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A more compliant prosthetic foot better accommodates added load while walking among Servicemembers with transtibial limb loss
Journal Pre-proofs A More Compliant Prosthetic Foot Better Accommodates Added Load while Walking among Servicemembers with Transtibial Limb Loss Barri L. Schnall, Christopher L. Dearth, Jonathan M. Elrod, Pawel R. Golyski, Sara R. Koehler-McNicholas, Samuel F. Ray, Andrew H. Hansen, Brad D. Hendershot PII: DOI: Reference:
S0021-9290(19)30629-3 https://doi.org/10.1016/j.jbiomech.2019.109395 BM 109395
To appear in:
Journal of Biomechanics
Received Date: Revised Date: Accepted Date:
13 June 2019 3 October 2019 6 October 2019
Please cite this article as: B.L. Schnall, C.L. Dearth, J.M. Elrod, P.R. Golyski, S.R. Koehler-McNicholas, S.F. Ray, A.H. Hansen, B.D. Hendershot, A More Compliant Prosthetic Foot Better Accommodates Added Load while Walking among Servicemembers with Transtibial Limb Loss, Journal of Biomechanics (2019), doi: https:// doi.org/10.1016/j.jbiomech.2019.109395
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A More Compliant Prosthetic Foot Better Accommodates Added Load while Walking among Servicemembers with Transtibial Limb Loss
Barri L. Schnalla, Christopher L. Deartha-c, Jonathan M. Elroda, Pawel R. Golyskia, Sara R. Koehler-McNicholasd,e, Samuel F. Raya, Andrew H. Hansend,e, *Brad D. Hendershota,b,f
Affiliations: a Research
& Development Section, Department of Rehabilitation, Walter Reed National
Military Medical Center, Bethesda, MD, USA b DoD-VA
Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, USA
c Department
of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD,
USA d Minneapolis e Division
Department of Veterans Affairs Health Care System, Minneapolis, MN, USA
of Rehabilitation Science, Department of Rehabilitation Medicine, University of
Minnesota, Minneapolis, MN, USA f
Department of Rehabilitation Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
*Corresponding Author E-mail: [email protected]
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ABSTRACT Selecting an optimal prosthetic foot is particularly challenging for highly active individuals with limb loss, such as military personnel, who need to seamlessly perform a variety of demanding activities/tasks (often with and without external loads) while minimizing risk of musculoskeletal injuries over the longer term. Here, we expand on prior work by comparing biomechanical and functional outcomes in two prosthetic feet with the largest differences in mechanical response to added load (i.e., consistently “Compliant” and “Stiff” forefoot properties). In each foot, fourteen male Servicemembers with unilateral transtibial limb loss (from trauma) completed instrumented gait analyses in all combinations of two loading conditions (with and without 22kg weighted vest) and two walking speeds (1.34 and 1.52 m/s), as well as the Prosthesis Evaluation Questionnaire. With load, the Stiff (versus Compliant) foot was associated with ~2% lesser (p=0.043) sound limb peak loading, despite similar deformations across all conditions (evidenced by peak ankle dorsiflexion). Independent of load or walking speed, the Compliant (versus Stiff) foot provided 67.9% larger (p<0.001) prosthetic push-off, 17.7% larger (p=0.01) roll-over shape radii, and was subjectively favored by 10 participants. A more Compliant versus Stiff prosthetic foot therefore appears to better accommodate walking with and without added load, though smaller loads on the sound limb with the Stiff foot nevertheless support the notion that mechanical properties of prosthetic feet should be considered for longer-term (joint) health in light of near-term performance.
Keywords: Extremity trauma, ankle-foot prosthesis, load carriage, biomechanics
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1. INTRODUCTION
Load carriage (i.e., walking with load(s) beyond body weight) is an essential ambulatory task and often a fundamental requirement in many recreational or occupational contexts. While walking with added load results in a number a biomechanical consequences (Attwells et al., 2006; Majumdar et al., 2010; Quesada et al., 2000), the biological ankle-foot system maintains consistent ankle joint kinematics and roll-over shape characteristics with the addition of loads beyond body weight (Attwells et al., 2006; Birrell and Haslam, 2009; Hansen and Childress, 2005a). This result is of particular importance for persons with lower limb loss, as prosthetic ankle-foot components typically behave like springs and deform proportionally with added load. While limited evidence suggests persons with lower limb loss generally accommodate to added loads in similar ways as uninjured individuals, indeed, added load induces greater deformations in the prosthetic (versus sound) ankle-foot (Doyle et al., 2014; Schnall et al., 2014). As such, a better understanding of the specific interaction between prosthetic device and end-user, while walking with and without added load, is of paramount clinical importance not only for optimizing near-term outcomes (i.e., functional performance), but also mitigating longer-term consequences (i.e., joint degeneration or pain); the latter of which are already highly prevalent among persons with limb loss (e.g., Gailey et al., 2008) and could likely be exacerbated by load carriage.
Mechanical properties of prosthetic feet affect biomechanical, functional, and subjective outcomes. Greater hindfoot/forefoot stiffness is associated with lesser prosthesis energy return and push-off work, as well as greater sound-side ground reaction forces and sagittal knee
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moments (Adamczyk et al., 2017; Morgenroth et al., 2011). Lesser prosthetic foot stiffness also necessitates greater muscular responses in the residual limb (Fey et al., 2011). Indeed, a doubleblind evaluation indicated prosthetic feet with more compliant versus stiff forefeet provided (~15%) smaller sagittal “ankle” moments, and were especially preferred for activities like navigating uneven terrains or slopes/stairs (Raschke et al., 2015). Prosthesis users can also somewhat reliably and sensitively detect changes in prosthesis stiffness, supporting the use of such an outcome in prescription tools (Shepherd et al., 2018). However, there remains a general lack of criteria for objective prosthesis prescription (Hofstad et al., 2004), especially in the context of walking with added load.
To objectively characterize prosthetic feet, it is critical to evaluate both the device and humandevice interaction (Major and Fey, 2017). In the context of walking with and without added load, Koehler-McNicholas et al. (2018) recently evaluated both the mechanical characteristics (i.e., forefoot stiffness) of nine prosthetic feet intended for high-activity users, as well as dynamic function (i.e., roll-over shape and late-stance energy return) in a small (n=3) sample of persons with unilateral limb loss. Results from this study showed that while feet with more compliant forefoot structures provided greater late-stance energy return, feet with stiffer forefoot structures (particularly when loaded above body mass) better accommodated added load due to smaller deflections and changes in roll-over shape, and thus respond more similarly to the biological ankle-foot system. Of note, all nine feet expressed minimal differences (6-16%) in roll-over shape radii between loading conditions, despite clear differences in their mechanical properties. Prosthetic feet with larger forefoot stiffness also displayed the smallest changes in effective foot length between loading conditions. Nevertheless, additional work is needed to more completely
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evaluate the overall biomechanical (i.e., beyond just the prosthetic foot itself) outcomes in a larger sample to better understand the statistical significance and clinical relevance (Childers and Takahashi, 2018). Thus, here we expand on these efforts by selecting the two prosthetic feet with the largest differences in mechanical response to added load (i.e., the most consistently “Compliant” and “Stiff” forefoot; ~0.04±0.01 %BW/mm and ~0.09±0.01 %BW/mm, respectively; Koehler-McNicholas et al., 2018) to compare biomechanical outcomes between feet, with and without added load. In particular, we hypothesized the Stiff versus Compliant prosthetic foot would behave more biomechanically similar with and without added load, thereby minimizing the “drop-off” effect (where the user “drops” onto their sound limb during prosthetic to sound limb weight shift, due to a short effective prosthetic foot length; Hansen et al., 2006; Klodd et al., 2010) and reducing reliance on the contralateral (sound) limb, as evidenced by smaller sound-side peak vertical ground reaction force (vGRF) and first peak external knee adduction moment (EKAM). Such a focus is of particular importance for understanding (biomechanical) risk factors for musculoskeletal conditions secondary to limb loss, and thus better informing not only prosthesis design or prescription practices for near-term performance, but also other clinical decision making in the context of long-term health.
2. METHODS Participants Fourteen male Servicemembers with traumatic, unilateral transtibial limb loss participated in this study (Table 1). All participants were MFCL K4-level who had been ambulating independently without an assistive device (other than the prosthesis), had no diagnosed neurological deficits influencing their ability to follow complex commands, did not regularly use powered prosthetic
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devices, and were not in discomfort as measured by a score of less than 4/10 on a Visual Analog Scale for pain (Jensen et al., 2003). All participants provided informed consent to study procedures approved by the Walter Reed National Military Medical Center Institutional Review Board.
Experimental Design Each participant completed biomechanical and subjective testing in two prosthetic feet via a randomized and counterbalanced cross-over design: (1) an ankle-foot prosthesis with a "Compliant" forefoot (Soleus Tactical, College Park Industries, Warren, MI, USA), and (2) an ankle-foot prosthesis with a "Stiff” forefoot (Thrive, Freedom Innovation, Irvine, CA, USA). Biomechanical testing included eight walking conditions, consisting of all combinations of both prosthetic feet (Compliant and Stiff), two forced speeds (1.34 m/s and 1.52 m/s), and two loading conditions (with and without a 22.2 kg weighted vest). To evaluate subjective preference, participants also completed the Prosthetic Evaluation Questionnaire (PEQ; Legro et al., 1998) after testing in each foot.
Experimental Procedures Upon arrival, participants were given the Compliant and Stiff prosthesis in accordance with manufacturer guidelines based on body mass and foot size, and were fit and aligned by a certified prosthetist (note, participants used their conventional socket and suspension system for both feet). While there is no consensus definition for required accommodation timing to a new prosthetic foot (Wanamaker et al., 2017), prior to testing in each foot, participants wore the device for approximately 15 minutes (walking; without additional load) and subsequently indicated comfort with the new foot. 6
For each biomechanical condition, participants walked along a 15-meter walkway, with speeds enforced within 5% of desired speed via auditory feedback using a custom LabVIEW program (National Instruments, Austin, TX), until five clean foot strikes were recorded on each limb. Clean strikes were defined as full foot contact on a singular force platform. All participants wore similar combat boots, to enhance ecological validity and since previous work has demonstrated an effect of footwear on ankle-foot rollover (Curtze et al., 2009). Full-body kinematics were collected at 120 Hz by tracking 39 reflective markers (modified Cleveland Clinic) using an 18camera optical motion capture system (Qualisys, Gotenberg, Sweden). Ground reaction forces were simultaneously collected at 1200 Hz using six force plates embedded in the walkway (AMTI, Watertown, MA, USA). After completing walking trials and before switching to the next foot, participants completed the PEQ.
Dependent Measures and Data Analyses All biomechanical data were processed and analyzed using Visual 3D (C-Motion Inc., Germantown, MD, USA) and Matlab (Mathworks, Natick, MA, USA). Kinematic and kinetic data were first low pass filtered at 6 and 20 Hz, respectively, using a 4th order Butterworth filter. Instantaneous radius of curvature (Curtze et al., 2009) was calculated to assess the roll-over shape, and the maximum instantaneous radius of curvature was extracted to assess differences between foot, speed, and load conditions. Briefly, instantaneous radius of curvature gauges the curvature of a prosthetic foot during single support by calculating the forward velocity of the foot center of pressure as a function of shank angle (Curtze et al., 2009); a larger radius of curvature will be interpreted here as more stable (Bruijn et al., 2012). Additionally, peaks in
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sound limb vertical ground reaction forces (vGRFs) were extracted, while sound limb external knee adduction moment (EKAM) and prosthetic limb ankle-foot powers were calculated. Prosthetic limb ankle-foot powers were used to quantify energy storage and return using a unified deformable segment model (Takahashi et al., 2012). Note, as in prior work (Doyle et al., 2014), all kinetic outcomes were normalized by body mass (body mass + 22.2kg) for conditions without (with) added load, respectively.
For all discrete dependent variables, two-way repeated measures ANOVAs determined the presence of main effects for prosthetic foot type (Compliant and Stiff), walking speed (1.34 and 1.52 m/s), and loading condition (with and without 22kg), and their first-order interactions. Statistical significance was concluded at p<0.05. Differences between prosthetic feet in PEQ scores were interpreted according to minimal detectable change values (Resnik and Borgia, 2011). All statistical analyses were performed in SPSS 21 (IBM, Armonk, NY). Summary values are reported as means (standard deviations).
3. RESULTS Biomechanical Outcomes Prosthetic-side peak ankle dorsiflexion angles were similar (p=0.825) between the Compliant versus Stiff foot (18.3 [2.6]° versus 18.5 [3.2]°, respectively) and, overall, 5.8% larger with added load (p<0.0001) and 4.7% larger at the faster speed (p=0.002). Of note, the timing of peak prosthetic ankle dorsiflexion occurred 1.1% earlier (p=0.037) in the gait cycle with the Compliant versus Stiff foot. Prosthetic-side maximum radius of curvature displayed only main effects of foot, speed, and load (Fig. 1). Maximum radius of curvature was 17.7% larger (p=0.01) with the Compliant versus Stiff foot, 9.7% larger (p<0.001) at the faster speed, and 5.3% smaller 8
(p=0.014) with compared to without added load. Positive prosthesis work (i.e., energy return) was 67.9% larger (p<0.001) with the Compliant versus Stiff foot (Fig. 2), and was 17.1% larger (p<0.001) at the faster speed. Negative work done by the prosthesis (i.e., energy stored or dissipated) was 38.1% larger (p<0.001) on the Compliant versus Stiff foot, and was 16.0% larger (p<0.001) at the faster walking speed. Both positive and negative work done by the prosthetic foot were similar (positive p=0.162; negative p=0.074) between load conditions. For the soundside peak vGRF, there was a foot × load interaction (p=0.043); with versus without load, soundside peak vGRF was 2.0% smaller in the Stiff foot, but similar in the Compliant foot (Fig. 3). Overall, sound-side peak vGRF was also 9.3% larger (p<0.001) at the faster speed, and 7.3% larger (p<0.001) in the Stiff foot. Sound-side (normalized) peak EKAM was similar (p=0.16) between feet, but 11.2% larger (p=0.003) in unloaded versus loaded conditions, and 7.2% larger (p=0.029) at the faster speed (Fig. 4).
Temporal-spatial outcomes (Table 2) were similar (p>0.075) between the Compliant and Stiff foot, with a main effect of speed (all p<0.001, except for step width p=0.051). With versus without load, step lengths were smaller on both the prosthetic (2.5%; p=0.008) and sound (1.0%; p=0.003) sides; double limb support times were 2.7% larger (p=0.001) with load.
Subjective Outcomes Group means in six PEQ subscales were greater for the Compliant versus Stiff foot (Table 2). When grading the first question on the PEQ (overall satisfaction), 10 out of 13 participants indicated preference for the Compliant foot (one subject did not complete questionnaires for both feet).
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4. DISCUSSION
The overarching goal of this study was to identify optimal prosthesis design parameters in the context of walking with and without added load, by first comparing two prosthetic feet with relatively Compliant versus Stiff forefoot structures when mechanically loaded beyond bodyweight. We hypothesized the Stiff (versus Compliant) prosthetic foot, by mimicking the properties of the biological foot which minimizes deformation with added load (Kelly et al., 2014), would diminish sound limb loads during walking with loads beyond bodyweight. Consistent with our hypothesis, the Stiff (versus Compliant) foot was associated with lesser sound-limb (first peak) vGRF when walking with added load, despite similar functional deformations (i.e., peak ankle dorsiflexion); however, there were no differences in sound-limb EKAM between the Stiff and Compliant foot.
Similar to previous literature, in the current study we identified larger prosthetic ankle deformations with versus without added load, yet there were no differences in deformation between the Compliant and Stiff foot, despite appreciable differences in their design and previously characterized stiffness profiles (Koehler-McNicholas et al., 2018). Here, walking with added load in the Stiff versus Compliant foot also resulted in smaller sound-side vGRF, and minimal changes in EKAM (though peaks were larger prior to normalization). Note that prior mechanical testing indicated the Stiff foot had a greater stiffness overall (i.e., not just above body weight; Koehler-McNicholas et al., 2018) and, here, peak vGRFs were larger in the Stiff versus Compliant foot (1.20 [0.13] versus 1.14 [0.12] N/kg, respectively); outcomes likely related to the 10
design and (overall) stiffness of each foot (Koehler-McNicholas et al., 2018). Walking without added load, increasing prosthetic foot stiffness is associated with greater (first) peak vGRF on the sound limb, as well as peak knee flexion moment (Fey et al., 2011). Prior simulations suggest decreasing prosthetic ankle stiffness minimizes knee joint contact forces, albeit with greater metabolic cost and muscle activity (Fey et al., 2012). Also, human subjects testing of prosthetic feet similarly indicate those providing greater push-off are associated with larger reductions in leading (sound) limb EKAM (Grabowski and D’Andrea, 2013; Morgenroth et al., 2011). Among uninjured individuals, walking with added load typically results in biomechanical adaptations that, in part, help stabilize the system and/or reduce the transmission of forces through the body (Harman et al., 2000; Kinoshita, 1985). Prior work among persons with unilateral limb loss identified similar adaptations when walking with added load (Doyle et al., 2014; Schnall et al., 2014); however, these adaptations tended to exacerbate common gait deviations associated with limb loss, such as the relatively greater reliance on the sound versus prosthetic limb for load bearing, and induced larger deformations of the prosthetic ankle-foot.
In contrast to prior work (Hansen and Childress, 2005b), maximizing overall prosthetic push-off versus optimizing stiffness profiles (i.e., mimicking biological ankle-foot stiffness behaviors with load) seems more beneficial for walking with and without added load, though within physiological constraints (Quesada et al., 2016). Here, we observed larger roll-over shape radii in the Compliant versus Stiff foot, though without interaction for the loading condition, and in contrast to our prior work (albeit calculated using a different methodology; mean vs. instantaneous). Though as in this previous study (Koehler-McNicholas et al., 2018), we similarly conclude that rollover shape parameters were insensitive to walking with added load, and less of
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a contribution to the proposed “drop-off effect” that could exacerbate sound-side limb loading. Nevertheless, gait stability and symmetry may be influenced by prosthetic foot parameters, such as preserving margins of stability with an energy storing and return versus SACH foot (Houdijk et al., 2018), or a less stiff prosthetic foot enhancing mediolateral balance during turns (Shell et al., 2017) and decreasing variability in prosthetic limb swing time, step time, and swing time symmetry might suggest improvements in stability of walking (Major et al., 2017). While common changes in temporal-spatial outcomes with added load were observed here (i.e., shorter step lengths, greater double limb support), these were again without any notable differences between the Compliant versus Stiff foot. Similarly, there were no main or interaction effects (P>0.07) in body posture (e.g., trunk forward flexion). There was an overwhelming subjective preference for the Compliant foot, which is consistent with previous work (Raschke et al., 2015) and, as noted earlier, likely resulting from the biomechanical consequence of greater positive push-off provided relative to the Stiff foot.
There are a number of methodological aspects (e.g., foot alignment and accommodation, walking speed, load magnitude/distribution), as identified and discussed previously (Koehler-McNicholas et al., 2018), that were ultimately chosen for purposes of enhancing clinical relevance and ecological validity. Additionally, while it is ultimately possible that different prosthetic foot lengths/manufacturer-prescribed stiffness categories limit comparisons to the prior mechanical testing, the anthropometric characteristics of the current sample were overall similar to those in our prior work, and the consistent 22kg load as a function of BW in the current sample results in a mean of 24.5%BW (range= 17.3 - 31.8%BW). Moreover, footwear can also influence the mechanical characteristics and responses of prosthetic feet; it is therefore possible that utilizing
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combat boots for both mechanical and subsequent human subjects testing in the current study, while consistent (across participants/conditions) and ecologically valid (again, in a somewhat military-specific context), ultimately masked/altered mechanical responses (i.e., a convergence of behavior). However, despite footwear generally increasing compliance of ankle-foot systems (notably in the hiking boot versus barefoot conditions), these effects have been found to be smallest in the forefoot region (Major et al., 2018). We also did not mechanically evaluate stiffness of both the heel and forefoot, though prosthetic forefoot response in mid-late stance has the largest influence on contralateral knee mechanics in early-mid stance (Fey et al., 2012). Nevertheless, future work should consider more comprehensively evaluating the accommodation of prosthetic feet to walking with added load across a broader continuum of mechanical properties, such as through use of additive manufacturing (Fey et al., 2011) or a prosthesis emulator (Caputo and Collins, 2014) to more selectively vary prosthesis parameters.
In summary, while the Stiff prosthetic foot did result in (albeit marginally) smaller sound-side vGRF when walking with versus without added load, the prosthesis with a more Compliant forefoot ultimately provided larger prosthetic push-off, larger roll-over shape radii (more stability), and was generally more favored according to subjective ratings. As such, maximizing overall prosthetic push-off versus optimizing stiffness profiles (within physiological constraints) seems more beneficial for walking, with and without added load, in the context of near-term performance for highly functional prosthesis users, and may have important implications for long-term health outcomes (e.g., musculoskeletal health). Nevertheless, additional work is needed to better understand the longer-term outcomes of prosthesis design and clinical decisionmaking, as well as during other activities with seemingly greater impact (e.g., jumping/drop
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landing, jogging/running), that will collectively guide the development and prescription of highly adaptive and responsive prosthetic feet for Servicemembers, Veterans, and civilians participating in physically demanding occupations or recreational activities.
5. ACKNOWLEDGEMENTS This work was supported, in part, by the BADER Consortium via the Congressionally Designated Medical Research Program (Award number W81XWH-11-2-0222) and the DoD-VA Extremity Trauma and Amputation Center of Excellence. The views expressed in this manuscript are those of the authors, and do not necessarily reflect the official policies of the Departments of the Army, Navy, Defense, nor the United States Government. The identification of specific products or instrumentation is considered an integral part of the scientific endeavor and does not constitute endorsement or implied endorsement on the part of the authors, Department of Defense, or any component agency.
6. CONFLICT OF INTEREST STATEMENT We declare that all authors have no financial or personal relationships with other persons or organizations that might inappropriately influence our work presented therein.
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Major, M.J., Fey, N.P., 2017. Considering passive mechanical properties and patient user motor performance in lower limb prosthesis design optimization to enhance rehabilitation outcomes. Physical Therapy Reviews 22, 202-216. Major, M.J., Scham, J., Orendurff, M., 2018. The effects of common footwear on stance-phase mechanical properties of the prosthetic foot-shoe system. Prosthetics and Orthotics International 42, 198-207. Majumdar, D., Pal, M.S., Majumdar, D., 2010. Effects of military load carriage on kinematics of gait. Ergonomics 53, 782-791. Morgenroth, D.C., Segal, A.D., Zelik, K.E., Czerniecki, J.M., Klute, G.K., Adamczyk, P.G., et al., 2011. The effect of prosthetic foot push-off on mechanical loading associated with knee osteoarthritis in lower extremity amputees. Gait & Posture 34, 502-507. Quesada, P.M., Mengelkoch, L.J., Hale, R.C., Simon, S.R., 2000. Biomechanical and metabolic effects of varying backpack loading on simulated marching. Ergonomics 43, 293-309. Quesada, R.E., Caputo, J.M., Collins, S.H., 2016. Increasing ankle push-off work with a powered prosthesis does not necessarily reduce metabolic rate for transtibial amputees. Journal of biomechanics 49, 3452-3459. Raschke, S.U., Orendurff, M.S., Mattie, J.L., Kenyon, D.E., Jones, O.Y., Moe, D., et al., 2015. Biomechanical characteristics, patient preference and activity level with different prosthetic feet: a randomized double blind trial with laboratory and community testing. Journal of biomechanics 48, 146-152. Resnik, L., Borgia, M., 2011. Reliability of outcome measures for people with lower-limb amputations: distinguishing true change from statistical error. Physical therapy 91, 555-565. Schnall, B.L., Hendershot, B.D., Bell, J.C., Wolf, E.J., 2014. Kinematic analysis of males with transtibial amputation carrying military loads. Journal of Rehabilitation Research & Development 51. Shell, C.E., Segal, A.D., Klute, G.K., Neptune, R.R., 2017. The effects of prosthetic foot stiffness on transtibial amputee walking mechanics and balance control during turning. Clinical Biomechanics 49, 56-63. Shepherd, M.K., Azocar, A.F., Major, M.J., Rouse, E.J., Year The Difference Threshold of Ankle-Foot Prosthesis Stiffness for Persons with Transtibial Amputation. In 2018 7th IEEE International Conference on Biomedical Robotics and Biomechatronics (Biorob). Takahashi, K.Z., Kepple, T.M., Stanhope, S.J., 2012. A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait. J Biomech 45, 2662-2667.
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Table 1. Individual and mean (standard deviation; SD) participant demographics. Participant
Age (yr)
Stature (cm)
Body Mass (kg)
Affected Side
01
36
178.5
89.7
L
6.5
02
47
182.5
89.9
L
8.8
03
22
173.0
87.4
L
1.6
04
37
183.5
84.4
R
3.2
05
33
185.0
100.2
L
12.5
06
39
181.0
90.5
R
10.9
07
42
182.0
76.8
L
8.9
08
39
188.5
127.1
R
10.2
09
29
174.5
83.8
L
9.6
10
41
167.5
98.2
L
6.4
11
33
185.0
96.8
R
12.3
12
42
171.0
89.4
R
3.2
13
32
174.5
95.5
R
5.7
14
41
170.0
69.2
R
0.9
Mean
36.6 (6.4)
178.3 (6.5)
91.4
N/A
7.2
(SD)
(13.3)
Time since limb loss (yr)
(3.9)
19
Table 2: Mean ± 1 SD temporal-spatial outcomes by condition (foot/speed/load). * = main effect of load; † = main effect of speed; ‡ = main effect of foot.
No Load (BW) Compliant Foot Measure
Added Load (BW + 22kg) Stiff Foot
Compliant Foot
Stiff Foot
1.34
1.52
1.34
1.52
1.34
1.52
1.34
1.52
Actual Speed (m/s)
1.34 ± 0.05
1.54 ± 0.05
1.34 ± 0.07
1.52 ± 0.06
1.32 ± 0.04
1.52 ± 0.06
1.33 ± 0.04
1.54 ± 0.06
Cadence (steps/min) †
109 ± 5
115 ± 5
109 ± 4
116 ± 4
109 ± 6
116 ± 5
110 ± 5
118 ± 4
Stride Width (m)
0.15 ± 0.02
0.15 ± 0.02
0.14 ± 0.02
0.15 ± 0.02
0.15 ± 0.03
0.15 ± 0.03
0.15 ± 0.02
0.15 ± 0.03
32.56 ± 1.21
31.21 ± 1.05
32.36 ± 1.19
30.90 ± 1.19
33.48 ± 1.26
32.07 ± 0.84
33.19 ± 1.14
31.73 ± 1.39
0.76 ± 0.03
0.82 ± 0.03
0.75 ± 0.04
0.81 ± 0.03
0.74 ± 0.03
0.80 ± 0.04
0.73 ± 0.04
0.79 ± 0.04
0.72 ± 0.04
0.78 ± 0.04
0.73 ± 0.04
0.79 ± 0.04
0.72 ± 0.05
0.77 ± 0.05
0.72 ± 0.04
0.78 ± 0.04
66.02 ± 1.08
65.25 ± 1.08
65.56 ± 0.99
64.79 ±0.89
65.72 ± 0.93
65.42 ± 1.01
65.74 ± 1.12
65.23 ± 1.67
66.56 ± 0.90
65.97 ± 1.20
66.81 ± 0.57
66.11 ± 0.64
66.81 ± 1.74
66.63 ± 1.23
67.33 ± 0.77
66.44 ± 1.29
Double Limb Support (% Stride) † * Prosthetic-side Step Length (m) † * Sound-side Step Length (m) † * Prosthetic-side Stance Time (% Stride) † Sound-side Stance Time (% Stride) † *
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Figures Figure 1: Maximum instantaneous radius of curvature. Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to stature. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 2: Prosthetic-side mechanical power and work. Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 3: Sound-side vertical ground reaction force (vGRF). Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 4: Sound-side external knee adduction moment (EKAM). Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot.
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S0021-9290(19)30629-3 https://doi.org/10.1016/j.jbiomech.2019.109395 BM 109395
To appear in:
Journal of Biomechanics
Received Date: Revised Date: Accepted Date:
13 June 2019 3 October 2019 6 October 2019
Please cite this article as: B.L. Schnall, C.L. Dearth, J.M. Elrod, P.R. Golyski, S.R. Koehler-McNicholas, S.F. Ray, A.H. Hansen, B.D. Hendershot, A More Compliant Prosthetic Foot Better Accommodates Added Load while Walking among Servicemembers with Transtibial Limb Loss, Journal of Biomechanics (2019), doi: https:// doi.org/10.1016/j.jbiomech.2019.109395
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Published by Elsevier Ltd.
A More Compliant Prosthetic Foot Better Accommodates Added Load while Walking among Servicemembers with Transtibial Limb Loss
Barri L. Schnalla, Christopher L. Deartha-c, Jonathan M. Elroda, Pawel R. Golyskia, Sara R. Koehler-McNicholasd,e, Samuel F. Raya, Andrew H. Hansend,e, *Brad D. Hendershota,b,f
Affiliations: a Research
& Development Section, Department of Rehabilitation, Walter Reed National
Military Medical Center, Bethesda, MD, USA b DoD-VA
Extremity Trauma and Amputation Center of Excellence, Bethesda, MD, USA
c Department
of Surgery, Uniformed Services University of the Health Sciences, Bethesda, MD,
USA d Minneapolis e Division
Department of Veterans Affairs Health Care System, Minneapolis, MN, USA
of Rehabilitation Science, Department of Rehabilitation Medicine, University of
Minnesota, Minneapolis, MN, USA f
Department of Rehabilitation Medicine, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
*Corresponding Author E-mail: [email protected]
1
ABSTRACT Selecting an optimal prosthetic foot is particularly challenging for highly active individuals with limb loss, such as military personnel, who need to seamlessly perform a variety of demanding activities/tasks (often with and without external loads) while minimizing risk of musculoskeletal injuries over the longer term. Here, we expand on prior work by comparing biomechanical and functional outcomes in two prosthetic feet with the largest differences in mechanical response to added load (i.e., consistently “Compliant” and “Stiff” forefoot properties). In each foot, fourteen male Servicemembers with unilateral transtibial limb loss (from trauma) completed instrumented gait analyses in all combinations of two loading conditions (with and without 22kg weighted vest) and two walking speeds (1.34 and 1.52 m/s), as well as the Prosthesis Evaluation Questionnaire. With load, the Stiff (versus Compliant) foot was associated with ~2% lesser (p=0.043) sound limb peak loading, despite similar deformations across all conditions (evidenced by peak ankle dorsiflexion). Independent of load or walking speed, the Compliant (versus Stiff) foot provided 67.9% larger (p<0.001) prosthetic push-off, 17.7% larger (p=0.01) roll-over shape radii, and was subjectively favored by 10 participants. A more Compliant versus Stiff prosthetic foot therefore appears to better accommodate walking with and without added load, though smaller loads on the sound limb with the Stiff foot nevertheless support the notion that mechanical properties of prosthetic feet should be considered for longer-term (joint) health in light of near-term performance.
Keywords: Extremity trauma, ankle-foot prosthesis, load carriage, biomechanics
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1. INTRODUCTION
Load carriage (i.e., walking with load(s) beyond body weight) is an essential ambulatory task and often a fundamental requirement in many recreational or occupational contexts. While walking with added load results in a number a biomechanical consequences (Attwells et al., 2006; Majumdar et al., 2010; Quesada et al., 2000), the biological ankle-foot system maintains consistent ankle joint kinematics and roll-over shape characteristics with the addition of loads beyond body weight (Attwells et al., 2006; Birrell and Haslam, 2009; Hansen and Childress, 2005a). This result is of particular importance for persons with lower limb loss, as prosthetic ankle-foot components typically behave like springs and deform proportionally with added load. While limited evidence suggests persons with lower limb loss generally accommodate to added loads in similar ways as uninjured individuals, indeed, added load induces greater deformations in the prosthetic (versus sound) ankle-foot (Doyle et al., 2014; Schnall et al., 2014). As such, a better understanding of the specific interaction between prosthetic device and end-user, while walking with and without added load, is of paramount clinical importance not only for optimizing near-term outcomes (i.e., functional performance), but also mitigating longer-term consequences (i.e., joint degeneration or pain); the latter of which are already highly prevalent among persons with limb loss (e.g., Gailey et al., 2008) and could likely be exacerbated by load carriage.
Mechanical properties of prosthetic feet affect biomechanical, functional, and subjective outcomes. Greater hindfoot/forefoot stiffness is associated with lesser prosthesis energy return and push-off work, as well as greater sound-side ground reaction forces and sagittal knee
3
moments (Adamczyk et al., 2017; Morgenroth et al., 2011). Lesser prosthetic foot stiffness also necessitates greater muscular responses in the residual limb (Fey et al., 2011). Indeed, a doubleblind evaluation indicated prosthetic feet with more compliant versus stiff forefeet provided (~15%) smaller sagittal “ankle” moments, and were especially preferred for activities like navigating uneven terrains or slopes/stairs (Raschke et al., 2015). Prosthesis users can also somewhat reliably and sensitively detect changes in prosthesis stiffness, supporting the use of such an outcome in prescription tools (Shepherd et al., 2018). However, there remains a general lack of criteria for objective prosthesis prescription (Hofstad et al., 2004), especially in the context of walking with added load.
To objectively characterize prosthetic feet, it is critical to evaluate both the device and humandevice interaction (Major and Fey, 2017). In the context of walking with and without added load, Koehler-McNicholas et al. (2018) recently evaluated both the mechanical characteristics (i.e., forefoot stiffness) of nine prosthetic feet intended for high-activity users, as well as dynamic function (i.e., roll-over shape and late-stance energy return) in a small (n=3) sample of persons with unilateral limb loss. Results from this study showed that while feet with more compliant forefoot structures provided greater late-stance energy return, feet with stiffer forefoot structures (particularly when loaded above body mass) better accommodated added load due to smaller deflections and changes in roll-over shape, and thus respond more similarly to the biological ankle-foot system. Of note, all nine feet expressed minimal differences (6-16%) in roll-over shape radii between loading conditions, despite clear differences in their mechanical properties. Prosthetic feet with larger forefoot stiffness also displayed the smallest changes in effective foot length between loading conditions. Nevertheless, additional work is needed to more completely
4
evaluate the overall biomechanical (i.e., beyond just the prosthetic foot itself) outcomes in a larger sample to better understand the statistical significance and clinical relevance (Childers and Takahashi, 2018). Thus, here we expand on these efforts by selecting the two prosthetic feet with the largest differences in mechanical response to added load (i.e., the most consistently “Compliant” and “Stiff” forefoot; ~0.04±0.01 %BW/mm and ~0.09±0.01 %BW/mm, respectively; Koehler-McNicholas et al., 2018) to compare biomechanical outcomes between feet, with and without added load. In particular, we hypothesized the Stiff versus Compliant prosthetic foot would behave more biomechanically similar with and without added load, thereby minimizing the “drop-off” effect (where the user “drops” onto their sound limb during prosthetic to sound limb weight shift, due to a short effective prosthetic foot length; Hansen et al., 2006; Klodd et al., 2010) and reducing reliance on the contralateral (sound) limb, as evidenced by smaller sound-side peak vertical ground reaction force (vGRF) and first peak external knee adduction moment (EKAM). Such a focus is of particular importance for understanding (biomechanical) risk factors for musculoskeletal conditions secondary to limb loss, and thus better informing not only prosthesis design or prescription practices for near-term performance, but also other clinical decision making in the context of long-term health.
2. METHODS Participants Fourteen male Servicemembers with traumatic, unilateral transtibial limb loss participated in this study (Table 1). All participants were MFCL K4-level who had been ambulating independently without an assistive device (other than the prosthesis), had no diagnosed neurological deficits influencing their ability to follow complex commands, did not regularly use powered prosthetic
5
devices, and were not in discomfort as measured by a score of less than 4/10 on a Visual Analog Scale for pain (Jensen et al., 2003). All participants provided informed consent to study procedures approved by the Walter Reed National Military Medical Center Institutional Review Board.
Experimental Design Each participant completed biomechanical and subjective testing in two prosthetic feet via a randomized and counterbalanced cross-over design: (1) an ankle-foot prosthesis with a "Compliant" forefoot (Soleus Tactical, College Park Industries, Warren, MI, USA), and (2) an ankle-foot prosthesis with a "Stiff” forefoot (Thrive, Freedom Innovation, Irvine, CA, USA). Biomechanical testing included eight walking conditions, consisting of all combinations of both prosthetic feet (Compliant and Stiff), two forced speeds (1.34 m/s and 1.52 m/s), and two loading conditions (with and without a 22.2 kg weighted vest). To evaluate subjective preference, participants also completed the Prosthetic Evaluation Questionnaire (PEQ; Legro et al., 1998) after testing in each foot.
Experimental Procedures Upon arrival, participants were given the Compliant and Stiff prosthesis in accordance with manufacturer guidelines based on body mass and foot size, and were fit and aligned by a certified prosthetist (note, participants used their conventional socket and suspension system for both feet). While there is no consensus definition for required accommodation timing to a new prosthetic foot (Wanamaker et al., 2017), prior to testing in each foot, participants wore the device for approximately 15 minutes (walking; without additional load) and subsequently indicated comfort with the new foot. 6
For each biomechanical condition, participants walked along a 15-meter walkway, with speeds enforced within 5% of desired speed via auditory feedback using a custom LabVIEW program (National Instruments, Austin, TX), until five clean foot strikes were recorded on each limb. Clean strikes were defined as full foot contact on a singular force platform. All participants wore similar combat boots, to enhance ecological validity and since previous work has demonstrated an effect of footwear on ankle-foot rollover (Curtze et al., 2009). Full-body kinematics were collected at 120 Hz by tracking 39 reflective markers (modified Cleveland Clinic) using an 18camera optical motion capture system (Qualisys, Gotenberg, Sweden). Ground reaction forces were simultaneously collected at 1200 Hz using six force plates embedded in the walkway (AMTI, Watertown, MA, USA). After completing walking trials and before switching to the next foot, participants completed the PEQ.
Dependent Measures and Data Analyses All biomechanical data were processed and analyzed using Visual 3D (C-Motion Inc., Germantown, MD, USA) and Matlab (Mathworks, Natick, MA, USA). Kinematic and kinetic data were first low pass filtered at 6 and 20 Hz, respectively, using a 4th order Butterworth filter. Instantaneous radius of curvature (Curtze et al., 2009) was calculated to assess the roll-over shape, and the maximum instantaneous radius of curvature was extracted to assess differences between foot, speed, and load conditions. Briefly, instantaneous radius of curvature gauges the curvature of a prosthetic foot during single support by calculating the forward velocity of the foot center of pressure as a function of shank angle (Curtze et al., 2009); a larger radius of curvature will be interpreted here as more stable (Bruijn et al., 2012). Additionally, peaks in
7
sound limb vertical ground reaction forces (vGRFs) were extracted, while sound limb external knee adduction moment (EKAM) and prosthetic limb ankle-foot powers were calculated. Prosthetic limb ankle-foot powers were used to quantify energy storage and return using a unified deformable segment model (Takahashi et al., 2012). Note, as in prior work (Doyle et al., 2014), all kinetic outcomes were normalized by body mass (body mass + 22.2kg) for conditions without (with) added load, respectively.
For all discrete dependent variables, two-way repeated measures ANOVAs determined the presence of main effects for prosthetic foot type (Compliant and Stiff), walking speed (1.34 and 1.52 m/s), and loading condition (with and without 22kg), and their first-order interactions. Statistical significance was concluded at p<0.05. Differences between prosthetic feet in PEQ scores were interpreted according to minimal detectable change values (Resnik and Borgia, 2011). All statistical analyses were performed in SPSS 21 (IBM, Armonk, NY). Summary values are reported as means (standard deviations).
3. RESULTS Biomechanical Outcomes Prosthetic-side peak ankle dorsiflexion angles were similar (p=0.825) between the Compliant versus Stiff foot (18.3 [2.6]° versus 18.5 [3.2]°, respectively) and, overall, 5.8% larger with added load (p<0.0001) and 4.7% larger at the faster speed (p=0.002). Of note, the timing of peak prosthetic ankle dorsiflexion occurred 1.1% earlier (p=0.037) in the gait cycle with the Compliant versus Stiff foot. Prosthetic-side maximum radius of curvature displayed only main effects of foot, speed, and load (Fig. 1). Maximum radius of curvature was 17.7% larger (p=0.01) with the Compliant versus Stiff foot, 9.7% larger (p<0.001) at the faster speed, and 5.3% smaller 8
(p=0.014) with compared to without added load. Positive prosthesis work (i.e., energy return) was 67.9% larger (p<0.001) with the Compliant versus Stiff foot (Fig. 2), and was 17.1% larger (p<0.001) at the faster speed. Negative work done by the prosthesis (i.e., energy stored or dissipated) was 38.1% larger (p<0.001) on the Compliant versus Stiff foot, and was 16.0% larger (p<0.001) at the faster walking speed. Both positive and negative work done by the prosthetic foot were similar (positive p=0.162; negative p=0.074) between load conditions. For the soundside peak vGRF, there was a foot × load interaction (p=0.043); with versus without load, soundside peak vGRF was 2.0% smaller in the Stiff foot, but similar in the Compliant foot (Fig. 3). Overall, sound-side peak vGRF was also 9.3% larger (p<0.001) at the faster speed, and 7.3% larger (p<0.001) in the Stiff foot. Sound-side (normalized) peak EKAM was similar (p=0.16) between feet, but 11.2% larger (p=0.003) in unloaded versus loaded conditions, and 7.2% larger (p=0.029) at the faster speed (Fig. 4).
Temporal-spatial outcomes (Table 2) were similar (p>0.075) between the Compliant and Stiff foot, with a main effect of speed (all p<0.001, except for step width p=0.051). With versus without load, step lengths were smaller on both the prosthetic (2.5%; p=0.008) and sound (1.0%; p=0.003) sides; double limb support times were 2.7% larger (p=0.001) with load.
Subjective Outcomes Group means in six PEQ subscales were greater for the Compliant versus Stiff foot (Table 2). When grading the first question on the PEQ (overall satisfaction), 10 out of 13 participants indicated preference for the Compliant foot (one subject did not complete questionnaires for both feet).
9
4. DISCUSSION
The overarching goal of this study was to identify optimal prosthesis design parameters in the context of walking with and without added load, by first comparing two prosthetic feet with relatively Compliant versus Stiff forefoot structures when mechanically loaded beyond bodyweight. We hypothesized the Stiff (versus Compliant) prosthetic foot, by mimicking the properties of the biological foot which minimizes deformation with added load (Kelly et al., 2014), would diminish sound limb loads during walking with loads beyond bodyweight. Consistent with our hypothesis, the Stiff (versus Compliant) foot was associated with lesser sound-limb (first peak) vGRF when walking with added load, despite similar functional deformations (i.e., peak ankle dorsiflexion); however, there were no differences in sound-limb EKAM between the Stiff and Compliant foot.
Similar to previous literature, in the current study we identified larger prosthetic ankle deformations with versus without added load, yet there were no differences in deformation between the Compliant and Stiff foot, despite appreciable differences in their design and previously characterized stiffness profiles (Koehler-McNicholas et al., 2018). Here, walking with added load in the Stiff versus Compliant foot also resulted in smaller sound-side vGRF, and minimal changes in EKAM (though peaks were larger prior to normalization). Note that prior mechanical testing indicated the Stiff foot had a greater stiffness overall (i.e., not just above body weight; Koehler-McNicholas et al., 2018) and, here, peak vGRFs were larger in the Stiff versus Compliant foot (1.20 [0.13] versus 1.14 [0.12] N/kg, respectively); outcomes likely related to the 10
design and (overall) stiffness of each foot (Koehler-McNicholas et al., 2018). Walking without added load, increasing prosthetic foot stiffness is associated with greater (first) peak vGRF on the sound limb, as well as peak knee flexion moment (Fey et al., 2011). Prior simulations suggest decreasing prosthetic ankle stiffness minimizes knee joint contact forces, albeit with greater metabolic cost and muscle activity (Fey et al., 2012). Also, human subjects testing of prosthetic feet similarly indicate those providing greater push-off are associated with larger reductions in leading (sound) limb EKAM (Grabowski and D’Andrea, 2013; Morgenroth et al., 2011). Among uninjured individuals, walking with added load typically results in biomechanical adaptations that, in part, help stabilize the system and/or reduce the transmission of forces through the body (Harman et al., 2000; Kinoshita, 1985). Prior work among persons with unilateral limb loss identified similar adaptations when walking with added load (Doyle et al., 2014; Schnall et al., 2014); however, these adaptations tended to exacerbate common gait deviations associated with limb loss, such as the relatively greater reliance on the sound versus prosthetic limb for load bearing, and induced larger deformations of the prosthetic ankle-foot.
In contrast to prior work (Hansen and Childress, 2005b), maximizing overall prosthetic push-off versus optimizing stiffness profiles (i.e., mimicking biological ankle-foot stiffness behaviors with load) seems more beneficial for walking with and without added load, though within physiological constraints (Quesada et al., 2016). Here, we observed larger roll-over shape radii in the Compliant versus Stiff foot, though without interaction for the loading condition, and in contrast to our prior work (albeit calculated using a different methodology; mean vs. instantaneous). Though as in this previous study (Koehler-McNicholas et al., 2018), we similarly conclude that rollover shape parameters were insensitive to walking with added load, and less of
11
a contribution to the proposed “drop-off effect” that could exacerbate sound-side limb loading. Nevertheless, gait stability and symmetry may be influenced by prosthetic foot parameters, such as preserving margins of stability with an energy storing and return versus SACH foot (Houdijk et al., 2018), or a less stiff prosthetic foot enhancing mediolateral balance during turns (Shell et al., 2017) and decreasing variability in prosthetic limb swing time, step time, and swing time symmetry might suggest improvements in stability of walking (Major et al., 2017). While common changes in temporal-spatial outcomes with added load were observed here (i.e., shorter step lengths, greater double limb support), these were again without any notable differences between the Compliant versus Stiff foot. Similarly, there were no main or interaction effects (P>0.07) in body posture (e.g., trunk forward flexion). There was an overwhelming subjective preference for the Compliant foot, which is consistent with previous work (Raschke et al., 2015) and, as noted earlier, likely resulting from the biomechanical consequence of greater positive push-off provided relative to the Stiff foot.
There are a number of methodological aspects (e.g., foot alignment and accommodation, walking speed, load magnitude/distribution), as identified and discussed previously (Koehler-McNicholas et al., 2018), that were ultimately chosen for purposes of enhancing clinical relevance and ecological validity. Additionally, while it is ultimately possible that different prosthetic foot lengths/manufacturer-prescribed stiffness categories limit comparisons to the prior mechanical testing, the anthropometric characteristics of the current sample were overall similar to those in our prior work, and the consistent 22kg load as a function of BW in the current sample results in a mean of 24.5%BW (range= 17.3 - 31.8%BW). Moreover, footwear can also influence the mechanical characteristics and responses of prosthetic feet; it is therefore possible that utilizing
12
combat boots for both mechanical and subsequent human subjects testing in the current study, while consistent (across participants/conditions) and ecologically valid (again, in a somewhat military-specific context), ultimately masked/altered mechanical responses (i.e., a convergence of behavior). However, despite footwear generally increasing compliance of ankle-foot systems (notably in the hiking boot versus barefoot conditions), these effects have been found to be smallest in the forefoot region (Major et al., 2018). We also did not mechanically evaluate stiffness of both the heel and forefoot, though prosthetic forefoot response in mid-late stance has the largest influence on contralateral knee mechanics in early-mid stance (Fey et al., 2012). Nevertheless, future work should consider more comprehensively evaluating the accommodation of prosthetic feet to walking with added load across a broader continuum of mechanical properties, such as through use of additive manufacturing (Fey et al., 2011) or a prosthesis emulator (Caputo and Collins, 2014) to more selectively vary prosthesis parameters.
In summary, while the Stiff prosthetic foot did result in (albeit marginally) smaller sound-side vGRF when walking with versus without added load, the prosthesis with a more Compliant forefoot ultimately provided larger prosthetic push-off, larger roll-over shape radii (more stability), and was generally more favored according to subjective ratings. As such, maximizing overall prosthetic push-off versus optimizing stiffness profiles (within physiological constraints) seems more beneficial for walking, with and without added load, in the context of near-term performance for highly functional prosthesis users, and may have important implications for long-term health outcomes (e.g., musculoskeletal health). Nevertheless, additional work is needed to better understand the longer-term outcomes of prosthesis design and clinical decisionmaking, as well as during other activities with seemingly greater impact (e.g., jumping/drop
13
landing, jogging/running), that will collectively guide the development and prescription of highly adaptive and responsive prosthetic feet for Servicemembers, Veterans, and civilians participating in physically demanding occupations or recreational activities.
5. ACKNOWLEDGEMENTS This work was supported, in part, by the BADER Consortium via the Congressionally Designated Medical Research Program (Award number W81XWH-11-2-0222) and the DoD-VA Extremity Trauma and Amputation Center of Excellence. The views expressed in this manuscript are those of the authors, and do not necessarily reflect the official policies of the Departments of the Army, Navy, Defense, nor the United States Government. The identification of specific products or instrumentation is considered an integral part of the scientific endeavor and does not constitute endorsement or implied endorsement on the part of the authors, Department of Defense, or any component agency.
6. CONFLICT OF INTEREST STATEMENT We declare that all authors have no financial or personal relationships with other persons or organizations that might inappropriately influence our work presented therein.
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REFERENCES Adamczyk, P.G., Roland, M., Hahn, M.E., 2017. Sensitivity of biomechanical outcomes to independent variations of hindfoot and forefoot stiffness in foot prostheses. Human movement science 54, 154-171. Attwells, R.L., Birrell, S.A., Hooper, R.H., Mansfield, N.J., 2006. Influence of carrying heavy loads on soldiers' posture, movements and gait. Ergonomics 49, 1527-1537. Birrell, S.A., Haslam, R.A., 2009. The effect of military load carriage on 3-D lower limb kinematics and spatiotemporal parameters. Ergonomics 52, 1298-1304. Bruijn, S.M., Bregman, D.J., Meijer, O.G., Beek, P.J., van Dieën, J.H., 2012. Maximum Lyapunov exponents as predictors of global gait stability: a modelling approach. Medical engineering & physics 34, 428-436. Caputo, J.M., Collins, S.H., 2014. A universal ankle–foot prosthesis emulator for human locomotion experiments. Journal of Biomechanical Engineering 136, 035002. Childers, W.L., Takahashi, K.Z., 2018. Increasing prosthetic foot energy return affects wholebody mechanics during walking on level ground and slopes. Scientific Reports 8, 5354. Curtze, C., Hof, A.L., van Keeken, H.G., Halbertsma, J.P., Postema, K., Otten, B., 2009. Comparative roll-over analysis of prosthetic feet. J Biomech 42, 1746-1753. Doyle, S.S., Lemaire, E.D., Besemann, M., Dudek, N.L., 2014. Changes to level ground transtibial amputee gait with a weighted backpack. Clinical Biomechanics 29, 149-154. Fey, N.P., Klute, G.K., Neptune, R.R., 2011. The influence of energy storage and return foot stiffness on walking mechanics and muscle activity in below-knee amputees. Clinical Biomechanics 26, 1025-1032. Fey, N.P., Klute, G.K., Neptune, R.R., 2012. Optimization of Prosthetic Foot Stiffness to Reduce Metabolic Cost and Intact Knee Loading During Below-Knee Amputee Walking: A Theoretical Study. Journal of Biomechanical Engineering 134, 111005-111005-111010. Gailey, R., Allen, K., Castles, J., Kucharik, J., Roeder, M., 2008. Review of secondary physical conditions associated with lower-limb amputation and long-term prosthesis use. Journal of Rehabilitation Research & Development 45. Grabowski, A.M., D’Andrea, S., 2013. Effects of a powered ankle-foot prosthesis on kinetic loading of the unaffected leg during level-ground walking. Journal of neuroengineering and rehabilitation 10, 49. Hansen, A.H., Childress, D.S., 2005a. Effects of adding weight to the torso on roll-over characteristics of walking. Journal of Rehabilitation Research and Development 42, 381. 15
Hansen, A.H., Childress, D.S., 2005b. Effects of adding weight to the torso on roll-over characteristics of walking. Journal of Rehabilitation Research & Development 42. Hansen, A.H., Meier, M.R., Sessoms, P.H., Childress, D.S., 2006. The effects of prosthetic foot roll-over shape arc length on the gait of trans-tibial prosthesis users. Prosthetics and Orthotics International 30, 286-299. Harman, E., Hoon, K., Frykman, P., Pandorf, C., 2000. The effects of backpack weight on the biomechanics of load carriage. ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA MILITARY PERFORMANCEDIV. Hofstad, C.J., van der Linde, H., van Limbeek, J., Postema, K., 2004. Prescription of prosthetic ankle‐foot mechanisms after lower limb amputation. The Cochrane Library. Houdijk, H., Wezenberg, D., Hak, L., Cutti, A.G., 2018. Energy storing and return prosthetic feet improve step length symmetry while preserving margins of stability in persons with transtibial amputation. Journal of neuroengineering and rehabilitation 15, 76. Jensen, M.P., Chen, C., Brugger, A.M., 2003. Interpretation of visual analog scale ratings and change scores: a reanalysis of two clinical trials of postoperative pain. The Journal of pain 4, 407-414. Kelly, L.A., Cresswell, A.G., Racinais, S., Whiteley, R., Lichtwark, G., 2014. Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch. Journal of The Royal Society Interface 11, 20131188. Kinoshita, H., 1985. Effects of different loads and carrying systems on selected biomechanical parameters describing walking gait. Ergonomics 28, 1347-1362. Klodd, E., Hansen, A., Fatone, S., Edwards, M., 2010. Effects of prosthetic foot forefoot flexibility on gait of unilateral transtibial prosthesis users. Journal of Rehabilitation Research & Development 47. Koehler-McNicholas, S.R., Nickel, E.A., Barrons, K., Blaharski, K.E., Dellamano, C.A., Ray, S.F., et al., 2018. Mechanical and dynamic characterization of prosthetic feet for high activity users during weighted and unweighted walking. PLOS ONE 13, e0202884. Legro, M.W., Reiber, G.D., Smith, D.G., Del Aguila, M., Larsen, J., Boone, D., 1998. Prosthesis evaluation questionnaire for persons with lower limb amputations: assessing prosthesis-related quality of life. Archives of Physical Medicine and Rehabilitation 79, 931-938. Major, M., Twiste, M., Kenney, L., Howard, D., 2017. The effects of prosthetic ankle stiffness on stability of gait in people with trans-tibial amputation. Journal of Rehabilitation Research and Development 53, 839-852.
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Major, M.J., Fey, N.P., 2017. Considering passive mechanical properties and patient user motor performance in lower limb prosthesis design optimization to enhance rehabilitation outcomes. Physical Therapy Reviews 22, 202-216. Major, M.J., Scham, J., Orendurff, M., 2018. The effects of common footwear on stance-phase mechanical properties of the prosthetic foot-shoe system. Prosthetics and Orthotics International 42, 198-207. Majumdar, D., Pal, M.S., Majumdar, D., 2010. Effects of military load carriage on kinematics of gait. Ergonomics 53, 782-791. Morgenroth, D.C., Segal, A.D., Zelik, K.E., Czerniecki, J.M., Klute, G.K., Adamczyk, P.G., et al., 2011. The effect of prosthetic foot push-off on mechanical loading associated with knee osteoarthritis in lower extremity amputees. Gait & Posture 34, 502-507. Quesada, P.M., Mengelkoch, L.J., Hale, R.C., Simon, S.R., 2000. Biomechanical and metabolic effects of varying backpack loading on simulated marching. Ergonomics 43, 293-309. Quesada, R.E., Caputo, J.M., Collins, S.H., 2016. Increasing ankle push-off work with a powered prosthesis does not necessarily reduce metabolic rate for transtibial amputees. Journal of biomechanics 49, 3452-3459. Raschke, S.U., Orendurff, M.S., Mattie, J.L., Kenyon, D.E., Jones, O.Y., Moe, D., et al., 2015. Biomechanical characteristics, patient preference and activity level with different prosthetic feet: a randomized double blind trial with laboratory and community testing. Journal of biomechanics 48, 146-152. Resnik, L., Borgia, M., 2011. Reliability of outcome measures for people with lower-limb amputations: distinguishing true change from statistical error. Physical therapy 91, 555-565. Schnall, B.L., Hendershot, B.D., Bell, J.C., Wolf, E.J., 2014. Kinematic analysis of males with transtibial amputation carrying military loads. Journal of Rehabilitation Research & Development 51. Shell, C.E., Segal, A.D., Klute, G.K., Neptune, R.R., 2017. The effects of prosthetic foot stiffness on transtibial amputee walking mechanics and balance control during turning. Clinical Biomechanics 49, 56-63. Shepherd, M.K., Azocar, A.F., Major, M.J., Rouse, E.J., Year The Difference Threshold of Ankle-Foot Prosthesis Stiffness for Persons with Transtibial Amputation. In 2018 7th IEEE International Conference on Biomedical Robotics and Biomechatronics (Biorob). Takahashi, K.Z., Kepple, T.M., Stanhope, S.J., 2012. A unified deformable (UD) segment model for quantifying total power of anatomical and prosthetic below-knee structures during stance in gait. J Biomech 45, 2662-2667.
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Wanamaker, A.B., Andridge, R.R., Chaudhari, A.M., 2017. When to biomechanically examine a lower-limb amputee: A systematic review of accommodation times. Prosthetics and Orthotics International 41, 431-445.
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Table 1. Individual and mean (standard deviation; SD) participant demographics. Participant
Age (yr)
Stature (cm)
Body Mass (kg)
Affected Side
01
36
178.5
89.7
L
6.5
02
47
182.5
89.9
L
8.8
03
22
173.0
87.4
L
1.6
04
37
183.5
84.4
R
3.2
05
33
185.0
100.2
L
12.5
06
39
181.0
90.5
R
10.9
07
42
182.0
76.8
L
8.9
08
39
188.5
127.1
R
10.2
09
29
174.5
83.8
L
9.6
10
41
167.5
98.2
L
6.4
11
33
185.0
96.8
R
12.3
12
42
171.0
89.4
R
3.2
13
32
174.5
95.5
R
5.7
14
41
170.0
69.2
R
0.9
Mean
36.6 (6.4)
178.3 (6.5)
91.4
N/A
7.2
(SD)
(13.3)
Time since limb loss (yr)
(3.9)
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Table 2: Mean ± 1 SD temporal-spatial outcomes by condition (foot/speed/load). * = main effect of load; † = main effect of speed; ‡ = main effect of foot.
No Load (BW) Compliant Foot Measure
Added Load (BW + 22kg) Stiff Foot
Compliant Foot
Stiff Foot
1.34
1.52
1.34
1.52
1.34
1.52
1.34
1.52
Actual Speed (m/s)
1.34 ± 0.05
1.54 ± 0.05
1.34 ± 0.07
1.52 ± 0.06
1.32 ± 0.04
1.52 ± 0.06
1.33 ± 0.04
1.54 ± 0.06
Cadence (steps/min) †
109 ± 5
115 ± 5
109 ± 4
116 ± 4
109 ± 6
116 ± 5
110 ± 5
118 ± 4
Stride Width (m)
0.15 ± 0.02
0.15 ± 0.02
0.14 ± 0.02
0.15 ± 0.02
0.15 ± 0.03
0.15 ± 0.03
0.15 ± 0.02
0.15 ± 0.03
32.56 ± 1.21
31.21 ± 1.05
32.36 ± 1.19
30.90 ± 1.19
33.48 ± 1.26
32.07 ± 0.84
33.19 ± 1.14
31.73 ± 1.39
0.76 ± 0.03
0.82 ± 0.03
0.75 ± 0.04
0.81 ± 0.03
0.74 ± 0.03
0.80 ± 0.04
0.73 ± 0.04
0.79 ± 0.04
0.72 ± 0.04
0.78 ± 0.04
0.73 ± 0.04
0.79 ± 0.04
0.72 ± 0.05
0.77 ± 0.05
0.72 ± 0.04
0.78 ± 0.04
66.02 ± 1.08
65.25 ± 1.08
65.56 ± 0.99
64.79 ±0.89
65.72 ± 0.93
65.42 ± 1.01
65.74 ± 1.12
65.23 ± 1.67
66.56 ± 0.90
65.97 ± 1.20
66.81 ± 0.57
66.11 ± 0.64
66.81 ± 1.74
66.63 ± 1.23
67.33 ± 0.77
66.44 ± 1.29
Double Limb Support (% Stride) † * Prosthetic-side Step Length (m) † * Sound-side Step Length (m) † * Prosthetic-side Stance Time (% Stride) † Sound-side Stance Time (% Stride) † *
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Figures Figure 1: Maximum instantaneous radius of curvature. Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to stature. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 2: Prosthetic-side mechanical power and work. Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 3: Sound-side vertical ground reaction force (vGRF). Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot. Figure 4: Sound-side external knee adduction moment (EKAM). Ensemble averages (top) and extracted peaks ± 1 SD (bottom) by foot and load condition, displayed separately for the 1.34 m/s (left) and 1.52 m/s (right) speeds. Values are normalized to body mass (body mass + 22 kg) for the no load (additional load) conditions. * = main effect of load; † = main effect of speed; ‡ = main effect of foot.
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