Stiffness Categories Research Articles

Design and Mechanical Validation of Commercially Viable, Personalized Passive Prosthetic Feet

Abstract Current high-performance prosthetic feet work well for many users, but the low resolution of size and stiffness categories may limit walking performance for certain users. A line of prosthetic feet with a high resolution of sizes and stiffnesses, designed through amputee-specific personalization, could provide clinical and economic value. The lower leg trajectory error (LLTE) design framework facilitates the design of high-performance, amputee-specific prosthetic feet; however, previous foot prototypes were not designed to satisfy the economic, mechanical, and aesthetic requirements for commercial adoption. The aims of this work were to understand how a personalized, affordable prosthetic foot can align with the clinical-commercial ecosystem, innovate a viable future product, and inform other prosthesis designers of considerations required to connect innovation to real-world implementation. We evaluated needs by identifying how products, capital, and services flow between stakeholders, and we elucidated design requirements for a personalized prosthetic foot that can be manufactured, distributed, and clinically provided. Based on material properties and manufacturing process capabilities, computer numerically controlled (CNC) machining of Nylon 6/6 satisfies these requirements. We present a novel parametric foot architecture that can be CNC machined, fits within a commercial foot shell, and can be designed for individual users’ body characteristics and activity levels. Prototypes made using the new foot design behaved as anticipated (1–12% error in modeled displacement), satisfied industry-standard strength (ISO 10328) and mechanical performance (AOPA dynamic heel/keel) requirements, and elicited positive feedback from both amputees and prosthetists.

The effect of prosthetic foot stiffness category on intact limb knee loading associated with osteoarthritis in people with transtibial amputation

Lower limb prosthesis users are at an increased risk of developing osteoarthritis in their intact knee. There is a scarcity of literature examining how the stiffness properties of commercially available prosthetic feet impact gait mechanics, including knee loading biomechanical variables that have been associated with the development of osteoarthritis. This study aimed to isolate the effect of commercial prosthetic foot stiffness on intact knee loading, prosthetic foot–ankle biomechanics, and user perception. Seventeen males with unilateral transtibial amputation were fit with three consecutive foot stiffness categories of a standardized energy-storing prosthetic foot in a randomized order and while blinded to foot condition. Biomechanical and self-report data were collected during level-ground walking in a motion analysis laboratory. As prosthetic foot stiffness increased, contralateral knee external adduction moment significantly decreased between stiff vs. medium and stiff vs. soft foot conditions. Prosthetic foot rollover radius increased as foot stiffness increased. However, prosthetic foot–ankle push-off peak power and work decreased as foot stiffness increased. On average, users favored the medium stiffness condition and were able to correctly identify the foot stiffness condition. Overall, these results raise questions about the relative contributions of foot stiffness and ankle push-off power to changes in contralateral knee loading. The findings contribute to our understanding of the relationships between prosthetic foot mechanical properties and gait biomechanical variables at the contralateral knee when prosthetic foot stiffness is modified without a corresponding alignment adjustment.

Greater than recommended stiffness and power setting of a stance-phase powered leg prosthesis can improve step-to-step transition work and effective foot length ratio during walking in people with transtibial amputation.

People with unilateral transtibial amputation (TTA) using a passive-elastic prosthesis exhibit lower positive affected leg trailing work (ALtrail Wpos) and a greater magnitude of negative unaffected leg leading work (ULlead Wneg) during walking than non-amputees, which may increase joint pain and osteoarthritis risk in the unaffected leg. People with TTA using a stance-phase powered prosthesis (e.g., BiOM, Ottobock, Duderstadt, Germany) walk with increased ALtrail Wpos and potentially decreased magnitude of ULlead Wneg compared to a passive-elastic prosthesis. The BiOM includes a passive-elastic prosthesis with a manufacturer-recommended stiffness category and can be tuned to different power settings, which may change ALtrail Wpos, ULlead Wneg, and the prosthesis effective foot length ratio (EFLR). Thirteen people with TTA walked using 16 different prosthetic stiffness category and power settings on a level treadmill at 0.75-1.75m/s. We constructed linear mixed effects models to determine the effects of stiffness category and power settings on ALtrail Wpos, ULlead Wneg, and EFLR and hypothesized that decreased stiffness and increased power would increase ALtrail Wpos, not change and decrease ULlead Wneg magnitude, and decrease and not change prosthesis EFLR, respectively. We found there was no significant effect of stiffness category on ALtrail Wpos but increased stiffness reduced ULlead Wneg magnitude, perhaps due to a 0.02 increase in prosthesis EFLR compared to the least stiff category. Furthermore, we found that use of the BiOM with 10% and 20% greater than recommended power increased ALtrail Wpos and decreased ULlead Wneg magnitude at 0.75-1.00m/s. However, prosthetic power setting depended on walking speed so that use of the BiOM increased ULlead Wneg magnitude at 1.50-1.75m/s compared to a passive-elastic prosthesis. Ultimately, our results suggest that at 0.75-1.00m/s, prosthetists should utilize the BiOM attached to a passive-elastic prosthesis with an increased stiffness category and power settings up to 20% greater than recommended based on biological ankle values. This prosthetic configuration can allow people with unilateral transtibial amputation to increase ALtrail Wpos and minimize ULlead Wneg magnitude, which could reduce joint pain and osteoarthritis risk in the unaffected leg and potentially lower the metabolic cost of walking.

Effects of prosthetic stiffness and added mass on metabolic power and asymmetry in female runners with a leg amputation.

Similar to nonamputees, female athletes with unilateral transtibial amputation (TTA) using running-specific leg prostheses (RSPs) may have worse running economy and higher rates of running-related injury than male athletes. Optimizing RSP configuration for female athletes could improve running economy and minimize biomechanical asymmetry, which has been associated with running-related injury. Nine females with a TTA ran at 2.5 m/s while we measured metabolic rates and ground reaction forces. Subjects used an RSP with a manufacturer-recommended stiffness category, one category less stiff and two categories less stiff than recommended. Use of an RSP two categories less stiff resulted in 3.0% lower net metabolic power (P = 0.04), 7.8% lower affected leg stiffness (P = 6.01 × 10-4), increased contact time asymmetry (P = 0.04), and decreased stance average vertical ground reaction force asymmetry (P = 0.04) compared with a recommended stiffness category RSP. Lower RSP stiffness (kN/m) values were associated with lower net metabolic power (P = 0.02), lower affected leg stiffness (P = 1.36 × 10-4), longer affected leg contact time (P = 1.46 × 10-4), and similar affected leg peak and stance-average vertical ground reaction force compared with higher RSP stiffness values. Subjects then used the RSP stiffness category that elicited the lowest net metabolic power with 100 g, 200 g, and 300 g added distally. We found no significant effects of added mass on net metabolic power, biomechanics, or asymmetry. These results suggest that female runners with a TTA could decrease metabolic power during running while minimizing biomechanical asymmetries, which have been associated with running-related injury, by using an RSP two categories less stiff than manufacturer recommended.NEW & NOTEWORTHY Females with unilateral transtibial amputation can improve running performance through reductions in net metabolic power by using a running-specific prosthesis (RSP) that is less stiff than manufacturer-recommended. Lower RSP stiffness values are associated with greater leg stiffness and contact time asymmetry, and lower stance-average vertical ground reaction force asymmetry. However, we found that adding mass to the RSP did not affect net metabolic power and stance-phase biomechanical asymmetries during running.

Cost – effectiveness analysis of hyaluronic acid injection relative to oral medication for knee osteoarthritis treatment at Nguyen Trai hospital in the period of 2022 – 2023

Objective Pharmacological treatments, primarily oral NSAIDs, constituted 73.9% usage for knee osteoarthritis. Despite the known adverse effects of NSAIDs, they are recommended for KOA management. Hyaluronic acid injections, an emerging alternative, lack consensus and evidence of cost-effectiveness in Vietnam. This study aimed to analyze the cost-effectiveness of hyaluronic acid injections relative to oral medication treatment in patients with KOA from health insurance payer’s perspective. Methods: A retrospective study was conducted using electronic medical records of KOA patients from March 1, 2022, to May 31, 2023, at Nguyen Trai Hospital to analyze costs. A cross-sectional descriptive study of two groups receiving hyaluronic acid injections (HA) or oral medication treatment (PO) was conducted using the WOMAC scale converted to EQ-5D-5L to measure treatment effectiveness in QALYs. Seemingly unrelated regression equation was utilized to estimate the Incremental Cost-effectiveness Ratio (ICER) of HA relative to PO while simutaneously adjusting for other confounding factors. Results: The PO group exhibited a higher total WOMAC score than the HA group (PO group: 45.12; HA group: 44.29), indicating greater severity in the WOMAC Pain, Function, and Stiffness categories. The QALYs of HA group was higher than those of the PO group, with QALYs values of 0,719 and 0,661, respectively. The total medical direct costs increased by 6.232.445 VND, and QALYs increased by 0,041 when using HA compared to PO. The ICER reached a 151.184.110 VND/QALY gained. With WTP of 1GDP and 3GDP, the probability of achieving cost-effectiveness of HA compared to using PO was respectively 20.06% and 100%. Conclusions: The study demonstrated that ICER based on QALYs of hyaluronic acid injections is cost-effective compared to the standard oral medication approach. Keywords: Cost analysis; WOMAC; Cost-effectiveness analysis; Hyaluronic acid injections; Knee osteoarthritis;

Low-profile prosthetic foot stiffness category and size, and shoes affect axial and torsional stiffness and hysteresis.

Passive-elastic prosthetic feet are manufactured with numerical stiffness categories and prescribed based on the user's body mass and activity level, but mechanical properties, such as stiffness values and hysteresis are not typically reported. Since the mechanical properties of passive-elastic prosthetic feet and footwear can affect walking biomechanics of people with transtibial or transfemoral amputation, characterizing these properties can provide objective metrics for comparison and aid prosthetic foot prescription and design. We characterized axial and torsional stiffness values, and hysteresis of 33 categories and sizes of a commercially available passive-elastic prosthetic foot model [Össur low-profile (LP) Vari-flex] with and without a shoe. We assumed a greater numerical stiffness category would result in greater axial and torsional stiffness values but would not affect hysteresis. We hypothesized that a greater prosthetic foot length would not affect axial stiffness values or hysteresis but would result in greater torsional stiffness values. We also hypothesized that including a shoe would result in decreased axial and torsional stiffness values and greater hysteresis. Prosthetic stiffness was better described by curvilinear than linear equations such that stiffness values increased with greater loads. In general, a greater numerical stiffness category resulted in increased heel, midfoot, and forefoot axial stiffness values, increased plantarflexion and dorsiflexion torsional stiffness values, and decreased heel, midfoot, and forefoot hysteresis. Moreover, for a given category, a longer prosthetic foot size resulted in decreased heel, midfoot, and forefoot axial stiffness values, increased plantarflexion and dorsiflexion torsional stiffness values, and decreased heel and midfoot hysteresis. In addition, adding a shoe to the prosthetic foot resulted in decreased heel and midfoot axial stiffness values, decreased plantarflexion torsional stiffness values, and increased heel, midfoot, and forefoot hysteresis. Our results suggest that manufacturers should adjust the design of each category to ensure the mechanical properties are consistent across different sizes and highlight the need for prosthetists and researchers to consider the effects of shoes in combination with prostheses. Our results can be used to objectively compare the LP Vari-flex prosthetic foot to other prosthetic feet to inform their prescription, design, and use for people with a transtibial or transfemoral amputation.

Retinal neurovascular alteration in type 2 diabetes with renal impairment in association with systemic arterial stiffness

BackgroundDiabetic retinopathy (DR) patients should be alert for subclinical macroangiopathy. We aimed to investigate the association between retinal neurovascular alteration and systemic arterial stiffness in type 2 diabetes mellitus (type 2 DM) patients with varying degrees of renal impairment.MethodsThe study included 170 patients with confirmed diagnosis of type 2 DM aged ≥18 years old. Renal function was assessed by estimated glomerular filtration rate (eGFR). Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV) and ankle brachial index (ABI). Retinal neurovascular parameters were derived from Optical Coherence Tomography (OCT)/OCT-Angiography, represented by vessel density (VD Central, Inner, Outer, Full), foveal avascular zone (FAZ area and FAZ perimeter) of the superficial capillary plexus, the average of macular ganglion cell-inner plexiform layer thickness (ave mGC-IPLt) and the average of retinal nerve fiber layer thickness (aveRNFLt). The association between variables among the groups (according to renal function, diabetic retinopathy (DR) severity, and arterial stiffness categories) were analyzed by regression analysis with multiple hypothesis testing commands.ResultsOut of the 265 eyes, the mean DM duration and HbA1c were 6.21 ± 6.37 years and 8.44 ± 2.06% respectively. While the mean of eGFR, baPWV and ABI were 66.78 ± 32.80 ml/min/1.73m2, 15.49 ± 3.07 m/s, and 1.05 ± 0.12, respectively. Patients with more severe renal impairment demonstrated longer DM duration (p < 0.001), higher baPWV (p < 0.0001), and retinal vascular alteration. Proliverative DR group showed the lowest eGFR (p < 0.0001), highest baPWV (p < 0.0001), and retinal neurovascular changes. Significantly lower eGFR and retinal vascular alteration were found in the baPWV > 14 group. Some neurovascular parameters were significantly negatively correlated with baPWV; moreover, retinal neurovascular changes were also noted in the abnormal ABI group.ConclusionsThe strong association between changes in the retinal neurovascular system, DR severity, renal impairment, and arterial stiffness in type 2 DM was confirmed. Patients with more severe renal impairment had higher levels of arterial stiffness, more severe DR and retinal neurovascular alteration. Retinal neurovascular changes seen in OCT/OCTA might mimic renal microvascular alteration and systemic arterial stiffness. Therefore, assessment of baPWV and OCT/OCTA should be integrated in DR screening to enhance cardiovascular risk stratification and prognosis as well as to provide clinically useful early identification of subclinical micro- and macrovascular alterations.

Structural dependence of concentrated skim milk curd on micellar restructuring

This study was conducted to establish an understanding of how milk concentration modulates the rennet curd structure. Rennet-induced gelation and renneting under slow acidification achieved using glucono-δ-lactone (GDL) and structural properties of reconstituted skim milk gels at two concentration levels (9 and 25 % total solids) were studied by measuring variations in (a) viscoelastic behaviour, (b) micellar size, charge density, diffusivity, and (c) hydrophobicity using dynamic rheometry, dynamic light scattering and fluorimetry, respectively. Concentrated milk showed a greater estimated hydrodynamic radius of casein micelles, lower zeta (ζ)-potential, ratio of serum to total Calcium (Ca) and charge density and increased surface hydrophobicity, all supporting the view that micellar restructuring particularly sub-particle transfer takes place and contributes to rapid gelation. Moreover, hydrophobic interactions occurred very quickly (within 5 min in combined gels, 10 min for renneting only), demonstrating their pivotal role during the flocculation stage. All gels exhibited a solid viscoelastic character as the elastic modulus (G′) was greater than loss modulus (G″) while both G′ and tan δ (G''/G′) were frequency-dependent. Frequency sweeps classified the concentrated gels into three stiffness categories caused by the level of rennet or GDL as rigid, hard and soft, whereas an increased flow-like behaviour (high tan δ), restricted diffusion and excessive water retention revealed limited structural rearrangements (contraction & macrosyneresis) during curd ageing. Acidification increased the diffusion rate in control curd, thus, enhanced contractive rearrangements, macrosyneresis and curd strength. Findings suggest that micellar restructuring induced by milk concentration is the principal modulator of the curd structure.

Spring-mass behavioural adaptations to acute changes in prosthetic blade stiffness during submaximal running in unilateral transtibial prosthesis users

BackgroundIndividuals with lower-limb amputation can use running specific prostheses (RSP) that store and then return elastic energy during stance. However, it is unclear whether varying the stiffness category of the same RSP affects spring-mass behaviour during self-selected, submaximal speed running in individuals with unilateral transtibial amputation. Research questionThe current study investigates how varying RSP stiffness affects limb stiffness, running performance, and associated joint kinetics in individuals with a unilateral transtibial amputation. MethodsKinematic and ground reaction force data were collected from eight males with unilateral transtibial amputation who ran at self-selected submaximal speeds along a 15 m runway in three RSP stiffness conditions; recommended habitual stiffness (HAB) and, following 10-minutes of familiarisation, stiffness categories above (+1) and below (-1) the HAB. Stance-phase centre of mass velocity, contact time, limb stiffness’ and joint/RSP work were computed for each limb across RSP stiffness conditions. ResultsWith increased RSP stiffness, prosthetic limb stiffness increased, whilst intact limb stiffness decreased slightly (p<0.03). Centre of mass forward velocity during stance-phase (p<0.02) and contact time (p<0.04) were higher in the intact limb and lower in the prosthetic limb but were unaffected by RSP stiffness. Intact limb hip joint positive work increased for both the +1 and -1 conditions but remained unchanged across conditions in the prosthetic limb (p<0.02). SignificanceIn response to changes in RSP stiffness, there were acute increased mechanical demands on the intact limb, reflecting a reliance on the intact limb during running. However, overall running speed was unaffected, suggesting participants acutely adapted to an RSP of a non-prescribed stiffness.

Running-specific prosthesis model, stiffness and height affect biomechanics and asymmetry of athletes with unilateral leg amputations across speeds.

Athletes with transtibial amputation (TTA) use running-specific prostheses (RSPs) to run. RSP configuration likely affects the biomechanics of such athletes across speeds. We determined how the use of three RSP models (Catapult, Sprinter and Xtend) with three stiffness categories (recommended, ±1), and three heights (recommended, ±2 cm) affected contact length (Lc), stance average vertical ground reaction force (Favg), step frequency (fstep) and asymmetry between legs for 10 athletes with unilateral TTA at 3–7 m s−1. The use of the Xtend versus Catapult RSP decreased Lc (p = 2.69 × 10−7) and Favg asymmetry (p = 0.032); the effect on Lc asymmetry diminished with faster speeds (p = 0.0020). The use of the Sprinter versus Catapult RSP decreased Favg asymmetry (p = 7.00 × 10−5); this effect was independent of speed (p = 0.90). The use of a stiffer RSP decreased Lc asymmetry (p ≤ 0.00033); this effect was independent of speed (p ≥ 0.071). The use of a shorter RSP decreased Lc (p = 5.86 × 10−6), Favg (p = 8.58 × 10−6) and fstep asymmetry (p = 0.0011); each effect was independent of speed (p ≥ 0.15). To minimize asymmetry, athletes with unilateral TTA should use an Xtend or Sprinter RSP with 2 cm shorter than recommended height and stiffness based on intended speed.

Prosthetic forefoot and heel stiffness across consecutive foot stiffness categories and sizes.

Prosthetic foot stiffness plays a key role in the functional mobility of lower limb prosthesis users. However, limited objective data exists to guide selection of the optimal prosthetic foot stiffness category for a given individual. Clinicians often must rely solely on manufacturer recommendations, which are typically based on the intended user's weight and general activity level. Availability of comparable forefoot and heel stiffness data would allow for a better understanding of differences between different commercial prosthetic feet, and also between feet of different stiffness categories and foot sizes. Therefore, this study compared forefoot and heel linear stiffness properties across manufacturer-designated stiffness categories and foot sizes. Mechanical testing was completed for five types of commercial prosthetic feet across a range of stiffness categories and three foot-sizes. Data were collected for 56 prosthetic feet, in total. Testing at two discrete angles was conducted to isolate loading of the heel and forefoot components, respectively. Each prosthetic foot was loaded for six cycles while force and displacement data were collected. Forefoot and heel measured stiffness were both significantly associated with stiffness category (p = .001). There was no evidence that the relationships between stiffness category and measured stiffness differed by foot size (stiffness category by size interaction p = .80). However, there were inconsistencies between the expected and measured stiffness changes across stiffness categories (i.e., magnitude of stiffness changes varied substantially between consecutive stiffness categories of the same feet). While statistical results support that, on average, measured stiffness is positively correlated with stiffness category, force-displacement data suggest substantial variation in measured stiffness across consecutive categories. Published objective mechanical property data for commercial prosthetic feet would likely therefore be helpful to clinicians during prescription.

Characterizing the Mechanical Stiffness of Passive-Dynamic Ankle-Foot Orthosis Struts.

People with lower limb impairment can participate in activities such as running with the use of a passive-dynamic ankle-foot orthosis (PD-AFO). Specifically, the Intrepid Dynamic Exoskeletal Orthosis (IDEO) is a PD-AFO design that includes a carbon-fiber strut, which attaches posteriorly to a custom-fabricated tibial cuff and foot plate and acts in parallel with the impaired biological ankle joint to control sagittal and mediolateral motion, while allowing elastic energy storage and return during the stance phase of running. The strut stiffness affects the extent to which the orthosis keeps the impaired biological ankle in a neutral position by controling sagittal and mediolateral motion. The struts are currently manufactured to a thickness that corresponds with one of five stiffness categories (1 = least stiff, 5 = most stiff) and are prescribed to patients based on their body mass and activity level. However, the stiffness values of IDEO carbon-fiber struts have not been systematically determined, and these values can inform dynamic function and biomimetic PD-AFO prescription and design. The PD-AFO strut primarily deflects in the anterior direction (ankle dorsiflexion), and resists deflection in the posterior direction (ankle plantarflexion) during the stance phase of running. Thus, we constructed a custom apparatus and measured strut stiffness for 0.18 radians (10°) of anterior deflection and 0.09 radians (5°) of posterior deflection. We measured the applied moment and strut deflection to compute angular stiffness, the quotient of moment and angle. The strut moment-angle curves for anterior and posterior deflection were well characterized by a linear relationship. The strut stiffness values for categories 1–5 at 0.18 radians (10°) of anterior deflection were 0.73–1.74 kN·m/rad and at 0.09 radians (5°) of posterior deflection were 0.86–2.73 kN·m/rad. Since a PD-AFO strut acts in parallel with the impaired biological ankle, the strut and impaired biological ankle angular stiffness sum to equal total stiffness. Thus, strut stiffness directly affects total ankle joint stiffness, which in turn affects ankle motion and energy storage and return during running. Future research is planned to better understand how use of a running-specific PD-AFO with different strut stiffness affects the biomechanics and metabolic costs of running in people with lower limb impairment.

Effects on prosthetic foot ankle power on transfemoral amputee gait

Prosthetic feet are available in a range of stiffness categories, however, there is limited evidence to guide optimal selection during prosthetic foot prescription. The aim of this study was to determine the effect of commercial prosthetic foot stiffness category on foot-ankle biomechanics, gait symmetry, community ambulation, and relative foot stiffness perception.Participants were fit in randomized order with three consecutive stiffness categories of a commonly-prescribed prosthetic foot. Prosthetic foot roll-over shape and ankle push-off power and work were determined via data collected during walking in a motion analysis laboratory. Step activity was recorded during community use of each foot. Self-reported perception of relative foot stiffness was assessed with an ad hoc survey.Seventeen males with transtibial amputation completed the study. Prosthetic foot roll-over radius increased with increased prosthetic foot stiffness categories (p < 0.001). Both prosthetic ankle push-off peak power and work decreased with increased foot stiffness categories (p = 0.002). There was no association between prosthetic foot stiffness category and step length symmetry or steps per day. When assessed post-accommodation, there was no association between relative foot stiffness perception and the stiffness category across prosthetic foot conditions.Prosthetic foot stiffness category was significantly associated with changes in prosthetic foot-ankle biomechanical variables, however, was not associated with changes in gait symmetry or community ambulation. Relative prosthetic foot stiffness perception after accommodation was generally inconsistent with the order of prosthetic foot stiffness categories.While there were quantifiable differences in prosthetic foot-ankle biomechanics across stiffness categories, no significant differences were detected in gait symmetry or mean daily step count in the community. Furthermore, after community use, participants perceptions of relative stiffness across feet were generally inconsistent with the order of prosthetic foot stiffness categories. These findings raise questions as to whether changes in commercial prosthetic foot stiffness category (within a clinically relevant range) affect subjective and objective measures relevant to successful outcomes from prosthetic foot prescription.

The effect of prosthetic foot stiffness on foot-ankle biomechanics and relative foot stiffness perception in people with transtibial amputation

BackgroundProsthetic feet are available in a range of stiffness categories, however, there is limited evidence to guide optimal selection during prosthetic foot prescription. The aim of this study was to determine the effect of commercial prosthetic foot stiffness category on foot-ankle biomechanics, gait symmetry, community ambulation, and relative foot stiffness perception. MethodsParticipants were fit in randomized order with three consecutive stiffness categories of a commonly-prescribed prosthetic foot. Prosthetic foot roll-over shape and ankle push-off power and work were determined via data collected during walking in a motion analysis laboratory. Step activity was recorded during community use of each foot. Self-reported perception of relative foot stiffness was assessed with an ad hoc survey. FindingsSeventeen males with transtibial amputation completed the study. Prosthetic foot roll-over radius increased with increased prosthetic foot stiffness categories (p < 0.001). Both prosthetic ankle push-off peak power and work decreased with increased foot stiffness categories (p = 0.002). There was no association between prosthetic foot stiffness category and step length symmetry or steps per day. When assessed post-accommodation, there was no association between relative foot stiffness perception and the stiffness category across prosthetic foot conditions. InterpretationProsthetic foot stiffness category was significantly associated with changes in prosthetic foot-ankle biomechanical variables, however, was not associated with changes in gait symmetry or community ambulation. Relative prosthetic foot stiffness perception after accommodation was generally inconsistent with the order of prosthetic foot stiffness categories. Clinical relevanceWhile there were quantifiable differences in prosthetic foot-ankle biomechanics across stiffness categories, no significant differences were detected in gait symmetry or mean daily step count in the community. Furthermore, after community use, participants perceptions of relative stiffness across feet were generally inconsistent with the order of prosthetic foot stiffness categories. These findings raise questions as to whether changes in commercial prosthetic foot stiffness category (within a clinically relevant range) affect subjective and objective measures relevant to successful outcomes from prosthetic foot prescription.

Prosthetic shape, but not stiffness or height, affects the maximum speed of sprinters with bilateral transtibial amputations.

Running-specific prostheses (RSPs) have facilitated an athlete with bilateral transtibial amputations to compete in the Olympic Games. However, the performance effects of using RSPs compared to biological legs remains controversial. Further, the use of different prosthetic configurations such as shape, stiffness, and height likely influence performance. We determined the effects of using 15 different RSP configurations on the maximum speed of five male athletes with bilateral transtibial amputations. These athletes performed sets of running trials up to maximum speed using three different RSP models (Freedom Innovations Catapult FX6, Össur Flex-Foot Cheetah Xtend and Ottobock 1E90 Sprinter) each with five combinations of stiffness category and height. We measured ground reaction forces during each maximum speed trial to determine the biomechanical parameters associated with different RSP configurations and maximum sprinting speeds. Use of the J-shaped Cheetah Xtend and 1E90 Sprinter RSPs resulted in 8.3% and 8.0% (p<0.001) faster maximum speeds compared to the use of the C-shaped Catapult FX6 RSPs, respectively. Neither RSP stiffness expressed as a category (p = 0.836) nor as kN·m-1 (p = 0.916) affected maximum speed. Further, prosthetic height had no effect on maximum speed (p = 0.762). Faster maximum speeds were associated with reduced ground contact time, aerial time, and overall leg stiffness, as well as with greater stance-average vertical ground reaction force, contact length, and vertical stiffness (p = 0.015 for aerial time, p<0.001 for all other variables). RSP shape, but not stiffness or height, influences the maximum speed of athletes with bilateral transtibial amputations.

Prosthetic model, but not stiffness or height, affects maximum running velocity in athletes with unilateral transtibial amputations

The running-specific prosthetic (RSP) configuration used by athletes with transtibial amputations (TTAs) likely affects performance. Athletes with unilateral TTAs are prescribed C- or J-shaped RSPs with a manufacturer-recommended stiffness category based on body mass and activity level, and height based on unaffected leg and residual limb length. We determined how 15 different RSP model, stiffness, and height configurations affect maximum running velocity (vmax) and the underlying biomechanics. Ten athletes with unilateral TTAs ran at 3 m/s to vmax on a force-measuring treadmill. vmax was 3.8–10.7% faster when athletes used J-shaped versus C-shaped RSP models (p < 0.05), but was not affected by stiffness category, actual stiffness (kN/m), or height (p = 0.72, p = 0.37, and p = 0.11, respectively). vmax differences were explained by vertical ground reaction forces (vGRFs), stride kinematics, leg stiffness, and symmetry. While controlling for velocity, use of J-shaped versus C-shaped RSPs resulted in greater stance average vGRFs, slower step frequencies, and longer step lengths (p < 0.05). Stance average vGRFs were less asymmetric using J-shaped versus C-shaped RSPs (p < 0.05). Contact time and leg stiffness were more asymmetric using the RSP model that elicited the fastest vmax (p < 0.05). Thus, RSP geometry (J-shape versus C-shape), but not stiffness or height, affects vmax in athletes with unilateral TTAs.

Stiffness and energy storage characteristics of energy storage and return prosthetic feet.

Mechanical properties of prosthetic feet can significantly influence amputee gait, but how they vary with respect to limb loading and orientation is infrequently reported. The objective of this study is to measure stiffness and energy storage characteristics of prosthetic feet across limb loading and a range of orientations experienced in typical gait. This study included mechanical testing. Force-displacement data were collected at combinations of 15 sagittal and 5 coronal orientations and used to calculate stiffness and energy storage across prosthetic feet, stiffness categories, and heel wedge conditions. Stiffness and energy storage were highly non-linear in both the sagittal and coronal planes. Across all prosthetic feet, stiffness decreased with greater heel, forefoot, medial, and lateral orientations, while energy storage increased with forefoot, medial, and lateral loading orientations. Stiffness category was proportional to stiffness and inversely proportional to energy storage. Heel wedge effects were prosthetic foot dependent. Orientation, manufacturer, stiffness category, and heel wedge inclusion greatly influenced stiffness and energy storage characteristics. These results and an available graphical user interface tool may help improve clinical prescriptions by providing prosthetists with quantitative measures to compare prosthetic feet.

Dynamic characterisation of Össur Flex-Run prosthetic feet for a more informed prescription.

The current method of prescribing composite running-specific energy-storing-and-returning feet is subjective and is based only on the amputee's static body weight/mass. The aim was to investigate their dynamic characteristics and create a relationship between these dynamic data and the prescription of foot. Experimental Assessment. This article presents the modal analysis results of the full range of Össur Flex-Run™ running feet that are commercially available (1LO-9LO) using experimental modal analysis technique under a constant mass at 53 kg and boundary condition. It was shown that both the undamped natural frequency and stiffness increase linearly from the lowest to the highest stiffness category of foot which allows for a more informed prescription of foot when tuning to a matched natural frequency. The low damping characteristics determined experimentally that ranged between 1.5% and 2.0% indicates that the feet require less input energy to maintain the steady-state cyclic motion before take-off from the ground. An analysis of the mode shapes also showed a unique design feature of these feet that is hypothesised to enhance their performance. A better understanding of dynamic characteristics of the feet can help tune the feet to the user's requirements in promoting a better gait performance. The dynamic data determined from this study are needed to better inform the amputees in predicting the natural frequency of the foot prescribed. The amputees can intuitively tune the cyclic body rhythm during walking or running to match with the natural frequency. This could eventually promote a better gait performance.

Factors influencing the production of structural plywood in Tasmania, Australia from Eucalyptus nitens rotary peeled veneer

Harvested logs supplied from five fibre-managed Eucalyptus nitens plantation coupes with different growing environments were assessed for quality and stiffness. Billets extracted from the logs were rotary peeled for veneer. When averaged across the five coupes, 30% of veneer recovered could be used directly in structural plywood production and an additional 20–25% could be used after further processing. In visual assessment most veneer was assigned an Australian/New Zealand Standard AS/NZS2269.0:2012 Quality D. Acoustic testing during processing showed veneer peeled from a drier and lower elevation coupe had significantly higher dynamic MOE values than veneer processed from logs harvested from wetter higher elevation coupes. To examine the utility of the E. nitens peeled veneer in the production of structural plywood, it was combined with veneer of a known higher stiffness, rotary peeled from regrowth forest Tasmanian oak species logs. Structural seven-ply panels were manufactured from the veneer prepared in three different ply arrangements. Mechanical testing of the panels in accordance with AS/NZS2269.0:2012 showed that an F17 target stress-grade panel product of 83% E. nitens and 17% Tasmanian oak species could be produced, if E. nitens veneer of higher stiffness were selected from veneer segregated by estimated dynamic Modulus of Elasticity value. Panels with 50% E. nitens and 50% Tasmanian oak veneer could be produced by selecting E. nitens veneer of lower stiffness after segregation. In the majority of panels tested stress-grade rating was limited by perpendicular bending strength. Outcomes from the study indicate that structural plywood can be manufactured using differing proportions of E. nitens veneer, rotary peeled from fibre-managed plantations, provided it can be segregated into stiffness categories and selected to achieve a target stress-grade.

Prosthetic model, but not stiffness or height, affects the metabolic cost of running for athletes with unilateral transtibial amputations.

Running-specific prostheses enable athletes with lower limb amputations to run by emulating the spring-like function of biological legs. Current prosthetic stiffness and height recommendations aim to mitigate kinematic asymmetries for athletes with unilateral transtibial amputations. However, it is unclear how different prosthetic configurations influence the biomechanics and metabolic cost of running. Consequently, we investigated how prosthetic model, stiffness, and height affect the biomechanics and metabolic cost of running. Ten athletes with unilateral transtibial amputations each performed 15 running trials at 2.5 or 3.0 m/s while we measured ground reaction forces and metabolic rates. Athletes ran using three different prosthetic models with five different stiffness category and height combinations per model. Use of an Ottobock 1E90 Sprinter prosthesis reduced metabolic cost by 4.3 and 3.4% compared with use of Freedom Innovations Catapult [fixed effect (β) = -0.177; P < 0.001] and Össur Flex-Run (β = -0.139; P = 0.002) prostheses, respectively. Neither prosthetic stiffness (P ≥ 0.180) nor height (P = 0.062) affected the metabolic cost of running. The metabolic cost of running was related to lower peak (β = 0.649; P = 0.001) and stance average (β = 0.772; P = 0.018) vertical ground reaction forces, prolonged ground contact times (β = -4.349; P = 0.012), and decreased leg stiffness (β = 0.071; P < 0.001) averaged from both legs. Metabolic cost was reduced with more symmetric peak vertical ground reaction forces (β = 0.007; P = 0.003) but was unrelated to stride kinematic symmetry (P ≥ 0.636). Therefore, prosthetic recommendations based on symmetric stride kinematics do not necessarily minimize the metabolic cost of running. Instead, an optimal prosthetic model, which improves overall biomechanics, minimizes the metabolic cost of running for athletes with unilateral transtibial amputations.NEW & NOTEWORTHY The metabolic cost of running for athletes with unilateral transtibial amputations depends on prosthetic model and is associated with lower peak and stance average vertical ground reaction forces, longer contact times, and reduced leg stiffness. Metabolic cost is unrelated to prosthetic stiffness, height, and stride kinematic symmetry. Unlike nonamputees who decrease leg stiffness with increased in-series surface stiffness, biological limb stiffness for athletes with unilateral transtibial amputations is positively correlated with increased in-series (prosthetic) stiffness.