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Ground reaction force and 3D biomechanical characteristics of walking in short-leg walkers
Gait & Posture 24 (2006) 487–492 www.elsevier.com/locate/gaitpost
Ground reaction force and 3D biomechanical characteristics of walking in short-leg walkers Songning Zhang a,c,*, Kurt G. Clowers b, Douglas Powell a a
Biomechanics/Sports Medicine Lab, The University of Tennessee, 1914 Andy Holt Avenue, Knoxville, TN 37996-2700, USA b Anthropometry and Biomechanics Facility, NASA Johnson Space Center, Houston, USA c Shanghai University of Sport, Shanghai, China Received 23 September 2005; received in revised form 1 December 2005; accepted 11 December 2005
Abstract Short-leg walking boots offer several advantages over traditional casts. However, their effects on ground reaction forces (GRF) and threedimensional (3D) biomechanics are not fully understood. The purpose of the study was to examine 3D lower extremity kinematics and joint dynamics during walking in two different short-leg walking boots. Eleven (five females and six males) healthy subjects performed five level walking trials in each of three conditions: two testing boot conditions, Gait Walker (DeRoyal Industries, Inc.) and Equalizer (Royce Medical Co.), and one pair of laboratory shoes (Noveto, Adidas). A force platform and a 6-camera Vicon motion analysis system were used to collect GRFs and 3D kinematic data during the testing session. A one-way repeated measures analysis of variance (ANOVA) was used to evaluate selected kinematic, GRF, and joint kinetic variables ( p < 0.05). The results revealed that both short-leg walking boots were effective in minimizing ankle eversion and hip adduction. Neither walker increased the bimodal vertical GRF peaks typically observed in normal walking. However, they did impose a small initial peak (<1 BW) earlier in the stance phase. The Gait Walker also exhibited a slightly increased vertical GRF during midstance. These characteristics may be related to the sole materials/design, the restriction of ankle movements, and/or the elevated heel heights of the tested walkers. Both walkers appeared to increase the demand on the knee extensors while they decreased the demand of the knee and hip abductors based on the joint kinetic results. # 2005 Elsevier B.V. All rights reserved. Keywords: Short-leg walker; Walking boot; Gait; 3D biomechanics; Walking
1. Introduction Short-leg rigid immobilization devices are commonly used in treatment of acute and chronic injuries, and post surgical interventions [1–10]. Fiberglass short-leg casts have been traditionally used for these situations. Improvements in prefabricated short-leg boots have provided an alternative to traditional cast immobilization [4,11]. Walking boots offer several advantages over traditional casts: ease of removal for purpose of exercises, edema treatment, examination and cleaning, less expensive, and less adverse effects on kinematic and kinetic gait patterns than a synthetic walking cast [11]. * Corresponding author. Tel.: +1 865 974 4716; fax: +1 865 974 8981. E-mail address: [email protected] (S. Zhang). 0966-6362/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2005.12.003
Indications for use of short-leg walking boots include ankle and foot fractures, severe ankle sprains, chronic tendinopathy, post surgical stabilization, and prevention and treatment of ulceration due to sensory deficit in diabetic patients [11,12]. Several studies [13–16] have examined plantar pressure distributions wearing different walkers but limited information is available about the three-dimensional (3D) lower extremity kinematics and kinetics of gait while wearing walking boots [11]. Pollo et al. [11] examined 3D kinematics and joint moments of walking in several walkers, a cast and shoes. They concluded that short-leg walking boots elicit less adverse effects of kinematics and kinetics in gait compared to the synthetic walking cast. To the knowledge of the authors, this is the only 3D biomechanical study on walkers in gait published in the literature. Furthermore, the
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information on ground reaction forces (GRF) of gait in walking boots is not available in the literature. Further examinations of GRF and related aspects of gait patterns in short-leg walkers may provide useful information to clinicians and patients with regard to long-term effects since walkers may often be worn for a lengthy period of time (up to six months). Therefore, the objective of this study was to examine characteristics of lower extremity 3D kinematics, ground reaction forces, and joint dynamics during walking in two different types of short-leg walking boots.
2. Methods
lateral side of the greater trochanter, on the lateral and medial femoral epicondyles and the malleoli, and on the head of first and fifth metatarsal, to determine the respective joint/segment centers at the beginning of the data collection session. Due to the usage of the walkers, the medial and lateral malleolar markers in the walker conditions were placed on the respective sites on the medial and lateral plastic side arms of the walkers. The widths at the ankle with and without the walker were measured with a caliper and two virtual makers were set up to locate the true location of the ankle and to estimate the ankle joint center. The hip joint center was estimated from the pelvic and hip anatomical markers using a modified method by Seidel et al. [17].
2.1. Subjects 2.3. Short-leg walking boots Eleven healthy subjects (age: 27.4 7.8 years, body mass: 72.0 13.4 kg, height: 1.76 0.08 m) with no history of major injuries to their lower extremity participated in the study. Among the subjects, five were female (age: 24.6 3.4 years, body mass: 61.3 9.0 kg, height: 1.69 0.03 m) and six were male (age: 29.7 9.9 years, body mass: 80.9 9.3 kg, height: 1.82 0.05 m) participants. Each subject signed an informed consent form approved by the Institutional Review Board at The University of Tennessee prior to the actual data collection. 2.2. Experimental protocol and instrumentation Each subject performed five level walking trials in each of three conditions: two testing boots and one pair of laboratory shoes. Prior to testing, each subject walked in one randomly selected walking boot until he/she felt comfortable. The average walking speed of each subject was determined from three walking trials at a preferred pace in the walking boot using a pair of photocells (63501 IR, Lafayette Instrument Inc., IN, USA) placed at shoulder height. The walking speed was monitored to ensure that it fell within the range of 10% of the average walking speed. The boot conditions were arranged with one of the walkers always being randomly tested first (to obtain the preferred walking speed) and the shoe condition tested last. A force platform (600 Hz, American Mechanical Technology Inc., MA, USA) was used to measure the ground reaction forces during testing. Three-dimensional kinematic data of right lower extremity were simultaneously collected using a 6-camera motion analysis system (120 Hz, Vicon Motion Systems Ltd., Oxford, UK). Reflective tracking markers (Fig. 1) were placed through a thin thermoplastic shell (attached to a Velcro sensitive elastic wrap) on the thigh and leg, and directly on the foot (the walker conditions) or shoe (the shoe condition) of the right side of the body. Tracking markers were placed on both sides of the pelvis via a Velcro sensitive elastic strap. Anatomical reflective markers were also placed on the anterior/posterior iliac spines and iliac crest of both sides of the pelvis, on the
Subjects wore two different walking boots, Gait Walker (DeRoyal Industries, Inc., Powell, TN) and Equalizer (Royce Medical Co., Camarillo, CA), on the right side and a laboratory shoe on the left side in the boot conditions during the test session. The linen wrap inside the walkers was cut at the heel and lateral part of the mid and anterior walkers to expose the skin for the attachment of the anatomical/tracking markers on the foot (Fig. 1). Medial and lateral plastic leg supports and Velcro straps of the walkers were not altered; therefore, the integrity of the walkers was maintained. They also wore a pair of the laboratory running shoes (Noveto, Adidas) in the shoe condition. 2.4. Data and statistical analysis Kinematic and GRF data were smoothed at 6 and 20 Hz, respectively, using a fourth-order Butterworth low-pass filter. The 3D kinematic and joint kinetic variables were computed using Visual3D software suite (C-Motion, Inc., MD, USA), and the critical events and additional variables were further determined by a customized computer program. Internal moments of the lower extremity joints were computed in Visual3D. The ground reaction forces and joint moments were normalized to the participant’s body mass, yielding units of N/kg and N m/kg, respectively. The inversion/eversion of the ankle joint was computed as the subtalar joint movement in the coronal plane. A one-way repeated measures of analysis of variance (ANOVA) was used to evaluate selected kinematic, GRF, and joint kinetic variables (SPSS, 12.0). Post hoc comparisons were conducted with an alpha level ( p < 0.05) adjusted for multiple comparisons through a Bonferroni procedure.
3. Results The participants in the study performed the walking trials at a mean velocity of 1.24 0.18 m/s. The female and male participants walked at similar speeds, 1.22 and 1.26 m/s,
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trials (Table 2). The eversion ROM was greater for the Gait Walker compared to the no walker condition. In addition, the hip abduction ROM for the Gait Walker and Equalizer walkers were significantly smaller than those for the shoes. In addition to the two vertical GRF peaks associated with the loading response (Max 2) and terminal stance (Max 3) commonly observed in walking in shoes, an apparent peak (Max 1) occurs earlier than the peak of loading response for the two walker conditions (Fig. 2). The statistical results indicated no significant differences for the GRF related variables between the test conditions (Table 3). For the joint kinetics, the peak plantarflexor moment that occurs later in the stance phase for the two walker conditions was greater than the no walker trials (Fig. 3a). In both walker conditions, the peak knee extensor moments were greater than the no walker trials. On the other hand, the statistical results showed a significantly smaller peak dorsiflexor moment for Gait Walker compared to the no walker and Equalizer walker conditions during earlier stance (Fig. 3b). The maximum ankle inversion moment for the Gait Walker condition was significantly greater than the no walker (Fig. 4). The peak knee abduction moments for the two walkers were smaller than the shoe condition; the same moment variable for Equalizer was also smaller than Gait Walker. Finally, the peak hip abduction moment for Equalizer was significantly smaller than the shoe condition.
Fig. 1. Reflective markers placements on the lower extremity and pelvis.
respectively. The ANOVA results showed a significantly greater maximum knee flexion angle for Gait Walker compared to the no walker condition (Table 1). No other variables related to the peaks and ranges of motion (ROM) of the three lower extremity joints were found significant between the testing conditions. The peak ankle eversion angle was found significantly smaller than the no walker
4. Discussions The kinematic data from this study showed no major changes in the peaks and ROMs of lower extremity joint kinematics in the sagittal plane with the exception of a slight increase in max knee flexion during the Gait Walker walking condition. However, the range of motion from heel strike did
Table 1 Average peak and ROM (8) of lower extremity joint angles in sagittal plane: mean standard deviation Condition
No walker Gait Walker Equalizer a
Ankle (8)
Knee (8)
Hip (8)
Dorsiflexion
ROM
Flexion
ROM
Extension
ROM
11.9 3.4 11.1 4.3 10.4 3.8
5.7 4.6 7.3 4.3 5.4 2.8
15.5 8.7 22.7 4.9 a 19.5 6.1
8.5 5.4 9.5 4.7 10.4 3.7
0.6 10.9 2.4 9.5 4.0 11.4
37.1 5.4 37.2 4.4 36.4 5.2
Significantly different from Gait Walker.
Table 2 Average peak and ROM (8) of lower extremity joint angles in frontal plane: mean standard deviation Condition
Ankle (8) Eversion
No walker Gait Walker Equalizer a
4.5 2.3 2.8 4.6 0.8 2.8 a
Significantly different from Gait Walker.
Knee (8)
Hip (8)
ROM
Adduction
ROM
Adduction
ROM
8.7 3.3 1.8 4.9a 6.6 4.6
4.6 2.9 3.9 2.2 1.5 3.4
3.3 1.8 2.4 2.5 2.1 2.2
5.8 2.8 5.1 3.6 6.1 3.2
8.3 2.4 6.1 2.0 a 6.0 2.3 a
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Fig. 3. Average peak extensor moments (a) and flexor moments (b) lower extremity joints (N m/kg) in sagittal plane; (1) significantly different from no walker and (2) significantly different from Gait Walker.
maximum eversion angle and hip adduction range of motion. These data suggest that both walkers restrict motions of the subtalar and hip joints in the frontal plane. The reduced hip adduction may be related the restriction provided by the walkers at the ankle/foot complex. The previous study [11] demonstrated no significant differences of hip and knee kinematics in sagittal (flexion/extension) Fig. 2. Representative curves of vertical ground reaction force for: no walker (A), Gait Walker (B), and Equalizer (C).
not statistically differ from the Equalizer and the shoe walking trials. Major differences of joint kinematics were seen in the frontal plane. The walking trials in the Gait Walker showed reduced range of motion for subtalar joint eversion and hip adduction compared to the walking trials in shoes. The Equalizer walker also exhibited reduced Table 3 Average peak vertical ground reaction force (N/kg): mean standard deviation Condition
Max 1
Max 2
Max 3
No walker Gait Walker Equalizer
– 8.91 1.49 7.37 2.74
10.77 0.59 10.27 0.72 10.72 0.61
10.68 0.41 10.47 0.59 10.43 0.44
(–) No apparent peak observed.
Fig. 4. Average peak joint moments (N m/kg) of lower extremity joints in frontal plane; (1) significantly different from no walker and (2) significantly different from Gait Walker.
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and frontal (adduction/abduction) planes between the walker conditions. Our data basically agreed with the finding. The data for both walkers from this study showed the early peak in the vertical GRF right after the heel strike and prior to the loading response (Fig. 2). Both walkers have a Polyurethane outsole, a Polypropylene midsole, and a hard form as the insole. Their heel height is greater than the laboratory shoes. A closer examination of the walkers and shoes used in this study showed that the heel thickness taken at the mid heel region were 2.4, 3.2, and 3.6 cm on average for the shoes, Equalizer, and Gait Walker, respectively. The raised heel height on the walker side artificially increases the limb length discrepancy. The sole materials/construction, the restriction of ankle movements, and the heel height may contribute to the observed initial GRF impact that is absent from the shoe walking. The vertical ground reaction force profile for the two walkers also demonstrated a marked difference that occurs between the loading response and terminal stance (Fig. 2). The GRF curve for normal walking in shoes shows a typical smooth valley between the two peaks. The GRF curve for the Equalizer walker showed a more similar pattern to the shoe walking compared to the Gait Walker. The GRF curve for the Gait Walker trial demonstrated an elevated portion between the peaks. The elevated portion of the GRF curve is associated with stance phase when the walker is rolled from the heel strike to the midstance. An examination of the outsole of the two walkers showed that both walkers have a curve at the heel region, which should facilitate the progression of the body from heel strike to midstance. The Equalizer walker has a smooth and slightly greater curve throughout the outsole from the heel to the toe region. The Gait Walker shows a flatter curve in the outsole, especially at the region between the heel and the mid-foot, which is almost entirely flat. The measurements on the shoes and walkers indicated that the forefoot thickness (taken at the region of the third metatarsal head) was 1.9, 2.2, and 3.1 cm on average for the shoes, Equalizer and Gait Walker, respectively. For the testing shoes, the thickness difference between the forefoot and heel regions is 0.5 cm, whereas the differences were 1.1 and 0.5 cm for Equalizer and Intuition, respectively. The differences further verified our initial observed differences in the sole designs in these walkers. The greater heel thickness with respect to its forefoot region was observed in the Equalizer walkers and this may facilitate transition from the heel strike to the toe-off as the center of mass progresses forward. This may be especially necessary while wearing a walker due to the restricted ankle dorsi-/ plantarflexion. On the other hand, the smaller difference of the heel–forefoot thickness seen in the shoes and Gait Walker compared to the Equalizer does not affect normal walking in regular shoes since the ankle joints can dorsi-/ plantarflex freely to accommodate the rolling action needed to facilitate the forward progression of the center of mass during the stance. However, this transition process may be somewhat more restricted wearing the Gait Walker due to
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the smaller thickness difference between the heel and forefoot regions and the flatter outsole curve of the walker, leading to the elevated vertical ground reaction force around the midstance. This may be also related to the increased maximum knee flexion in the earlier stance associated with the walker to accommodate the need for the forward body progression. On the other hand, the elevated GRF suggests that the Gait Walker was able to maintain a low but rather ‘‘constant’’ load and avoid abrupt changes in the ground reaction force during midstance. This unique characteristic may benefit patients by decreasing loading rates between the two GRF peaks and promoting healing by maintaining a relatively constant load. So far, the authors have not been able to find published documents on GRF characteristics of walkers in gait. Pollo et al. [11] report the ground reaction forces in their study. The peak knee abduction moment for the Gait Walker and Equalizer walkers were both found to be significantly smaller than the shoe condition. The Equalizer walker also demonstrated a reduction in the peak hip abduction moment. These reductions occur in early stance phase and may be related to diminished needs of knee and hip abductors to restrain adductions of the joints in the early stance due to the application of the walkers. Pollo et al. also found decreased knee and hip abduction moments for some of the tested walkers in early stance phase [11]. The knee moment is considered to be important in maintaining appropriate loading to the lateral and medial compartments of the knee [11] and therefore the mediolateral stability. The increased inversion ankle moment seen in the Gait Walker is related to the diminished eversion ROM, suggesting the better performance of the walker in restricting subtalar joint motion during the earlier support phase. The greater peak knee extensor moment for both walkers compared to the shoe walking trials may be related to the constraint provided by the arm supports and straps of the walkers to the ankle joint movements and the increased mass (walker) attached to the leg and foot, which in turn require the knee extensors to exert a greater torque to extend the knee to facilitate the rolling from the heel strike to the toe-off during the stance phase. The greater heel thickness observed in the walkers may also increase the length of the walker side’s limb and thus place it at a slight disadvantage. This ‘‘increased’’ leg length requires the knee extensors to exert greater amount of torque to raise the center of mass to the required height for a smooth transition across the midstance. It was reported that the Equalizer walker along with another walker (Cam walker) also had greater knee extensor moments [11]. The authors suggested this increased moments may lead to increased loading applied to the tibiofemoral and patellofemoral joints. The joint moment data from this study also indicated a smaller peak dorsiflexor moment for the Gait Walker. This reduction occurring in the earlier stance phase showed a decreased involvement of dorsiflexors in the walker conditions. This suggests that the restriction from a walker may reduce the need for the
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dorsiflexors to actively oppose the plantarflexion seen in the earlier stance phase. However, both walkers showed an increased plantarflexor moment in late stance phase, suggesting an elevated effort from the plantarflexors during push-off. It is unclear why this occurred.
5. Conclusion This study showed both short-leg walking boots, DeRoyal’s Gait Walker and Royce’s Equalizer, were effective in minimizing motion of ankle eversion and hip adduction in frontal plane. Both walkers did not increase the two peak ground reaction forces observed in normal walking in shoes. However, they did impose a small initial peak (<1 BW) in early stance phase. Due to the difference in sole design, the Gait Walker exhibited a slightly elevated vertical ground reaction force around midstance. Both walkers increased the demand on knee extensors while they decreased the effort of the knee and hip abductors. Both walkers have different sole materials/construction, restricted ankle movements, greater weight, and greater heel heights compared to the shoes used in the study and some of the observed biomechanics differences including the observed initial peak may be related to these differences. Although untested, it is logical to hypothesize that placing an orthotic insert in the shoe of the unaffected limb may relieve the initial GRF peak associated with the heel height difference. Since the walkers may be worn for a long period of time, the observed initial vertical GRF peak may impose some adverse effect on the affected limb. The effects of the observed biomechanical changes of the affected side on the movements of the unaffected limb are almost entirely unknown. If the compensatory changes on the unaffected side do occur, it may cause undesirable outcomes such as pain in sacroiliac joint and low back due to prolonged usage of a short-leg walker. Finally, some of the significant differences are small and their clinical impacts have yet to be investigated. Therefore, further studies on these aspects of short-leg walkers are warranted.
Acknowledgments This study was funded by a grant from DeRoyal Industries, Inc., a grant from Charlie and Mai Coffey
Endowment, and a grant from the Scholarly Activity and Research Incentive Fund at The University of Tennessee.
References [1] Wapner KL, Chao W. Nonoperative treatment of posterior tibial tendon dysfunction. Clin Orthop 1999;39–45. [2] Crincoli MG, Trepman E. Immobilization with removable walking brace for treatment of chronic foot and ankle pain. Foot Ankle Int 2001;22:725–30. [3] Kader D, Saxena A, Movin T, Maffulli N. Achilles tendinopathy: some aspects of basic science and clinical management. Br J Sports Med 2002;36:239–49. [4] Kadel NJ, Segal A, Orendurff M, Shofer J, Sangeorzan B. The efficacy of two methods of ankle immobilization in reducing gastrocnemius, soleus, and peroneal muscle activity during stance phase of gait. Foot Ankle Int 2004;25:406–9. [5] Maffulli N, Kader D. Tendinopathy of tendo achillis. J Bone Joint Surg Br 2002;84:1–8. [6] King DM. Experience with the below-knee total-contact cast in the management of tibial fractures. Aust N Z J Surg 1975;45:54–6. [7] Preto A. Patellar tendon bearing and cast braces: total contact orthoses in the weight-bearing treatment of tibial and femoral shaft fractures. Ona J 1977;4:10–1. [8] Crates JM, Richardson EG. Treatment of stage I posterior tibial tendon dysfunction with medial soft tissue procedures. Clin Orthop 1999;46–9. [9] Cole BJ, Freedman KB, Taksali S, Hingtgen B, DiMasi M, Bach Jr BR, et al. Use of a lateral offset short-leg walking cast before high tibial osteotomy. Clin Orthop 2003;209–17. [10] Matricali GA, Deroo K, Dereymaeker G. Outcome and recurrence rate of diabetic foot ulcers treated by a total contact cast: short-term followup. Foot Ankle Int 2003;24:680–4. [11] Pollo FE, Gowling TL, Jackson RW. Walking boot design: a gait analysis study. Orthopedics 1999;22:503–7. [12] Randolph AL, Nelson M, deAraujo MP, Perez-Millan R, Wynn TT. Use of computerized insole sensor system to evaluate the efficacy of a modified ankle–foot orthosis for redistributing heel pressures. Arch Phys Med Rehabil 1999;80:801–4. [13] Baumhauer JF, Wervey R, McWilliams J, Harris GF, Shereff MJ. A comparison study of plantar foot pressure in a standardized shoe, total contact cast, and prefabricated pneumatic walking brace. Foot Ankle Int 1997;18:26–33. [14] Crenshaw SJ, Pollo FE, Brodsky JW. The effect of ankle position on plantar pressure in a short leg walking boot. Foot Ankle Int 2004;25:69–72. [15] Nawoczenski DA, Birke JA, Coleman WC. Effect of rocker sole design on plantar forefoot pressures. J Am Podiatr Med Assoc 1988;78:455–60. [16] Pollo FE, Brodsky JW, Crenshaw SJ, Kirksey C. Plantar pressures in fiberglass total contact casts vs. a new diabetic walking boot. Foot Ankle Int 2003;24:45–9. [17] Seidel GK, Marchinda DM, Dijkers M, Soutas-Little RW. Hip joint center location from palpable bony landmarks—a cadaver study. J Biomech 1995;28:995–8.
Ground reaction force and 3D biomechanical characteristics of walking in short-leg walkers Songning Zhang a,c,*, Kurt G. Clowers b, Douglas Powell a a
Biomechanics/Sports Medicine Lab, The University of Tennessee, 1914 Andy Holt Avenue, Knoxville, TN 37996-2700, USA b Anthropometry and Biomechanics Facility, NASA Johnson Space Center, Houston, USA c Shanghai University of Sport, Shanghai, China Received 23 September 2005; received in revised form 1 December 2005; accepted 11 December 2005
Abstract Short-leg walking boots offer several advantages over traditional casts. However, their effects on ground reaction forces (GRF) and threedimensional (3D) biomechanics are not fully understood. The purpose of the study was to examine 3D lower extremity kinematics and joint dynamics during walking in two different short-leg walking boots. Eleven (five females and six males) healthy subjects performed five level walking trials in each of three conditions: two testing boot conditions, Gait Walker (DeRoyal Industries, Inc.) and Equalizer (Royce Medical Co.), and one pair of laboratory shoes (Noveto, Adidas). A force platform and a 6-camera Vicon motion analysis system were used to collect GRFs and 3D kinematic data during the testing session. A one-way repeated measures analysis of variance (ANOVA) was used to evaluate selected kinematic, GRF, and joint kinetic variables ( p < 0.05). The results revealed that both short-leg walking boots were effective in minimizing ankle eversion and hip adduction. Neither walker increased the bimodal vertical GRF peaks typically observed in normal walking. However, they did impose a small initial peak (<1 BW) earlier in the stance phase. The Gait Walker also exhibited a slightly increased vertical GRF during midstance. These characteristics may be related to the sole materials/design, the restriction of ankle movements, and/or the elevated heel heights of the tested walkers. Both walkers appeared to increase the demand on the knee extensors while they decreased the demand of the knee and hip abductors based on the joint kinetic results. # 2005 Elsevier B.V. All rights reserved. Keywords: Short-leg walker; Walking boot; Gait; 3D biomechanics; Walking
1. Introduction Short-leg rigid immobilization devices are commonly used in treatment of acute and chronic injuries, and post surgical interventions [1–10]. Fiberglass short-leg casts have been traditionally used for these situations. Improvements in prefabricated short-leg boots have provided an alternative to traditional cast immobilization [4,11]. Walking boots offer several advantages over traditional casts: ease of removal for purpose of exercises, edema treatment, examination and cleaning, less expensive, and less adverse effects on kinematic and kinetic gait patterns than a synthetic walking cast [11]. * Corresponding author. Tel.: +1 865 974 4716; fax: +1 865 974 8981. E-mail address: [email protected] (S. Zhang). 0966-6362/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2005.12.003
Indications for use of short-leg walking boots include ankle and foot fractures, severe ankle sprains, chronic tendinopathy, post surgical stabilization, and prevention and treatment of ulceration due to sensory deficit in diabetic patients [11,12]. Several studies [13–16] have examined plantar pressure distributions wearing different walkers but limited information is available about the three-dimensional (3D) lower extremity kinematics and kinetics of gait while wearing walking boots [11]. Pollo et al. [11] examined 3D kinematics and joint moments of walking in several walkers, a cast and shoes. They concluded that short-leg walking boots elicit less adverse effects of kinematics and kinetics in gait compared to the synthetic walking cast. To the knowledge of the authors, this is the only 3D biomechanical study on walkers in gait published in the literature. Furthermore, the
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information on ground reaction forces (GRF) of gait in walking boots is not available in the literature. Further examinations of GRF and related aspects of gait patterns in short-leg walkers may provide useful information to clinicians and patients with regard to long-term effects since walkers may often be worn for a lengthy period of time (up to six months). Therefore, the objective of this study was to examine characteristics of lower extremity 3D kinematics, ground reaction forces, and joint dynamics during walking in two different types of short-leg walking boots.
2. Methods
lateral side of the greater trochanter, on the lateral and medial femoral epicondyles and the malleoli, and on the head of first and fifth metatarsal, to determine the respective joint/segment centers at the beginning of the data collection session. Due to the usage of the walkers, the medial and lateral malleolar markers in the walker conditions were placed on the respective sites on the medial and lateral plastic side arms of the walkers. The widths at the ankle with and without the walker were measured with a caliper and two virtual makers were set up to locate the true location of the ankle and to estimate the ankle joint center. The hip joint center was estimated from the pelvic and hip anatomical markers using a modified method by Seidel et al. [17].
2.1. Subjects 2.3. Short-leg walking boots Eleven healthy subjects (age: 27.4 7.8 years, body mass: 72.0 13.4 kg, height: 1.76 0.08 m) with no history of major injuries to their lower extremity participated in the study. Among the subjects, five were female (age: 24.6 3.4 years, body mass: 61.3 9.0 kg, height: 1.69 0.03 m) and six were male (age: 29.7 9.9 years, body mass: 80.9 9.3 kg, height: 1.82 0.05 m) participants. Each subject signed an informed consent form approved by the Institutional Review Board at The University of Tennessee prior to the actual data collection. 2.2. Experimental protocol and instrumentation Each subject performed five level walking trials in each of three conditions: two testing boots and one pair of laboratory shoes. Prior to testing, each subject walked in one randomly selected walking boot until he/she felt comfortable. The average walking speed of each subject was determined from three walking trials at a preferred pace in the walking boot using a pair of photocells (63501 IR, Lafayette Instrument Inc., IN, USA) placed at shoulder height. The walking speed was monitored to ensure that it fell within the range of 10% of the average walking speed. The boot conditions were arranged with one of the walkers always being randomly tested first (to obtain the preferred walking speed) and the shoe condition tested last. A force platform (600 Hz, American Mechanical Technology Inc., MA, USA) was used to measure the ground reaction forces during testing. Three-dimensional kinematic data of right lower extremity were simultaneously collected using a 6-camera motion analysis system (120 Hz, Vicon Motion Systems Ltd., Oxford, UK). Reflective tracking markers (Fig. 1) were placed through a thin thermoplastic shell (attached to a Velcro sensitive elastic wrap) on the thigh and leg, and directly on the foot (the walker conditions) or shoe (the shoe condition) of the right side of the body. Tracking markers were placed on both sides of the pelvis via a Velcro sensitive elastic strap. Anatomical reflective markers were also placed on the anterior/posterior iliac spines and iliac crest of both sides of the pelvis, on the
Subjects wore two different walking boots, Gait Walker (DeRoyal Industries, Inc., Powell, TN) and Equalizer (Royce Medical Co., Camarillo, CA), on the right side and a laboratory shoe on the left side in the boot conditions during the test session. The linen wrap inside the walkers was cut at the heel and lateral part of the mid and anterior walkers to expose the skin for the attachment of the anatomical/tracking markers on the foot (Fig. 1). Medial and lateral plastic leg supports and Velcro straps of the walkers were not altered; therefore, the integrity of the walkers was maintained. They also wore a pair of the laboratory running shoes (Noveto, Adidas) in the shoe condition. 2.4. Data and statistical analysis Kinematic and GRF data were smoothed at 6 and 20 Hz, respectively, using a fourth-order Butterworth low-pass filter. The 3D kinematic and joint kinetic variables were computed using Visual3D software suite (C-Motion, Inc., MD, USA), and the critical events and additional variables were further determined by a customized computer program. Internal moments of the lower extremity joints were computed in Visual3D. The ground reaction forces and joint moments were normalized to the participant’s body mass, yielding units of N/kg and N m/kg, respectively. The inversion/eversion of the ankle joint was computed as the subtalar joint movement in the coronal plane. A one-way repeated measures of analysis of variance (ANOVA) was used to evaluate selected kinematic, GRF, and joint kinetic variables (SPSS, 12.0). Post hoc comparisons were conducted with an alpha level ( p < 0.05) adjusted for multiple comparisons through a Bonferroni procedure.
3. Results The participants in the study performed the walking trials at a mean velocity of 1.24 0.18 m/s. The female and male participants walked at similar speeds, 1.22 and 1.26 m/s,
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trials (Table 2). The eversion ROM was greater for the Gait Walker compared to the no walker condition. In addition, the hip abduction ROM for the Gait Walker and Equalizer walkers were significantly smaller than those for the shoes. In addition to the two vertical GRF peaks associated with the loading response (Max 2) and terminal stance (Max 3) commonly observed in walking in shoes, an apparent peak (Max 1) occurs earlier than the peak of loading response for the two walker conditions (Fig. 2). The statistical results indicated no significant differences for the GRF related variables between the test conditions (Table 3). For the joint kinetics, the peak plantarflexor moment that occurs later in the stance phase for the two walker conditions was greater than the no walker trials (Fig. 3a). In both walker conditions, the peak knee extensor moments were greater than the no walker trials. On the other hand, the statistical results showed a significantly smaller peak dorsiflexor moment for Gait Walker compared to the no walker and Equalizer walker conditions during earlier stance (Fig. 3b). The maximum ankle inversion moment for the Gait Walker condition was significantly greater than the no walker (Fig. 4). The peak knee abduction moments for the two walkers were smaller than the shoe condition; the same moment variable for Equalizer was also smaller than Gait Walker. Finally, the peak hip abduction moment for Equalizer was significantly smaller than the shoe condition.
Fig. 1. Reflective markers placements on the lower extremity and pelvis.
respectively. The ANOVA results showed a significantly greater maximum knee flexion angle for Gait Walker compared to the no walker condition (Table 1). No other variables related to the peaks and ranges of motion (ROM) of the three lower extremity joints were found significant between the testing conditions. The peak ankle eversion angle was found significantly smaller than the no walker
4. Discussions The kinematic data from this study showed no major changes in the peaks and ROMs of lower extremity joint kinematics in the sagittal plane with the exception of a slight increase in max knee flexion during the Gait Walker walking condition. However, the range of motion from heel strike did
Table 1 Average peak and ROM (8) of lower extremity joint angles in sagittal plane: mean standard deviation Condition
No walker Gait Walker Equalizer a
Ankle (8)
Knee (8)
Hip (8)
Dorsiflexion
ROM
Flexion
ROM
Extension
ROM
11.9 3.4 11.1 4.3 10.4 3.8
5.7 4.6 7.3 4.3 5.4 2.8
15.5 8.7 22.7 4.9 a 19.5 6.1
8.5 5.4 9.5 4.7 10.4 3.7
0.6 10.9 2.4 9.5 4.0 11.4
37.1 5.4 37.2 4.4 36.4 5.2
Significantly different from Gait Walker.
Table 2 Average peak and ROM (8) of lower extremity joint angles in frontal plane: mean standard deviation Condition
Ankle (8) Eversion
No walker Gait Walker Equalizer a
4.5 2.3 2.8 4.6 0.8 2.8 a
Significantly different from Gait Walker.
Knee (8)
Hip (8)
ROM
Adduction
ROM
Adduction
ROM
8.7 3.3 1.8 4.9a 6.6 4.6
4.6 2.9 3.9 2.2 1.5 3.4
3.3 1.8 2.4 2.5 2.1 2.2
5.8 2.8 5.1 3.6 6.1 3.2
8.3 2.4 6.1 2.0 a 6.0 2.3 a
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Fig. 3. Average peak extensor moments (a) and flexor moments (b) lower extremity joints (N m/kg) in sagittal plane; (1) significantly different from no walker and (2) significantly different from Gait Walker.
maximum eversion angle and hip adduction range of motion. These data suggest that both walkers restrict motions of the subtalar and hip joints in the frontal plane. The reduced hip adduction may be related the restriction provided by the walkers at the ankle/foot complex. The previous study [11] demonstrated no significant differences of hip and knee kinematics in sagittal (flexion/extension) Fig. 2. Representative curves of vertical ground reaction force for: no walker (A), Gait Walker (B), and Equalizer (C).
not statistically differ from the Equalizer and the shoe walking trials. Major differences of joint kinematics were seen in the frontal plane. The walking trials in the Gait Walker showed reduced range of motion for subtalar joint eversion and hip adduction compared to the walking trials in shoes. The Equalizer walker also exhibited reduced Table 3 Average peak vertical ground reaction force (N/kg): mean standard deviation Condition
Max 1
Max 2
Max 3
No walker Gait Walker Equalizer
– 8.91 1.49 7.37 2.74
10.77 0.59 10.27 0.72 10.72 0.61
10.68 0.41 10.47 0.59 10.43 0.44
(–) No apparent peak observed.
Fig. 4. Average peak joint moments (N m/kg) of lower extremity joints in frontal plane; (1) significantly different from no walker and (2) significantly different from Gait Walker.
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and frontal (adduction/abduction) planes between the walker conditions. Our data basically agreed with the finding. The data for both walkers from this study showed the early peak in the vertical GRF right after the heel strike and prior to the loading response (Fig. 2). Both walkers have a Polyurethane outsole, a Polypropylene midsole, and a hard form as the insole. Their heel height is greater than the laboratory shoes. A closer examination of the walkers and shoes used in this study showed that the heel thickness taken at the mid heel region were 2.4, 3.2, and 3.6 cm on average for the shoes, Equalizer, and Gait Walker, respectively. The raised heel height on the walker side artificially increases the limb length discrepancy. The sole materials/construction, the restriction of ankle movements, and the heel height may contribute to the observed initial GRF impact that is absent from the shoe walking. The vertical ground reaction force profile for the two walkers also demonstrated a marked difference that occurs between the loading response and terminal stance (Fig. 2). The GRF curve for normal walking in shoes shows a typical smooth valley between the two peaks. The GRF curve for the Equalizer walker showed a more similar pattern to the shoe walking compared to the Gait Walker. The GRF curve for the Gait Walker trial demonstrated an elevated portion between the peaks. The elevated portion of the GRF curve is associated with stance phase when the walker is rolled from the heel strike to the midstance. An examination of the outsole of the two walkers showed that both walkers have a curve at the heel region, which should facilitate the progression of the body from heel strike to midstance. The Equalizer walker has a smooth and slightly greater curve throughout the outsole from the heel to the toe region. The Gait Walker shows a flatter curve in the outsole, especially at the region between the heel and the mid-foot, which is almost entirely flat. The measurements on the shoes and walkers indicated that the forefoot thickness (taken at the region of the third metatarsal head) was 1.9, 2.2, and 3.1 cm on average for the shoes, Equalizer and Gait Walker, respectively. For the testing shoes, the thickness difference between the forefoot and heel regions is 0.5 cm, whereas the differences were 1.1 and 0.5 cm for Equalizer and Intuition, respectively. The differences further verified our initial observed differences in the sole designs in these walkers. The greater heel thickness with respect to its forefoot region was observed in the Equalizer walkers and this may facilitate transition from the heel strike to the toe-off as the center of mass progresses forward. This may be especially necessary while wearing a walker due to the restricted ankle dorsi-/ plantarflexion. On the other hand, the smaller difference of the heel–forefoot thickness seen in the shoes and Gait Walker compared to the Equalizer does not affect normal walking in regular shoes since the ankle joints can dorsi-/ plantarflex freely to accommodate the rolling action needed to facilitate the forward progression of the center of mass during the stance. However, this transition process may be somewhat more restricted wearing the Gait Walker due to
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the smaller thickness difference between the heel and forefoot regions and the flatter outsole curve of the walker, leading to the elevated vertical ground reaction force around the midstance. This may be also related to the increased maximum knee flexion in the earlier stance associated with the walker to accommodate the need for the forward body progression. On the other hand, the elevated GRF suggests that the Gait Walker was able to maintain a low but rather ‘‘constant’’ load and avoid abrupt changes in the ground reaction force during midstance. This unique characteristic may benefit patients by decreasing loading rates between the two GRF peaks and promoting healing by maintaining a relatively constant load. So far, the authors have not been able to find published documents on GRF characteristics of walkers in gait. Pollo et al. [11] report the ground reaction forces in their study. The peak knee abduction moment for the Gait Walker and Equalizer walkers were both found to be significantly smaller than the shoe condition. The Equalizer walker also demonstrated a reduction in the peak hip abduction moment. These reductions occur in early stance phase and may be related to diminished needs of knee and hip abductors to restrain adductions of the joints in the early stance due to the application of the walkers. Pollo et al. also found decreased knee and hip abduction moments for some of the tested walkers in early stance phase [11]. The knee moment is considered to be important in maintaining appropriate loading to the lateral and medial compartments of the knee [11] and therefore the mediolateral stability. The increased inversion ankle moment seen in the Gait Walker is related to the diminished eversion ROM, suggesting the better performance of the walker in restricting subtalar joint motion during the earlier support phase. The greater peak knee extensor moment for both walkers compared to the shoe walking trials may be related to the constraint provided by the arm supports and straps of the walkers to the ankle joint movements and the increased mass (walker) attached to the leg and foot, which in turn require the knee extensors to exert a greater torque to extend the knee to facilitate the rolling from the heel strike to the toe-off during the stance phase. The greater heel thickness observed in the walkers may also increase the length of the walker side’s limb and thus place it at a slight disadvantage. This ‘‘increased’’ leg length requires the knee extensors to exert greater amount of torque to raise the center of mass to the required height for a smooth transition across the midstance. It was reported that the Equalizer walker along with another walker (Cam walker) also had greater knee extensor moments [11]. The authors suggested this increased moments may lead to increased loading applied to the tibiofemoral and patellofemoral joints. The joint moment data from this study also indicated a smaller peak dorsiflexor moment for the Gait Walker. This reduction occurring in the earlier stance phase showed a decreased involvement of dorsiflexors in the walker conditions. This suggests that the restriction from a walker may reduce the need for the
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dorsiflexors to actively oppose the plantarflexion seen in the earlier stance phase. However, both walkers showed an increased plantarflexor moment in late stance phase, suggesting an elevated effort from the plantarflexors during push-off. It is unclear why this occurred.
5. Conclusion This study showed both short-leg walking boots, DeRoyal’s Gait Walker and Royce’s Equalizer, were effective in minimizing motion of ankle eversion and hip adduction in frontal plane. Both walkers did not increase the two peak ground reaction forces observed in normal walking in shoes. However, they did impose a small initial peak (<1 BW) in early stance phase. Due to the difference in sole design, the Gait Walker exhibited a slightly elevated vertical ground reaction force around midstance. Both walkers increased the demand on knee extensors while they decreased the effort of the knee and hip abductors. Both walkers have different sole materials/construction, restricted ankle movements, greater weight, and greater heel heights compared to the shoes used in the study and some of the observed biomechanics differences including the observed initial peak may be related to these differences. Although untested, it is logical to hypothesize that placing an orthotic insert in the shoe of the unaffected limb may relieve the initial GRF peak associated with the heel height difference. Since the walkers may be worn for a long period of time, the observed initial vertical GRF peak may impose some adverse effect on the affected limb. The effects of the observed biomechanical changes of the affected side on the movements of the unaffected limb are almost entirely unknown. If the compensatory changes on the unaffected side do occur, it may cause undesirable outcomes such as pain in sacroiliac joint and low back due to prolonged usage of a short-leg walker. Finally, some of the significant differences are small and their clinical impacts have yet to be investigated. Therefore, further studies on these aspects of short-leg walkers are warranted.
Acknowledgments This study was funded by a grant from DeRoyal Industries, Inc., a grant from Charlie and Mai Coffey
Endowment, and a grant from the Scholarly Activity and Research Incentive Fund at The University of Tennessee.
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