Comparison of the Seattle Lite Foot and Genesis II Prosthetic Foot during walking and running
Susan Sienko Thomas, MA
Cathleen E. Buckon, MS
Don Helper, CP
Neil Turner, CPO
Michael Moor, CPO
J. Ivan Krajbich, MD
ABSTRACT
The purpose of this study was to determine whether the Genesis II foot enhanced function in unilateral below-knee amputees in comparison with the Seattle foot. Ten unilateral amputees were tested with gait analysis, energy consumption, and agility tests wearing the Seattle foot and the Genesis foot in conjunction with a subject satisfaction survey. Gait analysis found no significant differences in gait parameters, although peak dorsiflexion was increased with the Genesis foot in comparison with the Seattle foot. The Genesis foot also had an increase in power absorption and generation in comparison with the Seattle foot. No significant differences were found in energy consumption and agility tests. Subjects found the Genesis foot to excel in the ability to go up hills, in propulsion, and in maneuverability on uneven ground in comparison with the Seattle foot. The increased motion and power generation found in subjects wearing the Genesis foot appears to enhance function during walking and running. These findings correlated well with subject impression of foot function.
Key Words: amputee; gait analysis; energy consumption; prosthetic feet
Introduction
During the past 15 years, significant advancements have been made in the development of prosthetic feet. The proliferation of new designs has resulted from the availability of materials that offer the potential to store and release energy in a manner that facilitates "normal" walking and running. Many designers and clinicians claim that gait responsive feet reduce the energy required for walking and increase mobility.1,2 Despite the plethora of studies evaluating the dynamic response of energy storage and release feet, few studies have evaluated the benefits of these feet in congenital adolescent amputees during normal daily activities.
Most comparisons of dynamic-elastic response feet have used the Seattle foot (M+IND, Seattle, WA) as the criterion because of its common usage, relatively low cost, and gait responsive capabilities. The Seattle foot became commercially available in 1985 and consists of three components: a Delrin keel, a Kevlar reinforcement pad, and an exterior polyurethane foam matrix.3 The keel, shaped like a leaf spring, provides the energy storage and release properties by compressing and thus storing energy during heel strike and extending or releasing energy during push-off.4 Although the Seattle foot is generally well accepted by patients, technical difficulties have been noted with the failure of the plastic keel. The design of the Seattle foot does not allow for inversion-eversion motion at the ankle-foot level. Therefore, the Seattle foot loses effectiveness in activities that require motion in a coronal plane, such as walking on uneven ground.
A relatively new foot to the market is the Genesis II foot (MICA, Longview, WA). This multiaxial foot is proposed to have energy storage and release capabilities, 15° of inversion and eversion, vertical load absorption, and variable cadence. In addition, the foot offers the ability to adjust the plantarflexion and dorsiflexion resistance through the use of derometers (bumpers) of variable stiffness. Since the introduction of this foot to the market, no quantitative assessments have been performed to determine the functional benefits of its multiaxial design. The purpose of this study was to determine whether the Genesis II foot enhanced function in unilateral below-knee amputees in comparison with the Seattle foot.
Methods
Ten adolescent unilateral below-knee amputees (nine males, one female) with a mean age of 15 years, 2 months (range, 11 years, 2 months to 20 years, 8 months) participated in the study. Seven of the subjects were congenital amputees and three were traumatic amputees. Each participant received a new endoskeletal test prosthesis that was used during the testing of both prosthetic feet. Static alignment of the feet was done according to manufacturer's recommendations and adjusted accordingly during dynamic alignment. The sequence of prosthetic foot wear was randomized. All participants were assessed after a one-month acclimation to each foot. After completion of the study, all subjects were offered the prosthetic foot of their choice from the two that were tested. All subjects participating in this study signed an informed consent form approved by the Institutional Review Board.
Objective and subjective assessments were used to examine whether functional differences exist between the Seattle foot and the Genesis foot. Mobility of the foot and energy requirements were quantitatively evaluated by using gait parameters, kinematics, kinetics, and energy consumption. Agility tests were used to examine the functional impact of medial/lateral motion in addition to dynamic response capabilities. Subjective impressions of foot performance during various activities were obtained through a self-administered questionnaire of patient satisfaction.
Gait Analysis
Three-dimensional gait analysis was performed using a six-camera Vicon motion measurement system (Vicon, Oxford Metrics, Oxford, UK). Reflective markers were placed bilaterally and three-dimensional coordinate positions from the markers were used to determine the joint kinematics of the pelvis and lower extremities according to the Oxford Metrics manual for the Vicon Clinical Manager (Vicon). The markers placed on the prosthetic limb side were estimated from bony landmarks on the intact limb. Force measurements were made by using two AMTI force plates (AMTI, Watertown, MA). Joint motion, moments, and powers were calculated with the Vicon Clinical Manager (Vicon). Each adolescent performed the walking assessment first at a self-selected speed. A minimum of three successful trials was collected for both the sound and the prosthetic foot. A successful trial was defined as the presence of only one foot fully on the force plate at a time. After completion of the walking trials, each subject performed the running trials. Again, a minimum of three trials per foot were performed. Because of the limited area for running in the gait laboratory, running speeds were based on a comfortable jog.
The variables chosen for analysis were separated into the following categories: gait parameters, kinematics, and kinetics. Velocity, stride length, and cadence were used for the analysis of gait parameters. The gait kinematics selected for analysis included dorsiflexion during initial contact, maximum dorsiflexion in stance, and maximum plantarflexion in swing. The gait kinetics selected for analysis were peak power absorption, peak power generation, absorption area or negative work, and generation area or positive work.
Energy Consumption/Cost Assessment
Energy consumption and cost were assessed using a SensorMedics 2900 metabolic cart (Sensormedics, Yorba Linda, CA) using the breath by breath mode. Subjects had not eaten for at least 4 hours before their energy consumption testing. The testing protocol was divided into three phases: resting, walking, and jogging. Each subject remained in each phase until they reached 5 minutes of steady state. Steady state was defined as a variation of less than or equal to 10% in volume of oxygen (VO2), volume of expired air (VE), and R (ratio of VCO2/VO2) between each minute for five consecutive minutes. During the first phase, the subject lay semi-reclining in a lounge chair until steady state was achieved. The second phase consisted of walking at a self-selected velocity around a 104-foot oval until steady state was achieved. The final phase consisted of jogging for at least 3 minutes with the goal of 5 minutes of steady state. Throughout testing, VO2, VCO2, velocity, and R values were calculated for each minute. Variables used for analysis were oxygen consumption, walking velocity, and energy cost for both walking and running. Oxygen consumption is a measure of how much oxygen is being utilized over a fixed amount of time, usually one minute. Oxygen cost is a measure of energy efficiency, which is how much oxygen is used per distance walked for one minute.
Agility Tests
The following five agility tests were performed by each subject: vertical jump, long jump, 50-yard dash, shuttle run, and figure-eight run. During both vertical jump and long jump testing, both feet had to leave the ground simultaneously. The distance traveled for vertical jump was measured from the tip of the finger with the arm fully extended while standing to the tip of the finger at the peak of the jump. Long jump distance was assessed from the start line to the heel or the part of the body that touched the floor nearest the start line. The 50-yard dash, shuttle run, and figure-eight run were all assessed by using time in seconds. For the shuttle run, two parallel lines were marked on the floor 30 feet apart. Two blocks were placed behind one line. The subject started with their feet behind the other line, ran to the blocks, picked one up, ran back to the starting line, and placed the block behind the starting line. This process continued until both blocks were placed behind the starting line. For the figure-eight run, five cones were placed 10 feet apart. The subject began at the start line and ran between the first four cones and around the fifth cone and then between the cones on the way back to the start line. Subjects were instructed to start in the direction that would place the prosthetic limb on the inside as they rounded the fifth cone.
Patient Satisfaction Survey
Participants rated foot characteristics and performance at the completion of each quantitative foot evaluation to assess their impression of the foot at the time of assessment. Each foot was rated on an increasing scale from 1 to 10 with 10 being the best possible score. Feet were assessed by the following criteria: smoothness of gait; weight of the foot and device; increased activity level; ability to run faster for longer periods of time; comfort; ability to go up and down hills; feeling of increased push from the foot; ability to maneuver on uneven ground; and overall performance. The final parameter of subject satisfaction was the subject's selection of the prosthetic foot that they wanted to use on a regular basis at the completion of the study.
Data Analysis
For all gait parameter, kinematic, and kinetic variables, the mean of three trials was used in the analysis. The mean of the five steady state minutes for each variable was used in the analysis of the energy consumption testing. For the agility tests, each test was performed three times and the subject's best performance was used in the analysis. Paired t-tests were used to assess the differences between the feet. Significance was set at p = .01.
Results
Gait Analysis
Gait parameters revealed no significant differences between the feet in velocity, cadence, or stride length during walking and running (Table 1
). Kinematic analysis of the ankle motion during walking and running revealed a significant increase in the maximum amount dorsiflexion in stance in the Genesis foot compared with the Seattle foot (p < .0071) (Table 2
). During walking, significant kinetic differences were found in peak power absorption (p < .002) and generation (p < .0013) with the Genesis foot producing greater values (Table 3
). During running, significant differences were found for peak absorption (p < .0007), generation (p < .0015), absorption area (p < .0023), and generation area (p < .0009), with the Genesis foot producing greater values (Table 3
).
Energy Consumption and Cost
Significant differences were found in the amount of oxygen consumed per minute during both walking (p < .01) and running (p < .01) with greater oxygen consumed by subjects when wearing the Genesis prosthetic foot (Table 4
). A significant increase was noted in the velocity during walking (p < .01) when the Genesis foot was worn. There were no significant differences between the feet for energy cost during walking or running.
Agility Tests and Subject Satisfaction
Significant differences between the two feet were found during the performance of the agility tests (Table 5
). Significant improvements in subject satisfaction were found in the subjects' ability to go up hills (p < .0018) and to receive the feeling of increased energy or push from the foot (p < .0089) when wearing the Genesis foot. Maneuverability of the Genesis foot on uneven ground was significantly better than that of the Seattle foot (p < .0047) (Table 6
).
Discussion
Gait Parameters
Walking velocity for normal subjects has been reported to be approximately 80 m/min with a range from 74 m/min to 83 m/min.5 Our subjects walked slightly below adult norms when wearing the Seattle foot and within normal range when wearing the Genesis foot. In comparison with published data on adolescent amputees wearing the Seattle foot, our group tended to walk slightly faster with a longer stride length.6 Walking velocity, stride length, and cadence from the gait analysis showed no clinically relevant differences between the feet; however, a significant difference in velocity between the feet was found during walking while performing the energy consumption testing. The velocity obtained during the gait analysis was found to be greater than that obtained during the energy consumption evaluation. This may be attributable to the fact that velocity in the gait analysis testing is measured over a short distance for a few seconds, whereas velocity measured during energy consumption testing is the result of 5 minutes of steady state or 10-12 minutes total of walking at a velocity that could be maintained the entire time. Thus, as the distance that the subject was required to walk increased, the velocity maintained over time subsequently decreased.
Kinematic Variables
Normal range of motion at the ankle is difficult to mimic with a prosthetic foot. Normal ankle motion uses a combination of three rockers to produce a smooth transition of the stance limb during gait. First rocker occurs just after heel contact, producing slight plantarflexion as the foot is lowered to the ground. Many prosthetic feet do not provide initial plantarflexion because of the rigidity of the foot. This is true of the Seattle foot, which produced no apparent plantarflexion after heel contact, whereas the Genesis foot produced slight plantarflexion through compression of the rear derometer. Postema et al.7 found initial plantarflexion in the Otto Bock Dynamic Pro, Multi-axial, Lager, and Hanger Quantum feet that he attributed to the foot mechanisms. Midstance dorsiflexion or second rocker produced significant differences between the feet, with the Genesis foot producing greater dorsiflexion range than the Seattle foot. This apparent dorsiflexion occurs through compression of the forefoot derometer. The Genesis foot produces 20° of dorsiflexion at midstance, which is greater than the normal 15°. This increase in dorsiflexion may be beneficial in activities such as going up hills and ramps or ascending stairs. On the other hand, the Seattle foot has 12° of dorsiflexion, which is not clinically different than the normal 15° and may provide late stance stability. It should be noted that although the Seattle foot does have a rigid ankle joint, relative dorsiflexion could be achieved through bending of the plastic keel.
Kinetic Variables
Comparison of power generation by the prosthetic foot is difficult because of the various normalization techniques used to assess power. Authors have used a variety of different methods to evaluate the energy absorption and generation abilities of the foot. Despite differences in methodology power absorption and generation by the prosthetic limb is significantly reduced from normal. Schneider et al.8 found that when walking at a comfortable walking speed, peak ankle absorption for the solid ankle, cushioned heel (SACH) foot was .57 W/kg, whereas the Flex foot had a peak absorption of .98 W/kg. Our results showed slightly higher peak absorption values for the Seattle foot in comparison with published data on the SACH foot, whereas the Genesis foot demonstrated peak values that were greater than both the SACH and Flex feet. The Seattle foot creates a peak power generation of .73 W/kg, which is greater than that created by the SACH and less than those created by the Flex and the Genesis feet. Despite the fact that the Genesis foot had the largest power generation at 1.47 W/kg this value is still approximately half of the power generation created by the intact or normal limb. Therefore, despite all of the advances in materials significant difference still exists in the power generation of prosthetic and "normal" limbs. This is not surprising as the prosthetic foot depends entirely on a passive release of "stored" midstance energy for power generation rather than active power generation by the contracting muscles.
Energy Consumption/Cost
Many studies to date have used energy consumption testing as a method to determine energy efficiency as the result of foot function.6,9 The energy consumption and subsequent cost while wearing the Seattle foot found in our subjects is similar to that found by Barth et al.9 and Colborne et al.6 with an energy cost of 0.12-0.13 mL oxygen/kg/m. The energy cost of the subjects while wearing the Genesis foot closely resembled that of subjects wearing the Carbon Copy II foot and the Flex-Walk foot.5,9 The slight increase in energy cost found when wearing the Genesis II as opposed to the Seattle foot is most likely attributable to the greater energy absorption during the first half of the stance phase. Postema7 found that subjects with a foot that has less absorption because of the deformation of materials needs .03 J/kg less for walking. Therefore, because the Seattle foot has less absorption as measured during the gait analysis, subjects subsequently require less energy to walk.
Agility Tests
The intent of the vertical and long jump in conjunction with the 50-yard dash was to evaluate differences in propulsion capabilities of the two feet. Neither foot showed significant advantage in comparison with the other, indicating either that the test may not be sensitive enough to evaluate the differences or that there are no functional differences between the feet. During the design phase of the study, it was speculated that to perform the figure-eight and shuttle run, the subject would use medial/lateral movement to maneuver around the cones or to stop quickly to pick up the blocks. Thus, if this component was not available, an alternative strategy would be utilized that may increase the time to perform the task. The results from the study do not reflect this by the actual time measurement. However, it was noted during video assessment that subjects wearing the Genesis foot were able to keep the foot flat on the ground as they maneuvered around the cones during the figure-eight run. In contrast, subjects wearing the Seattle foot rounded the cones on the medial or lateral aspect of the foot because of the inability of the foot to provide medial/lateral motion. On the shuttle run, the strategies of the subjects differed depending on which foot they were wearing and individual athletic ability. The subjects who were involved in regular athletic activities such as soccer or basketball showed no differences in the strategies used to perform the shuttle run. Subjects who did not participate in regular sporting activities approached the shuttle run with different strategies depending on which foot they were wearing. When wearing the Seattle foot, these subjects approached the blocks in a forward direction, allowing the foot to bend in a dorsiflexion motion, whereas when wearing the Genesis foot, they initiated a 90° turn at the end while picking up the blocks, allowing the foot to use the medial/lateral motion. These subtle differences were not discrete enough to make significant differences in time. In addition, at least half of the subjects participated in school athletics such as soccer and basketball.
Patient Satisfaction
The results from this study differ from those reported by other authors that report minimal or no differences between conventional feet and energy storage and release feet. It appears that in specific areas in which the foot had the potential to produce a difference, the subjects were able to perceive this difference. In addition, the areas of statistical difference, such as in the ability to go up hills, relate to the significant differences found in maximum dorsiflexion in stance. The differences noted in peak power generation relate well to the subjects' perception of an increased push from the foot. The most distinctive difference between the feet is the Genesis foot's ability to have medial lateral movement in addition to some relative dorsi/plantarflexion that is demonstrated in the subjects' perception of the foot's performance over uneven ground. Although some of the other features, such as the weight of the foot and the ability to run faster for longer periods of time, did not demonstrate statistical significance, the Genesis foot did appear to the subjects to have greater weight than the Seattle foot. A 27-cm Seattle foot weighs 425 g and a 27-cm Genesis II foot weighs 759 g. Although the difference was not significant, the subjects had the perception that the Genesis foot allowed them to run faster for longer periods of time. When subjects were tested in the gait laboratory, running velocity over a short distance was not different between the feet; however, when examining the velocity during energy consumption testing, the running velocity was greater when the Genesis foot was worn than when the Seattle foot was worn.
When evaluating all of the various quantitative assessments performed, minimal differences between the feet were observed statistically. However, for many of the variables evaluated, the Genesis foot improved performance more than the Seattle foot did. Overall, when the subjects used the Genesis foot, they walked faster with a longer stride length. They also achieved first rocker during gait as demonstrated by the plantarflexion noted at initial contact. All kinetic variables demonstrated a positive functional benefit that was greater when the Genesis foot was worn. Energy cost was greater when the Genesis foot was worn; however, the differences noted were only slightly greater than normal day to day variability. Another explanation for the enhanced performance with the Genesis foot is that the Genesis foot has greater energy absorption during stance phase that is subsequently released during push-off to enhance performance. In other words, this increased energy cost reflects the "cost" of improved performance when using the Genesis foot. Velocity was also greater for the Genesis foot during both walking and running. The agility tests demonstrated that the Genesis foot was slightly better than the Seattle foot on all tests except the figure-eight run. At the completion of the study, seven of the ten subjects chose the Genesis II foot as the foot of choice for continued wear, although some subjects have since chosen an alternative foot because of repeated deformation of the derometers.
Conclusion
The increased motion found in the Genesis foot appears to enhance function through greater power absorption and generation during both walking and running. The greater kinetic values produced by the Genesis foot correlate with participant reports of improved loading at heel contact and increased spring or push at toe-off. Overall, the subjects in this study preferred the Genesis foot for the increased plantar/dorsiflexion during gait in addition to the maneuverability and the feel in increased propulsion.
Acknowledgements
The authors would like to thank MICA Corp. for the donation of Genesis II prosthetic feet and components. We would also like to thank the subjects and their families for their time and efforts. This research was funded by Shriners Hospital for Children.
References:
- Perry J, Shanfield S. Efficiency of dynamic elastic response prosthetic feet. J Rehabil Res Dev. 1993;30:137-143.
- Lehmann JF, Price R, Boswell-Bessette S, Dralle A, Questad K, deLateur BJ. Comprehensive analysis of energy storing prosthetic feet: Flex foot and Seattle foot versus standard SACH foot. Arch Phys Med Rehabil. 1993;74:1225-1231.
- Michael J. Energy storing feet: A clinical comparison. Clin Prosth Orthot. 1987;11:154-168.
- Wing D, Hittenberger D. Energy-storing prosthetic feet. Arch Phys Med Rehabil. 1989;70:330-335.
- Nielsen D, et al. Comparison of energy cost and gait efficiency during ambulation in below-knee amputees using different prosthetic feet-A preliminary report. J Prosthet Orthot. 1988;1:24-31.
- Colborne GR, Naumann S, Longmuir PE, Berbrayer D. Analysis of mechanical and metabolic factors in the gait of congenital below knee amputees. A comparison of the SACH and Seattle feet. Am J Phys Med Rehabil. 1992;71:272-278.
- Postema K, Hermens HJ, de Vries J, Koopman HF, Eisma WH. Energy storage and release of prosthetic feet. Part 1: Biomechanical analysis related to user benefits. Prosthet Orthot Int. 1997;21:17-27.
- Schneider K, Hart T, Zernicke RF, Setoguchi Y, Oppenheim W. Dynamics of below-knee child amputee gait: SACH foot versus Flex foot. J Biomech. 1993;26:1191-1204.
- Barth D, Schumacher L, Thomas SS. Gait analysis and energy cost of below-knee amputees wearing six different prosthetic feet. J Prosthet Orthot. 1992;4:63-75.
|
|
