J.C.H. Goh

Effects of varying backpack loads on peak forces in the lumbosacral spine during walking

OBJECTIVE: To compare the differences in lumbosacral spine forces under varying backpack loads. DESIGN: A biomechanical model was used to determine the changes in peak forces in the L5/S1 joint with increasing backpack loads during level walking. BACKGROUND: Most studies involving varying external backpack loads have been concerned mainly with kinematic and physiological measurements. To the authors knowledge, there has been no investigation of the change in peak forces in the lumbosacral joint during the carriage of such loads. METHOD: Data acquisition was carried out using a 5-camera Vicon motion analysis system and two Kistler force plates. Ten male subjects with similar weights, height and age were recruited for this study. Three different backpack loading conditions were studied, that is walking with no load, with 15% BW and with 30% BW. RESULTS: It was observed that all the ten subjects while walking with heavier backpack load adopted a compensatory trunk flexion posture. However, kinematic gait parameters such as walking speed and stride length remained unchanged with the increasing loads. Walking with backpack load of 15%BW and 30%BW resulted in corresponding increase in lumbosacral force of 26.7% and 64% respectively when compared to walking without backpack load. CONCLUSION: In carrying a given packload during walking, it will give rise to a disproportionate force increase acting on the L5/S1 joint.

Sagittal knee joint kinematics and energetics in response to different landing heights and techniques.

Single-leg and double-leg landing techniques are common athletic maneuvers typically performed from various landing heights during intensive sports activities. However, it is still unclear how the knee joint responds in terms of kinematics and energetics to the combined effects of different landing heights and techniques. We hypothesized that the knee displays greater flexion angles and angular velocities, joint power and work in response to the larger peak ground reaction force from 0.6-m height, compared to 0.3-m height. We further hypothesized that the knee exhibits elevated flexion angles and angular velocities, joint power and work during double-leg landing, relative to single-leg landing. Ground reaction force, knee joint kinematics and energetics data were obtained from 10 subjects performing single-leg and double-leg landing from 0.3-m to 0.6-m heights, using motion-capture system and force-plates. Higher peak ground reaction force (p<0.05) was observed during single-leg landing and/or at greater landing height. We found greater knee flexion angles and angular velocities (p<0.05) during double-leg landing and/or at greater landing height. Elevated knee joint power and work were noted (p<0.05) during double-leg landing and/or at greater landing height. The knee joint is able to respond more effectively in terms of kinematics and energetics to a larger landing impact from an elevated height during double-leg landing, compared to single-leg landing. This allows better shock absorption and thus minimizes the risk of sustaining lower extremity injuries.

Effect of landing height on frontal plane kinematics, kinetics and energy dissipation at lower extremity joints

Lack of the necessary magnitude of energy dissipation by lower extremity joint muscles may be implicated in elevated impact stresses present during landing from greater heights. These increased stresses are experienced by supporting tissues like cartilage, ligaments and bones, thus aggravating injury risk. This study sought to investigate frontal plane kinematics, kinetics and energetics of lower extremity joints during landing from different heights. Eighteen male recreational athletes were instructed to perform drop-landing tasks from 0.3- to 0.6-m heights. Force plates and motion-capture system were used to capture ground reaction force and kinematics data, respectively. Joint moment was calculated using inverse dynamics. Joint power was computed as a product of joint moment and angular velocity. Work was defined as joint power integrated over time. Hip and knee joints delivered significantly greater joint power and eccentric work (p<0.05) than the ankle joint at both landing heights. Substantial increase (p<0.05) in eccentric work was noted at the hip joint in response to increasing landing height. Knee and hip joints acted as key contributors to total energy dissipation in the frontal plane with increase in peak ground reaction force (GRF). The hip joint was the top contributor to energy absorption, which indicated a hip-dominant strategy in the frontal plane in response to peak GRF during landing. Future studies should investigate joint motions that can maximize energy dissipation or reduce the need for energy dissipation in the frontal plane at the various joints, and to evaluate their effects on the attenuation of lower extremity injury risk during landing.

Biomechanical study on axillary crutches during single-leg swing-through gait

This paper describes a kinetic and kinematic study on axillary crutches during one-leg swing-through gait. The primary objective is to evaluate the interplay of forces at the crutch and body interfaces and to relate them in the understanding of problems associated with the use of axillary crutches. Ten normal adult male subjects with simulated left leg impairment participated in the study. For data acquisition, the VICON kinematic system, a Kistler force plate and an instrumented crutch (with force transducers at the two upper struts close to the axillary bar and one near the crutch tip) were used. Results showed that the peak ground reaction force on the weight-bearing leg during lower limb stance increased by 21.6 percent bodyweight. The peak reaction force transmitted to the arm during crutch stancc was 44.4 percent bodyweight. These increased loadings could be detrimental to patients with unsound weight-bearing leg and upper extremities respectively. When the crutches were used incorrectly, 34 percent bodyweight was carried by the underarm. This could cause undue pressure over the neurovascular structures at the axillary region.

Stump/socket pressure profiles of the pressure cast prosthetic socket

OBJECTIVE The aim was to evaluate stump/socket interface pressure in amputees wearing a socket developed by a pressure casting system.Design. Five unilateral transtibial amputees wore a pressure cast socket and walked at a self-selected speed. BACKGROUND The socket produces equally distributed pressure at the stump/socket interface, deviating from the conventional belief that pressure varies in proportion to the pain threshold of different tissues in the stump. METHODS The socket was fabricated while the subject placed his stump in a pressure chamber. Pressure was applied while he adopted a normal standing position. A specially built strain gauged type pressure transducer was used for measuring pressure distribution. Pressure and gait parameters were measured simultaneously while the subjects were standing and walking. RESULTS AND CONCLUSION The pressure cast technique was able to provide comfortable fitting sockets. A hydrostatic pressure profile was not evident during standing or gait. Results also showed that no standard pressure profile for the pressure cast socket was observed. This was expected as no rectifications were done on the pressure cast socket. Pressure profiles at 10%, 25% and 50% of gait cycle did not correlate with the pressure profiles previously proposed. RELEVANCE The hydrostatic theory is an attractive concept in socket design as it produces a stump/socket pressure profile that is evenly distributed. Furthermore, it is a method that is easily implemented, independent of a prosthetists skill and experience and reduces manufacturing time. However, there is still controversy surrounding the efficacy of this hydrostatic theory.

Shod landing provides enhanced energy dissipation at the knee joint relative to barefoot landing from different heights

Athletic shoes can directly provide shock absorption at the foot due to its cushioning properties, however it remains unclear how these shoes may affect the level of energy dissipation contributed by the knee joint. This study sought to investigate biomechanical differences, in terms of knee kinematics, kinetics and energetics, between barefoot and shod landing from different heights. Twelve healthy male recreational athletes were recruited and instructed to perform double-leg landing from 0.3-m and 0.6-m heights in barefoot and shod conditions. The shoe model tested was Brooks Maximus II. Markers were placed on the subjects based on the Plug-in Gait Marker Set. Force-plates and motion-capture system were used to capture ground reaction force (GRF) and kinematics data respectively. 2×2-ANOVA (barefoot/shod condition×landing height) was performed to examine differences in knee kinematics, kinetics and energetics between barefoot and shod conditions from different landing heights. Peak GRF was not significantly different (p=0.732-0.824) between barefoot and shod conditions for both landing heights. Knee range-of-motion, flexion angular velocity, external knee flexion moment, and joint power and work were higher during shod landing (p<0.001 to p=0.007), compared to barefoot landing for both landing heights. No significant interactions (p=0.073-0.933) were found between landing height and barefoot/shod condition for the tested parameters. While the increase in landing height can elevate knee energetics independent of barefoot/shod conditions, we have also shown that the shod condition was able to augment the level of energy dissipation contributed by the knee joint, via the knee extensors, regardless of the tested landing heights.

Fatigue testing of energy storing prosthetic feet

This paper describes a simple approach to the fatigue testing of prosthetic feet. A fatigue testing machine for prosthetic feet was designed as part of the programme to develop an energy storing prosthetic foot (ESPF). The fatigue tester does not simulate the loading pattern on the foot during normal walking. However, cyclic vertical loads are applied to the heel and forefoot during heel-strike and toe-off respectively, for 500,000 cycles. The maximum load applied was chosen to be 1.5 times that applied by the bodyweight of the amputee and the test frequency was chosen to be 2 Hz to shorten the test duration. Four prosthetic feet were tested: tvo Lambda feet (a newly developed ESPF), a Kingsley SACH foot and a Proteor SACH foot. It was found that the Lambda feet have very good fatigue properties. The Kingsley SACH foot performed better than the Proteor model, with no signs of wear at the heel. The results obtained using the simple approach was found to be comparable to the results from more complex fatigue machines which simulate the load pattern during normal walking. This suggests that simple load simulating machines, which are less costly and require less maintenance, are useful substitutes in studying the fatigue properties of prosthetic feet.

Repeated application of incremental landing impact loads to intact knee joints induces anterior cruciate ligament failure and tibiofemoral cartilage deformation and damage: A preliminary cadaveric investigation.

Anterior cruciate ligament (ACL) injury is a major problem worldwide and prevails during high-impact activities. It is not well-understood how the extent and distribution of cartilage damage will arise from repetitive landing impact loads that can lead to ACL failure. This study seeks to investigate the sole effect of repetitive incremental landing impact loads on the induction of ACL failure, and extent and distribution of tibiofemoral cartilage damage in cadaveric knees. Five cadaveric knees were mounted onto a material testing system at 70 degrees flexion to simulate landing posture. A motion-capture system was used to track rotational and translational motions of the tibia and femur, respectively. Each specimen was compressed at a single 10Hz haversine to simulate landing impact. The compression trial was successively repeated with increasing actuator displacement till a significant compressive force drop was observed. All specimens underwent ACL failure, which was confirmed via magnetic resonance scans and dissection. Volume analysis, thickness measurement and histological techniques were employed to assess cartilage lesion status. For each specimen, the highest peak compressive force (1.9-7.8kN) was at the final trial in which ACL failure occurred; corresponding posterior femoral displacement (7.6-18.0mm) and internal tibial rotation (0.6 degrees -4.7 degrees ) were observed. Significant compressive force drop (79.8-90.9%) was noted upon ACL failure. Considerable cartilage deformation and damage were found in exterior, posterior and interior femoral regions with substantial volume reduction in lateral compartments. Repeated application of incremental landing impact loads can induce both ACL failure and cartilage damage, which may accelerate the risk of developing osteoarthritis.

Internal Model Approach for Gait Modeling and Classification

In this paper, we present a novel approach to model and classify gait patterns based on internal models. An internal model consists of two sets of differential equations and a neural network in between. It can effectively describe dynamic movement primitives (DMP), hence is able to model the temporal-spatial gait patterns. An interesting feature of the internal model is, the nonlinear map generated by the neural network can also serve the purpose for gait pattern classification. In this work we use a single hidden layer feedforward network (SLFN), and show that the characteristics of gait patterns can be captured via the output layer weights. The experiment results based on EMGs of gait patterns at five different walking speeds are used to validate the internal model approach

Gait analysis study of an energy-storing prosthetic foot — a preliminary report

Abstract The objective of the study was to compare, by gait analysis, the performance of an energy-storing prosthetic foot fabricated from composite materials, known as the ‘Lambda Foot’, and the conventional SACH foot. An attempt was made to show quantitatively that the Lambda Foot has better energy characteristics during gait. Three active unilateral below-knee amputees (2 females and 1 male) participated in the gait analysis. The vicon motion analysis system and Kistler force plates were used in the study. Since the sample size was small, intra-comparison was made to give an indication of the overall trend. Stride characteristics (walking speed, cadence, single stance, and double stance) did not differ significantly between the two prosthetic feet. The Lamba Foot produced significantly larger ankle rotations at early and late stance, which more closely approximate to the natural ankle. The better energy characteristics of the Lambda Foot was shown in the large plantarflexion moment at the ankle of the Lambda Foot, when compared to the SACH foot. This was verified by the significantly higher energy values obtained at the ankle of the Lambda Foot. However, it is still approximately 60% less efficient than the normal, sound foot. The subjects expressed a liking for the Lambda Foot for being much lighter and offering a spring-like effect not experienced with the SACH foot.