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 of changing Prosthetic Foot Stiffness on 3D Hip Angles in Toddlers with versus without Unilateral Transtibial Amputations

Background: Pediatric prosthetists and physical therapists have observed that use of prosthetic feet with different stiffnesses affects external hip rotation during walking in toddlers with unilateral transtibial amputations (TTAs). A protocol for prescribing pediatric prosthetic feet is needed to minimize injury from improper biomechanics. Methods: 12 toddlers participated in this study (9 non-amputee, 3 with a TTA). Three custom passive prosthetic feet were made for each toddler with a TTA. Kinetic and kinematic data was at 0.50 m/s. Peak hip joint angles and range of motion were determined in the sagittal, frontal, and transverse planes. Results: The data suggest that use of a prosthetic foot more stiff than recommended most closely resembles non-amputee transverse hip angles throughout a stride. The recommended stiffness prosthetic foot led to a trend of greater peak hip external rotation compared to the non-amputee toddlers. Toddlers with a TTA exhibit a trend of greater peak hip joint flexion compared to non-amputee toddlers. There was no change in range of motion or symmetry with the varying stiffness prosthetic feet or between toddlers with a TTA and non-amputee toddlers. Discussion: Our results suggest that prosthetic foot stiffness does not affect frontal or sagittal plane hip joint angles, but does affect transverse plane hip joint angles. Future research is needed to determine the ideal degree of hip external rotation to inform prosthetic foot design and minimize long-term functional deficits in toddlers with a TTA

FRONTAL PLANE TAKE-OFF STEP MECHANICS OF LONG JUMPERS WITH AND WITHOUT A BELOW THE KNEE AMPUTATION

Frontal plane mechanics during the long jump take-off step are unknown for athletes with and without a transtibial amputation. This is an issue due to the importance of the knowledge for training and rehabilitation protocols or prosthetic design. In this study the take-off step of three long jumpers with and seven without a below the knee amputation (BKA) were analysed with regard to frontal plane mechanics. Three-dimensional motion capture (Vicon) and a force plate (Kistler) were used to capture kinematic and kinetic data. Inverse dynamic calculations (Dynamicus, Alaska) revealed differences in frontal plane center of mass kinematics and joint kinetics between groups. Specifically, athletes with BKA had lower medio-lateral ground reaction forces, lower frontal plane joint loads and an altered foot position pattern compared to non-amputee athletes

LONG JUMP MECHANICS – OLYMPIC VERSUS PARALYMPIC CHAMPION

In the last 20 years the long jump world record of athletes with an amputation of the lower extremities has improved by over two meters. However, there is no recent research on amputee long jumping and no information about amputee long jump kinetics. In this study the take-off step of an Olympic and a Paralympic champion were analyzed with regard to jumping mechanics. A 3D motion capturing system (Vicon) and a force plate (Kistler) were used to capture kinematic and kinetic data. Inverse dynamic calculations (Dynamicus, Alaska) revealed remarkable differences with respect to mechanical loading and motor solutions between the transtibial amputee and non-amputee long jumper. Mechanical constraints and material properties of the prosthesis might influence the kinematic chain of the amputee athlete and impose the need for an alternative motor solution

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, &plusmn;1), and three heights (recommended, &plusmn;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&ndash;7 m s&minus;1. The use of the Xtend versus Catapult RSP decreased Lc (p = 2.69 &times; 10&minus;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 &times; 10&minus;5); this effect was independent of speed (p = 0.90). The use of a stiffer RSP decreased Lc asymmetry (p &le; 0.00033); this effect was independent of speed (p &ge; 0.071). The use of a shorter RSP decreased Lc (p = 5.86 &times; 10&minus;6), Favg (p = 8.58 &times; 10&minus;6) and fstep asymmetry (p = 0.0011); each effect was independent of speed (p &ge; 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. &nbsp;</p

Locomotor adaptability in persons with unilateral transtibial amputation

Background Locomotor adaptation enables walkers to modify strategies when faced with challenging walking conditions. While a variety of neurological injuries can impair locomotor adaptability, the effect of a lower extremity amputation on adaptability is poorly understood. Objective Determine if locomotor adaptability is impaired in persons with unilateral transtibial amputation (TTA). Methods The locomotor adaptability of 10 persons with a TTA and 8 persons without an amputation was tested while walking on a split-belt treadmill with the parallel belts running at the same (tied) or different (split) speeds. In the split condition, participants walked for 15 minutes with the respective belts moving at 0.5 m/s and 1.5 m/s. Temporal spatial symmetry measures were used to evaluate reactive accommodations to the perturbation, and the adaptive/de-adaptive response. Results Persons with TTA and the reference group of persons without amputation both demonstrated highly symmetric walking at baseline. During the split adaptation and tied post-adaptation walking both groups responded with the expected reactive accommodations. Likewise, adaptive and de-adaptive responses were observed. The magnitude and rate of change in the adaptive and de-adaptive responses were similar for persons with TTA and those without an amputation. Furthermore, adaptability was no different based on belt assignment for the prosthetic limb during split adaptation walking. Conclusions Reactive changes and locomotor adaptation in response to a challenging and novel walking condition were similar in persons with TTA to those without an amputation. Results suggest persons with TTA have the capacity to modify locomotor strategies to meet the demands of most walking conditions despite challenges imposed by an amputation and use of a prosthetic limb

Depredation influences anglers’ perceptions on coastal shark management and conservation in the United States Gulf of Mexico

Overfishing, habitat degradation, and climate change have caused declines in shark populations throughout the world’s oceans. However, in the United States Gulf of Mexico (GoM), populations of several coastal shark species are starting to stabilize following decades of successful regulations and enforcement. The stabilization of coastal shark populations, coupled with increases in recreational fishing effort, has the potential to escalate human-wildlife interactions. The most often reported conflict is shark depredation, the partial or complete removal of a hooked species by a shark. Reported increases in shark depredation within the last several years have begun to erode angler support for shark conservation, potentially undermining decades of previous work. To address these concerns, we implemented a GoM-wide online survey to characterize the impact of depredation on recreational reef fish anglers’ fishing satisfaction and perceptions of shark management and conservation. Our results revealed that most recreational anglers in the GoM have witnessed depredation but have not changed their fishing behaviors. In contrast, anglers’ viewpoints on managing shark populations were split between reducing population sizes and maintaining current population levels. As coastal shark populations in the GoM continue to recover, shark depredation is likely to increase. Consequently, efforts to characterize anglers’ satisfaction and perceptions are a critical component of future shark conservation initiatives

Individual Leg and Joint Work during Sloped Walking for People with a Transtibial Amputation Using Passive and Powered Prostheses

People with a transtibial amputation using passive-elastic prostheses exhibit reduced prosthetic ankle power and push-off work compared to non-amputees and compensate by increasing their affected leg (AL) hip joint work and unaffected leg (UL) ankle, knee, and hip joint and leg work during level-ground walking. Use of a powered ankle–foot prosthesis normalizes step-to-step transition work during level-ground walking over a range of speeds for people with a transtibial amputation, but the effects on joint work during level-ground, uphill, and downhill walking have not been assessed. We investigated how use of passive-elastic and powered ankle–foot prostheses affect leg joint biomechanics during level-ground and sloped walking. 10 people with a unilateral transtibial amputation walked at 1.25 m/s on a dual-belt force-measuring treadmill at 0°, ±3°, ±6°, and ±9° using their own passive-elastic and a powered prosthesis (BiOM T2, BionX Medical Technologies, Inc., Bedford, MA, USA) while we measured kinematic and kinetic data. We calculated AL and UL prosthetic, ankle, knee, hip, and individual leg positive, negative, and net work. Use of a powered compared to passive-elastic ankle–foot prosthesis resulted in greater AL prosthetic and individual leg net work on uphill and downhill slopes. Over a stride, AL prosthetic positive work was 23–30% greater (p &lt; 0.05) during walking on uphill slopes of +6°, and +9°, prosthetic net work was up to 10 times greater (more positive) (p ≤ 0.005) on all uphill and downhill slopes and individual leg net work was 146 and 82% more positive (p &lt; 0.05) at uphill slopes of +6° and +9°, respectively, with use of the powered compared to passive-elastic prosthesis. Greater prosthetic positive and net work through use of a powered ankle–foot prosthesis during uphill and downhill walking improves mechanical work symmetry between the legs, which could decrease metabolic cost and improve functional mobility in people with a transtibial amputation