Dominika Ignasiak

Thoracolumbar spine model with articulated ribcage for the prediction of dynamic spinal loading.

Musculoskeletal modeling offers an invaluable insight into the spine biomechanics. A better understanding of thoracic spine kinetics is essential for understanding disease processes and developing new prevention and treatment methods. Current models of the thoracic region are not designed for segmental load estimation, or do not include the complex construct of the ribcage, despite its potentially important role in load transmission. In this paper, we describe a numerical musculoskeletal model of the thoracolumbar spine with articulated ribcage, modeled as a system of individual vertebral segments, elastic elements and thoracic muscles, based on a previously established lumbar spine model and data from the literature. The inverse dynamics simulations of the model allow the prediction of spinal loading as well as costal joints kinetics and kinematics. The intradiscal pressure predicted by the model correlated well (R(2)=0.89) with reported intradiscal pressure measurements, providing a first validation of the model. The inclusion of the ribcage did not affect segmental force predictions when the thoracic spine did not perform motion. During thoracic motion tasks, the ribcage had an important influence on the predicted compressive forces and muscle activation patterns. The compressive forces were reduced by up to 32%, or distributed more evenly between thoracic vertebrae, when compared to the predictions of the model without ribcage, for mild thoracic flexion and hyperextension tasks, respectively. The presented musculoskeletal model provides a tool for investigating thoracic spine loading and load sharing between vertebral column and ribcage during dynamic activities. Further validation for specific applications is still necessary.

A rigid thorax assumption affects model loading predictions at the upper but not lower lumbar levels

A number of musculoskeletal models of the human spine have been used for predictions of lumbar and muscle forces. However, the predictive power of these models might be limited by a commonly made assumption; thoracic region is represented as a single lumped rigid body. This study hence aims to investigate the impact of such assumption on the predictions of spinal and muscle forces. A validated thoracolumbar spine model was used with a flexible thorax (T1-T12), a completely rigid one or rigid with thoracic posture updated at each analysis step. The simulations of isometric forward flexion up to 80°, with and without a 20kg hand load, were performed, based on the previously measured kinematics. Depending on the simulated task, the rigid model predicted slightly or moderately lower compressive loading than the flexible one. The differences were relatively greater at the upper lumbar levels (average underestimation of 14% at the T12L1 for flexion tasks and of 18% for flexion tasks with hand load) as compared to the lower levels (3% and 8% at the L5S1 for unloaded and loaded tasks, respectively). The rigid model with updated thoracic posture predicted compressive forces similar to those of the rigid model. Predicted muscle forces were, however, very different between the three models. This study indicates that the lumbar spine models with a rigid thorax definition can be used for loading investigations at the lowermost spinal levels. For predictions of upper lumbar spine loading, using models with an articulated thorax is advised.

Spinal kinematics during gait in healthy individuals across different age groups

Most studies investigating trunk kinematics have not provided adequate quantification of spinal motion, resulting in a limited understanding of the healthy spines biomechanical behavior during gait. This study aimed at assessing spinal motion during gait in adolescents, adults and older individuals. Fourteen adolescents (10-18years), 13 adults (19-35years) and 15 older individuals (≥65years) were included. Using a previously validated enhanced optical motion capture approach, sagittal and frontal plane spinal curvature angles and general trunk kinematics were measured during shod walking at a self-selected normal speed. Postural differences indicated that lumbar lordosis and thoracic kyphosis increase throughout adolescence and reach their peak in adulthood. The absence of excessive thoracic kyphosis in older individuals could be explained by a previously reported subdivision in those who develop excessive kyphosis and those who maintain their curve. Furthermore, adults displayed increased lumbar spine range of motion as compared to the adolescents, whereas the increased values in older individuals were found to be related to higher gait speeds. This dataset on the age-related kinematics of the healthy spine can serve as a basis for understanding pathological deviations and monitoring rehabilitation progression.

Correction tool for Active Shape Model based lumbar muscle segmentation

In the clinical environment, accuracy and speed of the image segmentation process plays a key role in the analysis of pathological regions. Despite advances in anatomic image segmentation, time-effective correction tools are commonly needed to improve segmentation results. Therefore, these tools must provide faster corrections with a low number of interactions, and a user-independent solution. In this work we present a new interactive correction method for correcting the image segmentation. Given an initial segmentation and the original image, our tool provides a 2D/3D environment, that enables 3D shape correction through simple 2D interactions. Our scheme is based on direct manipulation of free form deformation adapted to a 2D environment. This approach enables an intuitive and natural correction of 3D segmentation results. The developed method has been implemented into a software tool and has been evaluated for the task of lumbar muscle segmentation from Magnetic Resonance Images. Experimental results show that full segmentation correction could be performed within an average correction time of 6±4 minutes and an average of 68±37 number of interactions, while maintaining the quality of the final segmentation result within an average Dice coefficient of 0.92±0.03.

Thoracolumbar spine loading associated with kinematics of the young and the elderly during activities of daily living

Excessive mechanical loading of the spine is a critical factor in vertebral fracture initiation. Most vertebral fractures develop spontaneously or due to mild trauma, as physiological loads during activities of daily living might exceed the failure load of osteoporotic vertebra. Spinal loading patterns are affected by vertebral kinematics, which differ between elderly and young individuals. In this study, the effects of age-related changes in spine kinematics on thoracolumbar spinal segmental loading during dynamic activities of daily living were investigated using combined experimental and modeling approach. Forty-four healthy volunteers were recruited into two age groups: young (N = 23, age = 27.1 ± 3.8) and elderly (N = 21, age = 70.1 ± 3.9). The spinal curvature was assessed with a skin-surface device and the kinematics of the spine and lower extremities were recorded during daily living tasks (flexion-extension and stand-sit-stand) with a motion capture system. The obtained data were used as input for a musculoskeletal model with a detailed thoracolumbar spine representation. To isolate the effect of kinematics on predicted loads, other model properties were kept constant. Inverse dynamics simulations were performed in the AnyBody Modeling System to estimate corresponding spinal loads. The maximum compressive loads predicted for the elderly motion patterns were lower than those of the young for L2/L3 and L3/L4 lumbar levels during flexion and for upper thoracic levels during stand-to-sit (T1/T2-T8/T9) and sit-to-stand (T3/T4-T6/T7). However, the maximum loads predicted for the lower thoracic levels (T9/T10-L1/L2), a common site of vertebral fractures, were similar compared to the young. Nevertheless, these loads acting on the vertebrae of reduced bone quality might contribute to a higher fracture risk for the elderly.

Multi-segmental thoracic spine kinematics measured dynamically in the young and elderly during flexion

In contrast to the cervical and lumbar region, the normal kinematics of the thoracic spine have not been thoroughly investigated. The aim of this study was to characterize normal multi-segmental continuous motion of the whole thoracolumbar spine, during a flexion maneuver, in young and elderly subjects. Forty-two healthy volunteers were analyzed: 21 young (age=27.00±3.96) and 21 elderly (age=70.1±3.85). Spinal motion was recorded with a motion-capture system and analyzed using a 3rd order polynomial function to approximate spinal curvature throughout the motion sequence. The average motion profiles of the two age groups were characterized. Flexion timing of the thoracic region of the spine, as compared to the lumbar spine and hips, was found to be different in the two age groups (p=0.011): a delayed/sequential motion type was observed in most of the young, whereas mostly a simultaneous motion pattern was observed in the elderly subjects. A similar trend was observed in flexion of the lower thoracic segments (p=0.017). Differences between age groups were also found for regional and segmental displacements and velocities. The reported characterization of the thoracic spine kinematics may in the future support identification of abnormal movement or be used to improve biomechanical models of the spine.

FISICO: Fast Image SegmentatIon COrrection.

Background and Purpose In clinical diagnosis, medical image segmentation plays a key role in the analysis of pathological regions. Despite advances in automatic and semi-automatic segmentation techniques, time-effective correction tools are commonly needed to improve segmentation results. Therefore, these tools must provide faster corrections with a lower number of interactions, and a user-independent solution to reduce the time frame between image acquisition and diagnosis. Methods We present a new interactive method for correcting image segmentations. Our method provides 3D shape corrections through 2D interactions. This approach enables an intuitive and natural corrections of 3D segmentation results. The developed method has been implemented into a software tool and has been evaluated for the task of lumbar muscle and knee joint segmentations from MR images. Results Experimental results show that full segmentation corrections could be performed within an average correction time of 5.5±3.3 minutes and an average of 56.5±33.1 user interactions, while maintaining the quality of the final segmentation result within an average Dice coefficient of 0.92±0.02 for both anatomies. In addition, for users with different levels of expertise, our method yields a correction time and number of interaction decrease from 38±19.2 minutes to 6.4±4.3 minutes, and 339±157.1 to 67.7±39.6 interactions, respectively.

Simulation of Spinal Loading: Importance of Subject-Specific Posture and Motion Patterns

Introduction Mechanical factors play an important role in the development of spinal disorders (e.g., fracture, disc degeneration). The overall objective of our research is to develop simulation models to investigate the effects of posture and muscular strength on spinal segmental loading, and thus the associated risk of injury.5 The aims of the present study were to further investigate alignment- and kinematics-dependent loading patterns, based on literature and laboratory measures of posture and motion data from young and elderly subjects. Materials and Methods Twenty-four young and 22 elderly subjects volunteered to participate. Average group ages were 27.5 years (standard deviation [SD] = 4.0) and 68.3 years (SD = 3.9), respectively. None of the recruited participants had undergone spinal surgery and none suffered from any back condition. Ethical approval and written consent were obtained. Spinal posture was determined with a noninvasive skin-surface device (SpinalMouse, Idiag). The spinal contour was measured twice in four body positions: (1) standing neutral, (2) erect posture, (3) flexed forward position, and (4) hyperextended posture. A musculoskeletal model of the thoracolumbar spine5 was further developed in the AnyBody Modeling System (AnyBody Technology) combining properties of lumbar models previously established by deZee, 2007 and Han, 2011.6,7 The present model adds a fully articulated thoracic region and ribcage to our prior simulation model. Lumbar motion patterns were derived from fluoroscopy measurements8 during a flexion maneuver in two groups of volunteers: healthy and with low back pain. Three motion patterns were distinguished: (1) all intervertebral joints angulate simultaneously during flexion, (2) upper lumbar joints rotate first and are followed by lower joints in a sequential manner, and (3) angulation of lower levels precedes the upper ones. Segmental forces (compression and shear) were calculated for each motion pattern. Results An average spine curvature, found from the static measurements of the neutral upright posture, was characterized by thoracic kyphosis angles of 49.4 degrees (SD = 11.3) and 45.9 degrees (SD = 6.0) for the young and elderly groups, respectively. Lumbar (L1S1) lordosis angles were 27.4 degrees (SD = 10.6) and 20.4 degrees (SD = 13.1), respectively. Simulations of the sequential and simultaneous motion patterns revealed that fewer muscles and lower muscle activities were necessary to perform lumbar flexion than when the same magnitude of flexion was achieved using the generic spinal rhythm (SR) incorporated in the AnyBody base model (constant ratio of segmental motion). Consequently, compression forces were significantly reduced, by up to 1,200N or 55%, compared with the reference model (Fig. 1). Conclusion The degree of thoracic kyphosis for young subjects measured in our study (49.4 degrees) compares favorably with previous radiographic findings (47.5 degrees). The lumbar lordosis angle that we measured (27.4 degrees) is similar to that reported in other studies with skin-surface devices (23-33 degrees); however, these values are considerably lower than those obtained from methods based on medical imaging (44-63 degrees). Therefore, skin-based systems can be used for subject-specific model definition in the thoracic region, but correction is required for the lumbar region. A surprisingly high variability in the spine curvature was observed, even for young volunteers, highlighting the potential limitations of generic simulation models. Elderly subjects tended toward a lower degree of kyphosis and significantly less lordosis. We have seen in previous simulations that flattening of the back can lead to increased segmental forces during flexion. In contrast to our prior results with arbitrarily defined spinal motion patterns, we have shown that physiological alterations in the temporal sequence of segmental motion can have a substantial influence on muscle recruitment and segmental loading. Compensatory measures, for example, for easing pain, may therefore increase—or decrease—the risk of injury. These results imply that the vertebral kinematics have a profound effect on model predictions, strengthening the necessity to measure and implement realistic vertebral kinematics for spinal motion simulations. In the referenced fluoroscopic study (Okawa, 1998), only a small number of participants were measured, and the motion recording was limited to L2-L5 levels. Therefore, the next step in our investigation will be the combination of the musculoskeletal model with subject specific, whole-spine posture, and motion data from the young and elderly subjects. Disclosure of Interest D. Ignasiak: Conflict with AOSpine S. Ferguson: Conflict with AOSpine References Johnell O, Kanis JA. An estimate of the worldwide prevalence and disability associated with osteoporotic fractures. Osteoporos Int 2006;17(12):1726–1733 Huang MH, Barrett-Connor E, Greendale GA, Kado DM. Hyperkyphotic posture and risk of future osteoporotic fractures: the Rancho Bernardo study. J Bone Miner Res 2006;21(3):419–423 Briggs AM, van Dieën JH, Wrigley TV, et al. Thoracic kyphosis affects spinal loads and trunk muscle force. Phys Ther 2007;87(5):595–607 Sinaki M, Itoi E, Wahner HW, et al. Stronger back muscles reduce the incidence of vertebral fractures: a prospective 10 year follow-up of postmenopausal women. Bone 2002;30(6):836–841 Ignasiak D, et al. Proceedings of the Global Spine Congress; Hong Kong, HK; 2013 de Zee M, Hansen L, Wong C, Rasmussen J, Simonsen EB. A generic detailed rigid-body lumbar spine model. J Biomech 2007;40(6):1219–1227 Han KS, Rohlmann A, Yang SJ, Kim BS, Lim TH. Spinal muscles can create compressive follower loads in the lumbar spine in a neutral standing posture. Med Eng Phys 2011;33(4):472–478 Okawa A, Shinomiya K, Komori H, Muneta T, Arai Y, Nakai O. Dynamic motion study of the whole lumbar spine by videofluoroscopy. Spine 1998;23(16):1743–1749

The effect of muscle ageing and sarcopenia on spinal segmental loads

AbstractPurposeThe interrelations between age-related muscle deterioration (sarcopenia) and vertebral fractures have been suggested based on clinical observations, but the biomechanical relationships have not been explored. The study aim was to investigate the effects of muscle ageing and sarcopenia on muscle recruitment patterns and spinal loads, using musculoskeletal multi-body modelling.MethodsA generic AnyBody model of the thoracolumbar spine, including > 600 fascicles representing trunk musculature, was used. Several stages of normal ageing and sarcopenia were modelled by reduced strength of erector spinae and multifidus muscles (ageing from 3rd to 6th life decade: ≥ 60% of normal strength; sarcopenia: mild 60%, moderate 48%, severe 36%, very severe 24%), reflecting the reported decrease in cross-sectional area and increased fat infiltration. All other model parameters were kept unchanged. Full-range flexion was simulated using inverse dynamics with muscle optimization to predict spinal loads and muscle recruitment patterns.ResultsThe muscle changes due to normal ageing (≥ 60% strength) had a minor effect on predicted loads and provoked only slightly elevated muscle activities. Severe (36%) and very severe (24%) stages of sarcopenia, however, were associated with substantial increases in compression (by up to 36% or 318N) at the levels of the upper thoracic spine (T1T2–T5T6) and shear loading (by up to 75% or 176N) along the whole spine (T1T2–L4L5). The muscle activities increased for almost all muscles, up to 100% of their available strength.ConclusionsThe study highlights the distinct and detrimental consequences of sarcopenia, in contrast to normal ageing, on spinal loading and required muscular effort.Graphical abstract These slides can be retrieved under Electronic Supplementary Material.