Steven J. Stanhope

Relative contributions of the lower extremity joint moments to forward progression and support during gait

Abstract A method, which was found to be accurate within 0.54 m/s 2 , was developed to estimate the relative contributions of the net joint moments to forward progression and support in the gait of five normal subjects. Forward progression was produced primarily by the ankle plantar flexors with a significant assist from the knee extensors. Support was produced largely by the plantar flexors during single limb support and by a combination of ankle plantar flexors, knee extensors and hip extensors during double limb support.

Comparison of surface mounted markers and attachment methods in estimating tibial rotations during walking: an in vivo study

The overall goal of this work was to determine an optimal surface-tracking marker set for tracking motion of the tibia during natural cadence walking. Eleven different marker sets were evaluated. The marker sets differed in the location they were attached to the shank, the method used to attach the marker sets to the segment and the physical characteristics of the marker sets. Angular position during stance for each marker set was expressed relative to the orientation of the tibia as measured using bone anchored markers. A marker set consisting of four markers attached to a rigid shell positioned over the distal lateral shank and attached to the leg using an underwrap attachment yielded the best estimate of tibial rotation. Rotational deviations of+/-2 degrees about the medio-lateral and antero-posterior axes, and+/-4 degrees about the longitudinal axis did occur even when using the optimal set of markers.

Surface movement errors in shank kinematics and knee kinetics during gait

Abstract The movement of surface mounted targets (SMT) on a shell at the mid-shank and of bone mounted targets attached to the distal shank using a Percutaneous Skeletal Tracker (PST) were simultaneously measured during free-speed walking of three adult subjects having different body types. Surface movement errors in shank kinematic estimates were determined by expressing the segmental motion derived from the SMT relative to the PST-based segment coordinate system (SCS) located at the segment center of gravity. The greatest errors were along and around the shank longitudinal axis, with peak magnitudes of 10 mm of translation and 8° of rotation in one subject. Estimates of knee joint center locations differed by less than 11 mm in each SCS direction. Differences in estimates of net knee joint forces and moments were most prominent during stance phase, with magnitudes up to 39 N in the shank mediolateral direction and 9 N.m about the mediolateral axis. The differences in kinetics were primarily related to the effect of segment position and orientation on the expression of joint forces and on the magnitude and expression of joint moments.

Clinical characteristics of flexed posture in elderly women.

Objectives: To investigate the relationships between the severity of flexed posture (FP), skeletal fragility, and functional status level in elderly women.

Flexibility of anticipatory postural adjustments revealed by self-paced and reaction-time arm movements.

In standing humans, it is not certain whether anticipatory postural adjustments associated with rapid, voluntary elbow flexion movements (focal movements) originate as a selection from preset synergies or as the result of specific planning of motor commands. We studied these muscle recruitment patterns when the same focal movement was made under behavioral conditions of a self-paced task (SPT) and a reaction-time task (RTT). While standing still, eight normal subjects performed focal movements under the SPT and RTT behavioral conditions and under three different biomechanical conditions: (1) unloaded-upright, (2) loaded-upright (holding a 3800-g metal bar), and (3) unloaded-forward leaning. Anticipatory postural adjustments were quantified using the latency and duration of electromyographic (EMG) data and the center of pressure (COP) displacement data. Postural-kinematic [joint and body center of gravity (COG) motion] data were used to quantify the anticipatory postural programs effectiveness at preventing postural movement. Focal movement kinematics and associated EMG activity differed due to biomechanical but not behavioral (SPT vs. RTT) conditions. The maximum and net displacement of the body COG measurements did not differ between the behavioral conditions. The amplitude, timing, and net movements of lower extremity joints were influenced by the behavioral conditions. However, the behavioral conditions significantly affected the phasing (including order of activation) and duration of anticipatory postural EMG activity and the phasing of COP displacements under certain biomechanical conditions. These findings support the theory that anticipatory postural adjustments are planned in detail.

Manufacture of Passive Dynamic Ankle–Foot Orthoses Using Selective Laser Sintering

Ankle-foot orthosis (AFO) designs vary in size, shape, and functional characteristics depending on the desired clinical application. Passive Dynamic (PD) Response ankle-foot orthoses (PD-AFOs) constitute a design that seeks to improve walking ability for persons with various neuromuscular disorders by passively (like a spring) providing variable levels of support during the stance phase of gait. Current PD-AFO manufacturing technology is either labor intensive or not well suited for the detailed refinement of PD-AFO bending stiffness characteristics. The primary objective of this study was to explore the feasibility of using a rapid freeform prototyping technique, selective laser sintering (SLS), as a PD-AFO manufacturing process. Feasibility was determined by replicating the shape and functional characteristics of a carbon fiber AFO (CF-AFO). The study showed that a SLS-based framework is ideally suited for this application. A second objective was to determine the optimal SLS material for PD-AFOs to store and release elastic energy; considering minimizing energy dissipation through internal friction is a desired material characteristic. This study compared the mechanical damping of the CF-AFO to PD-AFOs manufactured by SLS using three different materials. Mechanical damping evaluation ranked the materials as Rilsantrade D80 (best), followed by DuraFormtrade PA and DuraFormtrade GF. In addition, Rilsantrade D80 was the only SLS material able to withstand large deformations.

The effect of variation in knee center location estimates on net knee joint moments

To test the sensitivity of knee flexion-extension moment patterns to variation in estimates of the knee center location (KCL), inverse dynamics analysis was performed using three different KCLs for data collected from 18 healthy adult subjects who walked at five different speeds (25%, 50%, 75%, 100% and 125% of 0.785 statures.s< ?? opnbop ?? ?-1). The KCL, which was determined using data from static subject calibration trials, was varied in software by plus or minus 10 mm in the anteroposterior direction. The effect of this KCL variation on knee moments was similar across subjects and at all five walking speeds. The relative knee center variation effect, expressed as a percentage of the mean knee moment, was progressively greater at slower walking speeds, up to 123% of the first extensor peak at the slowest speed. The implication of these results is that, while KCL variation does not affect the general shape of the moment pattern at more natural walking speeds, it can change the sign of the moment-and thus the interpretation-when the moment magnitude is small (e.g. at the very slow speeds used by some patients). When knee moments are of magnitudes less than or equal to the KCL variation effect, one cannot confidently interpret them as representing either a net flexor or extensor knee control strategy. Copyright 1998 Elsevier Science B.V.

Community-Based Adaptive Physical Activity Program for Chronic Stroke: Feasibility, Safety, and Efficacy of the Empoli Model

Objective. To determine whether Adaptive Physical Activity (APA-stroke), a community-based exercise program for participants with hemiparetic stroke, improves function in the community. Methods. Nonrandomized controlled study in Tuscany, Italy, of participants with mild to moderate hemiparesis at least 9 months after stroke. Forty-nine participants in a geographic health authority (Empoli) were offered APA-stroke (40 completed the study). Forty-four control participants in neighboring health authorities (Florence and Pisa) received usual care (38 completed the study). The APA intervention was a community-based progressive group exercise regimen that included walking, strength, and balance training for 1 hour, thrice a week, in local gyms, supervised by gym instructors. No serious adverse clinical events occurred during the exercise intervention. Outcome measures included the following: 6-month change in gait velocity (6-Minute Timed Walk), Short Physical Performance Battery (SPPB), Berg Balance Scale, Stroke Impact Scale (SIS), Barthel Index, Hamilton Rating Scale for Depression, and Index of Caregivers Strain. Results. After 6 months, the intervention group improved whereas controls declined in gait velocity, balance, SPPB, and SIS social participation domains. These between-group comparisons were statistically significant at P < .00015. Individuals with depressive symptoms at baseline improved whereas controls were unchanged (P < .003). Oral glucose tolerance tests were performed on a subset of participants in the intervention group. For these individuals, insulin secretion declined 29% after 6 months (P = .01). Conclusion. APA-stroke appears to be safe, feasible, and efficacious in a community setting.

Kinematic-based technique for event time determination during gait.

A kinematic-based technique for the estimation of the times at which gait events occur is presented. A kinematic-based model (KM) is defined by the trajectory of a point, which has an anatomically fixed location on the subjects body, about a time at which a measurement system defined gait event takes place. The times at which subsequent occurrences of the gait event takes place are determined by identifying the kinematic pattern that best fits the previously defined KM. The results of an experiment that used the gait patterns of a normal and a pathological walker indicate that the accuracy of the algorithm is limited by the kinematic data sampling interval and that optimal kinematic predictors of gait event times occur within the primary (sagittal) plane of motion. The technique is intended to obviate the need for multiple force plates, instrumented floors and instruments which are worn by the subject for the purpose of determining the times at which gait events occur.

Joint moment control of mechanical energy flow during normal gait

The study purpose was to estimate the ability of joint moments to transfer mechanical energy through the leg and trunk during gait. A segmental power analysis of five healthy adult subjects revealed that internal joint extensor moments removed energy from the leg and added energy to the trunk, while flexor moments and gravity produced the opposite effects. The only exception to this pattern was during the push off phase of gait when the ankle plantar flexor moment added energy to both the leg and the trunk. Pairs of joint moments with opposite energetic effects (knee extensor vs gravity, hip flexor vs ankle plantar flexor) worked together to balance energy flows through the segments. This intralimb coordination suggests that moments with contradictory effects are generated simultaneously to control mechanical energy flow within the body during walking.