A Comparison of Approaches for Segmenting the Reaching and Targeting Motion Primitives in Functional Upper Extremity Reaching Tasks.

There is growing interest in the kinematic analysis of human functional upper extremity movement (FUEM) for applications such as health monitoring and rehabilitation. Deconstructing functional movements into activities, actions, and primitives is a necessary procedure for many of these kinematic analyses. Advances in machine learning have led to progress in human activity and action recognition. However, their utility for analyzing the FUEM primitives of reaching and targeting during reach-to-grasp and reach-to-point tasks remains limited. Domain experts use a variety of methods for segmenting the reaching and targeting motion primitives, such as kinematic thresholds, with no consensus on what methods are best to use. Additionally, current studies are small enough that segmentation results can be manually inspected for correctness. As interest in FUEM kinematic analysis expands, such as in the clinic, the amount of data needing segmentation will likely exceed the capacity of existing segmentation workflows used in research laboratories, requiring new methods and workflows for making segmentation less cumbersome. This paper investigates five reaching and targeting motion primitive segmentation methods in two different domains (haptics simulation and real world) and how to evaluate these methods. This work finds that most of the segmentation methods evaluated perform reasonably well given current limitations in our ability to evaluate segmentation results. Furthermore, we propose a method to automatically identify potentially incorrect segmentation results for further review by the human evaluator. Clinical impact: This work supports efforts to automate aspects of processing upper extremity kinematic data used to evaluate reaching and grasping, which will be necessary for more widespread usage in clinical settings.

Modeling a rotator cuff tear: Individualized shoulder muscle forces influence glenohumeral joint contact force predictions.

BACKGROUND: Rotator cuff tears in older individuals may result in decreased muscle forces and changes to force distribution across the glenohumeral joint. Reduced muscle forces may impact functional task performance, altering glenohumeral joint contact forces, potentially contributing to instability or joint damage risk. Our objective was to evaluate the influence of rotator cuff muscle force distribution on glenohumeral joint contact force during functional pull and axilla wash tasks using individualized computational models. METHODS: Fourteen older individuals (age 63.4 yrs. (SD 1.8)) were studied; 7 with rotator cuff tear, 7 matched controls. Muscle volume measurements were used to scale a nominal upper limb model's muscle forces to develop individualized models and perform dynamic simulations of movement tracking participant-derived kinematics. Peak resultant glenohumeral joint contact force, and direction and magnitude of force components were compared between groups using ANCOVA. FINDINGS: Results show individualized muscle force distributions for rotator cuff tear participants had reduced peak resultant joint contact force for pull and axilla wash (P ≤ 0.0456), with smaller compressive components of peak resultant force for pull (P = 0.0248). Peak forces for pull were within the glenoid. For axilla wash, peak joint contact was directed near/outside the glenoid rim for three participants; predictions required individualized muscle forces since nominal muscle forces did not affect joint force location. INTERPRETATION: Older adults with rotator cuff tear had smaller peak resultant and compressive forces, possibly indicating increased instability or secondary joint damage risk. Outcomes suggest predicted joint contact force following rotator cuff tear is sensitive to including individualized muscle forces.

Shoulder Strength Requirements for Upper Limb Functional Tasks: Do Age and Rotator Cuff Tear Status Matter?

Understanding upper limb strength requirements for daily tasks is imperative for early detection of strength loss that may progress to disability due to age or rotator cuff tear. We quantified shoulder strength requirements for 5 upper limb tasks performed by 3 groups: uninjured young adults and older adults, and older adults with a degenerative supraspinatus tear prior to repair. Musculoskeletal models were developed for each group representing age, sex, and tear-related strength losses. Percentage of available strength used was quantified for the subset of tasks requiring the largest amount of shoulder strength. Significant differences in strength requirements existed across tasks: upward reach 105° required the largest average strength; axilla wash required the largest peak strength. However, there were limited differences across participant groups. Older adults with and without a tear used a larger percentage of their shoulder elevation (p < .001, p < .001) and external rotation (p < .001, p = .017) strength than the young adults, respectively. Presence of a tear significantly increased percentage of internal rotation strength compared to young (p < .001) and uninjured older adults (p = .008). Marked differences in strength demand across tasks indicate the need for evaluating a diversity of functional tasks to effectively detect early strength loss, which may lead to disability.

Analysis of effects of loading and postural demands on upper limb reaching in older adults using statistical parametric mapping.

Continuous time-series data are frequently distilled into single values and analyzed using discrete statistical methods, underutilizing large datasets. Statistical parametric mapping (SPM) allows hypotheses over the entire spectrum, but consistency with discrete analyses of kinematic data is unclear. We applied SPM to evaluate effect of load and postural demands during reaching on thoracohumeral kinematics in older and young adults, and examined consistency between one-dimensional SPM and discrete analyses of the same dataset. We hypothesized that older adults would choose postures that bring the humerus anterior to the frontal plane (towards flexion) even for low demand tasks, and that SPM would reveal differences persisting over larger temporal portions of the reach. Ten healthy older (72.4±3.1yrs) and 16 young (22.9±2.5yrs) adults reached upward and forward with high and low loads. SPM and discrete t-tests were used to analyze group effects for elevation plane, elevation, and axial rotation joint angles and velocity. Older adults used more positive (anterior) elevation plane and less elevated postures to initiate and terminate reaching (p<0.008), with long duration differences during termination. When reaching upward, differences in elevation persisted over longer temporal periods at midreach for high loads (32-58% of reach) compared to low load (41-45%). SPM and discrete analyses were consistent, but SPM permitted clear identification of temporal periods over which differences persisted, while discrete methods allowed analysis of extracted values, like ROM. This work highlights the utility of SPM to analyze kinematics time series data, and emphasizes importance of task selection when assessing age-related changes in movement.

Relationship between maximum isometric joint moment and functional task performance in patients with brachial plexus injury: A pilot study.

We evaluated whether subjects with brachial plexus injury (BPI) adapted their movements to reduce the mechanical demand on their impaired upper extremity. In 6 subjects with unilateral BPI with C5 and C6 involvement, we measured bilateral maximum isometric shoulder and elbow strength, and computed joint kinematics and net muscle-generated joint moments during 7 unimanual functional tasks. Compared to the unimpaired extremity, maximum strength in shoulder abduction, extension, and external rotation was 60% (p=0.02), 49% (p=0.02), and 75% (p=0.02) lower, respectively, on the impaired side. Significant kinematic and kinetic differences were observed only when reaching to the back of the head. However, because of substantially reduced strength in their impaired upper extremities, subjects used a significantly higher percentage of their maximum strength during several tasks and along several directions of movement. The peak percentage of maximal strength subjects used across tasks was 32% (p=0.03) and 29% (p=0.03) more on their impaired side in shoulder extension and external rotation, respectively. Subjects had less reserve strength available for performing upper extremity tasks and, therefore, may be less adaptive to strength declines due to injury progression and normal aging. Quantitatively measuring maximal strength may help clinicians ensure that patients maintain sufficient upper extremity strength to preserve long-term functional ability.

The effects of a rotator cuff tear on activities of daily living in older adults: A kinematic analysis.

Rotator cuff tears (RCT) in older individuals may compound age-associated physiological changes and impact their ability to perform daily functional tasks. Our objective was to quantify thoracohumeral kinematics for functional tasks in 18 older adults (mean age=63.3±2.2), and compare findings from nine with a RCT to nine matched controls. Motion capture was used to record kinematics for 7 tasks (axilla wash, forward reach, functional pull, hair comb, perineal care, upward reach to 90°, upward reach to 105°) spanning the upper limb workspace. Maximum and minimum joint angles and motion excursion for the three thoracohumeral degrees of freedom (elevation plane, elevation, axial rotation) were identified for each task and compared between groups. The RCT group used greater minimum elevation angles for axilla wash and functional pull (p≤0.0124) and a smaller motion excursion for functional pull (p=0.0032) compared to the control group. The RCT group also used a more internally rotated maximum axial rotation angle than controls for functional reach, functional pull, hair comb, and upward reach to 105° (p≤0.0494). The most differences between groups were observed for axial rotation, with the RCT group using greater internal rotation to complete functional tasks, and significant differences between groups were identified for all three thoracohumeral degrees of freedom for functional pull. We conclude that older adults with RCT used more internal rotation to perform functional tasks than controls. The kinematic differences identified in this study may have consequences for progression of shoulder damage and further functional impairment in older adults with RCT.

Assessments of Fatty Infiltration and Muscle Atrophy From a Single Magnetic Resonance Image Slice Are Not Predictive of 3-Dimensional Measurements.

PURPOSE: To (1) determine whether standard clinical muscle fatty infiltration and atrophy assessment techniques using a single image slice for patients with a rotator cuff tear (RCT) are correlated with 3-dimensional measures in older individuals (60+ years) and (2) to determine whether age-associated changes to muscle morphology and strength are compounded by an RCT. METHODS: Twenty older individuals were studied: 10 with an RCT of the supraspinatus (5 men and 5 women) and 10 matched controls. Clinical imaging assessments (Goutallier and Fuchs scores and cross-sectional area ratio) were performed for participants with RCTs. Three-dimensional measurements of rotator cuff muscle and fat tissues were obtained for all participants using magnetic resonance imaging (MRI). Isometric joint moment was measured at the shoulder. RESULTS: There were no significant associations between single-image assessments and 3-dimensional measurements of fatty infiltration for the supraspinatus and infraspinatus muscles. Compared with controls, participants with RCTs had significantly increased percentages of fatty infiltration for each rotator cuff muscle (all P ≤ .023); reduced whole muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles (all P ≤ .038); and reduced fat-free muscle volume for the supraspinatus, infraspinatus, and subscapularis muscles (all P ≤ .027). Only the teres minor (P = .017) fatty infiltration volume was significantly greater for participants with RCTs. Adduction, flexion, and external rotation strength (all P ≤ .021) were significantly reduced for participants with RCTs, and muscle volume was a significant predictor of strength for all comparisons. CONCLUSIONS: Clinical scores using a single image slice do not represent 3-dimensional muscle measurements. Efficient methods are needed to more effectively capture 3-dimensional information for clinical applications. Participants with RCTs had increased fatty infiltration percentages that were likely driven by muscle atrophy rather than increased fat volume. The significant association of muscle volume with strength production suggests that treatments to preserve muscle volume should be pursued for older patients with RCTs. LEVEL OF EVIDENCE: Level II, diagnostic study, with development of diagnostic criteria on the basis of consecutive patients with universally applied reference gold standard.

Can self-report instruments of shoulder function capture functional differences in older adults with and without a rotator cuff tear?

Rotator cuff tears (RCT) are prevalent in older individuals and may compound age-associated functional declines. Our purpose was to determine whether self-report measures of perceived functional ability are valid for older patients with RCT. Twenty five subjects participated (12M/13F; age=63.9±3.0years); 13 with RCT and 12 controls (CON). Participants completed self-report measures of shoulder function (SST, ASES, WORC) and health-related quality of life (SF-36). Isometric joint moment and range of motion (ROM) were measured at the shoulder. Relationships among functional self-reports, and between these measures and joint moment and ROM were assessed; group differences for total and subcategory scores were evaluated. There were significant correlations among self-reports (rs=0.62-0.71, p⩽0.02). For RCT subjects, ASES was associated with all joint moments except adduction (p⩽0.02); SST, ASES, and WORC were associated with abduction and external rotation ROM (p⩽0.04). For RCT subjects, SST and WORC were associated with SF-36 physical function subcategory scores (p⩽0.05). The RCT group scored worse than CON on all functional self-reports (p<0.01) and WORC and ASES subcategories (p<0.01). In conclusion, SST, ASES, and WORC demonstrate utility and discriminant validity for older individuals by distinguishing those with RCT, but this work suggests prioritizing ASES given its stronger association with functional group strength.

Quantitative Analysis of Three-Dimensional Distribution and Clustering of Intramuscular Fat in Muscles of the Rotator Cuff.

The purpose of this study was to (1) develop and present a technique to quantitatively assess three-dimensional distribution and clustering of intramuscular fat and (2) use the technique to compare spatial characteristics of intramuscular fat in rotator cuff muscles of older adults with and without a supraspinatus tear. Moran's Index (I), an existing quantitative measure of clustering, was extended for use with MRI to allow comparisons across individuals with different size muscles. Sixteen older adults (>60 years) with (N = 6) and without (N = 10) a degenerative supraspinatus tear participated. Following 3D Dixon MRIs of the shoulder, which separates fat from water, rotator cuff muscles were segmented and sectioned and fat% and Moran's I were calculated to assess distribution and clustering, respectively. Moran's I ranged was 0.40-0.92 and 0.39-0.76 for the tear and control subjects, respectively. Compared to uninjured controls, tear subjects demonstrated increased fat distribution (p = 0.036) and clustering (p = 0.020) distally in the supraspinatus. Tear subjects had more pronounced distribution (p < 0.001) and clustering distally (p < 0.001) than proximally. Other rotator cuff muscles exhibited different patterns of fat clustering and distribution. This technique, which we applied to quantify spatial characteristics of intramuscular fat, can be applied to assess clustering of fat in other pathologies and tissues.

Age-related structural changes in upper extremity muscle tissue in a nonhuman primate model.

BACKGROUND: Longitudinal studies of upper extremity aging in humans include logistical concerns that animal models can overcome. The vervet is a promising species with which to study aging-related processes. However, age-related changes in upper extremity muscle structure have not been quantified in this species. This study measured age-related changes to muscle structure, examined relationships between muscle structure and measures of physical performance, and evaluated the presence of rotator cuff tears. METHODS: Muscle structure (volume, optimal fiber length, and physiologic cross-sectional area (PCSA)) of 10 upper extremity muscles was quantified from the right upper limb of 5 middle-aged and 6 older adult female vervets. RESULTS: Total measured PCSA was smaller (P = .001) in the older adult vervets than in the middle-aged vervets. Muscle volume reduction predominate the age-related reductions in PCSA. Total measured PCSA was not correlated to any measures of physical performance. No rotator cuff tears were observed. Supraspinatus volume was relatively larger and deltoid volume relatively smaller in the vervet compared with a human. CONCLUSIONS: The vervet is an appropriate translational model for age-related upper extremity muscle volume loss. Functional measures were not correlated to PCSA, suggesting the vervets may have enough strength for normal function despite loss of muscle tissue. Reduced relative demand on the supraspinatus may be responsible for the lack of naturally occurring rotator cuff tears.

Functional Loss With Displacement of Medial Epicondyle Humerus Fractures: A Computer Simulation Study.

BACKGROUND: Assessment and management of the medial humeral epicondyle fracture remains controversial, with conflicting reports of displacement direction and consequent functional deficits unclear. The purpose of this study was to define biomechanically likely directions of medial epicondyle fracture displacement and to determine possible changes in muscle function related to that displacement. METHODS: A 3-dimensional computer model of the upper extremity was used to simulate the consequences of medial epicondyle fracture displacements from 1 to 20 mm in the anterior, medial, and inferior directions relative to the humerus with the elbow at 90-degree flexion and neutral forearm rotation (a replication of accepted positions for clinical strength testing). Muscle length and force were calculated following displacement. Maximum isometric wrist flexion moments were calculated over the full range of wrist motion based on known force-generating properties of the muscles. RESULTS: Anterior displacement resulted in shortened muscles and reduced wrist flexion moment, with a decrease in strength averaging 2% for every 1 mm of anterior fragment displacement at neutral wrist position (maximum decrease of 39% with 20 mm displacement). In contrast, displacement in the medial and inferior directions resulted in stretched muscles and increased wrist flexion moments and therefore are not biomechanically likely. CONCLUSIONS: Computer simulation of a medial epicondyle fracture suggests that anterior displacement could result in a dramatic loss of initial muscle strength and function. Medial displacement is unlikely to occur in vivo due to consequential muscle lengthening, suggesting that alternatives to the historical use of AP radiographs to assess displacement of this fracture are needed. CLINICAL RELEVANCE: Our work provides a biomechanical explanation for anterior displacement of medial epicondyle fractures observed radiographically and motivates alternative methods of fracture assessment. A functional basis for determining acceptable displacement of medial epicondyle fractures is suggested; however, all individual clinical factors should be considered.

Non-anatomical capsular closure of a standard parapatellar knee arthrotomy leads to patellar maltracking and decreased range of motion: a cadaver study.

PURPOSE: A parapatellar approach disrupts the medial soft tissue stabilizers of the patella. We hypothesized that soft tissue realignment during arthrotomy closure of native cadaveric knees influences patellar kinematics leading to decreased range of motion. METHODS: Parapatellar arthrotomy was performed in seven native human cadaveric knees that did not contain arthroplasty components. Capsular closure was performed with figure-of-eight sutures in five different positions for each specimen. The capsule was closed anatomically, and then shifted 1.5 or 3 cm distal, or 1.5 or 3 cm proximal relative to surgical markings of the patellar poles. In each closure position, real-time patellar kinematics and range of motion were recorded using a navigation system with patellar tracking function. RESULTS: Maximum knee flexion was significantly reduced with closure shifted 3 cm proximal (133° ± 8.2°, p < 0.001) or distal (139° ± 6.4°, p < 0.05) compared to anatomical closure (147° ± 4.1°). All closure positions significantly influenced patellar rotation at 45°, 90°, and 120° of flexion (p < 0.001). Closure 1.5 or 3 cm distal increased lateral patellar shift relative to the mechanical axis (p < 0.01). Patellar tilt was significantly decreased at 90° and 120° by closure 3 cm distal (p < 0.01) and at 120° when closed 1.5 cm distal (p < 0.05). CONCLUSIONS: Imprecise arthrotomy closure significantly impacted patellar kinematics and passive range of motion. Therefore, every effort should be made to provide anatomical closure of the extensor mechanism to preserve native patellar movement kinematics. LEVEL OF EVIDENCE: V.

Effect of strain rate on the material properties of human liver parenchyma in unconfined compression.

The liver is one of the most frequently injured organs in abdominal trauma. Although motor vehicle collisions are the most common cause of liver injuries, current anthropomorphic test devices are not equipped to predict the risk of sustaining abdominal organ injuries. Consequently, researchers rely on finite element models to assess the potential risk of injury to abdominal organs such as the liver. These models must be validated based on appropriate biomechanical data in order to accurately assess injury risk. This study presents a total of 36 uniaxial unconfined compression tests performed on fresh human liver parenchyma within 48 h of death. Each specimen was tested once to failure at one of four loading rates (0.012, 0.106, 1.036, and 10.708 s-1) in order to investigate the effects of loading rate on the compressive failure properties of human liver parenchyma. The results of this study showed that the response of human liver parenchyma is both nonlinear and rate dependent. Specifically, failure stress significantly increased with increased loading rate, while failure strain significantly decreased with increased loading rate. The failure stress and failure strain for all liver parenchyma specimens ranged from -38.9 kPa to -145.9 kPa and from -0.48 strain to -1.15 strain, respectively. Overall, this study provides novel biomechanical data that can be used in the development of rate dependent material models and the identification of tissue-level tolerance values, which are critical to the validation of finite element models used to assess injury risk.

Biomechanical response of human spleen in tensile loading.

Blunt splenic injuries are most frequently caused as a result of motor vehicle collisions and are associated with high mortality rates. In order to accurately assess the risk of automotive related spleen injuries using tools such as finite element models, tissue level tolerance values and suitable material models must be developed and validated based on appropriate biomechanical data. This study presents a total of 41 tension tests performed on spleen parenchyma coupons and 29 tension tests performed on spleen capsule/parenchyma coupons. Standard dog-bone coupons were obtained from fresh human spleen and tested within 48 h of death. Each coupon was tested once to failure at one of the four loading rates to investigate the effects of rate dependence. Load and acceleration data were obtained at each of the specimen grips. High-speed video and optical markers placed on the specimens were used to measure local displacement. Failure stress and strain were calculated at the location of failure in the gage length of the coupon. The results of the study showed that both the spleen parenchyma and the capsule are rate dependent, with higher loading rates yielding higher failure stresses and lower failure strains. The results also show that the failure stress of the splenic capsule is significantly greater than that of the underlying parenchyma. Overall, this study provides novel biomechanical data that demonstrate the rate dependent tissue level tolerance values of human spleen tissue in tensile loading, which can aid in the improvement of finite element models used to assess injury risk in blunt trauma.

The tolerance of the maxilla to blunt impact.

This study reports the results of 38 infraorbital maxilla impacts performed on male cadavers. Impacts were performed using an unpadded, cylindrical impactor (3.2 kg) at velocities between 1 and 5 m/s. The peak force and acoustic emission data were used to develop a statistical relationship of fracture risk as a function of impact force. Acoustic emission sensors were used to provide a noncensored measure of the maxilla tolerance and were essential due to the increase in impactor force after fracture onset. Parametric and nonparametric techniques were used to estimate the risk of fracture tolerance. The nonparametric technique produced an estimated 50% risk of fracture between 970 and 1223 N. The results obtained from the parametric and nonparametric techniques were in good agreement. Peak force values achieved in this study were similar to those of previous work and were unaffected by impactor velocity. The results of this study suggest that an impact to the infraorbital maxilla is a load-limited event due to compromise of structural integrity.

The tolerance of the frontal bone to blunt impact.

The current understanding of the tolerance of the frontal bone to blunt impact is limited. Previous studies have utilized vastly different methods, which limits the use of statistical analyses to determine the tolerance of the frontal bone. The purpose of this study is to determine the tolerance of the frontal bone to blunt impact. Acoustic emission sensors were used to provide a noncensored measure of the frontal bone tolerance and were essential due to the increase in impactor force after fracture onset. In this study, risk functions for fracture were developed using parametric and nonparametric techniques. The results of the statistical analyses suggest that a 50% risk of frontal bone fracture occurs at a force between 1885 N and 2405 N. Subjects that were found to have a frontal sinus present within the impacted region had a significantly higher risk of sustaining a fracture. There was no association between subject age and fracture force. The results of the current study suggest that utilizing peak force as an estimate of fracture tolerance will overestimate the force necessary to create a frontal bone fracture.

The tolerance of the nasal bone to blunt impact.

The nasal bone is among the most frequently broken facial bone due to all types of trauma and is the most frequently fractured facial bone due to motor vehicle collisions. This study reports the results of anterior-posterior impacts performed on male cadavers using a free-falling impactor with a flat impacting surface. The force at fracture onset was determined using an acoustic emission sensor. These non-censored data were utilized in parametric and non-parametric techniques to determine a relationship between applied force and fracture risk. Based on these analyses a 50% risk of fracture corresponded to an applied force of approximately 450 to 850 N. There was no correlation between fracture force and anthropometric measures of the nasal bone. Interestingly, age had a statistically significant relationship with the risk of nasal bone fracture. This study demonstrates the need for a non-censored measure of fracture occurrence when evaluating structures that can continue to support load after fracture onset.

Biomechanical response of human liver in tensile loading.

Motor vehicle collisions commonly result in serious life threatening liver injuries. Although finite element models are becoming an integral tool in the reduction of automotive related liver injuries, the establishment of accurate material models and tissue level tolerance values is critical for accurate injury risk assessment. This study presents a total of 51 tension tests performed on human liver parenchyma at various loading rates in order to characterize the viscoelastic and failure properties of human liver. Standard dog-bone coupons were obtained from fresh human livers and tested within 48 hours of death. Each coupon was tested once to failure at one of four loading rates (0.008 s(-1), 0.089 s(-1), 0.871 s(-1), and 9.477 s(-1)) to investigate the effects of rate dependence. Load and acceleration data were obtained from each of the specimen grips. High-speed video and optical markers placed on the specimens were used to measure local displacement. Failure stress and strain were calculated at the location of failure in the gage length of the coupon. The results of the study showed that liver parenchyma is rate dependent, with higher rate tests giving higher failure stresses and lower failure strains. The failure strains for all tests ranged from 11% to 54% and the failure stresses ranged from 7 kPa to 95 kPa. This study provides novel biomechanical data that can be used in the development of both rate dependent material models and tissue level tolerance values critical for the validation of finite element models used to assess injury risk in automobile collisions.

Effect of strain rate on the tensile material properties of human placenta.

Automobile crashes are the largest cause of injury death for pregnant females and the leading cause of traumatic fetal injury mortality in the United States. Computational models, useful tools to evaluate the risk of fetal loss in motor vehicle crashes, are based on a limited number of quasistatic material tests of the placenta. This study presents a total of 64 uniaxial tensile tests on coupon specimens from six human placentas at three strain rates. Material properties of the placental tissue were evaluated at strain rates of 0.07/s, 0.70/s, and 7.00/s. The test data have average failure strains of 0.34, 0.36, and 0.37, respectively. Failure stresses of 10.8 kPa, 11.4 kPa, and 18.6 kPa correspond to an increase in strain rate from 0.07/s to 7.0/s. The results indicate rate dependence only when comparing the highest strain rate of 7.0/s to either of the lower rates. There is no significant rate dependence between 0.07/s and 0.70/s. When compared with previous testing of placental tissue, the current study addresses the material response to more strain rates as well as provides a much larger set of available data. In summary, tensile material properties for the placenta have been determined for use in computational modeling of pregnant occupant kinematics in events ranging from low impact activities to severe impacts such as in motor vehicle crashes.

Freezing affects the mechanical properties of bovine liver - biomed 2009.

The need to quantify the mechanical properties of human abdominal organs is becoming increasingly important in the automotive industry due to the large incidence of injuries to these organs as a result of motor vehicle crashes. The need to develop appropriate preservation and testing methodology is of particular importance because of how quickly abdominal organ tissues degrade after death. The purpose of this study was to determine the effects of freezing on the mechanical properties of bovine liver parenchyma in uni-axial tension. In the current study, one fresh never frozen bovine liver was divided in half. One half was frozen and then thawed prior to preparation, and the other half tested immediately. Each half was sliced and stamped so that multiple parenchyma tension coupons were produced. A total of 16 failure tests were performed at an average strain rate of 0.07 s-1, 8 fresh and 8 previously frozen, using a custom uni-axial tension system. The results showed that there was no statistically significant difference (p=0.07) in the average failure stress between fresh and previously frozen tissue. However, the average failure strain of the previously frozen tissue was found to be significantly less (p>0.01) than the average failure strain of the fresh tissue. It was concluded from these data that in order to obtain accurate tensile mechanical properties of bovine liver parenchyma, the liver must not be frozen prior to testing.