Aline H. Vrieling

Balance control on a moving platform in unilateral lower limb amputees

OBJECTIVE To study balance control on a moving platform in lower limb amputees. DESIGN Observational cohort study. PARTICIPANTS Unilateral transfemoral and transtibial amputees and able-bodied control subjects. INTERVENTIONS Balance control on a platform that moved in the anteroposterior direction was tested with eyes open, blindfolded and while performing a dual task. MAIN OUTCOME MEASURES Weight bearing symmetry, anteroposterior ground reaction force and centre of pressure shift. RESULTS Compared to able-bodied subjects, in amputees the anteroposterior ground reaction force was larger in the prosthetic and non-affected limb, and the centre of pressure displacement was increased in the non-affected limb and decreased in the prosthetic limb. In amputees body weight was loaded more on the non-affected limb. Blindfolding or adding a dual task did not influence the outcome measures importantly. CONCLUSION The results of this study indicate that experienced unilateral amputees with a high activity level compensate for the loss of ankle strategy by increasing movements and loading in the non-affected limb. The ability to cope with balance perturbations is limited in the prosthetic limb. To enable amputees to manage all possible balance disturbances in real life in a safe manner, we recommend to improve muscle strength and control in the non-affected limb and to train complex balance tasks in challenging environments during rehabilitation.

Uphill and downhill walking in unilateral lower limb amputees

OBJECTIVE To study adjustment strategies in unilateral amputees in uphill and downhill walking. DESIGN Observational cohort study. SUBJECTS Seven transfemoral, 12 transtibial unilateral amputees and 10 able-bodied subjects. METHODS In a motion analysis laboratory the subjects walked over a level surface and an uphill and downhill slope. Gait velocity and lower limb joint angles were measured. RESULTS In uphill walking hip and knee flexion at initial contact and hip flexion in swing were increased in the prosthetic limb of transtibial amputees. In downhill walking transtibial amputees showed more knee flexion on the prosthetic side in late stance and swing. Transfemoral amputees were not able to increase prosthetic knee flexion in uphill and downhill walking. An important adjustment strategy in both amputee groups was a smaller hip extension in late stance in uphill and downhill walking, probably related with a shorter step length. In addition, amputees increased knee flexion in early stance in the non-affected limb in uphill walking to compensate for the shorter prosthetic limb length. In downhill walking fewer adjustments were necessary, since the shorter prosthetic limb already resulted in lowering of the body. CONCLUSION Uphill and downhill walking can be trained in rehabilitation, which may improve safety and confidence of amputees. Prosthetic design should focus on better control of prosthetic knee flexion abilities without reducing stability.

Gait adjustments in obstacle crossing, gait initiation and gait termination after a recent lower limb amputation

Objective: To describe the adjustments in gait characteristics of obstacle crossing, gait initiation and gait termination that occur in subjects with a recent lower limb amputation during the rehabilitation process. Design: Prospective and descriptive study. Subjects: Fourteen subjects with a recent transfemoral, knee disarticulation or transtibial amputation. Methods: Subjects stepped over an obstacle and initiated and terminated gait at four different times during the rehabilitation process. Outcome measures: Success rate, gait velocity and lower limb joint angles in obstacle crossing, centre of pressure shift and peak anteroposterior ground reaction force in gait initiation and termination. Results: In obstacle crossing amputees increased success rate, gait velocity and swing knee flexion of the prosthetic limb. Knee flexion in transfemoral and knee disarticulation amputees was not sufficient for safe obstacle crossing, which resulted in a circumduction strategy. In gait initiation and termination amputees increased the anteroposterior ground reaction force and the centre of pressure shift in the mediolateral direction in both tasks. Throughout the rehabilitation process the centre of pressure was shifted anteriorly before single-limb stance on the trailing prosthetic limb in gait initiation, whereas in gait termination the centre of pressure in single-limb stance remained posterior when leading with the prosthetic limb. Conclusion: Subjects with a recent amputation develop adjustment strategies to improve obstacle crossing, gait initiation and gait termination. Innovations in prosthetic design or training methods may ease the learning process of these tasks.

Controlling Propulsive Forces in Gait Initiation in Transfemoral Amputees

During prosthetic gait initiation, transfemoral (TF) amputees control the spatial and temporal parameters that modulate the propulsive forces, the positions of the center of pressure (CoP), and the center of mass (CoM). Whether their sound leg or the prosthetic leg is leading, the TF amputees reach the same end velocity. We wondered how the CoM velocity build up is influenced by the differences in propulsive components in the legs and how the trajectory of the CoP differs from the CoP trajectory in able bodied (AB) subjects. Seven TF subjects and eight AB subjects were tested on a force plate and on an 8 m long walkway. On the force plate, they initiated gait two times with their sound leg and two times with their prosthetic leg. Force measurement data were used to calculate the CoM velocity curves in horizontal and vertical directions. Gait initiated on the walkway was used to determine the leg preference. We hypothesized that because of the differences in propulsive components, the motions of the CoP and the CoM have to be different, as ankle muscles are used to help generate horizontal ground reaction force components. Also, due to the absence of an active ankle function in the prosthetic leg, the vertical CoM velocity during gait initiation may be different when leading with the prosthetic leg compared to when leading with the sound leg. The data showed that whether the TF subjects initiated a gait with their prosthetic leg or with their sound leg, their horizontal end velocity was equal. The subjects compensated the loss of propulsive force under the prosthesis with the sound leg, both when the prosthetic leg was leading and when the sound leg was leading. In the vertical CoM velocity, a tendency for differences between the two conditions was found. When initiating gait with the sound leg, the downward vertical CoM velocity at the end of the gait initiation was higher compared to when leading with the prosthetic leg. Our subjects used a gait initiation strategy that depended mainly on the active ankle function of the sound leg; therefore, they changed the relative durations of the gait initiation anticipatory postural adjustment phase and the step execution phase. Both legs were controlled in one single system of gait propulsion. The shape of the CoP trajectories, the applied forces, and the CoM velocity curves are described in this paper.

Stabilizing moments of force on a prosthetic knee during stance in the first steps after gait initiation.

In this study, the occurrences of stabilizing and destabilizing external moments of force on a prosthetic knee during stance, in the first steps after gait initiation, in inexperienced users were investigated. Primary aim was to identify the differences in the external moments during gait initiation with the sound leg leading and the prosthetic leg leading. A prosthetic leg simulator device, with a flexible knee, was used to test able-bodied subject, with no walking aid experience. Inverse dynamics calculations were preformed to calculate the external moments. The subjects learned to control the prosthetic leg within 100 steps, without walking aids, evoking similar patterns of external moments of force during the steps after the gait initiation, either with their sound leg loading or prosthetic leg leading. Critical phases in which a sudden flexion of the knee can occur were found just after heelstrike and just before toe off, in which the external moment of force was close to the internal moment produced by a knee extension aiding spring in the opposite direction.

Controlling horizontal deceleration during gait termination in transfemoral amputees : Measurements and simulations

In this study we investigated how leading limb angles combined with active ankle moments of a sound ankle or passive stiffness of a prosthetic ankle, influence the center of mass (CoM) velocity during the single limb support phase in gait termination. Also, we studied how the trailing limb velocity influences the CoM velocity during this phase. We analyzed force plate data from a group of experienced transfermoral (TF) amputee subjects using a prosthetic limb, and the outcome from a two-dimensional mathematical forward dynamics model. We found that when leading with the sound limb, the subjects came almost to a full stop in the single limb support phase, without the use of the prosthetic limb. When leading with the prosthetic limb, the CoM deceleration was less in a relatively short single limb support phase, with a fast forward swing of the trailing sound limb. Slowing down the heavier trailing sound limb, compared to the prosthetic limb, results in a relatively larger braking force at the end of the swing phase. The simulations showed that only narrow ranges of leading limb angle and ankle moments could be used to achieve the same CoM velocities with the mathematical model as the average start and end velocities of the prosthetic limb user. We conclude that users of prosthetic limbs have a narrow range of options for the dynamics variables to achieve a target CoM velocity. The lack of active control in the passive prosthetic ankle prevents the TF amputee subjects from producing sufficient braking force when terminating gait with the prosthetic limb leading, forcing the subjects to use both limbs as a functional unit, in which the sound limb is mostly responsible for the gait termination.

Cancer treatment induced metabolic syndrome : Improving outcome with lifestyle

Increasing numbers of long-term cancer survivors face important treatment related adverse effects. Cancer treatment induced metabolic syndrome (CTIMetS) is an especially prevalent and harmful condition. The aetiology of CTIMetS likely differs from metabolic syndrome in the general population, but effective treatment and prevention methods are probably similar. In this review, we summarize the potential mechanisms leading to the development of CTIMetS after various types of cancer treatment. Furthermore, we propose a safe and accessible method to treat or prevent CTIMetS through lifestyle change. In particular, we suggest that a lifestyle intervention and optimization of energy balance can prevent or mitigate the development of CTIMetS, which may contribute to optimal survivorship care.

Principles of obstacle avoidance with a transfemoral prosthetic limb

In this study, conditions that enable a prosthetic knee flexion strategy in transfemoral amputee subjects during obstacle avoidance were investigated. This study explored the hip torque principle and the static ground principle as object avoidance strategies. A prosthetic limb simulator device was used to study the influence of applied hip torques and static ground friction on the prosthetic foot trajectory. Inverse dynamics were used to calculate the energy produced by the hip joint. A two-dimensional forward dynamics model was used to investigate the relation between obstacle-foot distance and the necessary hip torques utilized during obstacle avoidance. The study showed that a prosthetic knee flexion strategy was facilitated by the use of ground friction and by larger active hip torques. This strategy required more energy produced by the hip compared to a knee extension strategy. We conclude that when an amputee maintains enough distance between the distal tip of the foot and the obstacle during stance, he or she produces sufficiently high, yet feasible, hip torques and uses static ground friction, the amputee satisfies the conditions for enable stepping over an obstacle using a knee flexion strategy.

Predicting mobility outcome in lower limb amputees with motor ability tests used in early rehabilitation

Study design: Retrospective cohort study. Background: Persons with a lower limb amputation can regain mobility using a prosthetic device. For fast and adequate prescription of prosthetic components, it is necessary to predict the mobility outcome early in rehabilitation. Currently, prosthetic prescription is primarily based on empirical knowledge of rehabilitation professionals. Objective: In this study, we explored motor ability tests, to be completed without a prosthetic device, which have predictive value for mobility outcome at the end of rehabilitation. Methods: For this study, data of 82 patients with a lower limb amputation were included. The Single-limb standing balance test (Balance test), the Lower-Extremity Motor Coordination Test and the Amputee Mobility Predictor Assessment Tool (AMPnoPRO) were used as measures for motor ability. Mobility outcome was measured using the Timed Up and Go Test, the Two-Minute Walking Test and K levels were used. Results: The explained variance of the Balance test, the Lower-Extremity Motor Coordination Test and the AMPnoPRO was, respectively, 0.603, 0.534 and 0.649 on the Two-Minute Walking Test (linear regression); 0.597, 0.431 and 0.624 on the Timed Up and Go Test (linear regression); and 0.432, 0.420 and 0.526 on the K levels (logistic regression). Conclusion: The AMPnoPRO predicted mobility outcome statistically (largest amount of explained variance). Clinical relevance This study explored the possibility of statistically predicting mobility outcome in lower limb amputees at the end of rehabilitation, using motor ability tests conducted in early rehabilitation. This study suggests the use of the AMPnoPRO to predict mobility outcome in lower limb amputees.