions (i.e. at [Formula: see text] and [Formula: see text]. Biomechanical unconfined compression testing (Young's modulus) and histological assessment (Mankin score) served as the standards of reference. All samples were histologically intact (Mankin score, [Formula: see text]) and biomechanically reasonably homogeneous (Young's modulus, [Formula: see text] MPa). They could be visualized in their entirety by MRI and significant decreases in sample height [[Formula: see text]: [Formula: see text] mm; [Formula: see text]: [Formula: see text] mm; [Formula: see text]: [Formula: see text] mm; [Formula: see text] (repeated-measures ANOVA)] as well as pronounced T2 signal decay indicative of tissue pressurization were found as a function of compressive loading. In conclusion, our compression device has been validated for the noninvasive response-to-loading assessment of human articular cartilage by MRI in a close-to-physiological experimental setting. Thus, in a basic research context cartilage may be functionally evaluated beyond mere static analysis and in reference to histology and biomechanics.

In vivo measurements and numerical analysis of the biomechanical characteristics of the human periodontal ligament

The periodontal ligament is a complex tissue with respect to its biomechanical behaviour. It is important to understand the mechanical behaviour of the periodontal ligament during physiological loading in healthy patients as well as during the movement of the tooth in orthodontic treatment or in patients with periodontal disease, as these might affect the mechanical properties of the periodontal ligament (PDL). Up to now, only a limited amount of in vivo data is available concerning this issue. The aim of this study has been to determine the time dependent material properties of the PDL in an experimental in vivo study, using a novel device that is able to measure tooth displacement intraorally. Using the intraoral loading device, tooth deflections at various velocities were realised in vivo on human teeth. The in vivo investigations were performed on the upper left central incisors of five volunteers aged 21-33 years with healthy periodontal tissue. A deflection, applied at the centre of the crown, was linearly increased from 0 to 0.15mm in a loading period of between 0.1 and 5.0s. Individual numerical models were developed based on the experimental results to simulate the relationship between the applied force and tooth displacement. The numerical force/displacement curves were fitted to the experimental ones to obtain the material properties of the human PDL. For the shortest loading time of 0.1s, the experimentally determined forces were between 7.0 and 16.2N. The numerically calculated Young's modulus varied between 0.9MPa (5.0s) and 1.2MPa (0.1s). By considering the experimentally and numerically obtained force curves, forces decreased with increasing loading time. The experimental data gained in this study can be used for the further development and verification of a multiphasic constitutive law of the PDL.