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Charcot neuroarthropathy is a devastating condition that places patients at risk for poor outcomes. Although the condition was first described in 1703, knowledge of the causative agent(s) has yet to be fully understood. Recent advances in genetic research have helped to identify potential mechanisms and pathways for the enigmatic destruction and deformities that are often associated with the condition; however, alternative pathways have been proposed. For the purpose of this discussion, we will discuss the human leukocyte antigen, which is one of the most researched contributors to autoimmune pathology and, more recently, has been linked to diabetic complications.

Capturing the surface mechanics of musculoskeletal extremities would enhance the realism of life-like mechanics imposed on the limbs within surgical simulations haptics. Other fields that rely on surface manipulation, such as garment or prosthetic design, would also benefit from characterization of tissue surface mechanics. Eight homogeneous tissue models were developed for the upper and lower legs and arms of two donors. Ultrasound indentation data was used to drive an inverse finite element analysis for individualized determination of region-specific material coefficients for the lumped tissue. A novel calibration strategy was implemented by using a ratio based adjustment of tissue properties from linear regression of model predicted and experimental responses. This strategy reduced requirement of simulations to an average of under four iterations. These free and open-source specimen-specific models can serve as templates for simulations focused on mechanical manipulations of limb surfaces., Competing Interests: The authors have declared that no competing interests exist.

The skin, fat, and muscle of the musculoskeletal system provide essential support and protection to the human body. The interaction between individual layers and their composite structure dictate the body's response during mechanical loading of extremity surfaces. Quantifying such interactions may improve surgical outcomes by enhancing surgical simulations with lifelike tissue characteristics. Recently, a comprehensive tissue thickness and anthropometric database of in vivo extremities was acquired using a load sensing instrumented ultrasound to enhance the fidelity of advancing surgical simulations. However detailed anatomy of tissue layers of musculoskeletal extremities was not captured. This study aims to supplement that database with an enhanced dataset of in vitro specimens that includes ultrasound imaging supported by motion tracking of the ultrasound probe and two additional full field imaging modalities (magnetic resonance and computed tomography). The additional imaging datasets can be used in conjunction with the ultrasound/force data for more comprehensive modeling of soft tissue mechanics. Researchers can also use the image modalities in isolation if anatomy of legs and arms is needed.

Surface stiffness of bulk soft tissue in musculoskeletal extremities is important to consider in the design of prosthetics, exoskeletons, and protective gear. This knowledge is also foundational for surgical simulation and clinical interventions leveraging manipulation of the musculoskeletal surfaces. Injuries to musculoskeletal extremities are common and surgical and preventive interventions require interactions between various objects such as surgical tools and support surfaces with tissue boundaries. While a handful of investigations examined the variations in indentation mechanics due to pathology or injury specific sites, a comprehensive analysis across the surfaces of musculoskeletal extremities has not been completed. In this study we examine variations of surface stiffness across 8 sites of the upper and lower arms and legs for 95 subjects using an instrumented ultrasound device. Differences in surface stiffness were observed between gender, activity level, and indentation location groups. The lower arm posterior location had the highest average stiffness (3.89 × 10 -3  MPa/mm), while the lowest stiffness was observed at the upper leg posterior location (0.98 × 10 -3  MPa/mm). The differences between indentation sites were larger in magnitude when compared to differences due to demographics (gender and activity level). However the large ranges of the 95% confidence intervals suggest that an aggregated metric based on population or sub-group may not capture individual variations. This study implicates the motivation to explore tissue composition variations within the indentation sites as well as the potential importance to include variations in surface stiffness during surgical simulations., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Ultrasound is a popular and affordable imaging modality, but the nature of freehand ultrasound operation leads to unknown applied loads at non-quantifiable angles. The purpose of this paper was to demonstrate an instrumentation strategy for an ultrasound system to measure probe forces and orientation during freehand imaging to characterize the interaction between the probe and soft-tissue as well as enhance repeatability. The instrumentation included a 6-axis load cell, an inertial measurement unit, and an optional sensor for camera-based motion capture. A known method for compensation of the ultrasound probe weight was implemented, and a novel method for temporal synchronization was developed. While load and optical sensing was previously achieved, this paper presents a strategy for potential instrumentation on a variety of ultrasound machines. A key feature was the temporal synchronization, utilizing the electrocardiogram (EKG) feature built-in to the ultrasound. The system was used to perform anatomical imaging of tissue layers of musculoskeletal extremities and imaging during indentation on an in vivo subject and an in vitro specimen. The outcomes of the instrumentation strategy were demonstrated during minimal force and indentation imaging. In short, the system presented robust instrumentation of an existing ultrasound system to fully characterize the probe force, orientation, and optionally its movement during imaging while efficiently synchronizing all data. Researchers may use the instrumentation strategy on any EKG capable ultrasound systems if mechanical characterization of soft tissue or minimization of forces and deformations of tissue during anatomical imaging are desired., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Musculoskeletal extremities exhibit a multi-layer tissue structure that is composed of skin, fat, and muscle. Body composition and anthropometric measurements have been used to assess health status and build anatomically accurate biomechanical models of the limbs. However, comprehensive datasets inclusive of regional tissue anatomy and response under mechanical manipulation are missing. The goal of this study was to acquire and disseminate anatomical and mechanical data collected on extremities of the general population. An ultrasound system, instrumented with a load transducer, was used for in vivo characterization of skin, fat, and muscle thicknesses in the extremities of 100 subjects at unloaded (minimal force) and loaded (through indentation) states. For each subject, the unloaded and loaded state provided anatomic tissue layer measures and tissue indentation response for 48 and 8 regions, respectively. A publicly available web-based system has been used for data management and dissemination. This comprehensive database will provide the foundation for comparative studies in regional musculoskeletal composition and improve visual and haptic realism for computational models of the limbs.

Objective: The results of the single-arm, open-label extension phase of the Grafix (cryopreserved placental membrane; CPM; Osiris Therapeutics, Inc, Columbia, MD) multicenter, blinded, randomized, controlled clinical trial for chronic diabetic foot ulcers (DFUs) is reported., Materials and Methods: Twenty-six patients in the standard wound care (SWC) arm whose DFUs did not close in the blinded phase chose to receive weekly applications of the CPM in an open-label extension phase., Results: In the extension phase, 17 (65.4%) patients closed their wounds in a median of 34 days and 3 visits. There were fewer total adverse events (AEs) (24 CPM vs. 52 SWC) and index wound-related infections (5 CPM vs. 12 SWC) during the CPM application compared with the number of AEs for the same patients during the SWC treatment in the blinded phase of the trial., Conclusions: These results corroborate the benefits of this CPM combined with SWC over SWC alone for chronic DFUs previously reported for the blinded randomized phase of the trial, which directly relate to lower health care costs.

The dose-response effects of exercise in reduced gravity on musculoskeletal health have not been well documented. It is not known whether or not individualized exercise prescriptions can be effective in preventing the substantial loss in bone mineral density and muscle function that have been observed in space flight and in bed rest. In this study, typical daily loads to the lower extremities were quantified in free-living subjects who were then randomly assigned to control or exercise groups. Subjects were confined to 6-degree head-down bed rest for 84 days. The exercise group performed individually prescribed 1 g loaded locomotor exercise to replace their free-living daily load. Eleven subjects (5 exercise, 6 control) completed the protocol. Volumetric bone mineral density results from quantitative computed tomography demonstrated that control subjects lost significant amounts of bone in the intertrochanteric and total hip regions ( p  < 0.0125), whereas the exercise group showed no significant change from baseline in any region ( p  > 0.0125). Pre-and post-bed rest muscle volumes were calculated from analysis of magnetic resonance imaging data. The exercise group retained a larger percentage of their total quadriceps and gastrocnemius muscle volume (- 7.2% ± 5.9, - 13.8% ± 6.1, respectively) than their control counterparts (- 23.3% ± 5.9, - 33.0 ± 8.2, respectively; p  < 0.01). Both groups significantly lost strength in several measured activities ( p  < 0.05). The declines in peak torque during repeated exertions of knee flexion and knee extension were significantly less in the exercise group than in the control group ( p  < 0.05) but work done was not significantly different between groups ( p  > 0.05). The decline in VO 2max was 17% ± 18 in exercising subjects ( p  < 0.05) and 31% ± 13 in control subjects ( p  = 0.003; difference between groups was not significant p  = 0.26). Changes in blood and urine measures showed trends but no significant differences between groups ( p  > 0.05). In summary, the decline in a number of important measures of musculoskeletal and cardiovascular health was attenuated but not eliminated by a subject-specific program of locomotor exercise designed to replace daily load accumulated during free living. We conclude that single daily bouts of exposure to locomotor exercise can play a role in a countermeasures program during bed rest, and perhaps space flight, but are not sufficient in their own right to ensure musculoskeletal or cardiovascular health.

Background: Total-contact casting is an effective method to treat various pathologic abnormalities in patients with diabetic neuropathy, but its use is frequently associated with iatrogenic complications., Methods: The largest retrospective review to date of iatrogenic complications of total-contact casts was conducted over an 8-year period at Cleveland Clinic., Results: In the past 8 years, 23% of patients developed complications, and the most common complication was a new heel ulcer formation. Of these complications, 92.1% resolved, 6.4% were lost to follow-up, and 1.4% resulted in a partial foot amputation. Mean cast duration was 10.3 days for patients who developed a total-contact cast iatrogenic complication. The most common indication for the use of a total-contact cast was a neuropathic foot ulceration., Conclusions: The results of this study support the use of total-contact casting in the insensate patient with diabetes. However, adequate staff training in total-contact cast application is recommended to reduce complications.

In a randomised, controlled study, we compared the efficacy of Grafix(®) , a human viable wound matrix (hVWM) (N = 50), to standard wound care (n = 47) to heal diabetic foot ulcers (DFUs). The primary endpoint was the proportion of patients with complete wound closure by 12 weeks. Secondary endpoints included the time to wound closure, adverse events and wound closure in the crossover phase. The proportion of patients who achieved complete wound closure was significantly higher in patients who received Grafix (62%) compared with controls (21%, P = 0·0001). The median time to healing was 42 days in Grafix patients compared with 69·5 days in controls (P = 0·019). There were fewer Grafix patients with adverse events (44% versus 66%, P = 0·031) and fewer Grafix patients with wound-related infections (18% versus 36·2%, P = 0·044). Among the study subjects that healed, ulcers remained closed in 82·1% of patients (23 of 28 patients) in the Grafix group versus 70% (7 of 10 patients) in the control group (P = 0·419). Treatment with Grafix significantly improved DFU healing compared with standard wound therapy. Importantly, Grafix also reduced DFU-related complications. The results of this well-controlled study showed that Grafix is a safe and more effective therapy for treating DFUs than standard wound therapy., (© 2014 The Authors. International Wound Journal published by Medicalhelplines.com Inc and John Wiley & Sons Ltd.)

High plantar pressures have been associated with foot ulceration in people with diabetes, who can experience loss of protective sensation due to peripheral neuropathy. Therefore, characterization of elevated plantar pressure distributions can provide a means of identifying diabetic patients at potential risk of foot ulceration. Plantar pressure distribution classification can also be used to determine suitable preventive interventions, such as the provision of an appropriately designed insole. In the past, emphasis has primarily been placed on the identification of individual focal areas of elevated pressure. The goal of this study was to utilize k-means clustering analysis to identify typical regional peak plantar pressure distributions in a group of 819 diabetic feet. The number of clusters was varied from 2 to 10 to examine the effect on the differentiation and classification of regional peak plantar pressure distributions. As the number of groups increased, so too did the specificity of their pressure distributions: starting with overall low or overall high peak pressure groups and extending to clusters exhibiting several focal peak pressures in different regions of the foot. However, as the number of clusters increased, the ability to accurately classify a given regional peak plantar pressure distribution decreased. The balance between these opposing constraints can be adjusted when assessing patients with feet that are potentially "at risk" or while prescribing footwear to reduce high regional pressures. This analysis provides an understanding of the variability of the regional peak plantar pressure distributions seen within the diabetic population and serves as a guide for the preemptive assessment and prevention of diabetic foot ulcers., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Aims: The recurrence of foot ulcers is a significant problem in people with diabetic neuropathy. The purpose of this study was to measure in-shoe plantar pressures and other characteristics in a group of neuropathic patients with diabetes who had prior foot ulcers which had remained healed., Methods: This was an epidemiological cohort study of patients from diabetes clinics of two Swedish hospitals. From a database of 2625 eligible patients, 190 surviving patients with prior plantar ulcers of the forefoot (hallux or metatarsal heads) caused by repetitive stress were identified and 49 patients agreed to participate. Barefoot and in-shoe plantar pressures were measured during walking. Data on foot deformity, activity profiles and self-reported behaviour were also collected., Results: Mean barefoot plantar peak pressure at the prior ulcer site (556 kPa) was lower than in other published series, although the range was large (107-1192 kPa). Mean in-shoe peak pressure at this location averaged 207 kPa when measured with an insole sensor. Barefoot peak pressure only predicted approximately 35% of the variance of in-shoe peak pressure, indicating variation in the efficacy of the individual footwear prescriptions (primarily extra-depth shoes with custom insoles)., Conclusions: We propose that the mean value for in-shoe pressures reported in these patients be used as a target in footwear prescription for patients with prior ulcers. Although plantar pressure is only one factor in a multifaceted strategy to prevent ulcer recurrence, the quantitative focus on pressure reduction in footwear is likely to have beneficial effects.

Objective: The purpose of this study was to determine whether custom insoles tailored to contours of the barefoot pressure distribution and shape of a patient's foot can reduce plantar pressures in the metatarsal head (MTH) region to a greater extent than conventional custom insoles., Research Design and Methods: Seventy regions of elevated barefoot pressures (mean peak 834 kPa under MTHs) were identified in 20 subjects with diabetes. Foam box impressions of their feet were sent to three different orthotic supply companies for fabrication of custom insoles. One company was also given plantar pressure data, which were incorporated into the insole design. Measurements of in-shoe plantar pressures were recorded during gait for the three custom insoles in a flexible and a rocker-bottom shoe. Peak pressure and force-time integral were extracted for analysis., Results: In 64 of 70 regions, the shape-plus-pressure-based insole in the flexible shoe achieved superior unloading compared with the two shape-based insoles. On average, peak pressure was reduced by 32 and 21% (both P

We have outlined an approach to the nonsurgical treatment of diabetic foot ulcers based on an understanding of their etiology. We have emphasized the importance of off-loading as the crucial element to success in healing foot ulcers and preventing their recurrence in those with diabetes. Computerized design of custom insoles can allow the unloading of elevated plantar pressure while incorporating the shape of the foot, which was formerly the major criterion used insole design.

Background: The purpose of this study was to determine the extent to which measures of lower extremity strength and power contribute to the ability of older men and women to restore postural equilibrium using a single-step recovery following a large postural disturbance., Methods: The postural disturbance, which has been used as a surrogate for forward-directed falls, involved a sudden release from a forward-leaning angle. The ability to recover using a single step was evaluated as the maximum recoverable lean angle for 56 healthy older women and men. Maximum voluntary isometric and isokinetic strength was measured for ankle plantarflexion and dorsiflexion, knee flexion and extension, and hip flexion and extension. Discriminant analysis was used to determine the strength measures that best classified participants as members of the highest (n = 14) or lowest (n = 14) quartiles of maximum recoverable lean angle. Those variables were subsequently entered into a regression analysis to characterize the relationship between strength and maximum recoverable lean angle for the entire participant sample., Results: Maximum isokinetic dorsiflexion strength at 90 degrees /s satisfied the criteria of the stepwise discriminant analysis, and correctly classified 82.1% of the participants in the highest or lowest quartiles of maximum recoverable lean angle. The multiple regression procedure, performed on all participants (n = 56) revealed a significant quadratic relationship between maximum isokinetic dorsiflexion strength at 90 degrees /s and maximum recoverable lean angle (R2 = 0.295; p <.001)., Conclusions: Lower extremity strength makes a small, but significant contribution to maximum recoverable lean angle. However, because 70% of the shared variability remained unaccounted for, it is suggested that other performance factors, such as coordination, may be of greater importance to performance of this time-critical motor task.

Fall-related injuries are the most common and serious medical problems facing older adults. Recent studies of older adults have focused on the variability of step kinematics and the relationship to falling. The accuracy of step variability estimates is proportional to the number of steps that are collected. The use of an instrumented treadmill allows simultaneous collection of spatial and temporal step kinematics for a large number of continuous steps. The current study was conducted to determine the influence of age, walking velocity and handrail use on the variability of step kinematics using a treadmill protocol. Eighteen young adults (average age: 27.7 +/- 3.3 years) and 12 healthy older adults (average age: 73.4 +/- 2.3 years) were recruited from the community. Temporal and spatial gait parameters were quantified using custom designed software from measurements collected during treadmill walking. The primary independent variables were the variability of step length, step width, and step time. Step width variability of older adults was significantly larger than that of young adults. Walking velocity did not influence step kinematic variability. Handrail usage influenced the variability of step length and step width, but not of step time. The present results, and those of previous studies, point to a consistent relationship between age and step width variability. Since step width variability has been implicated in falls, further research is warranted., (Copyright 2003 Elsevier B.V.)

The variability of spatial and temporal step kinematics have separately been shown to prospectively predict falls by older adults. However, the published literature has not addressed the relative importance of the information related to locomotion control contributed by variability of spatial variables, temporal variables, or both. We conducted a post hoc analysis to determine the extent to which the variability of spatial and temporal step kinematics are independent descriptors of locomotion control in healthy young and older adults. A second purpose of the analysis was to establish the extent to which treadmill walking mimics overground walking using a benchmark for step kinematics. Eighteen young adults and 12 older adults walked at a self-selected velocity on an instrumented treadmill from which step length variability, step width variability and step time variability were computed. Stepwise discriminant analysis correctly classified group membership of 70 percent of the 30 subjects (i.e., young or older adult) using only step width variability (p=0.037, Wilk's lamda=0.854). Step width variability was 70+/-57 percent larger than step length variability (p<0.001). This relationship was similar to that of the benchmark established for overground locomotion. The results suggest that for healthy younger and older adults step width variability is a more meaningful descriptor of locomotion control than step length variability and step time variability. Given the potential clinical impact, further systematic study and improvement of the methods and technology for acquiring step kinematic data are warranted.

Variability of step kinematics has been associated with falls by older adults. However, between-study differences with regard to the number of steps used to compute variability have varied by an order of magnitude. If the number of steps used to compute variability is too low there is the potential for a statistically spurious outcome. On the other hand, for subjects with mobility impairments a protocol requiring too many steps to estimate variability imposes an unnecessary burden on the subjects. We have determined the minimum number of steps needed to estimate the variability of spatial and temporal step kinematics. More than 700 steps were collected during level walking on an instrumented treadmill. Accurate estimation of step kinematic variability required at least 400 steps. The increased error in estimating the mean and standard deviations of the step kinematic variables with too few steps can impose an experimental cost with regard to statistical design considerations. The extent to which translation of these results can be made to the variability of spatial and temporal step kinematics collected during over-ground walking awaits further research.

Purpose: The ability of a baseball infielder to respond to a batted ball may provide the best defense for avoiding injury. This study investigated the response times of young athletes performing a simulated baseball-fielding task to estimate the maximum velocity with which a baseball can leave the bat and allow a player, standing 13.7 m away, to safely respond to the approaching ball., Methods: Fifty boys and 50 girls between the ages of 8 and 16 yr participated. Baseballs were projected at the subjects who were standing in a standardized position behind a safety net. Two components of response time, reaction time and movement time, were determined using a motion capture system. The influences of baseball velocity (26.8 and 33.5 m.s(-1) and level of attention (full attention and attention splitting) on response time for a simulated baseball-fielding task were characterized. Based on the response times for each age group, the maximum exit-velocity from a baseball-bat interaction that would allow a young baseball player sufficient time to safely respond to an approaching baseball was calculated., Results: The results showed that subjects had sufficient time to respond to exit-velocities from 26.8 m.s-1 (8- to 9-yr-old group) to 33.5 m.s-1 (16-yr-old group). However, the accuracy of the response was negatively affected by baseball velocity., Conclusions: If the exit-velocities seen during actual competition exceed the calculated maximum exit-velocities for these age groups, then our preliminary data suggest that modifications to the game of baseball that would reduce the actual exit-velocities and serve as an effective means to reduce the potential for serious or catastrophic injury are warranted.

This investigation addressed the question of whether the muscle activation signal prior to movement onset, as measured by surface EMG, differs if the contraction to be performed is concentric (shortening) or eccentric (lengthening). Specifically, the purpose was to determine if differences in knee extensor muscle EMG prior to voluntary maximum concentric and eccentric contractions and initiated from the same knee joint angle are evident at a time before muscle length changes could be influential. A protocol was designed using isokinetic knee extensions. The EMG of the vastus lateralis, vastus medialis, rectus femoris, and hamstrings muscles and the associated knee extension moment were measured during the isometric phase preceding the onset of dynamometer motion. During this isometric phase the muscles initially contracted under identical conditions, irrespective of whether the contraction was to be concentric or eccentric. The EMG of the eccentric contractions was significantly smaller than that of the concentric contractions. However, the rate of change of knee extension moment generally did not differ between the two conditions. This was found for both the monoarticular and multiarticular knee extensor muscles. The results suggest that initial differences between the EMG of maximum voluntary concentric and eccentric knee extensor contractions are selected a priori and support the contention that the central nervous system distinguishes between maximum eccentric and concentric contractions. The emergence of differences in activation prior to muscle length changes suggests supraspinal influences.

Background: Inappropriate control of the vastus medialis oblique and vastus lateralis muscles by the central nervous system can contribute to maltracking of the patella., Hypothesis: The activation timing and amplitude of the vastus medialis oblique and vastus lateralis muscles will be different between normal subjects and patients with patellofemoral pain., Study Design: Controlled laboratory study., Methods: Subjects with patellofemoral pain and asymptomatic control subjects performed maximum voluntary knee extension contractions initiated from a flexed and an extended position. The activation timing and amplitude of the vastus lateralis and vastus medialis oblique muscles were quantified from the recorded electromyographic signals., Results: There were no between-group differences in activation timing. The activation amplitude of the vastus medialis oblique and vastus lateralis muscles of the patellofemoral pain subjects was altered to the greatest extent during eccentric contractions and differed significantly from that of control subjects., Conclusions: The activation amplitudes of the vastus medialis oblique and vastus lateralis muscles of subjects with patellofemoral pain are consistent with a laterally tracking patella during eccentric contractions., Clinical Relevance: The findings suggest the clinical importance of determining whether altered activation patterns are sensitive to rehabilitation, and, if so, if subjective reports of knee joint pain and function parallel changes in the activation patterns as a result of rehabilitation.

The practical determination of accurate body segment inertial parameters for the general older adult population remains a problem, especially in estimating these parameters for women and accounting for variations in body type. A method is presented for determining the mass and center of mass location of the body segments of individuals within the general population of older adults. Effects of sex and body type on older adult mass distribution are accounted for using 32 easily obtainable body measurements. The method is based on existing results from different data sources and employs a combination of validated estimation approaches, including: body mass and segment length proportions, linear and nonlinear regression equations, and a mathematical model of the trunk. The method was applied to a validation sample of healthy, community-dwelling older adults (29 men, 50 women). Predicted body mass was 96.7+/-4.8% and 95.7+/-3.7% of measured body mass in the men and women, respectively. The estimates of body segment mass and trunk center of mass location for the sample population approximate those reported in the literature, supporting the validity of the described method. By producing practical, subject-specific estimates of body segment inertial parameters, the method should allow more accurate biomechanical analyses of the older adult population.

The relationship described in the published literature between muscle strength and bone mineral density of older adults is not entirely certain. It is possible that the direct relationship reported in some studies is biased by failing to mathematically account for the biological influence of body weight and body height on both bone mineral density and muscle strength. This study sought to determine if the relationships between measures of lower extremity muscle strength and bone mineral density of the proximal femur are independent of body size (i.e., body height and body weight) in healthy older adults. We recruited 50 older women and 29 older men, all of whom were healthy community dwellers and not involved in resistance training. Quantitative analysis of the isometric strength of the bilateral ankle, knee, and hip joints and assessment of bone mineral density of the proximal femur were conducted. Muscle strength values were adjusted for the influence of body height and body weight using an allometric scaling procedure. The correlations between proximal femur bone mineral density and the unadjusted strength values were weak but statistically significant. After adjusting muscle strength to account for the influence of body height and body weight, the magnitudes of the correlations between bone mineral density and muscle strength diminished substantially and were not significantly different from zero. The results reveal that, for a typical sample of healthy older adults not involved in resistance training, the relationship between maximal isometric muscle strength of lower extremity joints and proximal femur bone mineral density is reliant on body size.

Unintentional injuries are the seventh leading cause of death in adults ages 65 and older, and the greatest number of these deaths results from fall-related injuries. In addition to the startling mortality, the morbidity associated with fall-related injuries, particularly hip fractures, has become a research imperative. This article reviews a series of studies that was undertaken to determine the biomechanical reasons that older adults are unable to recover from very large postural perturbations that are applied during locomotion that, if not corrected, can lead to a fall. Our protocol involves causing older adults to trip unexpectedly while walking normally in the laboratory. The results from this series of experiments were used to design an experiment that characterized the biomechanical similarities between recovery biomechanics after an induced trip and those following a large postural perturbation delivered by a motorized treadmill. Collectively, we have been able to document different recovery strategies and categories of falls by older adults following an induced trip; the biomechanical causes of these falls by older adults; and the very rapid motor adaptations that occur with repeated exposure to large perturbations that may be protective against falls from tripping and, therefore, reduce the substantial fall-related morbidity and mortality in older adults.

Objectives: To determine whether decreased lower extremity strength contributes to trip-related falls in older adults., Design: A cross-sectional sample of older adults were safety-harnessed and tripped while walking using a concealed, mechanical obstacle. Lower extremity strength was compared between trip outcome groups., Setting: A biomechanics research laboratory., Participants: Seventy-nine healthy, community-dwelling adults aged 65 and older (50 women)., Measurements: Ankle, knee, and hip flexion and extension strength were measured isometrically and isokinetically. Measured strengths were subjected to a factor analysis. Strength factor scores were compared between those who recovered from the trip and those who fell by three previously identified mechanisms: during-step, after-step, and elevating-response falls., Results: Seven common factors, one associated with each direction of exertion at each joint and one with the time rate of moment increase, explained 88% of the variance in measured strength. The during-step (n=5) fallers were significantly stronger in the ankle extension (plantarflexion), knee flexion, overall extension, and total strength factors than those who successfully recovered using a similar, lowering strategy (n=26). The elevating-response faller (n=1) was stronger in the plantarflexion and overall extension factors than most of those who recovered using a similar, elevating strategy (n=11). Two of three after-step fallers were among the weakest subjects tested., Conclusion: Weak older adults and the strongest older adults may be at greater risk of falling from a trip, although by different mechanisms. High strength may increase the likelihood of a during-step or elevating-response fall; decreased strength may increase the likelihood of an after-step fall.

Objective: To examine the recovery strategies employed during a treadmill acceleration task, to determine if mechanisms that contributed to failed recoveries on a motorized treadmill are the same general biomechanical mechanisms that contributed to falls from a trip, and to determine if failed recovery responses could be modified to allow for successful recoveries on subsequent trials., Design: A motorized treadmill was used to induce postural perturbations in healthy older adults., Background: Previously, we induced trips in older adults to identify the mechanisms of failed recovery. However, inducing trips is not a clinically practical test for identifying older adults who are predisposed to falling., Methods: Safety-harnessed older adults stood on a treadmill that was accelerated from 0 to 0.89 m/s to impose a postural perturbation. Recoveries were classified as successful (n=42) or failed (n=23). Selected biomechanical variables were calculated using motion analysis methods., Results: Initial failed recoveries had slower reaction times, shorter step lengths, and greater trunk flexion angles and velocities. Subjects who failed on the initial attempt modified their recovery strategy to successfully recover. The biomechanics of these recoveries resembled those used by subjects who successfully recovered on their initial attempt., Conclusions: The biomechanical mechanisms involved with a failed treadmill recovery mimic those responsible for failed recoveries from an induced trip. Subjects who failed on their initial recovery response made modifications allowing successful recoveries on subsequent attempts., Relevance: This protocol may be useful as a testing and rehabilitation tool for fall recovery.

Background: Tripping is a leading cause of falls in older adults, often resulting in serious injury. Although the requirements for recovery from a trip are well characterized, the mechanisms whereby trips by older adults actually result in falls are not known. This study sought to identify such mechanisms., Methods: Trips were induced during gait in 79 healthy, community-dwelling, safety-harnessed, older adults (50 women) using a concealed, mechanical obstacle. Kinematic and kinetic variables describing the recovery attempts were compared between those who fell and those who recovered. Subjects were analyzed according to the recovery strategy employed (lowering vs elevating) and the time of the "fall" (during step vs after step)., Results: Three apparent mechanisms of falling were identified. For a lowering strategy, during-step falls were associated with a faster walking speed at the time of the trip (91% +/- 8% vs 68% +/- 11% body height [bh] per second; p <.001) and delayed support limb loading (267 +/- 49 milliseconds vs 160 +/- 39 milliseconds; p <.001). After-step falls were associated with a more anterior head-arms-torso center of mass at the time of the trip (6.2 +/- 1.3 degrees vs 0.2 +/- 4.4 degrees; p <.01), followed by excessive lumbar flexion and buckling of the recovery limb. The elevating strategy fall was associated with a faster walking speed (93% vs 68% +/- 11% bh per second; p <.001) followed by excessive lumbar flexion., Conclusions: Walking quickly may be the greatest cause of falling following a trip in healthy older adults. An anterior body mass carriage, accompanied by back and knee extensor weakness, may also lead to falls following a trip. Deficient stepping responses did not contribute to the falls.

The purpose of the present study was to induce slips in healthy subjects as a means to determine if recovery from an induced slip is possible under conditions in which the displacements and velocities of the slipping foot exceed the generally accepted limits of 10cm and 50cm/s, respectively, and to determine if there are gait-related variables that predispose an individual to falling after a slip. Thirty-three young and barefoot adults, protected by an instrumented safety harness, were subjected to a single slipping trial following a series of unperturbed walking trials. The slip was induced when the bare foot contacted a vinyl sheet coated with mineral oil. Lower extremity kinematics were acquired using a video-based motion capture system. Fourteen and 12 subjects could be unambiguously categorized as having fallen or recovered, respectively. Four variables demonstrated significant between-group differences and two were used to compute the probability of the slip outcome using logistic regression. The variables were the displacement of the foot during the slip and the angle of the shank relative to the ground at the instant of ground contact just prior to the slip. Separate univariate logistic regressions using each variable were significant and correctly classified about 70% of the slip outcomes. The results demonstrated that previously published values for the displacement and velocity of the slipping foot, 10cm and 50cm/s, respectively, may not accurately represent the upper limits beyond which recovery is not possible. The results also demonstrated that heel-strike angle, reflective of stride length, exerts a significant influence on the outcome of a slip.

Objectives: To determine, in healthy older adults, the relationship between postural steadiness, stability limits, and the ability to recover balance from three postural disturbances requiring anteriorly directed stepping responses., Design: Analysis of multiple motor tasks in a cross-sectional sample of healthy older adults., Setting: A biomechanics research laboratory., Participants: Fifty women and 29 men aged 65 or older, all healthy, living in the community, participated in this study. Subjects were examined by a geriatrician to identify the presence of exclusionary factors., Measurements: Anterior-posterior and medial-lateral excursion distances of the center of pressure during quiet standing (postural steadiness), static leaning (static stability limits), and dynamic swaying (dynamic stability limits) were determined from ground reaction forces measured by a strain gauge forceplate. Within the same group of subjects, the maximum angle of forward lean from which a subject could recover with a single step, the ability to recover balance in response to an accelerated support surface, and the ability to recover balance after being tripped were determined., Results: Recovery from the three types of postural disturbances were found to be statistically independent. The postural steadiness and the stability limit variables were only weakly correlated. Postural steadiness and stability limits were not related to the maximum recoverable angle of lean. The average medial-lateral center of pressure speed during the postural steadiness test was significantly slower for those who failed to recover after tripping than for the subjects who recovered successfully. However, a logistic regression model failed to achieve statistical significance, suggesting that the difference may not be functionally important. The anterior-posterior static stability limits were significantly larger for subjects who recovered successfully than for those who failed to recover during the accelerated support surface test. Although logistic regression suggested that a reduced anterior-posterior stability limit represents a risk factor for failure to recover during this task, only nine of 28 failures could be properly classified, thus diminishing the functional importance of this finding., Conclusions: Because recovery following postural disturbances could not generally be predicted from measures of postural stability, these findings suggest that these measures of postural stability are of limited utility in identifying potential anteriorly directed fallers in healthy older adults.

Background: Falls are a significant source of morbidity and mortality in older adults, with up to 53% of these falls due to tripping. To aid in preventing trip-related falls, the factors that increase an individual's risk of falling following a trip must be identified. This study investigated whether an older adult's gait influences their risk of failing following a trip., Methods: Trips were induced during gait in 79 healthy, safety-harnessed, community-dwelling older adults using a concealed, mechanical obstacle. Associations between selected gait kinematic characteristics, recorded during normal walking, and the likelihood of falling following the trip were determined using logistic regression., Results: Older adults who walked faster, took more rapid steps, or took longer steps relative to their body height had a significantly increased likelihood of falling following the trip. Step width, average trunk flexion during gait, and the phase of gait in which the trip occurred did not affect the likelihood of falling. A multivariable logistic regression model correctly classified 89.8% of trip outcomes based on two gait characteristics: step time and step length. As predicted from their gait characteristics, the subjects, as a group, had a low likelihood of falling following a trip, but selected individuals had a high likelihood of falling., Conclusions: The incidence of trip-related falls in healthy older adults is determined primarily by the frequency of tripping and not the ability to recover from a trip. Older adults can reduce their likelihood of falling following a trip by not hurrying while walking.

This study extended findings of others related to the fatigue resistance of maximum voluntary knee extension contractions performed eccentrically on an isokinetic dynamometer. Twelve subjects performed either 75 unilateral isokinetic concentric MVCs or 75 unilateral isokinetic eccentric MVCs at 30 degrees s(-1). A uniquely-configured dynamometer provided the opportunity to describe the effect of the concentric or eccentric fatigue protocol on the concentric or eccentric MVC force of the contralateral limb, which was not involved in the fatigue protocol, immediately following the conclusion of the fatigue protocol. Eccentric MVC of the eccentrically fatigued group decreased significantly (13%, p = 0.001) although the decrease was significantly smaller than that of the concentric MVC of the concentrically fatigued group (39%). Concentric MVC of the contralateral limb was unaffected following the concentric fatigue protocol but the eccentric MVC of the contralateral limb increased 11% (p = 0.028) following the eccentric fatigue protocol. These results suggest that eccentric MVCs are not resistant to fatigue but do follow a different time course than fatigue induced with concentric contractions. The extent to which eccentrically performed MVCs fatigue may reflect the influence of protocol parameters such as the isokinetic speed, the number of repetitions, the criteria by which the protocol is terminated and the subject selection. However, the explanations for why eccentric MVCs fatigue to such a smaller extent necessitate further systematic investigation including electrophysiologic methods, as do the results relative to the contralateral leg. Both results can be considered within the framework of current thought about the disparate nature of nervous system control of eccentric contractions.

In the past decade there have been numerous publications reporting a significant and direct relationship between handgrip strength and bone mineral density (BMD) of the proximal femur in older adults. The present report challenges the appropriateness of the methods, and thus the conclusions used in these studies. Specifically, these studies failed to control for the concomitant influence of body weight on both BMD and muscle strength. In the present study, maximum handgrip strength was measured using a conventional hand-held hydraulic dynamometer. Bone mineral density of the proximal femur was measured using dual-energy X-ray absorptiometry (DXA). Using allometric scaling, the influence of body weight on the value of maximum handgrip strength was removed for the data of the women. A small, but significant relationship between BMD of the proximal femur and maximum handgrip strength was found that accounted for about 6% of the total variation. The relationship between BMD of the proximal femur and unscaled maximum handgrip strength was not significant for the men. The findings diminish the confidence in a protective effect of skeletal muscle on some nonadjacent skeletal structures and suggest that these relationships may benefit from being revisited. The results highlight the utility of allometric scaling in analyses in which the relationship between a physiological variable and a body dimension variable can be nonlinearly and simultaneously influenced by other body dimension variables that are not considered in the analysis and therefore are statistically uncontrolled.

In this study the functional abilities of eight one-stage bilateral total knee replacement (TKR) patients were compared to five two-stage bilateral TKR and nine control subjects. The TKR individuals were an average of 62 months post-operative. Based on gait analysis, ground reaction force profiles during walking and isometric knee strength assessment, the one-stage individuals did not differ significantly from the control subjects. The two-stage individuals had significantly less knee range of motion during gait and smaller vertical ground reaction forces during the braking phase than the control and one-stage individuals. To compare left and right sides, a symmetry index was computed and there were no significant differences among the three groups. Based on the variables tested in this biomechanical evaluation it can be concluded that for individuals facing bilateral knee replacement a one-stage procedure can result in functional capabilities at least comparable to a two-stage procedure.

Background: Falls are a significant source of morbidity and mortality in older adults, with up to 53% of these falls due to tripping. To aid in fall prevention, there is a need to identify the factors that determine whether a trip is recoverable and those factors that increase an older adult's risk of falling., Methods: Trips were induced during gait in 79 healthy, community-dwelling, safety-harnessed older adults (50 women) using a concealed, mechanical obstacle. Trip outcomes were graded as recoveries, falls, rope-assists, or misses. Kinematics were recorded during normal gait, without and with the safety harness. Selected gait parameters were compared to determine whether the experimental conditions affected gait at the time of the trip., Results: Thirty-nine trip outcomes were classified as recoveries, 10 as falls, 12 as rope-assists, and 18 as misses. Women fell more than four times as frequently as men. Women younger than 70 years fell more than three times as frequently as those older. Trip outcomes in the men were essentially unaffected by age. The foot obstructed to induce the trip did not affect the trip outcome. The presence of the safety harness had almost no effect on gait. The length of the stride preceding the trip did not differ from normal., Conclusions: The majority of trips in healthy older adults did not result in falls. Older women were more likely than men to fall following a trip. The likelihood of falling from a trip was greatest in the youngest older women.

The bilateral deficit results from the maximum voluntary force of a bilaterally performed task being smaller than the sum of the maximum voluntary force of the unilaterally performed tasks. It is underlain by the limitation of the neural drive during maximum bilateral contractions and has been hypothesized to reflect the inability to fully activate high threshold motor units. Because high threshold motor units atrophy in older adults, a smaller bilateral deficit in older adults compared to young adults would further support the hypothesis. Indeed, K. Häkkinen et al. in 1995 and 1996 reported no bilateral deficit in older adults performing rapid maximum contractions. The present study extends this investigation to slowly developed maximum contractions. The results demonstrated a bilateral deficit (p < .05). This result, combined with the age related decrease in the number of high threshold motor units, tends to refute the contention that selective restriction of high threshold motor units causes the bilateral deficit during maximum voluntary isometric ramp and hold contractions.

Purpose: The bilateral deficit is characterized by a decrease in maximum voluntary contraction (MVC) force during bilateral activation of homologous muscles compared with sum of the forces produced during unilateral MVC of the muscles. A proposed relationship between the bilateral deficit and the ability to activate high threshold motor units was investigated. The effects of muscle fatigue, induced using two contraction speeds, on the size of the bilateral deficit were measured. Based on previously published findings, it was expected that fast velocity isokinetic contractions compared with slow velocity isokinetic contractions would produce a larger bilateral deficit. It was hypothesized that following a unilateral fatigue protocol, the size of the bilateral deficit at the fast and slow velocities would be comparable., Methods: The bilateral deficit was measured for isokinetic knee extension in 20 men (age:25 +/- 3 yr) before and after a fatigue protocol performed at 30 and 150 degreesxs(-1)., Results: The size of the bilateral deficit was initially the same at both velocities. The fatigue protocol at each contraction speed significantly decreased the maximum voluntary knee extension moment. The size of the bilateral deficit was not influenced by the 150 degrees fatigue protocol (pretest: -14.0% post-test: -12.5%; P > 0.05). However, the size of the bilateral deficit increased following the 30 degreesxs(-1) fatigue protocol (pretest: -13.7%; post-test: -21.9%; P < 0.05)., Conclusions: The failure of the size of the bilateral deficit to be comparable at 30 and 150 degreesxs(-1) following fatigue is contrary to previous published reports that suggested reduced activation of high threshold motor unit is the primary mechanism underlying the bilateral deficit.