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Does muscle strength explain the gender difference in upper extremity kinematics while arresting a forward fall?
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Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
Methods: Analysis was conducted with a 3D finite element model of the shoulder, including scapula, humerus, cartilage and 6 major muscles: middle, anterior and posterior deltoid, supraspinatus, subscapularis, and infraspinatus. Bones were rigid and muscles were transverse isotropic. Contact forces caused by muscles wrapping on bony surfaces were accounted for. A rotation movement was performed in neutral abduction. Muscles forces were controlled by a complex feedback algorithm, which assigned constant force ratio to abductor muscles, while setting active and passive force to rotator muscles. Both the glenoid and humeral head were eroded to artificially reproduce an arthritic joint. Muscles forces, glenohumeral contact pressure, contact point location and humerus translation were calculated for the normal and arthritic joint. Results: For the eroded joint, muscles and joint forces were about two times higher, at any rotation angle. For the normal joint, glenohumeral contact point and humeral head remained centred. Conversely, for the eroded joint, eccentric contact point and large AP humerus translation were clearly related to the rocking-horse phenomenon. Conclusions: This study shows that the flattening of the glenohumeral joint increase muscles forces, which partly explains the reduced range of motion observed clinically. This study also suggest that shoulder arthroplasty should reconstruct the joint anatomy as normal as possible, with a particular attention to the radius of curvature.
6082 Tu, 12:15-12:30 (P18) MRI-based estimation of muscle volume and length following tendon transfer surgery
K.R.S. Holzbaur, G.E. Gold, M.E. Johanson, W.M. Murray. Bone and Joint Center, VA Pale Alto HCS, Pale Alto, CA, USA Tendon transfer surgeries that restore voluntary hand function after cervical spinal cord injury are not always as effective as expected. Clinically, it is accepted that most donor muscles lose at least one grade of muscle strength following tendon transfer. The reasons for the reduction in strength have not been established. We used magnetic resonance imaging (MRI) to determine if architectural parameters, which are measures of a muscle's force-generating capability, differ following surgical transfer of the brachioradialis to the flexor pollicis Iongus compared to nonimpaired controls. Axial MRI images were acquired from shoulder to wrist using a 3D spoiled gradient echo sequence in 3mm sections. We identified the boundaries of the brachioradialis on each image and used these contours to create three-dimensional surfaces, from which we calculated muscle volume and length. The volume of the transferred brachioradialis (49.8 cm 3) of an adult male with C6 level tetraplegia fell outside the 95% confidence interval around the mean brachioradialis volume (93.7±25.1 cm 3) measured in 5 nonimpaired male subjects of varying size. The volume of the transferred brachioradialis was 82% of brachioradialis volume in an age- and height-matched nonimpaired subject (60.7cm3). Muscle lengths were comparable for the two matched subjects (22.2 and 22.3cm, respectively); muscle lengths ranged from 21.2 to 28.6cm among the nonimpaired males. This study supports the hypothesis that reductions in muscle strength observed following tendon transfer are associated with muscle atrophy. Understanding how factors such as muscle atrophy contribute to variable surgical outcomes will lead to better treatment decisions.
3.1.5. Upper Extremity Injury 4297 Tu, 14:00-14:15 (P21) Achievable changes in bone mineral density influence predicted distal radius fracture load K.L. Troy, M.D. Grabiner. University ef Illineis at Chicago, Chicago, IL USA Fall-related upper extremity injuries are common in older adults due to their high incidence of falls and decreased bone quality. Because osteoporotic fractures are common in women, interventions to increase bone mineral density (BMD) have been attempted. Interventions are considered successful if BMD is increased by 2-4% [1]. Here, we addressed the extent to which changes in BMD influence predicted distal radius fracture load during impact. To do this we implemented a three-dimensional FE model that includes contact between the radius, scaphoid, lunate, and ligamentous constraints [2]. An axial load of 3 kN was applied across the scaphoid and lunate. The proximal radius was fixed in space. BMD changes of -4%, -2%, +2%, and +4%, were simulated in cortical, cancellous, and concurrently in both types of bone. In all simulations, failure occurred first in the cortical bone proximal to the radial styloid process. Secondary failure occurred in the cancellous bone below the subchondral surface near the palmar aspect of the radius. Fracture loads were estimated as 1.7-2.6 kN. Concurrent changes in cortical and cancellous bone had the most profound effect on fracture strength. A 4% increase in cancellous BMD increased predicted fracture strength by 3.4%, compared to 6.8% if both types of bone are changed. However, increasing cortical bone BMD decreased fracture strength by 1%. The relationship between changes
Oral Presentations in BMD and fracture load was nonlinear. Because failures occurred near the medial distal radius, localized increases in BMD may contribute to fracture prevention. Because upper extremity forces of about 2.5 kN are associated with falls from standing-height [3], modest changes in BMD, especially in targeted locations, may meaningfully affect the incidence of distal radius fractures. References
[1] Liberman UA, et al. N Engl J Med 1995; 333: 1437. [2] Troy KL, Grabiner MD. ORS, 2006. [3] Chiu J, Robinovitch SN. J Biomech 1998; 31: 1169. 7289 Tu, 14:15-14:30 (P21) Rotational stiffness and damping properties of the elbow extensor muscles under impact in young men and women A. Mathias, J.A. Ashton-Miller. Biemechanics Research Laboratory, University of Michigan, Ann Arbor, USA Whether or not the elbow buckles in a fall to the ground is determined by the wrist impact force, the elbow angle at impact, and the rotational stiffness and damping of the elbow extensor muscles. The goal of this study was to make measurements of the rotational stiffness and damping of the elbow extensor muscles under an impact load causing forced elbow flexion. Eight healthy young adults (3 males, 5 females) were tested. Responses were studied at three co-contraction levels (25, 50 & 75% MVC) and two initial flexion angles (10 & 250 flexion). The forearm kinematic (150 Hz) and impact force data (2kHz) were digitally low-pass filtered. Integrated surface electromyography data were collected at 2 kHz from the biceps brachii and the lateral and long heads of triceps brachii. A second-order rotational spring-damper model was used to approximate the properties of the elbow joint: T =/~ + b6 + kS, where T is applied torque, 8 is the angular displacement of the limb, / is the calculated moment of inertia of the limb, b is the damping coefficient, and k is the stiffness coefficient. An optimization program was used to find k and b, with trials being considered valid when the ratio of root-mean-square model error to maximum torque was less than 10%. The values of k and b were then normalized by subject body weight and height. Mean (SD) male and female normalized k and b values at 75% MVC and 100 flexion were 0.730 (0.167) and 0.349 (0.165) Nmrad -1 kg-1 m -1, and 0.041 (0.011) and 0.032 (0.011 ) Nms rad-1 kg -1 m-1 , respectively. Both elbow stiffness and damping significantly increased with muscle activation. Women had significantly lower normalized stiffness and damping parameters than men (56-83% and 47~0%, respectively), reflecting reports of similar differences in the lower extremities. This gender difference likely affects how the arms are used to arrest a fall. Acknowledgments: NIH P30 AG08808 and SCOR P50 AR 049480 grants 7291 Tu, 14:30-14:45 (P21) Does muscle strength explain the gender difference in upper extremity kinematics while arresting a forward fall? J.-H. Lo, J.A. Ashton-Miller. Biomechanics Research Laboratory, University of Michigan, Ann Arbor, Michigan, USA Case et al. (ISB, 2005) found that healthy young women permit four times less post-impact elbow deflection (termed A~Elbow) while arresting a forward fall initiated from a shoulder-height of 1 m than did healthy young men. We used a computer simulation to test the hypotheses that the smaller A~Elbo w in young and older women is due to their lower arm extensor strength normalized per unit body weight. A 7-1ink, sagittally-symmetric, direct dynamics model was developed to simulate forward falls. During the descent and impact phases, a proportionalderivative joint controller and a pair of agonist and antagonist joint torque actuators with assigned neuromuscular latencies, torque-angle, and torquevelocity properties were incorporated to drive each joint to its target angles. The model was assigned four different arm muscle strength levels representing age and gender-specific normalized shoulder and elbow strengths. For each of the four gender/age models, forward falls from the Case study were simulated using arm joint target angles which maximized A~Elbow without incurring head impact using an optimization method. The resulting A~Elbo w of the four gender/age models were then compared to examine muscle strength effects. The results show that, for same impact velocity and elbow angle at impact, the maximal A~Elbo w of young male (YM), old male (OM), young female (YF), and old female (OF) models were 710, 700, 670, and 350, respectively. The resulting negative work done by the elbow and shoulder joints (YM: -78 J; OM: -72 J; YF: -68 J; and OF: -40 J) and peak wrist impact force (YM: 1.013 kN; OM: 1.099 kN; YF: 1.187 kN; and OF: 1.343 kN) also decreased with decreasing elbow strength. We conclude that smaller A~Elbo w must be used in the presence of lower arm extensor strengths in order to prevent the elbows from buckling under impact and the head from striking the ground. Acknowledgements: NIH P30 AG08808
Journal of Biomechanics 2006, Vol. 39 (Suppl 1)
Methods: Analysis was conducted with a 3D finite element model of the shoulder, including scapula, humerus, cartilage and 6 major muscles: middle, anterior and posterior deltoid, supraspinatus, subscapularis, and infraspinatus. Bones were rigid and muscles were transverse isotropic. Contact forces caused by muscles wrapping on bony surfaces were accounted for. A rotation movement was performed in neutral abduction. Muscles forces were controlled by a complex feedback algorithm, which assigned constant force ratio to abductor muscles, while setting active and passive force to rotator muscles. Both the glenoid and humeral head were eroded to artificially reproduce an arthritic joint. Muscles forces, glenohumeral contact pressure, contact point location and humerus translation were calculated for the normal and arthritic joint. Results: For the eroded joint, muscles and joint forces were about two times higher, at any rotation angle. For the normal joint, glenohumeral contact point and humeral head remained centred. Conversely, for the eroded joint, eccentric contact point and large AP humerus translation were clearly related to the rocking-horse phenomenon. Conclusions: This study shows that the flattening of the glenohumeral joint increase muscles forces, which partly explains the reduced range of motion observed clinically. This study also suggest that shoulder arthroplasty should reconstruct the joint anatomy as normal as possible, with a particular attention to the radius of curvature.
6082 Tu, 12:15-12:30 (P18) MRI-based estimation of muscle volume and length following tendon transfer surgery
K.R.S. Holzbaur, G.E. Gold, M.E. Johanson, W.M. Murray. Bone and Joint Center, VA Pale Alto HCS, Pale Alto, CA, USA Tendon transfer surgeries that restore voluntary hand function after cervical spinal cord injury are not always as effective as expected. Clinically, it is accepted that most donor muscles lose at least one grade of muscle strength following tendon transfer. The reasons for the reduction in strength have not been established. We used magnetic resonance imaging (MRI) to determine if architectural parameters, which are measures of a muscle's force-generating capability, differ following surgical transfer of the brachioradialis to the flexor pollicis Iongus compared to nonimpaired controls. Axial MRI images were acquired from shoulder to wrist using a 3D spoiled gradient echo sequence in 3mm sections. We identified the boundaries of the brachioradialis on each image and used these contours to create three-dimensional surfaces, from which we calculated muscle volume and length. The volume of the transferred brachioradialis (49.8 cm 3) of an adult male with C6 level tetraplegia fell outside the 95% confidence interval around the mean brachioradialis volume (93.7±25.1 cm 3) measured in 5 nonimpaired male subjects of varying size. The volume of the transferred brachioradialis was 82% of brachioradialis volume in an age- and height-matched nonimpaired subject (60.7cm3). Muscle lengths were comparable for the two matched subjects (22.2 and 22.3cm, respectively); muscle lengths ranged from 21.2 to 28.6cm among the nonimpaired males. This study supports the hypothesis that reductions in muscle strength observed following tendon transfer are associated with muscle atrophy. Understanding how factors such as muscle atrophy contribute to variable surgical outcomes will lead to better treatment decisions.
3.1.5. Upper Extremity Injury 4297 Tu, 14:00-14:15 (P21) Achievable changes in bone mineral density influence predicted distal radius fracture load K.L. Troy, M.D. Grabiner. University ef Illineis at Chicago, Chicago, IL USA Fall-related upper extremity injuries are common in older adults due to their high incidence of falls and decreased bone quality. Because osteoporotic fractures are common in women, interventions to increase bone mineral density (BMD) have been attempted. Interventions are considered successful if BMD is increased by 2-4% [1]. Here, we addressed the extent to which changes in BMD influence predicted distal radius fracture load during impact. To do this we implemented a three-dimensional FE model that includes contact between the radius, scaphoid, lunate, and ligamentous constraints [2]. An axial load of 3 kN was applied across the scaphoid and lunate. The proximal radius was fixed in space. BMD changes of -4%, -2%, +2%, and +4%, were simulated in cortical, cancellous, and concurrently in both types of bone. In all simulations, failure occurred first in the cortical bone proximal to the radial styloid process. Secondary failure occurred in the cancellous bone below the subchondral surface near the palmar aspect of the radius. Fracture loads were estimated as 1.7-2.6 kN. Concurrent changes in cortical and cancellous bone had the most profound effect on fracture strength. A 4% increase in cancellous BMD increased predicted fracture strength by 3.4%, compared to 6.8% if both types of bone are changed. However, increasing cortical bone BMD decreased fracture strength by 1%. The relationship between changes
Oral Presentations in BMD and fracture load was nonlinear. Because failures occurred near the medial distal radius, localized increases in BMD may contribute to fracture prevention. Because upper extremity forces of about 2.5 kN are associated with falls from standing-height [3], modest changes in BMD, especially in targeted locations, may meaningfully affect the incidence of distal radius fractures. References
[1] Liberman UA, et al. N Engl J Med 1995; 333: 1437. [2] Troy KL, Grabiner MD. ORS, 2006. [3] Chiu J, Robinovitch SN. J Biomech 1998; 31: 1169. 7289 Tu, 14:15-14:30 (P21) Rotational stiffness and damping properties of the elbow extensor muscles under impact in young men and women A. Mathias, J.A. Ashton-Miller. Biemechanics Research Laboratory, University of Michigan, Ann Arbor, USA Whether or not the elbow buckles in a fall to the ground is determined by the wrist impact force, the elbow angle at impact, and the rotational stiffness and damping of the elbow extensor muscles. The goal of this study was to make measurements of the rotational stiffness and damping of the elbow extensor muscles under an impact load causing forced elbow flexion. Eight healthy young adults (3 males, 5 females) were tested. Responses were studied at three co-contraction levels (25, 50 & 75% MVC) and two initial flexion angles (10 & 250 flexion). The forearm kinematic (150 Hz) and impact force data (2kHz) were digitally low-pass filtered. Integrated surface electromyography data were collected at 2 kHz from the biceps brachii and the lateral and long heads of triceps brachii. A second-order rotational spring-damper model was used to approximate the properties of the elbow joint: T =/~ + b6 + kS, where T is applied torque, 8 is the angular displacement of the limb, / is the calculated moment of inertia of the limb, b is the damping coefficient, and k is the stiffness coefficient. An optimization program was used to find k and b, with trials being considered valid when the ratio of root-mean-square model error to maximum torque was less than 10%. The values of k and b were then normalized by subject body weight and height. Mean (SD) male and female normalized k and b values at 75% MVC and 100 flexion were 0.730 (0.167) and 0.349 (0.165) Nmrad -1 kg-1 m -1, and 0.041 (0.011) and 0.032 (0.011 ) Nms rad-1 kg -1 m-1 , respectively. Both elbow stiffness and damping significantly increased with muscle activation. Women had significantly lower normalized stiffness and damping parameters than men (56-83% and 47~0%, respectively), reflecting reports of similar differences in the lower extremities. This gender difference likely affects how the arms are used to arrest a fall. Acknowledgments: NIH P30 AG08808 and SCOR P50 AR 049480 grants 7291 Tu, 14:30-14:45 (P21) Does muscle strength explain the gender difference in upper extremity kinematics while arresting a forward fall? J.-H. Lo, J.A. Ashton-Miller. Biomechanics Research Laboratory, University of Michigan, Ann Arbor, Michigan, USA Case et al. (ISB, 2005) found that healthy young women permit four times less post-impact elbow deflection (termed A~Elbow) while arresting a forward fall initiated from a shoulder-height of 1 m than did healthy young men. We used a computer simulation to test the hypotheses that the smaller A~Elbo w in young and older women is due to their lower arm extensor strength normalized per unit body weight. A 7-1ink, sagittally-symmetric, direct dynamics model was developed to simulate forward falls. During the descent and impact phases, a proportionalderivative joint controller and a pair of agonist and antagonist joint torque actuators with assigned neuromuscular latencies, torque-angle, and torquevelocity properties were incorporated to drive each joint to its target angles. The model was assigned four different arm muscle strength levels representing age and gender-specific normalized shoulder and elbow strengths. For each of the four gender/age models, forward falls from the Case study were simulated using arm joint target angles which maximized A~Elbow without incurring head impact using an optimization method. The resulting A~Elbo w of the four gender/age models were then compared to examine muscle strength effects. The results show that, for same impact velocity and elbow angle at impact, the maximal A~Elbo w of young male (YM), old male (OM), young female (YF), and old female (OF) models were 710, 700, 670, and 350, respectively. The resulting negative work done by the elbow and shoulder joints (YM: -78 J; OM: -72 J; YF: -68 J; and OF: -40 J) and peak wrist impact force (YM: 1.013 kN; OM: 1.099 kN; YF: 1.187 kN; and OF: 1.343 kN) also decreased with decreasing elbow strength. We conclude that smaller A~Elbo w must be used in the presence of lower arm extensor strengths in order to prevent the elbows from buckling under impact and the head from striking the ground. Acknowledgements: NIH P30 AG08808