Elisa S. Arch

Passive-dynamic ankle-foot orthosis replicates soleus but not gastrocnemius muscle function during stance in gait: Insights for orthosis prescription.

Background: Passive-dynamic ankle–foot orthosis characteristics, including bending stiffness, should be customized for individuals. However, while conventions for customizing passive-dynamic ankle–foot orthosis characteristics are often described and implemented in clinical practice, there is little evidence to explain their biomechanical rationale. Objectives: To develop and combine a model of a customized passive-dynamic ankle–foot orthosis with a healthy musculoskeletal model and use simulation tools to explore the influence of passive-dynamic ankle–foot orthosis bending stiffness on plantar flexor function during gait. Study design: Dual case study. Methods: The customized passive-dynamic ankle–foot orthosis characteristics were integrated into a healthy musculoskeletal model available in OpenSim. Quasi-static forward dynamic simulations tracked experimental gait data under several passive-dynamic ankle–foot orthosis conditions. Predicted muscle activations were calculated through a computed muscle control optimization scheme. Results: Simulations predicted that the passive-dynamic ankle–foot orthoses substituted for soleus but not gastrocnemius function. Induced acceleration analyses revealed the passive-dynamic ankle–foot orthosis acts like a uniarticular plantar flexor by inducing knee extension accelerations, which are counterproductive to natural knee kinematics in early midstance. Conclusion: These passive-dynamic ankle–foot orthoses can provide plantar flexion moments during mid and late stance to supplement insufficient plantar flexor strength. However, the passive-dynamic ankle–foot orthoses negatively influenced knee kinematics in early midstance. Clinical relevance Identifying the role of passive-dynamic ankle–foot orthosis stiffness during gait provides biomechanical rationale for how to customize passive-dynamic ankle–foot orthoses for patients. Furthermore, these findings can be used in the future as the basis for developing objective prescription models to help drive the customization of passive-dynamic ankle–foot orthosis characteristics.

Passive-dynamic ankle-foot orthoses substitute for ankle strength while causing adaptive gait strategies: a feasibility study.

Bending stiffness of passive-dynamic ankle–foot orthoses (PD-AFOs) is a functional characteristic thought to restore lost ankle function due to weakened plantar flexors. However, lower extremity impairment profiles of patients are seldom limited to plantar flexion weakness, and PD-AFO characteristics often influence gait in other ways. Combined, all PD-AFO characteristics and patient impairments likely mask the main effect of PD-AFO bending stiffness and complicate the PD-AFO bending stiffness prescription process. In this study, we propose a biomechanical probing paradigm, where customized PD-AFOs with a range of precise stiffness values are worn by healthy subjects, to experimentally test a PD-AFO strength substitution hypothesis while simultaneously documenting gait adaptations to PD-AFO use. Two healthy subjects walked at a scaled velocity while wearing a series of three PD-AFOs that ranged in bending stiffness levels. Supporting the strength substitution hypothesis, peak ankle plantar flexion moments remained unchanged across PD-AFO stiffness conditions. Further biomechanical analyses documented a complex series of ankle related kinematic and kinetic adaptive movement strategies due to PD-AFO use. This study demonstrated the utility of the biomechanical probing paradigm to help understand the contribution of PD-AFO stiffness to ankle strength and its secondary effects on ankle biomechanics.

Method to Quantify Cadence Variability of Individuals with Lower-Limb Amputation

Introduction The ability to walk with different cadences (cadence variability) is considered an important factor for determining the functional ability of individuals with lower-limb amputation and making prosthetic recommendations. However, a method to quantify cadence variability of these individuals has never been presented before, so there are no standardized methodologies or values to guide prosthesis prescription. The purpose of this study was to develop and demonstrate feasibility of a method to quantify real-world cadence variability. Materials and Methods The method utilizes step-count data collected by an accelerometer-based activity monitor. Cadence at each minute is calculated. Then, the spread of the cadence data distribution during a 7-day observation period is measured to quantify cadence variability. To demonstrate feasibility, this method was applied to a set of step-count data for individuals with unilateral lower-limb amputation classified by their health care provider as a K2 or K3 ambulator. Results Results showed that this method was able to differentiate the cadence characteristics of individuals classified as K2 versus K3. On average, individuals classified as K2 walked with significantly less cadence variability than those classified as K3. Conclusions This study provides a novel method for objectively determining cadence variability and provides a foundation for ultimately developing normative cadence characteristic values for K2 and K3 levels.

Step count accuracy of StepWatch and FitBit One™ among individuals with a unilateral transtibial amputation

Background: Step counts, obtained via activity monitors, provide insight into activity level in the free-living environment. Accuracy assessments of activity monitors are limited among individuals with lower-limb amputations. Objectives: (1) To evaluate the step count accuracy of both monitors during forward-linear and complex walking and (2) compare monitor step counts in the free-living environment. Study design: Cross-sectional study. Methods: Adult prosthetic users with a unilateral transtibial amputation were equipped with StepWatch and FitBit One™. Participants completed an in-clinic evaluation to evaluate each monitor’s step count accuracy during forward linear and complex walking followed by a 7-day step count evaluation in the free-living environment. Results: Both monitors showed excellent accuracy during forward, linear walking (intraclass correlation coefficients = 0.97–0.99, 95% confidence interval = 0.93–0.99; percentage error = 4.3%–6.2%). During complex walking, percentage errors were higher (13.0%–15.5%), intraclass correlation coefficients were 0.88–0.90, and 95% confidence intervals were 0.69–0.96. In the free-living environment, the absolute percentage difference between monitor counts was 25.4%, but the counts had a nearly perfect linear relationship. Conclusion: Both monitors accurately counted steps during forward linear walking. StepWatch appears to be more accurate than FitBit during complex walking but a larger sample size may confirm these findings. FitBit consistently counted fewer steps than StepWatch during free-living walking. Clinical relevance The StepWatch and FitBit are acceptable tools for assessing forward, linear walking for individuals with transtibial amputation. Given the results’ consistenty in the free-living enviorment, both tools may ultimiately be able to be used to count steps in the real world, but more research is needed to confirm these findings.

Self-Reported Functional Mobility, Balance Confidence, and Prosthetic Use Are Associated With Daily Step Counts Among Individuals With a Unilateral Transtibial Amputation

BACKGROUND Adults postamputation are not meeting physical activity recommendations. Physical activity is an important consideration in prosthetic prescription. The objective of this study was to determine if functional mobility, balance confidence, and prosthetic use are associated with physical activity among adults with a lower-limb amputation. METHODS This study recruited patients aged 18-85 years with unilateral transtibial amputations. The Cumulative Illness Rating Scale was used to determine comorbidity burden. Participants completed the Prosthetic Evaluation Questionnaire-Mobility Section, Activities-specific Balance Confidence Scale, and Houghton Scale of Prosthetic Use and wore a StepWatch monitor for 7 days to obtain daily step counts. Linear regression was used to evaluate relationships between each self-report measure and step counts after controlling for covariates, that is, sex, age, time since initial amputation, and comorbidity burden. RESULTS Forty-seven participants had ≥5 days of step data and were included in this analysis. The Prosthetic Evaluation Questionnaire-Mobility Section [mean (SD): 35.0 (9.6) points] and Activities-specific Balance Confidence Scale [79.2% (15.9%)] each explained 13% of the variance in step count [5491 (4043) steps], whereas the Houghton Scale of Prosthetic Use [10.3 (1.2) points] explained 10% of the variance. CONCLUSION Self-reported functional mobility, balance confidence, and prosthetic use predict short-term average daily step counts as determined from research-grade accelerometers.

Evaluating the Relationship between Gait and Clinical Measures of Plantar Flexor Function

Individuals with plantar flexor weakness often require rehabilitation and/or orthoses, which should be personalized based on level of weakness. While plantar flexor weakness can be measured via peak plantar flexion moment during gait (MGAIT), motion analysis systems are often not clinically available. Clinical measures, such as the single-leg heel rise (SLHR) test and isometric muscle test, may provide surrogate measures of plantar flexor function during gait. However, it is currently unknown if a relationship(s) exists between such measures. This study evaluated the relationship between gait and clinical measures of plantar flexor function for typical individuals. Twenty-four participants underwent an instrumented gait analysis, from which MGAIT was calculated. Next, participants performed an isometric plantar flexor test, from which the maximum plantar flexion moment (MISO) was calculated. Finally, participants performed a SLHR test, from which maximum plantar flexion moment (MSLHR) and total work (Wtot_SLHR) were calculated. Via Pearson correlations, MSLHR was most strongly correlated to MGAIT (r = 0.56; p = 0.005). Wtot_SLHR was significantly correlated to MGAIT (r = 0.47; p = 0.019). MISO was not significantly correlated to MGAIT (r = 0.19; p = 0.363). MSLHR and/or Wtot_SLHR may provide clinically-feasible surrogate measures of plantar flexor function during gait.

Net ankle quasi-stiffness is influenced by walking speed but not age for older adult women

BACKGROUND Insufficient plantar flexor resistance due to plantar flexor weakness, an impairment common in patient populations, causes substantial gait deficits. The bending stiffness of passive-dynamic ankle-foot orthoses (PD-AFOs) has the capacity to replace lost plantar flexor resistance. Many patients who are prescribed PD-AFOs are older adults. While PD-AFO bending stiffness should be customized for patients, a method to objectively prescribe this stiffness does not exist. Quantifying natural plantar flexor resistance during non-pathological gait could provide a reference value for objectively prescribing PD-AFO bending stiffness. RESEARCH QUESTION This study investigated the effect of age on plantar flexor resistance in 113 participants above the age of 65 years. We did so while also considering the confounding influence of gait speed, an aspect known to be reduced with old age. METHODS Ambulatory, community-dwelling older adult women (ages 65-91 years) with no current or recent lower-extremity injuries or surgeries underwent an instrumented gait analysis at a self-selected speed. Plantar flexor resistance was quantified via net ankle quasi-stiffness (NAS) defined as the slope of ankle joint moment-angle curve during late stance. RESULTS showed that NAS was not significantly influenced by age (r = -0.11, p = 0.12), and that the confounding factor of walking speed had a significant, positive relationship with NAS (r = 0.59, p < 0.001). SIGNIFICANCE By determining that gait speed, not age, is related to NAS in older adults, this study represents the initial step towards objectively prescribing PD-AFO bending stiffness to achieve a targeted gait speed for older adults with plantar flexor weakness.

State of the Prescription Process for Dynamic Ankle-Foot Orthoses

Purpose of ReviewDynamic ankle-foot orthoses (AFOs) are assistive devices that can be prescribed to individuals with mobility limitations to support and align joints. Dynamic AFOs are a category of passive AFOs that can control ankle motion to address both ankle joint range of motion limitations and ankle muscle weakness. This control of motion is achieved through the dynamic AFO’s functional characteristics, namely bending stiffness, which need to be customized to each individual’s needs. However, current conventions for customizing dynamic AFOs for each individual are variable and often not clearly documented. The purpose of this review was to synthesize the current state of customizing functional characteristics of dynamic AFOs to provide a foundation for ultimately optimizing the prescription of AFOs.Recent FindingsDynamic AFO bending stiffness, bending axis, alignment, and footplate design were identified as key functional characteristics that can be customized. Studies showed that customizing these dynamic AFO functional characteristics has the ability to alter gait, and customizing multiple functional characteristics at once is key to improving individual outcomes.SummaryResearchers have continued to expand their knowledge on how dynamic AFO functional characteristics can impact individual outcomes. Continued research should work towards developing guidelines for prescribing dynamic AFO functional characteristics based on individuals’ level of needs. Additionally, researchers and clinicians need to work together to ultimately translate these scientific findings into clinical practice.

Orthotic Device Research

Orthoses are assistive devices that support joints through alignment, stabilization, or assisting weakened musculature. The cost associated with orthotic treatment is substantial, and the demand is outpacing the supply. Patient comfort and performance are influenced by orthosis fit (size or shape) as well as function (mechanical aspects). To achieve optimal performance outcomes, an orthosis must be customized to the individual patient. However, traditional fabrication methods do not readily support the objective prescription and manufacture of orthosis mechanical aspects. There is a need for processes that promote better patient outcomes. Here, we seek to identify promising approaches, contemporary methods, and existing gaps that may provide enhanced benefit and value to the orthotic user. This chapter examines the current state of patient care practices as well as cutting-edge research and technologies primarily associated with ankle-foot orthoses.