Spinal cord injury (SCI) is associated with a rapid loss of bone mass, resulting in severe osteop... more Spinal cord injury (SCI) is associated with a rapid loss of bone mass, resulting in severe osteoporosis and a 5- to 23-fold increase in fracture risk. Despite the seriousness of fractures in SCI, there are multiple barriers to osteoporosis diagnosis and wide variations in treatment practices for SCI-induced osteoporosis. We review the biological and structural changes that are known to occur in bone after SCI in the context of promoting future research to prevent or reduce risk of fracture in this population. We also review the most commonly used methods for assessing bone after SCI and discuss the strengths, limitations, and clinical applications of each method. Although dual-energy x-ray absorptiometry assessments of bone mineral density may be used clinically to detect changes in bone after SCI, 3-dimensional methods such as quantitative CT analysis are recommended for research applications and are explained in detail.
... This is a formidable challenge to scientists and clinicians. The extant litera-ture provides ... more ... This is a formidable challenge to scientists and clinicians. The extant litera-ture provides pieces of the solution to the challenge, necessary pieces that 112 Reed-Troy and Grabiner Page 139. ... 14. Pai YC, Patton J. Center of mass velocity-position predictions for balance con-trol. ...
INTRODUCTION Older adults have a high incidence of trip-related falls that contribute to signific... more INTRODUCTION Older adults have a high incidence of trip-related falls that contribute to significant morbidity and mortality. A surrogate treadmill task has been proposed as a potential fall-preventive training tool for older adults. Successful motor response training must elicit stepping strategies as similar as possible to those evoked during actual trips and must demonstrate motor skill acquisition. Differences in the foot trajectories after an actual trip compared to those during the treadmill task have been attributed to the presence of an obstacle [1]. Recent work has shown that the addition of an obstacle to the surrogate treadmill task increases step height and step length to more closely approximate stepping responses elicited during an actual trip [2]. Older adults have demonstrated the ability to modify failed stepping strategies and successfully recover on the subsequent trial during the treadmill task without the obstacle [3], but little is known about the underlying mo...
Study Design:Comparison of diagnostic tests; methodological validation.Objectives:Primary: to inv... more Study Design:Comparison of diagnostic tests; methodological validation.Objectives:Primary: to investigate the precision and reliability of a knee bone mineral density (BMD) assessment protocol that uses an existing dual energy X-ray absorptiometry (DXA) forearm acquisition algorithm in individuals with spinal cord injury (SCI). Secondary: to correlate DXA-based knee areal BMD with volumetric BMD assessments derived from quantitative computed tomography (QCT).Setting:Academic medical center, Chicago, IL, USA.Methods:Participants: a convenience sample of 12 individuals with acute SCI recruited for an observational study of bone loss and 34 individuals with chronic SCI who were screened for a longitudinal study evaluating interventions to increase BMD. Main outcome measures: root-mean-square standard deviation (RMS-SD) and intra/inter-rater reliability of areal BMD acquired at three knee regions using an existing DXA forearm acquisition algorithm; correlation of DXA-based areal BMD wit...
Spinal cord injury (SCI) is characterized by rapid bone loss and an increased risk of fragility f... more Spinal cord injury (SCI) is characterized by rapid bone loss and an increased risk of fragility fracture around regions of the knee. Our purpose was to quantify changes in torsional stiffness K and strength Tult at the proximal tibia due to actual bone loss and simulated bone recovery in acute SCI. Computed tomography scans were acquired on ten subjects with acute SCI at serial time points separated by a mean of 3.9months (range 3.0 to 4.8months). Reductions in bone mineral were quantified and a validated subject-specific finite element modeling procedure was used to predict changes in K and Tult. The modeling procedure was subsequently used to examine the effect of simulated hypothetical treatments, in which bone mineral of the proximal tibiae were restored to baseline levels, while all other parameters were held constant. During the acute period of SCI, subjects lost 8.3±4.9% (p<0.001) of their bone mineral density (BMD). Reductions in K (-9.9±6.5%; p=0.002) were similar in mag...
Bone strains resulting from physical activity are thought to be a primary driver of bone adaptati... more Bone strains resulting from physical activity are thought to be a primary driver of bone adaptation, but cannot be directly noninvasively measured. Because bone adapts nonuniformly, physical activity may make an important independent structural contribution to bone strength that is independent of bone mass and density. Our objective was to create and validate methods for subject-specific finite element (FE) model generation that would accurately predict the surface strains experienced by the distal radius during an in vivo loading task, and to apply these methods to a group of 23 women aged 23-35 to examine variations in strain, bone mass and density, and physical activity. Four cadaveric specimens were experimentally tested and specimen-specific FE models were developed to accurately predict periosteal surface strains (root mean square error=16.3%). In the living subjects, when 300N load was simulated, mean strains were significantly inversely correlated with BMC (r=-0.893), BMD (r...
Distal radius fracture strength has been quantified using in vitro biomechanical testing. These t... more Distal radius fracture strength has been quantified using in vitro biomechanical testing. These tests are frequently performed using one of two methods: (1) load is applied directly to the embedded isolated radius or (2) load is applied through the hand with the wrist joint intact. Fracture loads established using the isolated radius method are consistently 1.5 to 3 times greater than those for the intact wrist method. To address this discrepancy, a validated finite element modeling procedure was used to predict distal radius fracture strength for 22 female forearms under boundary conditions simulating the isolated radius and intact wrist method. Predicted fracture strength was highly correlated between methods (r = 0.94; p < 0.001); however, intact wrist simulations were characterized by significantly reduced cortical shell load carriage and increased stress and strain concentrations. These changes resulted in fracture strength values less than half those predicted for the i...
Individuals with spinal cord injury experience a rapid loss of bone mineral below the neurologica... more Individuals with spinal cord injury experience a rapid loss of bone mineral below the neurological lesion. The clinical consequence of this bone loss is a high rate of fracture around regions of the knee. The ability to predict the mechanical competence of bones at this location may serve as an important clinical tool to assess fracture risk in the spinal cord injury population. The purpose of this study was to develop, and statistically compare, non-invasive methods to predict torsional stiffness (K) and strength (Tult) of the proximal tibia. Twenty-two human tibiae were assigned to either a "training set" or a "test set" (11 specimens each) and mechanically loaded to failure. The training set was used to develop subject-specific finite element (FE) models, and statistical models based on dual energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT), to predict K and Tult; the test set was used for cross-validation. Mechanical testing produce...
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine
To better understand the mechanisms underlying spiral fracture we would like to carry out biomech... more To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6...
The prevention of fractures remains the primary clinical goal for osteoporosis treatment. Recentl... more The prevention of fractures remains the primary clinical goal for osteoporosis treatment. Recently, improved understanding of the factors influencing the risk of osteoporotic fracture has made the application of personalized medicine possible in this arena. At the epidemiologic level, the FRAX (World Health Organization) tool provides individual fracture risk estimates [1]. However, even greater benefit could stem from patient-specific fracture risk assessment techniques independent of epidemiologic classification, as well as the objective identification of patients meeting requirements for a particular treatment (ie, exercise or pharmacologic intervention). Numerical modeling techniques will no doubt become an integral part of this medical practice. In the study of osteoporosis, numerical models are often adopted to predict the mechanical behavior of bone in vivo. In this context, numerical models have reached a level of accuracy necessary to extract clinically relevant information and help guide clinical decision making . Although there are many types of numerical modeling techniques that can be used to examine the mechanical behavior of bone, we focus on the finite element method, as it is the most widely used and best developed technique for objects of complex geometry.
Bone strains resulting from physical activity are thought to be a primary driver of bone adaptati... more Bone strains resulting from physical activity are thought to be a primary driver of bone adaptation, but cannot be directly noninvasively measured. Because bone adapts nonuniformly, physical activity may make an important independent structural contribution to bone strength that is independent of bone mass and density. Our objective was to create and validate methods for subject-specific finite element (FE) model generation that would accurately predict the surface strains experienced by the distal radius during an in vivo loading task, and to apply these methods to a group of 23 women aged 23-35 to examine variations in strain, bone mass and density, and physical activity. Four cadaveric specimens were experimentally tested and specimen-specific FE models were developed to accurately predict periosteal surface strains (root mean square error=16.3%). In the living subjects, when 300 N load was simulated, mean strains were significantly inversely correlated with BMC (r=-0.893), BMD (...
Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and... more Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and, prospectively, in the community. Based on an emerging body of evidence, we hypothesize that using task-specific perturbation training as a stand-alone approach or in conjunction with conventional exercise-based approaches will improve the effectiveness of fall prevention interventions significantly.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2012
To better understand the mechanisms underlying spiral fracture we would like to carry out biomech... more To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6 6 53.2 Nm and 8.3 6 1.5°, respectively. Ultimate torque was highly correlated with DXA assessed bone mineral density (r = 0.87; p \ 0.001). The device presented is applicable to any torsional testing of long bone when only a single-axis linear actuator is available.
This study used quantitative computed tomography to assess changes in bone mineral at the proxima... more This study used quantitative computed tomography to assess changes in bone mineral at the proximal femur after acute spinal cord injury (SCI). Individuals with acute SCI experienced a marked loss of bone mineral from a combination of trabecular and endocortical resorption. Targeted therapeutic interventions are thus warranted in this population. Introduction SCI is associated with a rapid loss of bone mineral and an increased rate of fragility fracture. Some 10 to 20 % of these fractures occur at the proximal femur. The purpose of this study was to quantify changes to bone mineral, geometry, and measures of strength at the proximal femur in acute SCI. Methods Quantitative computed tomography analysis was performed on 13 subjects with acute SCI at serial time points separated by a mean of 3.5 months (range, 2.6-4.8 months). Changes in bone mineral content (BMC) and volumetric bone mineral density (vBMD) were quantified for integral, trabecular, and cortical bone at the femoral neck, trochanteric, and total proximal femur regions. Changes in bone volumes, cross-sectional areas, and surrogate measures of compressive and bending strength were also determined. Results During the acute period of SCI, subjects experienced a 2.7-3.3 %/month reduction in integral BMC (p< 0.001) and a 2.5-3.1 %/month reduction in integral vBMD (p<0.001). Trabecular BMC decreased by 3.1-4.7 %/month (p<0.001) and trabecular vBMD by 2.8-4.4 %/month (p< 0.001). A 3.9-4.0 %/month reduction was observed for cortical BMC (p<0.001), while the reduction in cortical vBMD was noticeably lower (0.8-1.0 %/month; p≤0.01). Changes in bone volume and cross-sectional area suggested that cortical bone loss occurred primarily through endosteal resorption. Declines in bone mineral were associated with a 4.9-5.9 %/month reduction in surrogate measures of strength.
Computed tomography and finite element modeling were used to assess bone mineral and stiffness lo... more Computed tomography and finite element modeling were used to assess bone mineral and stiffness loss at the knee following acute spinal cord injury (SCI). Marked bone mineral loss was observed from a combination of trabecular and endocortical resorption. Reductions in stiffness were 2-fold greater than reductions in integral bone mineral. Introduction SCI is associated with a rapid loss of bone mineral and an increased rate of fragility fracture. The large majority of these fractures occur around regions of the knee. Our purpose was to quantify changes to bone mineral, geometry, strength indices, and stiffness at the distal femur and proximal tibia in acute SCI. Methods Quantitative computed tomography (QCT) and patient-specific finite element analysis were performed on 13 subjects with acute SCI at serial time points separated by a mean of 3.5 months (range 2.6-4.8 months). Changes in bone mineral content (BMC) and volumetric bone mineral density (vBMD) were quantified for integral, trabecular, and cortical bone at epiphyseal, metaphyseal, and diaphyseal regions of the distal femur and proximal tibia. Changes in bone volumes, cross-sectional areas, strength indices and stiffness were also determined.
The potential of task-specific training as a fall-prevention intervention was studied. The primar... more The potential of task-specific training as a fall-prevention intervention was studied. The primary purpose of the study was to determine the extent to which a task-specific training protocol decreased the number of falls by middle-age and older women after a laboratory-induced trip. Secondary purposes were to explore the ability of trunk kinematics during the initial recovery step and the length of the initial recovery step to correctly classify the trip outcome and to quantify the extent to which the training protocol affected these variables. Healthy community-dwelling women (n = 52) were assigned to either a training group or a control group that received no training. Training group women participated in an individually tailored, task-specific training protocol during which forward-directed stepping responses were necessary to avoid a fall after treadmill-delivered postural disturbances. Following the protocol, the ability to avoid a fall after a laboratory-induced trip was assessed. The primary outcome variable was the success (recover) or failure (fall) of the posttrip stepping response. Compared with the control group, there were fewer falls by the trained women after the laboratory-induced trip (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001; odds ratio = 0.13). Using logistic regression, falls and recoveries after the trip were sensitively classified by trunk flexion angle at the completion of the initial recovery step and the length of the initial recovery step (sensitivity = 0.67, specificity = 0.98), the former of which improved as a result of the task-specific training protocol. The task-specific training protocol significantly reduced the number of falls after a laboratory-induced trip. Prospective study is required to determine whether this task-specific training reduces falls in the community and, consequently, may complement currently used exercise-based fall prevention intervention methods.
In an effort to improve bone strength and prevent fracture at the distal radius, we have develope... more In an effort to improve bone strength and prevent fracture at the distal radius, we have developed a mechanical loading intervention in which females cyclically load their forearm. To relate the applied stimulus with the bone adaptation response, an accurate characterization of the mechanical environment within the bone must be known. Finite element (FE) models have been an effective tool for both strain and fracture-risk assessment. An ideal model would simulate physiological loading scenarios with simplified boundary conditions, allowing for computationally efficient strain determination for numerous subjects. We are also interested in the ability of the FE method to predict fracture strength as a means to assess the effectiveness of our loading protocol. Here, we compared experimental surface strains and fracture loads with specimen-specific FE models for the purpose of validating our simplified boundary conditions and model generating algorithm.
Spinal cord injury (SCI) is associated with a rapid loss of bone mass, resulting in severe osteop... more Spinal cord injury (SCI) is associated with a rapid loss of bone mass, resulting in severe osteoporosis and a 5- to 23-fold increase in fracture risk. Despite the seriousness of fractures in SCI, there are multiple barriers to osteoporosis diagnosis and wide variations in treatment practices for SCI-induced osteoporosis. We review the biological and structural changes that are known to occur in bone after SCI in the context of promoting future research to prevent or reduce risk of fracture in this population. We also review the most commonly used methods for assessing bone after SCI and discuss the strengths, limitations, and clinical applications of each method. Although dual-energy x-ray absorptiometry assessments of bone mineral density may be used clinically to detect changes in bone after SCI, 3-dimensional methods such as quantitative CT analysis are recommended for research applications and are explained in detail.
... This is a formidable challenge to scientists and clinicians. The extant litera-ture provides ... more ... This is a formidable challenge to scientists and clinicians. The extant litera-ture provides pieces of the solution to the challenge, necessary pieces that 112 Reed-Troy and Grabiner Page 139. ... 14. Pai YC, Patton J. Center of mass velocity-position predictions for balance con-trol. ...
INTRODUCTION Older adults have a high incidence of trip-related falls that contribute to signific... more INTRODUCTION Older adults have a high incidence of trip-related falls that contribute to significant morbidity and mortality. A surrogate treadmill task has been proposed as a potential fall-preventive training tool for older adults. Successful motor response training must elicit stepping strategies as similar as possible to those evoked during actual trips and must demonstrate motor skill acquisition. Differences in the foot trajectories after an actual trip compared to those during the treadmill task have been attributed to the presence of an obstacle [1]. Recent work has shown that the addition of an obstacle to the surrogate treadmill task increases step height and step length to more closely approximate stepping responses elicited during an actual trip [2]. Older adults have demonstrated the ability to modify failed stepping strategies and successfully recover on the subsequent trial during the treadmill task without the obstacle [3], but little is known about the underlying mo...
Study Design:Comparison of diagnostic tests; methodological validation.Objectives:Primary: to inv... more Study Design:Comparison of diagnostic tests; methodological validation.Objectives:Primary: to investigate the precision and reliability of a knee bone mineral density (BMD) assessment protocol that uses an existing dual energy X-ray absorptiometry (DXA) forearm acquisition algorithm in individuals with spinal cord injury (SCI). Secondary: to correlate DXA-based knee areal BMD with volumetric BMD assessments derived from quantitative computed tomography (QCT).Setting:Academic medical center, Chicago, IL, USA.Methods:Participants: a convenience sample of 12 individuals with acute SCI recruited for an observational study of bone loss and 34 individuals with chronic SCI who were screened for a longitudinal study evaluating interventions to increase BMD. Main outcome measures: root-mean-square standard deviation (RMS-SD) and intra/inter-rater reliability of areal BMD acquired at three knee regions using an existing DXA forearm acquisition algorithm; correlation of DXA-based areal BMD wit...
Spinal cord injury (SCI) is characterized by rapid bone loss and an increased risk of fragility f... more Spinal cord injury (SCI) is characterized by rapid bone loss and an increased risk of fragility fracture around regions of the knee. Our purpose was to quantify changes in torsional stiffness K and strength Tult at the proximal tibia due to actual bone loss and simulated bone recovery in acute SCI. Computed tomography scans were acquired on ten subjects with acute SCI at serial time points separated by a mean of 3.9months (range 3.0 to 4.8months). Reductions in bone mineral were quantified and a validated subject-specific finite element modeling procedure was used to predict changes in K and Tult. The modeling procedure was subsequently used to examine the effect of simulated hypothetical treatments, in which bone mineral of the proximal tibiae were restored to baseline levels, while all other parameters were held constant. During the acute period of SCI, subjects lost 8.3±4.9% (p<0.001) of their bone mineral density (BMD). Reductions in K (-9.9±6.5%; p=0.002) were similar in mag...
Bone strains resulting from physical activity are thought to be a primary driver of bone adaptati... more Bone strains resulting from physical activity are thought to be a primary driver of bone adaptation, but cannot be directly noninvasively measured. Because bone adapts nonuniformly, physical activity may make an important independent structural contribution to bone strength that is independent of bone mass and density. Our objective was to create and validate methods for subject-specific finite element (FE) model generation that would accurately predict the surface strains experienced by the distal radius during an in vivo loading task, and to apply these methods to a group of 23 women aged 23-35 to examine variations in strain, bone mass and density, and physical activity. Four cadaveric specimens were experimentally tested and specimen-specific FE models were developed to accurately predict periosteal surface strains (root mean square error=16.3%). In the living subjects, when 300N load was simulated, mean strains were significantly inversely correlated with BMC (r=-0.893), BMD (r...
Distal radius fracture strength has been quantified using in vitro biomechanical testing. These t... more Distal radius fracture strength has been quantified using in vitro biomechanical testing. These tests are frequently performed using one of two methods: (1) load is applied directly to the embedded isolated radius or (2) load is applied through the hand with the wrist joint intact. Fracture loads established using the isolated radius method are consistently 1.5 to 3 times greater than those for the intact wrist method. To address this discrepancy, a validated finite element modeling procedure was used to predict distal radius fracture strength for 22 female forearms under boundary conditions simulating the isolated radius and intact wrist method. Predicted fracture strength was highly correlated between methods (r = 0.94; p < 0.001); however, intact wrist simulations were characterized by significantly reduced cortical shell load carriage and increased stress and strain concentrations. These changes resulted in fracture strength values less than half those predicted for the i...
Individuals with spinal cord injury experience a rapid loss of bone mineral below the neurologica... more Individuals with spinal cord injury experience a rapid loss of bone mineral below the neurological lesion. The clinical consequence of this bone loss is a high rate of fracture around regions of the knee. The ability to predict the mechanical competence of bones at this location may serve as an important clinical tool to assess fracture risk in the spinal cord injury population. The purpose of this study was to develop, and statistically compare, non-invasive methods to predict torsional stiffness (K) and strength (Tult) of the proximal tibia. Twenty-two human tibiae were assigned to either a "training set" or a "test set" (11 specimens each) and mechanically loaded to failure. The training set was used to develop subject-specific finite element (FE) models, and statistical models based on dual energy x-ray absorptiometry (DXA) and quantitative computed tomography (QCT), to predict K and Tult; the test set was used for cross-validation. Mechanical testing produce...
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine
To better understand the mechanisms underlying spiral fracture we would like to carry out biomech... more To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6...
The prevention of fractures remains the primary clinical goal for osteoporosis treatment. Recentl... more The prevention of fractures remains the primary clinical goal for osteoporosis treatment. Recently, improved understanding of the factors influencing the risk of osteoporotic fracture has made the application of personalized medicine possible in this arena. At the epidemiologic level, the FRAX (World Health Organization) tool provides individual fracture risk estimates [1]. However, even greater benefit could stem from patient-specific fracture risk assessment techniques independent of epidemiologic classification, as well as the objective identification of patients meeting requirements for a particular treatment (ie, exercise or pharmacologic intervention). Numerical modeling techniques will no doubt become an integral part of this medical practice. In the study of osteoporosis, numerical models are often adopted to predict the mechanical behavior of bone in vivo. In this context, numerical models have reached a level of accuracy necessary to extract clinically relevant information and help guide clinical decision making . Although there are many types of numerical modeling techniques that can be used to examine the mechanical behavior of bone, we focus on the finite element method, as it is the most widely used and best developed technique for objects of complex geometry.
Bone strains resulting from physical activity are thought to be a primary driver of bone adaptati... more Bone strains resulting from physical activity are thought to be a primary driver of bone adaptation, but cannot be directly noninvasively measured. Because bone adapts nonuniformly, physical activity may make an important independent structural contribution to bone strength that is independent of bone mass and density. Our objective was to create and validate methods for subject-specific finite element (FE) model generation that would accurately predict the surface strains experienced by the distal radius during an in vivo loading task, and to apply these methods to a group of 23 women aged 23-35 to examine variations in strain, bone mass and density, and physical activity. Four cadaveric specimens were experimentally tested and specimen-specific FE models were developed to accurately predict periosteal surface strains (root mean square error=16.3%). In the living subjects, when 300 N load was simulated, mean strains were significantly inversely correlated with BMC (r=-0.893), BMD (...
Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and... more Trip-specific perturbation training reduces trip-related falls after laboratory-induced trips and, prospectively, in the community. Based on an emerging body of evidence, we hypothesize that using task-specific perturbation training as a stand-alone approach or in conjunction with conventional exercise-based approaches will improve the effectiveness of fall prevention interventions significantly.
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 2012
To better understand the mechanisms underlying spiral fracture we would like to carry out biomech... more To better understand the mechanisms underlying spiral fracture we would like to carry out biomechanical tests of long bones loaded in torsion to failure. A device was fabricated to perform torsional tests of long bones using a single-axis linear actuator. The principal operation of the device was to transform the vertical displacement of a material testing machine's linear actuator into rotational movement using a spur gear and rack system. Accuracy and precision of the device were quantified using cast-acrylic rods with known torque-rotation behavior. Cadaveric experimentation was used to replicate a clinically relevant spiral fracture in eleven human proximal tibiae; strain-gage data were recorded for a single specimen. The device had an experimental error of less than 0.2 Nm and was repeatable to within 0.3%. Strain gage data were in line with those expected from pure torsion and the cadaveric tibiae illustrated spiral fractures at ultimate torque and rotation values of 130.6 6 53.2 Nm and 8.3 6 1.5°, respectively. Ultimate torque was highly correlated with DXA assessed bone mineral density (r = 0.87; p \ 0.001). The device presented is applicable to any torsional testing of long bone when only a single-axis linear actuator is available.
This study used quantitative computed tomography to assess changes in bone mineral at the proxima... more This study used quantitative computed tomography to assess changes in bone mineral at the proximal femur after acute spinal cord injury (SCI). Individuals with acute SCI experienced a marked loss of bone mineral from a combination of trabecular and endocortical resorption. Targeted therapeutic interventions are thus warranted in this population. Introduction SCI is associated with a rapid loss of bone mineral and an increased rate of fragility fracture. Some 10 to 20 % of these fractures occur at the proximal femur. The purpose of this study was to quantify changes to bone mineral, geometry, and measures of strength at the proximal femur in acute SCI. Methods Quantitative computed tomography analysis was performed on 13 subjects with acute SCI at serial time points separated by a mean of 3.5 months (range, 2.6-4.8 months). Changes in bone mineral content (BMC) and volumetric bone mineral density (vBMD) were quantified for integral, trabecular, and cortical bone at the femoral neck, trochanteric, and total proximal femur regions. Changes in bone volumes, cross-sectional areas, and surrogate measures of compressive and bending strength were also determined. Results During the acute period of SCI, subjects experienced a 2.7-3.3 %/month reduction in integral BMC (p< 0.001) and a 2.5-3.1 %/month reduction in integral vBMD (p<0.001). Trabecular BMC decreased by 3.1-4.7 %/month (p<0.001) and trabecular vBMD by 2.8-4.4 %/month (p< 0.001). A 3.9-4.0 %/month reduction was observed for cortical BMC (p<0.001), while the reduction in cortical vBMD was noticeably lower (0.8-1.0 %/month; p≤0.01). Changes in bone volume and cross-sectional area suggested that cortical bone loss occurred primarily through endosteal resorption. Declines in bone mineral were associated with a 4.9-5.9 %/month reduction in surrogate measures of strength.
Computed tomography and finite element modeling were used to assess bone mineral and stiffness lo... more Computed tomography and finite element modeling were used to assess bone mineral and stiffness loss at the knee following acute spinal cord injury (SCI). Marked bone mineral loss was observed from a combination of trabecular and endocortical resorption. Reductions in stiffness were 2-fold greater than reductions in integral bone mineral. Introduction SCI is associated with a rapid loss of bone mineral and an increased rate of fragility fracture. The large majority of these fractures occur around regions of the knee. Our purpose was to quantify changes to bone mineral, geometry, strength indices, and stiffness at the distal femur and proximal tibia in acute SCI. Methods Quantitative computed tomography (QCT) and patient-specific finite element analysis were performed on 13 subjects with acute SCI at serial time points separated by a mean of 3.5 months (range 2.6-4.8 months). Changes in bone mineral content (BMC) and volumetric bone mineral density (vBMD) were quantified for integral, trabecular, and cortical bone at epiphyseal, metaphyseal, and diaphyseal regions of the distal femur and proximal tibia. Changes in bone volumes, cross-sectional areas, strength indices and stiffness were also determined.
The potential of task-specific training as a fall-prevention intervention was studied. The primar... more The potential of task-specific training as a fall-prevention intervention was studied. The primary purpose of the study was to determine the extent to which a task-specific training protocol decreased the number of falls by middle-age and older women after a laboratory-induced trip. Secondary purposes were to explore the ability of trunk kinematics during the initial recovery step and the length of the initial recovery step to correctly classify the trip outcome and to quantify the extent to which the training protocol affected these variables. Healthy community-dwelling women (n = 52) were assigned to either a training group or a control group that received no training. Training group women participated in an individually tailored, task-specific training protocol during which forward-directed stepping responses were necessary to avoid a fall after treadmill-delivered postural disturbances. Following the protocol, the ability to avoid a fall after a laboratory-induced trip was assessed. The primary outcome variable was the success (recover) or failure (fall) of the posttrip stepping response. Compared with the control group, there were fewer falls by the trained women after the laboratory-induced trip (P &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001; odds ratio = 0.13). Using logistic regression, falls and recoveries after the trip were sensitively classified by trunk flexion angle at the completion of the initial recovery step and the length of the initial recovery step (sensitivity = 0.67, specificity = 0.98), the former of which improved as a result of the task-specific training protocol. The task-specific training protocol significantly reduced the number of falls after a laboratory-induced trip. Prospective study is required to determine whether this task-specific training reduces falls in the community and, consequently, may complement currently used exercise-based fall prevention intervention methods.
In an effort to improve bone strength and prevent fracture at the distal radius, we have develope... more In an effort to improve bone strength and prevent fracture at the distal radius, we have developed a mechanical loading intervention in which females cyclically load their forearm. To relate the applied stimulus with the bone adaptation response, an accurate characterization of the mechanical environment within the bone must be known. Finite element (FE) models have been an effective tool for both strain and fracture-risk assessment. An ideal model would simulate physiological loading scenarios with simplified boundary conditions, allowing for computationally efficient strain determination for numerous subjects. We are also interested in the ability of the FE method to predict fracture strength as a means to assess the effectiveness of our loading protocol. Here, we compared experimental surface strains and fracture loads with specimen-specific FE models for the purpose of validating our simplified boundary conditions and model generating algorithm.
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