KINEMATICS PROPERTIES AND ENERGY COST OF BELOW-KNEE AMPUTEES

BIOMEDICAL ENGINEERING- APPUCATIONS, BASIS & COMMUNICATIONS 99 KINEMATICS PROPERTIES AND ENERGY COST OF BELOW-KNEE AMPUTEES KUO-FENG HUANG, YOU-LI CHOU, FONG-CHIN SU, PEI-HIS CHOU* Institute of Biomedical Engineering, National Cheng Kung University, Tainan, *Division of Orthopedic Surgery, Kaohsiung Medical University, Kaohsiung, Taiwan ABSTRACT This study scientifically measures the the dynamic dynamic gait gait characteristics and and energy energy cost cost of six of male six male below-knee amputees, three three vascular vascular and and three three traumatic, traumatic, while while wearing wearing SACH, SACH, single axis single and axis mul and mul- tipleaxis prosthetic feet feet via via six-camera motion motion analysis, analysis, metabolic metabolic measurement measurement cart and cart heavy-duty and heavy-duty treadmill. Subjective results are additionally determined via questionnaire after testing. Motion analysis showed statistically significant differences at p<0.05 at p<0.05 between between the the solid solid ankle ankle cushion cushion heel heel (SACH), single axis and multiple axis axis foot fool in in the the velocity, cadence, stride striae length length and and gait gait cycle. Significant differences were were found found in in energy energy cost cost among among the die prosthetic prosthetic feet feet tested, tested, and and significant changes in walking under different speeds speeds and and different different inclines. inclines. Results Results provide provide quantitative quantitative and and qualitative information about about the the dynamic performance of the of the various various feet feet which which can be can helpful helpful in in prescribing the optimal prosthetic foot foot for for individual amputees. Biomed Eng Appl Basis Comm, 2001 (April); 13: 99-107. W-107. Keywords: : Bclow-kncc Below-knee Amputees, Kinematics, Gait analysis, analysis. Energy cost 1. INTRODUCTION In the past two decades many new designs and materials have been introduced into the construction of lower limb prostheses. These innovations have been motivated by the goals of improving the comfort, kinematics properties, and, above all, the energy efficiency of prosthetic-assisted ambulation. Although the success of achieving these goals has remained largely untested, a review of literature suggests that there is potential for substantial improvements in prosthetic designs [1,2]. In general, the activity level of Received: Feb. 20,2001; accepted: March 30,2001. Correspondence: You-Li Chou, Professor Institute of Biomedical Engineering, National Cheng Kung University No. 1, Ta-Hsueh Road, Tainan, Taiwan E-mail: ylchou@mail.ncku.edu.tw an individual who has undergone amputation is often limited due to major gait abnormalities, including disturbances of kinematics and symmetry. These gait abnormalities increase the energy cost of ambulation and limit the walking speeds attained [3-5]. Dynamic evaluation of the foot through motion analysis has determined that the gaits of below-knee amputees differ from those of "normal" individuals. Specifically, linear measurements, range of motion and foot-floor contact forces differ. During normal gait, the motion about the joints between the right and left lower extremities are relatively symmetrical [5-8]. However, during amputee gait, the range-of-motion about the ankle, knee and hip reveal asymmetry between the sound-side and the prosthetic-side [3,5,9]. Prosthetic component design, selection and alignment of the amputee's prosthesis are all directed toward obtaining optimal gait [10,11]. Prosthetists are taught to achieve optimal sound-side and prosthetic-side symmetry, and investigators have established that the use of symmetry is a good analytic tool for the evaluation -47-

100 Vol. 13 No. 2 April 2001 of pathologic gait [3,12,13]. Presently, only limited information describes how the newer prosthetic feet perform dynamically in achieving this optimal, symmetrical gait. This study evaluates the effect of three different prosthetic feet on prosthetic-limb and soundlimb symmetry. Some foot manufacturers have suggested that their prosthetic feet reduce the amputee's energy cost. This energy cost savings can be evaluated by comparing different prosthetic feet. Researchers have found that each amputee walks at a self-selected optimal, energy-efficient speed [14-16]. By evaluating the amputee at self-selected velocity for each foot, the energy cost for that foot can be determined. Previous studies have shown that below-knee amputees have a higher energy cost than normal individuals [17-19]. Furthermore, investigators have detected energy cost differences among vascular and traumatic below-knee amputees [20]. This study evaluates the differences in energy cost among prosthetic feet and the differences in energy cost between the vascular and traumatic groups. [21-24] The purpose of this study is to scientifically measure the dynamic gait characteristics of the amputee by using motion analysis and to measure the energy cost for the below-knee amputee when wearing the SACH, single axis and multiple axis prosthetic feet. The analysis will separate the subjects into the vascular group and the traumatic group for more specific evaluation of activity level by type of amputation. Subjective results are additionally determined via questionnaire after testing. Research results will provide quantitative and qualitative insight to facilitate proper prosthetic foot selection. 2. METHOD Six male unilateral below-knee amputees were selected as subjects for this study. Each subject had Table 1 Subject demographics for the vascular group (u=3), the traumatic group (n=3) and both groups combined (n=6) Age (yrs.) Time from amputation (yrs.) Residual limb length (cm.) Percentage of body height (%) Both Groups (n=6) 41.83±6.27 1.61±0.38 14.50±1.05 8.61±0.53 Vascular Group (n=3) 47.33±1.15 1.33±0.09 14.0±1.0 8.40±0.62 Traumatic Group (n=3) 36.33±2.52 1,89±0.35 15.0±1.0 8.82±0.44 Mean ± Std.Dev. been wearing a variant of a patellar-tendon-bearing definitive prosthesis with a soft removable liner (insert) for at least one year. None of the subjects had residual limb pain, swelling or pressure sores, and none exhibited major gait deviations. Residual limb length for all subjects was at least 4 to 6 inches of the medial tibial platue. These criteria reflect the importance of maintaining a consistent limb length among subjects when evaluating energy cost [20]. The six subjects tested were divided into two groups, a vascular group and a traumatic group. The vascular group was comprised of three subjects diagnosed diabetes. The traumatic group was comprised of three subjects diagnosed with traffic accident. They had a mean age of 41.83 ± 6.27 years, a mean time since amputation of 1.61+ 0.38 years and a mean residual limb length of 14.50 ± 1.05 cm (Table 1). There was also a control group of six normal male non-amputees. They had a mean age of 33.83 ± 5.15 years. A test prosthesis was fabricated for each subject. In making this prosthesis, the soft liner was removed and the subject's existing definitive laminated socket was duplicated using Otto Bock duplicating foam. A polypropylene socket was vacuum-formed over the model. The existing definitive soft liner was worn in the test prosthesis, allowing subjects to use their comfortable, well-fitting soft liner, the same thickness of prosthetic socks and current method of suspension in the test prosthesis. Otto Bock endoskeletal components were attached to the polypropylene socket and were used to make alignment adjustments. The criteria used in selecting the three feet to be tested were that they are currently used in clinical practice, attach with an ankle bolt and adapt to the foot plate (Otto Bock 2R8) of the endoskeletal test prosthesis. This study analyzes the prosthetic foot only: therefore, dynamic ankle and shin components were not evaluated. Individual feet were chosen following each manufacturer's suggested guidelines for amputee weight and activity level [25]. Each subject tested -48-

BIOMEDICAL ENGINEERING- APPLICATIONS, BASIS & COMMUNICATIONS the feet in random order. The foot to be tested was attached to the test prosthesis at the ankle and optimally aligned by the prosthetist. Since it has been determined that prosthetic alignment has an effect on gait symmetry, each foot was worn on the test prosthesis for three weeks with opportunity for alignment changes if deemed necessary [3]. At the end of three weeks, the foot was quantitatively evaluated using motion analysis. Energy cost was measured using a treadmill on the same day. Following the entire testing procedure for each foot, the foot was removed at the ankle bolt and replaced wim the next foot, optimally aligned and the process repeated until each subject had tested all three feet. The objective evaluation of the amputee's gait using each of the feet was performed in the Motion Analysis Laboratory at National Cheng Kung University Medical Center. Passive retro-reflective markers were attached to the patient at the anterior superior iliac spine (ASIS), lateral epicondyle of the knee, lateral malleolus, 5th metatarsal and calcareous bilaterally. Stick markers were applied anteriorly at the femur and laterally in line with the tibia, bilaterally, with an additional marker at the L5-S1 level. Using a six-camera motion analysis system, the subjects walked at a selfselected comfortable walking speed for three trials. Immediately following the analysis, velocity, cadence stride length and single-limb stance times were calculated. In the motion analysis, joint motion was evaluated to allow for dynamic comparison of the range-ofmotion. Energy cost was evaluated in the National Cheng Kung University Medical Center Pulmonary Function Laboratory. Equipment included a heavyduty treadmill (0.8 to 10.0 mph) metabolic measurement cart, valve with rubber mouthpiece and nose clip, and electrocadiography (ECG) electrodes (Figure 2). The metabolic measure cart allows noninvasive measurement of basic physiologic responses to exercise, including oxygen uptake, carbon dioxide production and heart rate. Subjects were tested by registered respiratory therapists using standard procedures for exercise testing. Energy cost was detected while walking by metabolic measurement cart. At the beginning, subjects had rested for 20 minutes and ECG electrodes were positioned before test. Subjects walked on the treadmill few times for trial and warm up. When subjects' heart rate reached 60% of the Maximum Heart Rate (220-Age), measurements of energy cost parameters were started to record for a minimum of 2 minutes [17]. Subjects walked on the treadmill at speeds of 1, 1.5 and 2 miles/hour on slopes of grades 0, 5 and 10 with three kinds of prosthetic feet (SACH, single axis and multiple axis foot). Measurements were recorded for 2 minutes at steady-state exercise intensity as determined by visual monitors plotting oxygen uptake against time. Heart rate was monitored continuously 101 for safety and to support steady-state occurrence. Energy cost was calculated by using data from a twominute interval during steady-state exercise. It was expressed in milliliters of oxygen uptake per kilogram of body weight per meter traveled: Energy Cost rate = ml 02/Kg-min [26]. We compare the energy cost in two ways. First way is that divided subjects into three different groups which wearing three different types of prosthetic feet respectively. Second way is that divided subjects into vascular and traumatic groups which wearing different prosthetic feet. After the experiment, a survey was conducted by questionnaire to determine the subjective comfort level of prosthetic foot (Table 2). 3. RESULTS AND DISCUSSION In motion analysis, significant differences were found in linear measurements (velocity, cadence, stride length, single-limb stance and step width) (Table 3), ankle dorsiflexion, the amount of ankle dorsiflexion change from early to late stance, and right and left step lengths. Early-stance initial plantarflexion of the ankle, total ankle range-of-motion were also collected and analyzed; however, no significant differences were found. Statistical analysis using the Krusita Willius test were used to evaluate gait cycle, questionnaire and energy cost. Wilcoxon signed rank test helped evaluate ankle range-of-motion. The level of statistical significance was p<0.05. The results of motion analysis showed statistically significant differences at p<0.05 between the SACH, single axis and multiple axis foot in the linear measurements of velocity, cadence, stride length and gait cycle, as shown in Fig. 1 and 2. The SACH test subjects walking at 86.90 cm/sec, 88.70 steps/minute, had a stride length of 116.50 centimeters. SACH test subjects had a prosthetic side stance phase 61.56 percent of the gait cycle and sound side stance phase 66.43 percent of the gait cycle. The single axis foot subjects walking at 93.40 cm/sec, 94.90 steps/minute, had a stride length of 116.90 centimeters, with a prosthetic side stance phase 59.14 percent of the gait cycle and sound side stance phase 68.14 percent of the gait cycle. The multiple axis foot subjects walking at 95.30 cm/sec, 96.40 steps/minute, had a stride length of 116.40 centimeters, with a prosthetic side stance phase 62.55 percent of the gait cycle and sound side stance phase 68.18 percent of the gait cycle. Normal males walking at 108.20 cm/sec, 102.30 steps/minute, had a stride length of about 126.80 centimeters. Normal stance phase was 60 percent of the gait cycle for each extremity. Within one complete stride, the distance from heel contact to opposite heel contact is the step length. -49-

102 Vol. 13 No. 2 April 2001 Table 2 Questionnaire for comfortable ambulation score(o means impossible, 7 means excellent) Questionnaire Score Normal walk 0 1 2 3 4 5 6 7 Walk on slope 0 1 2 3 4 5 6 7 Walk on grassland 0 1 2 3 4 5 6 7 Fast walk 0 1 2 3 4 5 6 7 Table 3. Linear measurement results of velocity, cadence, stride time, stride length, prosthetic stip length, sound stip length and step width from the motion analysis for the vascular group (n =3), the traumatic group (n=3) and normal values. * p<0.05 Foot type Normal SACH Single Multiple P-Value Velocity (m/sec) 108.20 86.90 t 2.92 93.40 ± 4.15 95.3±4.44 0.005* Cadence (steps/min) 102.30 88.70 ± 4.91 94.90 ± 6.54 96.40±6.37 0.044* Stride time (sec) 1,20 1.35±0.10 1.25±0.10 1.21±0.08 0.046* Stride length (cm) 126.80 116.50±3.33 116,90±3.15 116.40±2.58 0.95 Prosthetic step length (cm) 63.40 57.87±4.82 58.12±5.56 58.66±4.17 0.91 Sound step length (cm) 63.40 56.04±2.3 56.41±2,04 57.11±1.48 0.64 Step width (cm) 12.0 17.55±2.24 17.99±2,50 15.91±0.90 0.20 During normal gait, in this study, no significant step length difference was found between right and left leg step length for the six normal subjects. The traumatic group, when wearing the multiple axis foot, had a significantly shorter sound-limb step length. This suggests that the prosthetic foot dynamics of the more active traumatic amputee affects step-length symmetry. For the vascular group, step length for both sound and prosthetic limb was found to be shorter than that of the traumatic group. Hip, knee and ankle joint motion were also analyzed via motion analysis. Some significant differences were found in SACH foot late-stance ankle dorsiflexion during opposite heel contact, and also in the ankle initial plantarflexion to dorsiflexion change during early to late stance, starting shortly after heel contact. Symmetry between the sound limb and prosthetic limb was used for comparison. Late-stance ankle dorsiflexion which occurs at opposite heel contact is an important factor in amputee gait. This dorsiflexion affects the late-stance stability necessary for optimal late-stance balance and the advancement of the opposite extremity. Fig. 1, 2 and 3 illustrate flexion, extension, dorsiflexion and plantarflexion results by comparing the prosthetic limb to the sound -50-

BIOMEDICAL ENGINEERING- APPLICATIONS, BASIS & COMMUNICATIONS 103 comparing the prosthetic limb to the sound limb (represented by the zero horizontal axis) to evaluate symmetry for each of the prosthetic feet. The prosthetic limb, when wearing the SACH (n=6), showed significantly that the flexion angle of hip and knee joint and ankles dorsiflexion (p<0.05) was less than the sound limb. The single axis foot (n=6) did not exhibit any statistically significant difference in late-stance dorsiflexion and the flexion angle of hip and knee joints also the same. When wearing the multiple axis foot (n=6), the prosthetic limb had greater dorsiflexion than the sound limb, but at the flexion angle of hip and knee joints, the sound side was greater than that at prosthetic side. However there were no statistically significant difference beause it was so small. These results are important clinically, as they verify that the SACH provides good late-stance stability through limited dorsiflexion. This late-stance stability, for example, is required by amputees with anterior-knee instability on the prosthetic side resulting from a moderate knee flexion contracture, weak prosthetic-side knee extensors or poor late-stance balance. The multiple axis foot, on the other hand, provides less late-stance stability and more late-stance dorsiflexion ankle motion, which is desirable for higher activity levels or for activities requiring more ankle dorsiflexion. The opposite appeared to occur when wearing the SACH. The SACH showed less late-stance ankle dorsiflexion compared to the sound limb and exhibited a significantly longer sound-limb step length (p<0.05). As more late-stance dorsiflexion occurs with the multiple axis foot, a shorter sound-limb step length is required. Less late-stance dorsiflexion with the SACH results in a longer sound-limb step length. Therefore, step-length symmetry appears to be affected by the prosthetic foot in the more active amputee. Ankle joint range-of-motion occurring from initial plantarflexion to late-stance dorsiflexion is considered to be the change in dorsiflexion during stance phase of gait. This change in dorsiflexion is important because lower activity level amputees with a low velocity and a short step length can use a prosthetic foot with less change in dorsiflexion. Higher activity level amputees will need the prosthetic foot to provide a greater change in dorsiflexion. Activities affected by change in dorsiflexion, such as running or walking on inclines, also deserve special attention in prosthetic foot selection. By the result of energy cost, At rest, the energy cost parameters are not significant in three groups (traumatic, vascular and normal) (Fig. 4). We analyze the energy cost of walking at speed of 1.5 miles per hours and slope 0 which defined as comfortable walking speed. We divided the subjects by two ways. One is divided by types of prosthesis feet used (SACH, Table 4 Energy cost parameters collected during 2 minutes of walking averaged across all feet tested. Energy cost parameters Traumatic Vascular Normal p-value HR,beat/min 106.3±9.75 119.5±11.51 105.1±7.18 0.0001 02 pulse,ml/kg-beat 0.14±0.02 0.11±0.01 0.15±0.01 0.0830 RR,time/min 23.84±2.86 26.39±3.25 18.87±2.8 0.0001 Energy rate,m1o2/kg-min 11.84±2.69 13.98±1.28 10.01±2.04 0.0001* Respiratory exchange ratio(rer) 0.83±0.05 0.84±0.02 0.83±0.034 0.5563 Table 5 Comparing SACH, single axis and multiple axis feet for comfortable ambulation. Questionnaire SACH Single Multiple P-Value Normal walk 3.17±0.41 4.67±0.52 4.67±0.52 0.001* Walk on slope 2.50±0.55 3.67±0.52 4.67±0.52 0.001* Walk on grassland 1.17±0.41 2.83±0.41 4.50±0.55 0.001* Fast walk 1.33±0.52 2.67±1.21 4.50±1.05 0.001* -51-

104 Vol. 13 No. 2 April 2001 single axis and multiple axis foot). The other is divided by subjects symptom (traumatic and vascular group). We find that there is significant difference in energy cost rate if we use first division (Fig. 5). The multiple axis foot is more fit human kinematics, and has minimum physiological stress than the other feet. As regard to the heart rate (HR), respiratory rate (RR) and energy cost rat, traumatic group is more efficient than vascular group. The higher oxygen pulse of the traumatic group (0.14 ml/kg-beat VS. 0.11 ml/kg-beat) further demonstrates their better physical conditioning compared to the vascular group (Table 4). And this analysis result is same as the Barth's [21]. Respiratory exchange ratios between 0.83 and 0.84 indicate the three groups were working at aerobic levels. Significant differences were found in energy cost among the prosthetic feet tested, and significant changes in walking at speeds of 1, 1.5 and 2 miles per hour on slopes of grades 0, 5 and 10. Significant difference were found in energy cost among the prosthetic feet test, and significant changes in walking at speeds of 1, 1.5 and 2 miles per hour on slopes of grades 0, 5 and 10 (Fig. 6, 7 and 8). And this result fit the principle of human energy cost. This study find this increase energy cost to be 140 and 118 percent of normal for vascular and traumatic below knee amputees respectively. Comparable values were found in the current study. These increase reflect the demands on the remaining musculature. The lack of normal ankle mobility in loading response and single limb support necessitates compensatory gait patterns and muscle activity to provide stability and advancement over the foot. In the amputated limb, the large muscles controlling the hip and knee demonstrate more intense and prolonged electromyographic activity compared to those of persons without amputation and is consistent with the increased energy cost [26]. According to the result of questionnaire, multiple axis feet is the most comfortable type and single axis feet is the next. SACH type is the worst one comparing with the two types mentioned above. This results show significantly difference that the DOF of ankle joint of prosthetic feet is important factor of the comfortable of prosthesis (Table 5). We found that there is no sig- nificant difference in normal walk, walk on slope, walk on grassland and fast walk between traumatic group and vascular group. These results indicate that these two groups wore different types of prosthetic feet have the same comfort (Table 6). 4. CONCLUSION To provide helpful criteria in prosthetic foot selection for amputees, the significant results in this study can be summarized as follows. The SACH foot should be used when amputees require maximum latestance stability by limited dorsiflexion. This is necessary, for example, in amputees with poor late-stance stability resulting from weak knee extensors, kneeflexion contracture or poor mid-to late-stance balance. The SACH foot is also appropriate for lower-activitylevel amputees requiring less dorsiflexion. The single axis foot should be used when increased early-to late-stance change in dorsiflexion is desired. This is necessary for amputees walking on inclines or uneven terrain, or with higher activity levels requiring more ankle motion. The single axis foot's increased ankle motion better accommodates various walking surfaces and velocities. Therefore, it provides sound-limb and prosthetic-limb symmetry for amputees, making the single axis foot a good choice for average-activity-level amputees with no specific gait abnormalities or considerations. The multiple axis foot should be used when increased early-to late-stance change in dorsiflexion and maximum late-stance dorsiflexion is desired. The multiple axis foot better accommodates increased ankle range-of-motion requirements, such as variations in walking velocity and walking on inclines. The multiple axis foot is appropriate for moderate-activity-level amputees. Using the quantitative measures of motion analysis, some significant differences were found in gait cycle and range-of-motion of the various feet tested. These data provide information about the dynamic performance of the various feet which can be helpful in prescribing the optimal prosthetic foot for individual Table 6 Comparing traumatic and vascular groups for comfortable ambulation. Questionnaire Traumatic Vascular P-Value Normal walk 4.33±0.87 4.0010.87 0.4262 Walk on slope 3.67±1.22 3.56±0.89 0.8280 Walk on grassland 2.6711.50 3.0011.50 0.6437 Fast walk 2.3312.18 2.6711.87 0.7323-52-

BIOMEDICAL ENGINEERING- APPLICATIONS, BASIS & COMMUNICATIONS 105 70 60 50 40 30 20 10 0-10 -20-30 Hip Flex/Ext Knee Flex/Ext Ankle Dorsi/Plant flex El prosth.side 0 sound side Hip Flex/Ext Knee Flex/Ext Ankle Dorsi/Plant flex q prosth.side n sound side Fig. 1 Kinematics characteristics during walking Fig. 3 Kinematics characteristics during walking test, averaged for the SACH foot tested. The prostest, averaged for the multiple axis foot tested. thetic side is compared to the sound side. The prosthetic side is compared to the sound side. a -30 Hip Flex /Ext Knee Flex /Ext Ankle Dorsi/Plant flex q prosth. side 6.00 5.00 sound side d 4.00 5OO3.00 iv w 2.00 1.00 0.00 4.44 ±0.83 4.52 ±0.84 4.3±0.81 (m1oz/kg-min) q traunmatic n vascular n normal Fig. 2 Kinematics characteristics during walking Fig. 4 The average of energy cost rate of three test, averaged for the single axis foot tested. The different groups collected during 2 minutes of prosthetic side is compared to the sound side. resting. amputees. The vascular group had a significantly greater energy cost than traumatic group, and significant difference in energy cost occurred among the different prosthetic feet. Future studies may incorporate higher demand activity and a larger subject population is necessary to find further significant differences among prosthetic feet. In this study, the small subject population tested by motion analysis and metabolic measurement cart yielded large variability that may still hide some important differences in these feet. REFERENCES 1. Gitter A, Czerniecki JM, DeGroot DM, Biomechanical analysis of the influence of prosthetic feet on below-knee amputee walking. Am J Phys Med Recabil 1991 ;70: 142-8. 2. Gage JR, Hicks R. Gait analysis in prosthetics. Clinical Prosthetics and Orthotics 1985;9:17-23. 3. Hannah RE, Morrison JB, Chapman AE. Prostheses alignment. Effect of gait of persons with belowknee amputations. Arch Phys Med Rehabil 1984;65:159-62. 4. Wagner J, Sienko S, Supan T, Barth D. Motion analysis of SACH versus Fles-Foot in moderately active below-knee amputees. Cline Prosthet Orthot, Vol.11, pp _55-62, 1987. 5. Winter DA, Sienko SE, Biomechanics of below-knee amputee gait. J Biomech, 1988;21:361-7. 6. Culham EG, Peat M, Newell E : Below-knee amputation : A comparison of the effect of the SACH foot and single axis foot on electromyographic patterns during locomotion. Prosthet Orthot Int 1986;10:15-22. 7. Custon etal. Early Management of Elderly Dysvascular Below-knee Amputees. Journal of Prosthetics and Orthotics 1994;6:62-6. -53-

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