Comparative Effectiveness of Microprocessor-Controlled and Carbon-Fiber Energy-Storing-and-Returning Prosthetic Feet in Persons with Unilateral Transtibial Amputation: Patient-Reported Outcome Measures : JPO: Journal of Prosthetics and Orthotics

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Comparative Effectiveness of Microprocessor-Controlled and Carbon-Fiber Energy-Storing-and-Returning Prosthetic Feet in Persons with Unilateral Transtibial Amputation: Patient-Reported Outcome Measures

Kaluf, Brian BSE, CP, FAAOP; Duncan, Ashley EP-C; Bridges, William PhD

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Journal of Prosthetics and Orthotics 32(4):p 214-221, October 2020. | DOI: 10.1097/JPO.0000000000000288
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Recent advancements in prosthetic ankle-foot technology allow additional functionality for persons with transtibial amputation, namely, microprocessor control. Microprocessor ankles (MPAs) are designed to offer functional improvements over fixed-ankle energy-storing-and-returning (ESAR) prosthetic feet to affect socket comfort and mobility over level ground, uneven terrain, hills, and stairs.

Walking with a fixed-ankle ESAR foot, patients with unilateral transtibial amputation (UTA) often experience socket pressure and discomfort. When surveyed, patients rate socket comfort as the most important factor,1 and socket pressure-related skin complications frequently limit prosthesis use.2 A fixed-ankle ESAR foot exposes the residual limb to higher pressure when ambulating on stairs and slopes,3 as well as uneven terrain.4 High socket pressure experienced in these conditions are caused by the limited ankle motion and lack of slope accommodation in fixed-ankle ESAR feet.

Over level ground, fixed-ankle ESAR feet do not provide shock absorption and controlled plantarflexion during the first rocker of stance phase.5 This causes a delay in achieving foot flat and an unstable heel only foot contact.5 ESAR feet are shown to disrupt the forward progression of the center of pressure and negatively affect body weight acceptance of the amputated limb.6 Uneven terrain can pose an environmental barrier for patients with UTA, due to the interstep variability in the slope of the ground. On a simulated uneven walkway, patients using a fixed-ankle ESAR foot exhibit a destabilized gait pattern.7 In addition, walking with a fixed-ankle prosthesis on a nonflat road causes increased pressure on the residual limb.4 With a fixed-ankle ESAR foot, the reaction forces and pressure experienced by the residual limb are increased, and greater strength and balance are required by the patient to traverse uneven terrain.

Descending a hill, fixed-ankle ESAR feet cannot accommodate the slope to achieve foot-flat in a normal manner. This results in an unstable heel-only support when transferring weight onto the prosthesis,5 an increased knee flexion moment,8 and an increased pressure experienced by the residual limb through the socket.3 The combination of torque and pressure becomes too great for the residual limb to tolerate, and patients are forced to compensate by allowing their knee to rapidly flex. Patients fall forward onto their sound limb, causing a short prosthetic step duration and asymmetrical step length.8 The sound limb experiences greater loads and increased negative work at the hip and knee in lowering of the body mass in a controlled manner.9 Ascending a slope can be just as difficult for patients using fixed-ankle ESAR feet. The lack of slope accommodation at the ankle causes knee hyperextension of the residual limb9 and increased socket pressure.3 The knee hyperextension and pressures become too much for the residual limb to tolerate, and patients with UTA compensate by taking short step length and duration on the prosthesis, along with other gait deviations.10 The increased loads, gait deviations, and instability experienced while ascending and descending slopes with fixed-ankle ESAR feet limit mobility in the community for patients with UTA.

MPA technology was developed to address the above-described limitations of fixed-ankle ESAR prosthetic feet by providing articulation in the sagittal plane and adapting to changes in terrain. Commercially available MPAs have been studied since 2009 in 13 published research articles involving laboratory kinematic and kinetic analyses,9,11–18 intersocket pressure measurement,3 energetic evaluation,19,20 and patient-reported and performance-based outcome measures.21 Previous investigations included small sample sizes, with 16 participants accounted for the largest sample size, and most studies enrolled 10 participants or less. This low sample size limits the statistical power of these studies. In addition, the existing evidence consists mainly of investigations completed in controlled laboratory environments and focusing on instrumented gait analysis and energy expenditure.

Most previous studies also included the same MPA system, the Proprio Foot (Össur, Reykjavik, Iceland), which adapts to terrain during swing phase between steps only and has no ankle slope accommodation function within each stance phase. More recently developed MPA systems provide slope accommodation during stance phase on each step and therefore function differently than the Proprio Foot. These include Elan (Chas A Blatchford & Sons Ltd, Basingstoke, United Kingdom), Raize (Fillauer LLC, Chattanooga, TN, USA), Meridiam (Otto Bock, Duderstadt, Germany), and Kinnex (Freedom Innovations LLC, Irvine, CA, USA). Some of the prior research with the Proprio Foot may only characterize the benefits of systems with adaption during swing phase, whereas adaptation during stance phase from more recent MPA systems may provide functional differences and benefits to patients with UTA not reflected in prior research evidence.

There is a need to perform clinical research to examine effectiveness of MPA against traditional fixed-ankle ESAR prosthetic feet. Patient-reported outcome measures (PROMs) are standardized survey instruments used to quantify domains of prosthetic rehabilitation from the patient perspective and often address effects not observable in the clinic environment (e.g., balance, mobility, health-related quality of life).22 The aim of this study was to examine differences in patient-reported balance, mobility, socket comfort, and preference between a fixed-ankle ESAR foot and MPA following a 4-week accommodation period. It is hypothesized that the MPA will have higher patient-reported balance, mobility, and socket comfort, and be preferred more often when compared with the ESAR foot. The results of the current study will inform patients, practitioners, and payer sources, and impact clinical decision making regarding MPA technology by focusing on patient-reported outcome measures and benefits experienced in a real-world setting.



The Advarra Institutional Review Board (formerly called Chesapeake Institutional Review Board) approved a randomized crossover protocol of two ankle-foot configurations used during a 4-week accommodation period. A convenience sample of patients with UTA was recruited from a private prosthetic clinic with locations in three different states. Inclusion criteria were as follows: UTA, age 18 to 99 years, body weight less than 125 kg, nonpregnant, English speaking, current user of a prosthesis for at least 1 year, wear prosthesis 8 hrs a day or more, have a Medicare Functional Classification Level (MFCL) of K3 or higher, well-fitting and functioning prosthesis, does not require an ambulatory aid, and able to tolerate testing protocol including the ability to walk on slopes. Exclusion criteria were as follows: a presence or history of any condition that, in the view of the investigator, placed the participant at high risk of poor compliance or of not completing the study, or if a neurologic impairment known to cause gait and/or balance dysfunction was present.


The ankle-foot configurations consisted of a fixed-ankle ESAR foot (Pacifica LP; Freedom Innovations, Irvine, CA, USA) (Figure 1) and an MPA (Kinnex; Freedom Innovations, Irvine, CA, USA). The Kinnex comprises the same graphite foot module as the Pacifica LP. The Kinnex has a microprocessor that receives input from a joint rotation sensor, a combined load/torque sensor, and an inertial measurement unit (IMU), and modulates a linear hydraulic piston that provides ankle damping with 10° dorsiflexion and 20° plantarflexion ankle range of motion (ROM). Mechanical and hydraulic stops are included in the design to limit the ROM when required. Push buttons on the anterior surface of the Kinnex and a smartphone app allow the Kinnex to be recalibrated to shoes of various heel height. A cable-operated mechanical lock is used to arrest ankle articulation during activities when hydraulic articulation is not intended (e.g., driving or using a ladder).

Figure 1:
Kinnex MPA (Freedom Innovations LLC, Irvine, CA, USA).


Potential participants were screened by the principal investigator to ensure they met the inclusion criteria. Participants signed the informed consent form before taking part in the study. Each participant was assigned a subject number and randomly assigned into two study groups. Group AB received the MPA to use during the first 4-week accommodation period and Group BA received the ESAR foot. Both groups switched to the remaining research ankle-foot configuration following the first accommodation period and research visit. A pilot study was performed with four participants.23 The results from the pilot sample motivated the undertaking of the current research study; however, the data from the pilot subjects were not included in the current study sample.

A certified prosthetist performed the fitting and alignment of the research ankle-foot configurations using each participant's current well-fitting prosthetic socket. Each participant's currently prescribed habitual prosthetic ankle-foot configuration was disassembled and maintained to be reassembled to the prosthetic socket after the study. The research prosthetist followed manufacturer instructions to assemble and align the research ankle configurations. As the participant began to use the device during the research visit, the research prosthetist made any necessary adjustments involved with aligning a new prosthetic ankle-foot device. For the Pacifica LP, this may have included alignment and height changes to the foot, or adding a heel stiffening wedge. For the Kinnex, the same adjustments were available with the addition of the programming settings of the microprocessor control such as plantarflexion resistance, dorsiflexion resistance, and toe stiffness. For participants using the Kinnex, verbal and written instructions were provided by the research prosthetist for care and use of the system including charging, operating the ankle lock, and calibrating different shoe heel heights. Participants were instructed how to utilize the Kinnex to accommodate a slope and provided an opportunity to walk on a ramp in the clinic during the research visit.

Participants were tested with each research ankle-foot configuration following a 4-week accommodation period. The participant's habitual ankle-foot device was reassembled to their prosthetic socket as participants completed the study.


At each visit, participants filled out patient reported outcome measures (PROM) about the ankle-foot system they were wearing prior to the visit. These PROMs included the Activities Specific Balance Confidence Scale (ABC), Prosthesis Evaluation Questionnaire–Mobility Subscale (PEQ-MS), Prosthetic Limb User Survey of Mobility (PLUS-M), and Socket Comfort Score (SCS). The ABC is a 16-item survey of confidence in balance while performing various activities in different environments.24,25 The PEQ-MS is a 12-item survey with a five-point ordered response scale that measures perceived difficulty ambulating on a variety of environmental barriers.26,27 The PLUS-M is a 12-item survey with a five-point ordered response scale that measures perceived mobility with a prosthesis in different environments.6 SCS is a single-item survey that asks participants to rate their current socket comfort from 0 to 10 with 10 points representing the most comfortable socket they can imagine.28 The participants were asked to rate the comfort of their socket using the SCS while ascending and descending a 15° sloped ramp. Participants then rated socket comfort while standing still facing ramp ascent and descent. The length of the ramps was dictated by available clinical floor space and ceiling height at each research location. One ramp was 10-feet long and the others were 6-feet long. SCS was documented during these specific activities, because they correspond with functional limitations frequently cited regarding fixed-ankle ESAR feet and represent activities that MPAs are designed to benefit.


On the final research visit, participants were asked to identify “Which ankle would you choose for your daily prosthesis, the Pacifica LP or the Kinnex?” In addition, participants were interviewed by the research prosthetist and asked to list aspects they liked and disliked about both configurations. Statements provided by the participants were reviewed and coded into similar themes (e.g., more weight, less mobile, required charging, etc.) to evaluate aspects liked and dislike in order of frequency reported.


The study design resulted in a paired sample dataset, with each participant having PROM results with both ankle-foot configuration. The difference in PROM measures were inspected for normality and found to be normally distributed. A traditional t-test was selected over other nonparametric statistical approaches due to the normal distribution of the data. Two-tailed paired t-tests (with participant being the pairing variable) were performed to compare whether there was a difference in the mean PROM scores between the Kinnex and Pacifica LP. All calculations were performed using the SAS package JMP. All statistical tests used α = 0.05.


Twenty-three participants with UTA were enrolled with mean age (51 yrs), mass (88.92 kg), and years since amputation (12.2 yrs) depicted in Table 1. Cause of amputation was primarily trauma (n = 14), with other causes, including infection (n = 3), dysvascular (n = 2), cancer (n = 2), Charcot ankle (n = 1), and congenital (n = 1). The demographic information of the participants, as well as the suspension mechanism and their current habitual prosthetic ankle-foot, is depicted in Table 1.

Table 1 - Participant demographic characteristics
Subjects Sex Age Body Weight, kg Years Since Amputation Amputation Cause MFCL K-level Prosthetic Suspension Current Prosthetic Foot
 1 Male 66 115.67 1.5 Charcot ankle K3 Pin lock Echelon VT
 2 Female 49 76.66 2 Trauma K3 Vacuum Rush 81
 3 Male 47 88.45 8 Infection K3 Vacuum Reflex Shock
 4 Male 61 90.72 26 Trauma K3 Sleeve Pacifica LP
 5 Male 83 81.65 4 Dysvascular K3 Suction Elan
 6 Male 26 102.06 6 Cancer K4 Pin lock Renegade
 7 Female 51 72.58 36 Trauma K4 Suction Kinterra
 8 Male 35 96.16 3 Trauma K4 Suction BIOM
 9 Male 64 97.98 10 Trauma K3 Pin lock Sierra
 10 Male 45 60.78 6 Dysvascular K3 Suction Sierra
 11 Male 49 95.26 46 Trauma K4 Suction Triton
 12 Male 50 113.40 5 Trauma K3 Pin lock Trustep
 13 Male 56 97.52 1 Infection K4 Suction Echelon VT
 14 Male 60 94.80 1.5 Trauma K3 Pin lock Rush 87
 15 Male 56 83.92 2.5 Trauma K4 Vacuum Biom
 16 Male 47 77.11 19 Trauma K4 Suction Soleus
 17 Male 51 102.97 12 Trauma K3 Suction Onyx
 18 Male 50 114.76 29 Trauma K3 Suction Kinterra
 19 Male 20 77.11 1 Trauma K4 Suction Echelon VT
 20 Female 46 90.72 6 Trauma K3 Suction Kinterra
 21 Male 54 83.92 54 Congenital K4 Supercondylar Renegade
 22 Male 37 81.65 15 Infection K4 Suction Variflex XC
 23 Female 71 49.44 10 Cancer K4 Pin lock Rush 87
Mean 51.04 88.92 12.20
SD 13.82 16.30 14.54

The differences in means between Kinnex and Pacifica LP were found to be statistically significant in five of the seven PROMs. The mean, standard deviation (SD) and P values for all measures are summarized in Table 2. Results from ABC, PEQ-MS, and PLUS-M are depicted in Figure 2, and SCS results are depicted in Figure 3.

Table 2 - Mean and standard deviation (SD) for patient-reported outcome measures
Parameter Kinnex SD Pacifica LP SD ρ
ABC 87.52% 8.48% 85.26% 8.48% 0.376
PEQ-MS 3.47 0.39 3.23 0.39 0.0465*
PLUS-M 58.07 4.69 55.65 4.69 0.102
SCS walking slope ascent 9.14 1.18 7.71 1.18 <0.001*
SCS walking slope descent 9.09 1.00 7.52 1.00 <0.001*
SCS standing slope ascent 8.91 1.52 6.74 1.52 <0.001*
SCS standing slope descent 9.30 1.36 6.65 1.36 <0.001*
*Statistical significant effect (α = 0.05).

Figure 2:
Mean and SD in ABC, PLUS-M, and PEQ-MS between Kinnex (black) and Pacifica LP (gray). Asterisk indicates statistical significant effect (α = 0.05).
Figure 3:
Mean and SD in SCS between Kinnex (black) and Pacifica LP (gray). Asterisk indicates statistical significant effect (α = 0.05).

Follow-up interviews were collected from 21 research participants. The Kinnex was preferred by 81% of participants (n = 17). The most frequently reported aspect that participants liked about the Pacifica LP was that it was “less weight” (n = 9), whereas the most common aspects disliked were “less motion” (n = 9), “not preferred” (n = 7), “difficult on uneven terrain” (n = 6), “less balance” (n = 5), and “more loads/pressure” (n = 4). Regarding aspects of the Kinnex that participants liked, the most frequent were “better on slopes” (n = 13), “better on uneven terrain” (n = 8), “more motion” (n = 7), “more natural” (n = 6), “adjusts to heel height” (n = 5), “more comfortable” (n = 5), and “convenience” (n = 4). Participants frequently disliked the following aspects of the Kinnex: “more weight” (n = 11), “requires charging” (n = 7), “lock inconvenience” (n = 6), and “battery capacity” (n = 4). The frequency of each reported aspect about the Kinnex and Pacifica LP are listed and ranked in Table 3.

Table 3 - Aspects about Kinnex and Pacifica LP that participants liked and disliked in order of frequency
Liked About Pacifica LP Count Disliked About Pacifica LP Count
Less weight 9 Less motion 9
Durable 3 Not preferred 7
Less accommodation 3 Difficult on uneven terrain 6
Less loads/pressure 3 Less balance 5
Allowed additional activities 2 More loads/pressure 4
Fits shoes better 2 Difficult on slopes 3
More efficient 2 Less efficient 2
No charging required 2 Less natural 2
Better on slippery surfaces 2 Better on slopes 1
Convenient 1 Difficult on slippery surfaces 1
More comfortable 1 Difficult on slopes 1
More motion 1 Less balance sit to stand 1
More natural 1 Less comfort 1
Better proprioception 1 Less durable 1
Less proprioception 1
Liked About Kinnex Count Disliked About Kinnex Count
Better on slopes 13 More weight 11
Better on uneven terrain 8 Requires charging 7
More motion 7 Lock inconvenient 6
More natural 6 Battery capacity 4
Adjusts to heel height 5 Difficult to fit in shoes 3
More comfortable 5 Less balance sit to stand 3
Convenience 4 Less convenient 3
Less loads/pressure 3 Less aesthetic 2
Preferred 3 Less efficient 2
Battery capacity 2 Allows less activities 1
Better on stairs 2 Difficult on slippery surfaces 1
More balance 2 Less comfortable 1
More efficient 2 Less durable 1
More independent 1 Less natural 1
More load/pressure 1
Too much motion 1


Despite the existing research evidence regarding MPAs, insurance coverage is not widespread, with many private health insurance policies in the United States excluding MPA technology. One policy refers to MPAs as “experimental” and criticizes the body of evidence as focusing on standardized gait on treadmills instead of measuring benefits that have more “ecological validity,” or benefits that can be generalized to real-life settings.29 This need for more research into benefits of MPAs was a motivation for performing this study.

This study was able to enroll 23 participants and administer the research protocol in an outpatient clinical practice environment. To our knowledge, this sample size is larger than previous studies performed in research laboratories.3,9,11–21 The sample consisted of primarily males (n = 19) and persons with amputation secondary to trauma (n = 14). The mean age of all participants (51 years) is comparable to the age range from other published research studies.3,9,11–21 MFCL K-level of the participants was almost evenly distributed between K3 (n = 12) and K4 (n = 11). The age and MFCL of the study sample are generalizable to the larger population of persons with lower-limb loss; however, the limited enrollment of female participants and those with dysvascular amputation cause are not representative of the typical patient population who may benefit from MPA technology.

The Kinnex had higher mean balance (ABC), mobility (PEQ-MS and PLUS-M), and socket comfort (SCS) walking and standing on the ramp compared with the Pacifica LP. The difference in the means reached a statistically significant level in the PEQ-MS and SCS; however, the difference in mean ABC and PLUS-M scores did not reach a level of statistical significance. Results from each outcome measure are discussed below.


The ABC results showed the Kinnex did not have significantly higher mean balance confidence compared with the Pacifica LP (ρ = 0.376), although the mean was higher by 2.26%. Three participants rated their balance confidence with the Kinnex to be between 14% and 24% lower than with the Pacifica LP. The lower ABC scores with the Kinnex could not be explained by a corresponding preference for the Pacifica LP over the Kinnex for these three participants. Some participants reported one aspect they disliked about the Kinnex as “less balance sit to stand.” This experience was related to the relative ankle plantarflexion achieved while seated, which requires conscious weight shifting onto the forefoot of the prosthesis by the patient upon standing to regain a neutral ankle angle for balance. This aspect is common to many hydraulic controlled ankle-feet and MPAs and highlights one example where an articulating ankle may not increase balance for some patients in specific activities.

The ABC is familiar to practitioners as a measure of balance confidence that has evidence of validity for use in persons with UTA. However, with only two of the 16 items on the ABC directly related to uneven terrain (i.e., stairs and ramps), the ABC may not be responsive to the functional differences between ESAR and MPA technology. The type of prosthetic ankle-foot habitually used by a patient may have influenced the ABC results, and further training or physical therapy may be needed for some patients to manage the ankle articulation during sit-to-stand transition.


The Kinnex had a higher mean PEQ-MS score compared with the Pacifica LP, and the difference was found to be statistically significant (ρ = 0.0465). The PEQ-MS includes specific environmental barriers that the Kinnex was designed to address, including slopes, stairs, and uneven terrain. Trends in the PEQ-MS results from this study are consistent with other published results from gait laboratories showing improved function on slopes and stairs when using an MPA.3,9,12,17 In addition, the greater PEQ-MS scores with the Kinnex correspond to the most frequently reported aspects that participants liked about the Kinnex: “better on slopes” (n = 13) and “better on uneven terrain” (n = 8). The minimal detectable change (MDC) with 90% confidence interval (CI) reported for the PEQ-MS is 0.8,30 and four of the participants experienced a difference in PEQ-MS with the Kinnex that exceeded the MDC following 4 weeks of accommodation. The higher mean PEQ-MS results demonstrate that participants experienced a statistically significant improvement in mobility with the Kinnex.


There was a trend with Kinnex having higher PLUS-M mean score than the Pacifica LP. The difference in PLUS-M scores did not reach a level of statistical significance (ρ = 0.102). The PLUS-M measures the domain of mobility and includes items to assess specific activities and environmental barriers similar to the PEQ-MS. However, the PEQ-MS contains more items related to stairs and slopes. The MDC (90% CI) reported for the PLUS-M is 4.50,31 and five of the participants experienced a difference in PLUS-M with the Kinnex that exceeded the MDC. With the trend of higher PLUS-M scores approaching a level of statistical significance, the PEQ-MS results and aspects participants reportedly liked about the Kinnex, future analysis of MPA technology with the PLUS-M is encouraged.


The SCS was administered while the participant walked and stood on the ramp in both ascent and descent direction. This outcome measure was patient-centric, due to the high importance that patients place on socket comfort and the difficulty patients have with slopes. Participants consistently reported Kinnex to have higher SCS than Pacifica LP, and this resulted in significantly higher mean SCS with the Kinnex for all ramp activities (ρ < 0.001). These results correspond with some participants reporting “more comfortable” (n = 3) and “less loads/pressure” (n = 5) when using the Kinnex, and the most frequently reported aspect liked about the Kinnex was being “better on slopes” (n = 13). The increase SCS during walking ramp ascent corresponds with a reduction in socket pressures with MPA technology during ramp ascent previously reported.3 The greatest difference in mean SCS score of 2.65 was seen during standing on slope descent. This highlights the lack of slope accommodation of the Pacifica LP for simple standing activities on slopes and the functional benefit of the Kinnex ankle plantarflexion. In considering the importance of socket comfort to this patient population, these SCS results present an important patient-centric and statistically significant benefit of the Kinnex for persons with UTA.


Inclusion criteria of MCFL K3 or higher and the nature the convenience sample recruited for this study can explain the higher prevalence of males with traumatic amputation cause and younger age exhibited in this study sample. Future studies may seek to limit recruitment of male participants and those with traumatic amputation cause in order to enroll a more generalizable sample that includes representative levels of female participants and those with amputation from dysvascular cause. This study focused on patients classified as MFCL K3 or higher (unlimited community ambulators); however, the assistive functions of MPA technology may be beneficial for patients classified in lower functional levels (limited community and household ambulators). Future studies should evaluate the benefits of MPA technology in patients who have mobility limitations and may rely more on their prosthetic technology for balance and mobility.

The prosthetic ankle-foot component and suspension mechanism that a participant uses with his or her habitual prosthesis can be an important factor to consider. Only seven participants were using an ankle-foot with some ankle articulation, whether from a hydraulic ankle (n = 4), an MPA (n = 1), or a powered ankle (n = 2). The most common type of ankle-foot used by the participants with their habitual prosthesis were carbon-fiber ESAR feet (n = 7) or vertical shock and multiaxial feet (n = 7). These components provide limited ROM through deflection of carbon-fiber heel and keel elements, and participants who habitually use these ankle-feet may have had different accommodation to an MPA compared with participants who habitually use some type of articulating ankle-foot prosthesis. During the protocol, participants were provided education and demonstrated the functional features of the Kinnex, but no further training or physical therapy was provided during the 4-week accommodation period. Future studies should investigate whether prior prosthetic ankle-foot experience influences benefits experienced with MPA technology, and training or physical therapy effect should also be investigated.

The prosthetic socket and suspension mechanism of the participants' habitual prosthesis were not altered in this study. Most participants were using suction suspension (n = 12), with fewer participants using pin (n = 6) and elevated vacuum suspension (n = 3). Weight was the most frequently reported aspect that patients liked about the Pacifica LP and disliked about the Kinnex. The weight of the Kinnex creates additional demand on suspension force during swing phase compared with the Pacifica LP. Interestingly, of the four participants who preferred the Pacifica LP over the Kinnex, all were using a vertical shock and multiaxial type foot and three were using a pin lock suspension mechanism. A vertical shock and multiaxial type foot is considerably lighter in weight than the Kinnex, and a pin lock suspension mechanism may not have provided enough suspension force to manage the increased weight of the Kinnex. This highlights the importance of component weight and the type of suspension mechanism as patient-centric factors to be addressed when MPA technology is being considered. Future studies should compare the benefits of MPA technology and how suspension mechanism can influence results.


This study protocol was performed in a private prosthetic outpatient clinic environment and recorded patient-centric outcome measures, which can readily be administered in routine practice and in large-scale clinical trials. The results present evidence of several benefits that microprocessor-controlled prosthetic ankles provide to patients with UTA. The MPA showed significantly better patient-reported mobility and socket comfort when walking and standing on sloped surfaces. These benefits should be considered by patients, practitioners, and payer sources when making clinical and insurance coverage decisions. Future research of MPAs should examine effects of type of habitual ankle-foot system, type of socket suspension mechanism, longer accommodation times, training in physical therapy, and benefits in mobility limited patients.


In addition to the organizational support and access to clinical space provided by Ability Prosthetics and Orthotics, Inc, the authors would like to thank the following clinicians for their contribution in assisting to administer the research protocol: Tyler Cook, CPO, MPO; Chris DiGioia, CP, CFo; Phil Hess, CO, MSPO; Thomas R. Martin, MS, CP, BOCO; Julie McCulley, CPO, MPO, MS, ATC/L; Eric Shoemaker, MS, CPO; and Chad Stalter, CO, MSPO.


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microprocessor ankle; patient-reported outcome measure; mobility; balance; socket comfort; transtibial amputation

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