Cross slope gait biomechanics for individuals with and without a unilateral transtibial amputation.

BACKGROUND: This research was conducted to better understand compensatory strategies during cross-slope walking for adults with and without a unilateral transtibial amputation. METHODS: Fourteen individuals with unilateral transtibial amputation and 14 individuals with no lower limb amputation participated in this study. Motion and force data were captured while participants walked on a treadmill in a virtual reality environment for level and ± 5° cross slopes. Temporal-spatial parameters, kinematics (ankle, knee, hip, pelvis, trunk), and ground reaction forces were examined. FINDINGS: Compared to level, participants had similar step width but slightly longer steps for top-cross-slope and slightly shorter steps for bottom-cross-slope. Top-cross-slope required a more flexed limb with ankle eversion, and bottom-cross-slope required a more extended limb with ankle inversion. Participants had similar lateral pelvis and trunk motion for all walking conditions, but slightly more anterior trunk lean for top cross-slope with more anterior trunk lean observed for individuals with a lower limb amputation than without lower limb amputation. Participants with a lower limb amputation compensated for limited prosthetic ankle-foot dorsiflexion on the top-cross-slope by increasing prosthetic side hip flexion, reducing intact ankle/knee flexion, and increasing intact push-off force. INTERPRETATION: Gait adaptations during cross-slope walking were primarily in the lower extremities and were largely similar for those with and without a transtibial amputation. The information presented in this paper provides a better understanding of gait strategies adopted during cross-slope walking and can guide researchers and industry in prosthetic development.

Maintaining stable transtibial amputee gait on level and simulated uneven conditions in a virtual environment.

PURPOSE: This research compares gait strategies to maintain stable gait over a variety of non-level walking conditions for individuals with a transtibial amputation and able-bodied individuals. METHODS: Twelve people with unilateral transtibial amputation and twelve able-bodied individuals walked on a self-paced treadmill in a park-like virtual environment with level and continuous perturbation conditions. Walking stability was quantified by margin-of-stability, step parameters (walking speed, temporal and spatial parameters, and foot clearance), and gait variability (standard deviations for margin-of-stability, step parameters, and root-mean-square of trunk acceleration). RESULTS AND CONCLUSIONS: For non-level conditions, able-bodied and transtibial groups had greater root-mean-square of trunk acceleration and walked with a cautious and variable step strategy by changing speed, step width, foot clearance, margin-of-stability, and increasing step variability. Overall, able-bodied and transtibial amputee participants adopted similar strategies to maintain stable gait over non-level conditions, but the amputee group was more variable than the able-bodied group. These results demonstrated the importance of measuring gait variability, including trunk acceleration and step variability measures, when quantitatively assessing mobility for individuals with a transtibial amputation. Implications for rehabilitation Able-bodied and transtibial amputee groups adapted gait biomechanics for simulated uneven conditions. Adaptations for non-level conditions included increasing step width, margin-of stability, minimum foot clearance, and varying speed. Gait was also more variable for non-level conditions, with greater variability for transtibial amputee participants compared to able-bodied participants. These results highlight the importance of measuring variability when performing comprehensive walking assessment, particularly for active individuals who achieve maximal performance on standard assessments yet report functional limitations in daily living.

The effect of surface inclination and limb on knee loading measures in transtibial prosthesis users.

BACKGROUND: Osteoarthritis (OA) is a degenerative disease caused by the wearing of joint cartilage and bone. Literature has established that a prosthesis user's intact limb is at greater risk of developing OA. This study analyzed the effect of commonly encountered surface inclinations on knee joint loading measures in able-bodied and transtibial prosthesis users. METHODS: 12 transtibial prosthesis users and 12 able-bodied participants walked across level ground, up slope, down slope, and cross slope (further divided into top and bottom slope depending on the location of the limb being analyzed). First and second peak external knee adduction moment (KAM), external knee adduction moment rate, and external knee adduction moment impulse were extracted from the stance phase of gait. Mixed ANOVA statistics with Bonferonni post hoc analyses were performed. RESULTS: Significant limb differences were only found for KAM rate and first peak KAM. When compared to all other surfaces up slope had the significantly lowest KAM rate and was not significantly lower for all other tested variables. Down slope had significantly greater KAM rate than all surfaces except bottom slope. KAM second peak and KAM impulse analysis resulted in no significant differences. CONCLUSIONS: Individuals at risk for developing, or currently dealing with, knee OA could avoid walking for extended periods on down slope. Walking up moderate slopes may be considered as a complementary activity to level walking for rehabilitation and delaying OA progression. The lack of significant limb differences suggests that second peak KAM and KAM impulse may not be appropriate load-related indicators of OA initiation among prosthesis users without OA. KAM rate was the most sensitive joint loading variable and therefore should be investigated further as an appropriate variable for identifying OA risk in individuals with transtibial amputations.

Maintaining stable transfemoral amputee gait on level, sloped and simulated uneven conditions in a virtual environment.

PURPOSE: Describe and quantify how people with transfemoral amputations (TFA) maintain stable gait over a variety of surfaces; including, downhill and uphill, top and bottom-cross-slopes, medial-lateral translations, rolling hills and simulated rocky surfaces. METHODS: Ten TFA and ten matched people without amputations (NA) walked in a virtual environment with level, sloped and simulated uneven surfaces on a self-paced treadmill. Stability was quantified using medial-lateral margin of stability (ML-MoS), step parameters, and gait variability (standard deviations for speed, temporal-spatial parameters, foot clearance and root-mean-square of medial-lateral trunk acceleration). RESULTS AND CONCLUSIONS: TFA and NA adapted to non-level conditions by changing their walking speed, step width, and foot clearance. Variability for most parameters increased across conditions, compared to level. TFA walked slower than NA with shorter, wider and longer duration steps (most differences related to speed). ML-MoS did not change compared to level; however, ML-MoS was greater on the prosthetic side than both intact side and NA limbs. Foot clearance and root-mean-square of medial-lateral trunk acceleration were greater on the prosthetic side than the intact side and NA limbs. This research provides a comprehensive analysis of the different adaptations made by people without amputations compared to people with transfemoral amputations over non-level conditions and establishes significant differences between slopes and simulated uneven surfaces for TFA. Implications for Rehabilitation Transfemoral amputation and no amputation groups adapted walking biomechanics when traversing non-level surfaces. Greatest temporal-spatial gait adaptations were walking speed, step width and foot clearance. Gait parameter variability typically increased from the level condition in both groups. Transfemoral amputation group walked slower than no amputation group with shorter, wider steps and longer duration steps. This was related to speed. Transfemoral amputation group had more trunk motion variability on the prosthetic side than no amputation group; could be related to prosthetic fit.

Transtibial amputee gait during slope walking with the unity suspension system.

BACKGROUND: People with lower limb amputation may experience walking limitations on slopes because of missing musculoskeletal and neuromuscular systems. Elevated vacuum suspension could benefit transtibial amputee gait for slope walking, but research is lacking to inform clinical practice. METHODS: Twelve people with unilateral transtibial amputation were fitted with the Unity elevated vacuum suspension system (Össur) and Pro-Flex XC foot. 3D motion analysis was performed for 7° incline, 7° decline, and level walking within a CAREN-Extended system virtual Park environment. Randomized and blinded walking trials were completed with the vacuum active or inactive. RESULTS: Statistically significant differences (p < 0.05) were found between vacuum conditions when walking uphill or downhill for temporal spatial, kinematic, and kinetic gait parameters; however, effect sizes were small (r≤0.35). Prosthetic step length decreased for both vacuum conditions on downhill compared to uphill walking. Symmetry index was <10% for step length, step time, and stance time for both vacuum condition during downhill walking, indicating acceptable symmetry. During incline walking, step length was only symmetrical with active vacuum. Knee range of motion was not restricted, for both conditions. CONCLUSION: Active vacuum improved gait symmetry for incline walking, but the other differences between vacuum conditions were small and may not be clinically significant. Therefore, the Unity system approach for elevated vacuum suspension had a positive, but small, effect on walking and should maintain appropriate walking even with vacuum failure, until limb volume changes adversely affect socket fit (i.e., elevated vacuum helps control limb volume fluctuations over time).

Gait differences between K3 and K4 persons with transfemoral amputation across level and non-level walking conditions.

BACKGROUND:: A transfemoral amputee's functional level can be classified from K-level 0 (lowest) to K-level 4 (highest). Knowledge of the biomechanical differences between K3 and K4 transfemoral amputation could help inform clinical professionals and researchers in amputee care and gait assessment. OBJECTIVES:: Explore gait differences between K3- and K4-level transfemoral amputation across different surface conditions. STUDY DESIGN:: Cross-sectional study. METHODS:: Four K3 and six K4 transfemoral amputation and 10 matched able-bodied individuals walked in a virtual environment with simulated level and non-level surfaces on a self-paced treadmill. Stability measures included medial-lateral margin of stability, step parameters, and gait variability (standard deviations for speed, temporal-spatial parameters, root-mean-square of medial-lateral trunk acceleration). RESULTS:: K3 walked slower than K4 with wider steps, greater root-mean-square of medial-lateral trunk acceleration, and greater medial-lateral margin of stability standard deviations, indicating their stability was further challenged. K3 participants had greater asymmetry in double support time and trunk acceleration root-mean-square in the medial-lateral direction, but similar asymmetry overall. K3 participants had larger differences from AB and in more parameters than K4, although K4 differed from AB in trunk acceleration root-mean-square in the medial-lateral direction, walking speed, and double support time standard deviations. CONCLUSION:: The findings improve our understanding of K3 and K4 transfemoral amputation gait on slopes and simulated uneven surfaces. CLINICAL RELEVANCE: High performing and community ambulatory transfemoral amputees cannot match the ambulatory abilities of ablebodied individuals. Understanding gait differences between these groups under conditions that challenge balance is required to develop rehabilitation protocols and prosthetic componentry targeted at improving transfemoral amputee gait and overall mobility in their chosen environment.

Effects of the unity vacuum suspension system on transtibial gait for simulated non-level surfaces.

Walking on various surfaces encountered in everyday life requires lower limb prosthesis users to continually adapt their movement patterns. Elevated vacuum suspension systems could improve transtibial amputee gait on non-level surfaces; however, research is lacking to guide clinical practice. Twelve transtibial amputees were fitted with the Össur sleeveless vacuum suspension system (Unity). After a one month accommodation period, the CAREN-Extended system was used to evaluate gait on a self-paced treadmill when walking with continuous perturbations (medial-lateral translations, rolling hills, simulated uneven ground) with an active or inactive vacuum suspension system. Significant differences between active and inactive vacuum conditions (p<0.05) were found for some temporal-spatial and kinematic gait parameters, but the differences were small and not considered clinically significant. Our findings suggest that potential vacuum pump failures would not immediately affect gait performance in a moderately high functioning amputee population. However, residual limb volume changes over time due to the removal of elevated vacuum may adversely affect socket fit, leading to greater gait differences and reduced quality of life.

Center of pressure and total force analyses for amputees walking with a backpack load over four surfaces.

Understanding how load carriage affects walking is important for people with a lower extremity amputation who may use different strategies to accommodate to the additional weight. Nine unilateral traumatic transtibial amputees (K4-level) walked over four surfaces (level-ground, uneven ground, incline, decline) with and without a 24.5 kg backpack. Center of pressure (COP) and total force were analyzed from F-Scan insole pressure sensor data. COP parameters were greater on the intact limb than on the prosthetic limb, which was likely a compensation for the loss of ankle control. Double support time (DST) was greater when walking with a backpack. Although longer DST is often considered a strategy to enhance stability and/or reduce loading forces, changes in DST were only moderately correlated with changes in peak force. High functioning transtibial amputees were able to accommodate to a standard backpack load and to maintain COP progression, even when walking over different surfaces.

Evaluation of motion platform embedded with dual belt treadmill instrumented with two force plates.

Motek Medical's Computer Aided Rehabilitation Environment (CAREN)-Extended system is a virtual environment primarily used in physical rehabilitation and biomechanical research. This virtual environment consists of a 180 degree projection screen used to display a virtual scene, a 12-camera motion capture system, and a six degree of freedom actuated platform equipped with a dual-belt treadmill and two force plates. The goal of this article was to investigate the performance characteristics associated with a "treadmill-motion platform" configuration and how system operation can affect the data collected. Platform static and dynamic characteristics were evaluated by translating or rotating the platform over progressively larger distances and comparing input and measured values. Treadmill belt speed was assessed with and without a person walking on the platform and at different orientations. Force plate measurements were examined when the treadmill was in operation, during ambulation, and over time to observe the baseline drift. Platform acceleration was dependent on the distance travelled and system settings. Treadmill speed variability was greatest at faster speeds. Force plate measurements were affected by platform and treadmill operation, contralateral impact forces during gait, and baseline drift. Knowledge of performance characteristics and their effect on outcome data is crucial for effective design of CAREN research protocols and rehabilitation scenarios.

Fixed and self-paced treadmill walking for able-bodied and transtibial amputees in a multi-terrain virtual environment.

A self-paced treadmill automatically adjusts speed in real-time to match the user's walking speed, potentially enabling more natural gait than fixed-speed treadmills. This research examined walking speed changes for able-bodied and transtibial amputee populations on a self-paced treadmill in a multi-terrain virtual environment and examined gait differences between fixed and self-paced treadmill speed conditions. Twelve able-bodied (AB) individuals and 12 individuals with unilateral transtibial amputation (TT) walked in a park-like virtual environment with level, slopes, and simulated uneven terrain scenarios. Temporal-spatial and range-of-motion parameters were analyzed. Within the self-paced condition, all participants significantly varied walking speed (p<0.001) across different walking activities. Compared to level walking, participants reduced speed for uphill and hilly activities (p<0.001). TT also reduced speed downhill (p<0.001). Generally, differences in temporal-spatial and range-of-motion parameters between fixed and self-paced speed conditions were no longer significantly different with a speed covariate. However, for uphill walking, both groups decreased stride length during self-paced trials, and increased stride length during fixed-speed trials to maintain the constant speed (p<0.01). The results from this study demonstrated self-paced treadmill mode is important for virtual reality systems with multiple movement scenarios in order to elicit more natural gait across various terrain. Fixed-speed treadmills may induce gait compensations to maintain the fixed speed.

Whole-body angular momentum during stair ascent and descent.

The generation of whole-body angular momentum is essential in many locomotor tasks and must be regulated in order to maintain dynamic balance. However, angular momentum has not been investigated during stair walking, which is an activity that presents a biomechanical challenge for balance-impaired populations. We investigated three-dimensional whole-body angular momentum during stair ascent and descent and compared it to level walking. Three-dimensional body-segment kinematic and ground reaction force (GRF) data were collected from 30 healthy subjects. Angular momentum was calculated using a 13-segment whole-body model. GRFs, external moment arms and net joint moments were used to interpret the angular momentum results. The range of frontal plane angular momentum was greater for stair ascent relative to level walking. In the transverse and sagittal planes, the range of angular momentum was smaller in stair ascent and descent relative to level walking. Significant differences were also found in the ground reaction forces, external moment arms and net joint moments. The sagittal plane angular momentum results suggest that individuals alter angular momentum to effectively counteract potential trips during stair ascent, and reduce the range of angular momentum to avoid falling forward during stair descent. Further, significant differences in joint moments suggest potential neuromuscular mechanisms that account for the differences in angular momentum between walking conditions. These results provide a baseline for comparison to impaired populations that have difficulty maintaining dynamic balance, particularly during stair ascent and descent.

Amplitude effects of medio-lateral mechanical and visual perturbations on gait.

Falls during walking are a major contributor to accidental deaths and injuries that can result in debilitating hospitalization costs, lost productivity, and diminished quality of life. To reduce these losses, we must develop a more profound understanding of the characteristic responses to perturbations similar to those encountered in daily life. This study addresses this issue by building on our earlier studies that examined mechanical and visual perturbations in the same environment by applying the same continuous pseudo-random perturbations at multiple (3 mechanical, 5 visual) amplitudes. Walking variability during mechanical perturbations increased significantly with amplitude for all subjects and differences as measured by variabilities of step width, COM position, and COM velocity. These parameters were the only ones sensitive to the presence of visual perturbations, but none of them changed significantly with perturbation amplitude. Additionally, visual perturbation effects were far less consistent across participants, with several who were essentially unaffected by visual perturbations at any level. The homogeneity of the mechanical perturbation effects demonstrates that human responses to mechanical perturbations are similar because they are driven by kinetics that require similar corrections that must be made in order to maintain balance. Conversely, responses to visual perturbations are driven by the perceived need to make corrections and this perception is not accurate enough to produce amplitude-related corrections, even for a single participant, nor is this perception consistent across individuals. This latter finding is likely to be relevant to future visual perturbation studies and the diagnosis and rehabilitation of gait and balance disorders.

Gait characteristics of individuals with transtibial amputations walking on a destabilizing rock surface.

Individuals with transtibial amputation (TTA) have a high incidence of falls during walking. Environmental factors, such as uneven ground, often play a contributing role in these falls. The purpose of this study was to quantify the adaptations TTA made when walking on a destabilizing loose rock surface. In this study, 13 young TTA walked over a rock surface and level ground at four controlled speeds. Subjects successfully traversed the rock surface by adopting a conservative gait characterized by shorter and wider steps. They also took shorter steps with their prosthetic limbs and exhibited greater variability in foot placement when stepping onto their intact limb. Between-limb differences in step length and width variability increased at faster walking speeds. TTA increased hip and knee flexion during initial stance, which contributed lowering the whole-body center of mass. TTA also increased hip and knee flexion during swing, enabling them to significantly increase their toe clearance on the rock surface compared to level ground. Toe clearance on the prosthetic side was aided by increased ipsilateral hip flexion. The results suggest that TTA were able to adapt their gait to overcome the challenge imposed by the rock surface. These adaptations were asymmetric and initiated proximally.

Whole-body angular momentum in incline and decline walking.

Angular momentum is highly regulated over the gait cycle and is important for maintaining dynamic stability and control of movement. However, little is known regarding how angular momentum is regulated on irregular surfaces, such as slopes, when the risk of falling is higher. This study examined the three-dimensional whole-body angular momentum patterns of 30 healthy subjects walking over a range of incline and decline angles. The range of angular momentum was either similar or reduced on decline surfaces and increased on incline surfaces relative to level ground, with the greatest differences occurring in the frontal and sagittal planes. These results suggest that angular momentum is more tightly controlled during decline walking when the risk of falling is greater. In the frontal plane, the range of angular momentum was strongly correlated with the peak hip and knee abduction moments in early stance. In the transverse plane, the strongest correlation occurred with the knee external rotation peak in late stance. In the sagittal plane, all external moment peaks were correlated with the range of angular momentum. The peak ankle plantarflexion, knee flexion and hip extension moments were also strongly correlated with the sagittal-plane angular momentum. These results highlight how able-bodied subjects control angular momentum differently on sloped surfaces relative to level walking and provide a baseline for comparison with pathological populations that are more susceptible to falling.

Biomechanics of the ankle-foot system during stair ambulation: implications for design of advanced ankle-foot prostheses.

Unilateral lower limb prosthesis users display temporal, kinematic, and kinetic asymmetries between limbs while ascending and descending stairs. These asymmetries are due, in part, to the inability of current prosthetic devices to effectively mimic normal ankle function. The purpose of this study was to provide a comprehensive set of biomechanical data for able-bodied and unilateral transtibial amputee (TTA) ankle-foot systems for level-ground (LG), stair ascent (SA), and stair descent (SD), and to characterize deviations from normal performance associated with prosthesis use. Ankle joint kinematics, kinetics, torque-angle curves, and effective shapes were calculated for twelve able-bodied individuals and twelve individuals with TTA. The data from this study demonstrated the prosthetic limb can more effectively mimic the range of motion and power output of a normal ankle-foot during LG compared to SA and SD. There were larger differences between the prosthetic and able-bodied limbs during SA and SD, most evident in the torque-angle curves and effective shapes. These data can be used by persons designing ankle-foot prostheses and provide comparative data for assessment of future ankle-foot prosthesis designs.

Kinematic strategies for walking across a destabilizing rock surface.

It is important to understand how people adapt their gait when walking in real-world conditions with variable surface characteristics. This study quantified lower-extremity joint kinematics, estimated whole body center of mass height (COM(VT)), and minimum toe clearance (MTC) while 15 healthy, young subjects walked on level ground (LG) and a destabilizing loose rock surface (RS) at four controlled speeds. There were no significant differences in average step parameters (length, time, or width) between the walking surfaces. However, the variability of these parameters increased twofold on the RS compared to LG. When walking on the RS, subjects contacted the surface with a flatter foot and increased knee and hip flexion, which enabled them to lower COM(VT). Subjects exhibited increased hip and knee flexion and ankle dorsiflexion during swing on the RS. These changes contributed to a 3.8 times greater MTC on the RS compared to LG. Peak hip and knee flexion during early stance and swing increased with walking speed, contributing to decreased COM(VT) and increased MTC. Overall, subjects systematically adapted their movement kinematics to overcome the challenge imposed by the destabilizing loose rock surface.

The role of lower extremity joint powers in successful stair ambulation.

Ascending stairs is an important functional activity that is affected by lower extremity pathology including amputation. Although several studies have demonstrated stair ascent is more challenging than level ground walking, our understanding of the mechanics remains limited. The purpose of this study was to determine the association between lower extremity joint power generation and vertical COM acceleration (COM(A)) during stair ascent. Twenty-two healthy individuals underwent a biomechanical gait assessment while walking up a 16-step instrumented staircase. The association between the peak joint powers and peak COM(A) during stance were assessed with respect to timing and magnitude. With respect to timing, peak ankle joint power was highly correlated with peak COM(A) (R(2)=0.93), while peak knee and hip joint powers demonstrated limited association with COM(A) (R(2)=0.41 and 0.08, respectively). Only the magnitude of peak ankle power was associated with peak COM(A) (R(2)=0.3). Significant temporal and magnitude associations between peak ankle joint power and peak COM(A) suggest ankle power is a key contributor to COM(A). Although peak knee joint power and COM(A) are temporally associated, the association is weaker and the occurrence of peak joint knee power is nearly 10% after peak COM(A), suggesting knee joint power plays a lesser role in COM(A). These combined findings indicate the role of trail limb ankle plantarflexors should be recognized in the stair ascent cycle definition and demonstrate the potential importance of a power generated by the ankle plantarflexors to normalize stair ascent performance following lower extremity amputation.