Leg Length Discrepancy: Dynamic Balance Response during Gait

The biomechanical effects of limb length discrepancy on gait

Leg Length Discrepancy (LLD) causes a shift of the Center of Mass (CoM) of the human body, as well as an asymmetry in load distribution on the lower extremities. Existing LLD evaluation methods do not take into account this shift in the human body’s CoM. In this paper, a methodology and mechatronic system for the Evaluation and Compensation of LLD for Human Body Balancing are described. The human body’s CoM is measured with two force plates located on two parallel manipulators. Since persons with LLD experience a shift in their CoM, by raising the force plate that is under the shorter leg, the human body can be balanced. For this purpose, the Human Body Balancing Algorithm (HBBA) was proposed and developed. By running the HBBA, the height difference between the force plates under the left and right leg can be measured, which then represents the LLD evaluation. Based on this evaluation, it is possible to design and make a shoe insole which compensates the influence of LLD with the goal of equalizing the load on the legs. A virtual mathematical model of the system was created and the simulation results of the HBBA are presented. The mechatronic system, developed and used to conduct experiments and measurements, is described in detail.

Osteoarthritic knee pain is very common, as are leg length discrepancies (LLDs). The relationship between LLDs and osteoarthritic knee pain is not well understood. To confirm a clinical impression that osteoarthritic knee pain is more common in the short (ie, superior-presenting) leg, as measured by supine physical examination of 3 bony landmarks: the medial malleoli, the anterior superior iliac spines, and the iliac crests. The secondary objective was to measure the relative positions of the 3 bony landmarks to better understand functional contributions to LLD. A prospective single-occasion observational design was used. Patients who reported osteoarthritic knee pain during an office visit were recruited, and data were collected on 3 bony landmarks and which knee was usually most painful. Of the 32 participants who were recruited, 28 were women and 4 were men. Of the 17 participants who reported having right knee pain, 10 had a short right leg and 7 had a short left leg. Of the 15 participants who reported having left knee pain, 13 had a short left leg, 1 had a short right leg, and 1 had equal leg lengths. Knee pain was most severe in the short leg for 23 of 32 participants (71.9%). The most common pattern was for both iliac crests to be equal and the short leg to be concordant with a superior anterior superior iliac spine, which occurred in 23 of 32 participants (71.9%). In the present study population, the magnitude of LLD ranged from 0 to 2.1 cm. Osteoarthritic knee pain was more common in the apparent short leg. More sophisticated studies, including investigations into the role of pelvic torsion in knee pain, as well as investigations for interoperator reliability and validity, are needed to build on the findings reported in this observational study.

102. An introductory investigation of standing postural control ‘error’ and its relation to balance in adult spinal deformity surgery patients

To aid in the successful execution of goal-directed walking (discrete movement from a start location to an end target) the central nervous system forms a predictive motor plan. For the motor plan to be effective, it must be adapted in response to environmental changes. Despite motor planning being inherent to goal-directed walking, it is not understood how the nervous system adapts these plans to interact with changing environments. Our objective was to understand how people adapt motor plans of center of mass (COM) trajectory during goal-directed walking in response to a consistent change in environmental dynamics. Participants preformed a series of goal-directed walking trials in a novel environment created by a cable robot that applied a lateral force field to their COM. We hypothesized that participants would adapt to the environment by forming an internal model of their COM trajectory within the force field. Our findings support this hypothesis. Initially, we found COM trajectory significantly deviated in the same direction as the applied field, relative to baseline (no field) (p = 0.002). However, with practice in the field, COM trajectory adapted back to the baseline (p = 0.6). When we unexpectedly removed the field, participants demonstrated after-effects, COM trajectory deviated in the direction opposite of the field relative to baseline (p < 0.001). Our findings suggest that when performing a goal-directed walking task, people adapt a motor plan that predicts the COM trajectory that will emerge from the interaction between a specific set of motor commands and the external environment.

Since the center of mass (CoM) is related to ground reaction force (GRF), the CoM position is expected to be used in evaluation of walking ability. The purpose of this study was to examine the possibilities of using the CoM acceleration calculated from the CoM trajectory estimated by inertial sensor signals to obtain similar information as the GRF. In this paper, 16 m straight walking measurements were performed under different walking speeds with healthy subjects. CoM acceleration, which was calculated from CoM positions estimated by signals measured with inertial sensors, were analyzed for the steady state gait. Waveforms of the CoM acceleration were similar among subjects. Four peak values (negative peak near the toe off (TO) and positive peak near the initial contact (IC) of the opposite lower limb in the anteroposterior component, and the positive peak before the TO of the opposite lower limb and the negative peak of the mid-stance phase) showed significant correlations with walking speed, which were similar to the relationships between GRF and walking speed in previous studies. These results suggest that anteroposterior and vertical components of CoM acceleration estimated from inertial sensor signals have a possibility of estimating similar information as the GRF during walking. The relationship between positive peak value of the vertical component near the IC of the opposite side and walking speed was seemed to be different from a previous study, although it showed significant correlation with walking speed. Simultaneous measurements with inertial sensors and GRF are expected in the next study.

Vertical ground reaction force(vGRF) has been widely known as a qualitative features of human walking. While a human walks, the vGRF exhibits a double peak profile in which two maximal values appear from the heel contact to the toe off. So far, various studies have been mainly conducted in the field of biomechanics to elucidate the mechanism by which the double peak profile of the vGRF can be generated. In these researches, inverted pendulum models that allow the change in the length of the support leg have been considered as one of the minimal models. It is, however, known that the center of mass(COM) trajectory of human waling coincides well with the COM trajectory of the inverted pendulum with constant support leg length because changes in the length of legs during walking is small compared to the length. In this research, we propose a new minimal model for human walking based on the inverted pendulum model with fixed support leg length which can interpret the double peak profile of vGRF by considering double support phase. As a result of the verification by the numerical simulation, the proposed model was successfully confirmed that the double peak profile of vGRF can be reproduced in accordance with the COM trajectory of the inverted pendulum model with fixed support leg length.

Control of the motion of the body's center of mass in relation to the center of pressure during high-heeled gait

Postural instability marks a prevalent symptom of Parkinson’s disease (PD). It often manifests in increased body sway, which is commonly assessed by tracking the Center of Pressure (CoP). Yet, in terms of postural control, the body’s Center of Mass (CoM), and not CoP is what is regulated in a gravitational field. The aim of this study was to explore the effect of early- to mid-stage PD on these measures of postural control in response to unpredictable visual perturbations. We investigated three cohorts: (i) 18 patients with early to mid-stage PD [Hoehn & Yahr stage (1–3); 1.94 ± 0.70]; (ii) a group of 15 age-matched controls (ECT); and (iii) a group of 12 young healthy adults (YCT). Participants stood on a force plate to track their CoP, while the movement of their entire body was recorded with a video-based motion tracking system to monitor their CoM. A moving room paradigm was applied through a head-mounted virtual reality headset. The stimulus consisted of a virtual tunnel that stretched in the anterior-posterior direction which either remained static or moved back and forth in an unpredictable fashion.We found differences in mean sway amplitude (MSA) and mean velocities of CoP and CoM between the groups under both conditions, with higher MSA of CoP and CoM for PD and higher mean velocities of both variables for PD and ECT when compared with YCT. Visual perturbation increased mean CoP velocity in all groups but did not have effects on mean CoM velocity or MSA. While being significantly lower for the young adults, the net effect of visual perturbation on mean CoP velocity was similar between patients with PD and age-matched controls. There was no effect of the visual perturbation on mean CoM velocity for any of the groups.Our simultaneous assessment of CoP and CoM revealed that postural control is reflected differently in CoM and CoP. As the motion of CoM remained mostly unaffected, all groups successfully counteracted the perturbation and maintained their balance. Higher CoP velocity for PD and ECT revealed increased corrective motion needed to achieve this, which however was similar in both groups. Thus, our results suggest increased effort, expressed in CoP velocity, to be an effect of age rather than disease in earlier stages of PD.

ABSTRACTThe aim of this study was to advance current movement analysis methodology to enable a technique analysis in sports facilitating (1) concurrent comparison of the techniques between several athletes; (2) identification of potentially beneficial technique modifications and (3) a visual representation of the findings for feedback to the athletes. Six elite cross-country skiers, three world cup winners and three national elite, roller ski skated using the V2 technique on a treadmill while their movement patterns were recorded using 41 reflective markers. A principal component analysis performed on the marker positions resulted in multi-segmental “principal” movement components (PMs). A novel normalisation facilitated comparability of the PMs between athletes. Additionally, centre of mass (COM) trajectories were modelled. We found correlations between the athletes’ performance levels (judged from race points) and specific features in the PMs and in the COM trajectories. Plausible links between COM trajectories and PMs were observed, suggesting that better performing skiers exhibited a different, possibly more efficient use of their body mass for propulsion. The analysis presented in the current study revealed specific technique features that appeared to relate to the skiers’ performance levels. How changing these features would affect an individual athlete’s technique was visualised with animated stick figures.

In bipedal robot locomotion, generation of Center of Mass (CoM) trajectory forms an essential component in gait pattern generation using approximate models. Towards this, rolling sphere model as an approximate model has been widely studied for biped walk. In this work, the rolling sphere model is used to generate realizable bipedal walk by improving an existing approach. In doing so, a consistent CoM trajectory is derived with a desirable Zero Moment Point (ZMP) making the resulting gait more practical. The efficacy of the formulation has been validated through simulation using parameters of humanoid robot NAO.

The paper presents the development of a measurement system for dynamic stability analysis. The system is composed of an actuation device, that is a robotic platform with four degrees of freedom, and two measurement systems: a force platform, to measure the position of the centre of pressure (COP), and a vision system, to measure the position of the centre of mass (COM). The purpose of the system is to provide means to identify whether a subject behaves like an inverted pendulum (as the literature predicts for static posturography), when a dynamic perturbation is applied. This can be achieved by generating a movement of the robotic platform and, simultaneously, by measuring COP and COM trajectories and verify their coherence with the inverse pendulum model.

A main objective in bipedal walking is controlling the whole body to stay upright. One strategy that promotes this objective is to direct the ground reaction forces (GRFs) to a point above the center of mass (COM). In humans, such force patterns can be observed for unperturbed walking, but it is not known whether the same strategy is used for a walkway that changes in height. In this study, 11 volunteers stepped down off a visible (0, 10 and 20 cm) and a camouflaged (0 or 10 cm) curb while walking at two different speeds (1.2±0.1 and 1.7±0.1 m s-1). The results showed that in all conditions the GRFs pointed predominantly above the COM. Vectors directed from the center of pressure (COP) to the intersection point (IP) closely fitted the measured GRF direction not only in visible conditions (R2>97.5%) but also in camouflaged curb negotiation (R2>89.8%). Additional analysis of variables included in the calculation of the IP location showed considerable differences for the camouflaged curb negotiation: compared with level walking, the COP shifted posterior relative to the COM and the vertical GRFs were higher in the beginning and lower in later parts of the stance phase of the perturbed contact. The results suggest that IP behavior can be observed for both visible and camouflaged curb negotiation. For further regulation of the whole-body angle, the asymmetrical vertical GRFs could counteract the effect of a posterior shifted step.

Corner height influences center of mass kinematics and path trajectory during turning

Effect of loss of balance on biomechanics platform measures of sway: Influence of stance and a method for adjustment