Steven A. Gard

Effect of Ankle-Foot Orthosis Alignment and Foot-Plate Length on the Gait of Adults With Poststroke Hemiplegia

OBJECTIVE To investigate the effect of ankle-foot orthosis (AFO) alignment and foot-plate length on sagittal plane knee kinematics and kinetics during gait in adults with poststroke hemiplegia. DESIGN Repeated measures, quasi-experimental study. SETTING Motion analysis laboratory. PARTICIPANTS Volunteer sample of adults with poststroke hemiplegia (n=16) and able-bodied adults (n=12) of similar age. INTERVENTIONS Subjects with hemiplegia were measured walking with standardized footwear in 4 conditions: (1) no AFO (shoes only); (2) articulated AFO with 90 degrees plantar flexion stop and full-length foot-plate-conventionally aligned AFO (CAFO); (3) the same AFO realigned with the tibia vertical in the shoe-heel-height compensated AFO (HHCAFO); and (4) the same AFO (tibia vertical) with 3/4 length foot-plate-3/4 AFO. Gait of able-bodied control subjects was measured on a single occasion to provide a normal reference. MAIN OUTCOME MEASURES Sagittal plane ankle and knee kinematics and kinetics. RESULTS In adults with hemiplegia, walking speed was unaffected by the different conditions (P=.095). Compared with the no AFO condition, all AFOs decreased plantar flexion at initial contact and mid-swing (P<.001) and changed the peak knee moment in early stance from flexor to extensor (P<.000). Both AFOs with full-length foot-plates significantly increased the peak stance phase plantar flexor moment compared with no AFO and resulted in a peak knee extensor moment in early stance that was significantly greater than control subjects, whereas the AFO with three-quarter length foot-plate resulted in ankle dorsiflexion during stance and swing that was significantly less than control subjects. CONCLUSIONS These findings suggest that when an articulated AFO is to be used, a full-length foot-plate in conjunction with a plantar flexion stop may be considered to improve early stance knee moments for people with poststroke hemiplegia.

What Determines the Vertical Displacement of the Body During Normal Walking

Conventional wisdom states that the vertical excursion of the body is reduced by several of six “determinants” of gait to minimize the energy expenditure of walking. However, we have shown that pelvic obliquity and stance-phase knee flexion—the second and third determinants of gait—have little or no effect on the magnitude of the body’s vertical excursion during normal walking because the timing of these actions is wrong for reduction of vertical movement to occur. We believe that stance-phase knee flexion and pelvic obliquity provide shock absorption in normal walking during the loading response phase of gait. Our data show that for a given individual the vertical displacement of the body is determined by effective leg length, foot rocker radius, and step length. Using a rocker-based inverted pendulum model of walking, we have derived equations relating walking parameters such as the vertical excursion, step length, cadence, and walking speed. Results from our theoretical analysis compared favorably with actual measurements from able-bodied ambulators walking across a range of speeds from about 0.8 to 2.0 m/sec. We believe that some pathological gaits may be improved through modification of the foot rocker shape and by making adequate provisions for shock absorption.

The influence of stance-phase knee flexion on the vertical displacement of the trunk during normal walking

OBJECTIVE To determine the effect of stance-phase knee flexion on the trunks vertical displacement in normal walking. SUBJECTS Three able-bodied adult male volunteers. DESIGN Kinematic data describing the joint centers and joint angles of the legs and pelvis were collected from the subjects. The subjects walked at four target speeds (range, approximately 1.0 to 2.0 m/sec); a minimum of three trials of data at each walking speed were collected and processed. SETTING Clinical gait analysis laboratory. RESULTS Stance-phase knee flexion was not found to significantly reduce the peak-to-peak amplitude of the trunks vertical displacement in normal walking. The reason for this has to do with the timing (ie, phase) of the stance-phase knee flexion wave with respect to the trunks vertical displacement during the gait cycle. Stance-phase knee flexion in normal walking was found to reduce the mean elevation of the trunk by a few millimeters and to delay the trunks vertical displacement waveform by about 2% to 6% of the gait cycle from where it would have been otherwise. CONCLUSIONS Contrary to conventional wisdom, stance-phase knee flexion does not appreciably reduce the amount of vertical movement of the trunk in normal walking.

The effect of pelvic list on the vertical displacement of the trunk during normal walking

Abstract We measured pelvic list in three normal ambulators, and calculated the vertical displacement of the trunk that is due to pelvic list. Pelvic list was found to be maximum at approximately toe-off and nearly neutral (less than 2°) at midswing for freely-selected gait. The effect of pelvic list on the vertical displacement of the trunk, for normal, freely-selected gait, was mainly to decrease the mean vertical position by 2–4 mm and shift the waveform in phase by about 10–15° lag. The magnitude of the trunks vertical excursion was determined to be virtually unaffected by pelvic list. This finding is in conflict with conventional wisdom that pelvic list reduces the vertical excursion of the body during normal walking.

Gait characteristics of persons with bilateral transtibial amputations

The gait characteristics of persons with unilateral transtibial amputations are fairly well documented in the literature. However, much less is known about the gait of persons with bilateral transtibial amputations. This study used quantitative gait analysis to investigate the gait characteristics of 19 persons with bilateral transtibial amputations. To reduce variability between subjects, we fitted all subjects with Seattle Lightfoot II feet 2 weeks before their gait analyses. The data indicated that subjects walked with symmetrical temporospatial, kinematic, and kinetic parameters. Compared with nondisabled controls, the subjects with amputations walked with slower speeds and lower cadences, had shorter step lengths and wider step widths, and displayed hip hiking during swing phase. Additionally, compared with the nondisabled controls walking at comparable speeds, the subjects with amputations demonstrated reduced ankle dorsiflexion and knee flexion in stance phase, reduced peak ankle plantar flexor moment, reduced positive ankle power (i.e., energy return) in late stance, and increased positive and negative hip power. These results demonstrate the deficiencies in current prosthetic componentry and suggest that further research is needed to enhance prosthesis function and improve gait in persons with amputations.

The effect of a shock-absorbing pylon on the gait of persons with unilateral transtibial amputation

Shock-absorbing pylons (SAPs) are components that increase prosthetic compliance and provide shock absorption during walking, running, and other high-impact activities in persons with leg amputations. This study investigated the effect of SAPs on the gaits of persons who walk with transtibial prostheses. Two gait analyses were performed on 10 subjects walking with and without an Endolite TT (Telescopic-Torsion) Pylon. Comparison of kinematic and kinetic gait parameters indicated that few quantitative changes were found in the way people walked with and without the SAPs. The most consistent change among subjects was a reduction in the magnitude of an isolated-force transient that occurred during the prosthetic loading response phase, an effect that was more evident at higher speeds. Results from a questionnaire that was administered to subjects indicated they generally preferred walking with the SAP for reasons related to comfort. We conclude that SAPs may provide significant benefit for persons with transtibial amputations who are able to routinely walk at speeds above approximately 1.3 m/s.

The effect of trunk-flexed postures on balance and metabolic energy expenditure during standing.

Study Design. This study analyzed force plate, kinematic, and metabolic energy data of 14 able-bodied subjects standing statically with upright and trunk-flexed postures. Objective. To explore the effect of trunk-flexed postures on balance and metabolic energy expenditure during standing. Summary of Background Data. Abnormal trunk posture often occurs in the presence of spinal deformities, such as lumbar flatback. It is unclear whether alterations in trunk posture affect energy expenditure and the location of the body’s center of mass in the transverse plane (BCOMtrans) during standing. Methods. Kinematic, kinetic, and energy expenditure data were collected with upright trunk alignment and with 25° ± 7° and 50° ± 7° of trunk flexion from the vertical. The mean location of the BCOMtrans was estimated from the net center of pressure (COP), which is a weighted average of the COP beneath both feet. Results. The fore-aft position of the net COP under the base of support was not significantly different between postures (P < 0.08). At each posture, the net COP was located 16% of the foot length anterior to the ankle joint centers. However, with increasing trunk flexion, there was a significant increase in oxygen consumption rate (P < 0.001 for all postures). Conclusion. Compensatory actions, such as ankle plantarflexion and hip flexion, allowed the mean position of the net COP to remain within a narrowly defined region irrespective of trunk posture. Changes in muscle activity associated with a trunk-flexed posture and the associated compensations likely contributed to the increased energy expenditure.

A kinematic model to assess spinal motion during walking

Study Design and Objectives. A 3-dimensional multi-segment kinematic spine model was developed for noninvasive analysis of spinal motion during walking. Preliminary data from able-bodied ambulators were collected and analyzed using the model. Summary of Background Data. Neither the spine’s role during walking nor the effect of surgical spinal stabilization on gait is fully understood. Typically, gait analysis models disregard the spine entirely or regard it as a single rigid structure. Data on regional spinal movements, in conjunction with lower limb data, associated with walking are scarce. Methods. KinTrak software (Motion Analysis Corp., Santa Rosa, CA) was used to create a biomechanical model for analysis of 3-dimensional regional spinal movements. Measuring known angles from a mechanical model and comparing them to the calculated angles validated the kinematic model. Spine motion data were collected from 10 able-bodied adults walking at 5 self-selected speeds. These results were compared to data reported in the literature. Results. The uniaxial angles measured on the mechanical model were within 5° of the calculated kinematic model angles, and the coupled angles were within 2°. Regional spine kinematics from able-bodied subjects calculated with this model compared well to data reported by other authors. Conclusions. A multi-segment kinematic spine model has been developed and validated for analysis of spinal motion during walking. By understanding the spine’s role during ambulation and the cause-and-effect relationship between spine motion and lower limb motion, preoperative planning may be augmented to restore normal alignment and balance with minimal negative effects on walking.

The influence of four-bar linkage knees on prosthetic swing-phase floor clearance

ABSTRACT Four-bar linkage knees provide greater toe clearance during the swing phase of walking than do single-axis knees. The authors developed a computer model of a transfemoral prosthesis that allowed the kinematics of commercially available four-bar linkage knees and a single-axis knee to be simulated so legshortening could be characterized. A plot of hip-toe distance versus knee-flexion angle demonstrated fourbar knees are able to shorten the limb with less knee flexion than is needed using a single-axis knee. For a hip-knee angle combination at the time of minimum toe clearance during normal walking, contour plots revealed the four-bar knees have 0.9–3.2 cm greater toe clearance than do single-axis knees.

Biomechanical and energetic effects of a stance-control orthotic knee joint

Users of traditional knee-ankle-foot orthoses (KAFOs) walk with either locked or unlocked knee joints depending on the level of stability required. Some users may benefit from new stance-control KAFOs that prevent stance-phase knee flexion but allow swing-phase flexion. We collected data from nine nondisabled adults who walked with KAFOs that incorporated the Horton Stance-Control Orthotic Knee Joint (SCOKJ) in the locked, unlocked, and auto (which provides knee stability during stance phase and knee flexion during swing phase) modes to investigate the biomechanical and energetic effects of stance-control orthoses. Studying nondisabled subjects allowed us to analyze the effects of stance-control orthoses in a homogenous population. In general, gait kinematics for the auto and unlocked modes were more similar than for the auto and locked modes. Despite the elimination of hip hiking in the auto mode, oxygen cost was not different between the auto and locked modes (p > 0.99). The SCOKJ allowed our nondisabled subjects to walk with a more normal gait pattern; however, future research should explore the effect of stance-control orthoses on persons with gait pathology.