Biomechanical analysis of osteoporotic spines with diseases using CT-based finite element method

The eventuality of recurrent fractures on the adjacent level of fractured vertebra is becoming prevalent in this era. To date, the underlying cause of this phenomena is either due to low bone quality or adverse geometrical changes of the vertebral body, as a result of osteoporosis and vertebral compression fractures (VCFs). To further investigate the determinant factor of this phenomenon, an image based finite element analysis (FEA) was used to scrutinize the biomechanical response of spines that have been afflicted by different types of spinal deformities, namely; wedge-shaped, fish-shaped and plana-shaped vertebrae. The evaluation was made based on its structural integrity in accordance to stress and strain distributions, and fracture risks prediction. These findings were then further corroborated by evaluating other associating factors such as kyphotic deformity angle and bone density distribution in order to find the underlying cause of this symptom. The results showed that the low bone density due to osteoporosis has become the dominant factor in inciting the risks of subsequent fractures on the adjacent vertebrae. This is based on the contradictory relation between the number of the failure elements distributions and the degree of the kyphotic deformity angle, as described by the wedge-shaped vertebral fracture model. Obviously, the most highly structural deformed vertebra still could withstand any kinds of high input loads, provided that its structural formation is still intact and has not severely affected by osteoporosis. The high incidence of subsequent fractures following Balloon Kyphoplasty (BKP) in both the augmented and adjacent vertebrae is quickly becoming a clinically unresolvable complication. The underlying cause of this phenomenon is still unknown and to date medical practitioners are still unable to explain the fundamental cause of this phenomenon. To verify this claim, an image-based finite element analysis was used to investigate the effectiveness of BKP treatment of pre-operative and post-operative osteoporotic spine models. The three-dimensional (3D) non-linear finite element (FE) models of the thoracolumbar spine (T11-L3) were developed from CT-scan images. The biomechanical responses were evaluated based on the models’ load sharing mechanisms, load transfer mechanisms, stiffness recovery, stability, and kyphotic deformity restoration. The margin of safety for each of the models was evaluated under incrementally increased loads (1-10kN). This margin would be determined based on the fracture risk evaluation in accordance to the associated onset fracture load. The results showed that the BKP procedures play a significant role in enhancing the structural integrity of the treated spine by lowering the effect of the bone fracturing and optimizing the biomechanical alterations up to its pre-fracture level. However, the phenomenon of high incidence of vertebral bone failures on the augmented and its neighboring vertebrae indicates that the osteoporosis severity is the most influential factor in determining the sufficiency of the BKP treatment. Cage subsidence, pedicle screw loosening and instability are the most prevalent posterior lumbar interbody fusion (PLIF)-related complications. These may be attributed to interrelated mechanical, biomechanical and environmental factors. Current advancement in medical treatment has paved the way for the implementation of unilateral cages in an oblique position to overcome unintended mechanical and clinical shortcomings. To verify this claim, an imagebased finite element analysis (FEA) was used to evaluate several factors; cage subsidence, screw loosening and PLIF construct stability via stress profiles, fracture risk prediction and range of motion (ROM) evaluations in the different type of cage materials and cage orientations. Obviously, obliquely-placed unilateral fusion cage constructs with PI exhibited the most reliable biomechanical constructs by showing the smallest ROM and producing the minimal distortion stress at the cage-endplate and pedicle screw-bone interfaces. Moreover, these results also showed good agreement with the results obtained using fracture risks assessments by showing the lower numbers of deformation elements at the both contact interfaces in normal and traumatic events. In conclusion, biocompatible cage materials and structural symmetry are the most important criteria in achieving biomechanical advantage in PLIF surgery

Computer-aided detection in musculoskeletal projection radiography: A systematic review

This is the author accepted manuscript. The final version is available from WB Saunders via the DOI in this record.Objectives To investigated the accuracy of computer-aided detection (CAD) software in musculoskeletal projection radiography via a systematic review. Key findings Following selection screening, eligible studies were assessed for bias, and had their study characteristics extracted resulting in 22 studies being included. Of these 22 three studies had tested their CAD software in a clinical setting; the first study investigated vertebral fractures, reporting a sensitivity score of 69.3% with CAD, compared to 59.8% sensitivity without CAD. The second study tested dental caries diagnosis producing a sensitivity score of 68.8% and specificity of 94.1% with CAD, compared to sensitivity of 39.3% and specificity of 96.7% without CAD. The third indicated osteoporotic cases based on CAD, resulting in 100% sensitivity and 81.3% specificity. Conclusion The current evidence reported shows a lack of development into the clinical testing phase; however the research does show future promise in the variation of different CAD systems

The Effects of Vertebral Variation on the Mechanical Outcomes of Vertebroplasty

Osteoporotic vertebral compression fractures are a commonly encountered clinical problem that causes a reduced quality of life for a large proportion of those affected. One of the treatments for this type of fracture is vertebroplasty, where the injection of bone cement into the vertebral body aims to stabilise the vertebra and relieve pain. Despite being a frequently used treatment a number of studies and randomised clinical trials have questioned the efficacy of the procedure. These clinical trials and studies have suggested that the procedure is no more effective than a placebo in terms of pain relief. Finite Element (FE) models allow an investigation into the structural and geometric variation that affect the response to augmentation. However, current specimen specific FE models are limited due to the poor reproduction of cement augmentation behaviour. The aims of this thesis were to develop new methods of modelling the vertebral body in an augmented state, using these models as an input to a statistical shape and appearance model (SSAM). Methods were developed for experimental testing, cement augmentation and modelling through a specimen specific modelling approach to create and solve FE models. These methods were initially used with bovine tail vertebrae and then refined for the use of human lumbar vertebrae. These latter models formed the input set for the creation of a SSAM, where vertebral and augmentation variables were examined. Models of augmentation in human lumbar vertebrae achieved a good agreement with their experimental counterparts through the development of novel modelling techniques. A new SSAM method has been developed for human lumbar vertebrae and applied to evaluate the mechanical performance of vertebroplasty. The tools developed can now be applied to examine wider patient cohorts and other clinical therapies

A study of change in human trabecular bone structure with age and during osteoporosis

The objective of this work was to develop new techniques to view trabecular bone three-dimensionally, and to study its structure and the changes that occur with age and in osteoporosis; the methods used included 3D methods in the SEM, laser confocal microscopy, pseudo-holograms and a "continuous motion parallax method". A detailed analysis of trabecular bone from fourth lumbar vertebral bodies used macro-stereophotographs produced by tilting a sample 10°. Models are proposed for both normal and osteoporotic architecture. A quantitative analysis of the lengths of horizontally oriented trabeculae was carried out. A significant decrease in the number of both vertically and horizontally oriented trabeculae was found. The importance of the influence of different developmental patterns on the formation of the normal structure and of the changing vascularisation on osteoporotic structure are emphasised. Two-dimensional fast Fourier transform methods were employed to study changes in the spatial frequency of trabeculae as a function of orientation. A decrease in spatial frequency was observed in both sexes, but in males this was evident only after the mid-sixth decade in the limited sample studied. Contoured power spectra discriminated different trabecular patterns and the intensity mapping of optical density provided volume density information. Templated reverse transformation was used to study individual orientations of trabeculae. Changes in the quality of trabecular bone with age were also investigated using techniques that analyse bone before and after removal of unmineralised matrix. All specimens were less stiff after removal of osteoid; this was more marked in older specimens. Locally defective mineralisation would explain the changed behaviour observed in some old and osteoporotic specimens. Trabecular fracture patterns had a strong relationship to architecture and microstructure. Scanning electron microscopy was used to study trabecular surfaces. An uncoupling between resorption and formation was evident in older specimens. Two resorption patterns responsible for thinning and perforation and removal trabecular elements were identified. Trabecular microfractures were also investigated

A multi-center milestone study of clinical vertebral CT segmentation

A multiple center milestone study of clinical vertebra segmentation is presented in this paper. Vertebra segmentation is a fundamental step for spinal image analysis and intervention. The first half of the study was conducted in the spine segmentation challenge in 2014 International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI) Workshop on Computational Spine Imaging (CSI 2014). The objective was to evaluate the performance of several state-of-the-art vertebra segmentation algorithms on computed tomography (CT) scans using ten training and five testing dataset, all healthy cases; the second half of the study was conducted after the challenge, where additional 5 abnormal cases are used for testing to evaluate the performance under abnormal cases. Dice coefficients and absolute surface distances were used as evaluation metrics. Segmentation of each vertebra as a single geometric unit, as well as separate segmentation of vertebra substructures, was evaluated. Five teams participated in the comparative study. The top performers in the study achieved Dice coefficient of 0.93 in the upper thoracic, 0.95 in the lower thoracic and 0.96 in the lumbar spine for healthy cases, and 0.88 in the upper thoracic, 0.89 in the lower thoracic and 0.92 in the lumbar spine for osteoporotic and fractured cases. The strengths and weaknesses of each method as well as future suggestion for improvement are discussed. This is the first multi-center comparative study for vertebra segmentation methods, which will provide an up-to-date performance milestone for the fast growing spinal image analysis and intervention

The lumbar spine has an intrinsic shape specific to each individual that remains a characteristic throughout flexion and extension

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Comparative radiological anatomy of human, porcine and ovine vertebrae

Osteoporotic vertebral fractures represent an important health burden in the Western world, in particular given the aging population demographics of most Western countries. At present, the treatment options for osteoporotic vertebral fractures are limited, and often conservative, relying on medical pain management. Transpedicular spinal interventional techniques such as vertebroplasty and kyphoplasty offer a minimally invasive treatment option for osteoporotic vertebral fractures. However, there has been recent controversy regarding the efficacy of vertebroplasty for pain relief. Although these percutaneous techniques continue to be used and developed, there is no consensus on the pre-clinical testing of new instruments and cements. Human cadaveric vertebrae are expensive and of limited availability, and animal vertebrae offer a more easily accessible alternative, but there is no agreement within the literature as to which species best approximates the human. This thesis explores the currently available evidence comparing human and animal vertebrae, and performs comparison studies assessing basic morphometric measurements, bone texture, and statistical shape analysis, to decide upon the best animal model for the use in assessing novel transpedicular instruments and vertebral bone cements. The findings would also apply to developments in surgical transpedicular screws. The morphometry showed that sheep are generally closer to humans in the thoracic spine, whereas pigs are closer in the lumbar spine. Bone texture analysis demonstrated no significant differences in trabecular thickness between humans and either sheep or pigs. Statistical shape analysis corroborated the findings of basic morphometry. Taking the findings in combination, I would suggest that for the purposes of transpedicular techniques, the sheep is a closer model to the human in the thoracic spine, and the pig is closer in the lumbar spine

Statistical Properties of a Virtual Cohort for In Silico Trials Generated with a Statistical Anatomy Atlas

Osteoporosis-related hip fragility fractures are a catastrophic event for patient lives but are not frequently observed in prospective studies, and therefore phase III clinical trials using fractures as primary clinical endpoint require thousands of patients enrolled for several years to reach statistical significance. A novel answer to the large number of subjects needed to reach the desired evidence level is offered by In Silico Trials, that is, the simulation of a clinical trial on a large cohort of virtual patients, monitoring the biomarkers of interest. In this work we investigated if statistical aliasing from a custom anatomy atlas could be used to expand the patient cohort while retaining the original biomechanical characteristics. We used a pair-matched cohort of 94 post-menopausal women (at the time of the CT scan, 47 fractured and 47 not fractured) to create a statistical anatomy atlas through principal component analysis, and up-sampled the atlas in order to obtain over 1000 synthetic patient models. We applied the biomechanical computed tomography pipeline to the resulting virtual cohort and compared its fracture risk distribution with that of the original physical cohort. While the distribution of femoral strength values in the non-fractured sub-group was nearly identical to that of the original physical cohort, that of the fractured sub-group was lower than in the physical cohort. Nonetheless, by using the classification threshold used for the original population, the synthetic population was still divided into two parts of approximatively equal number