Ava D. Segal

The effect of walking speed on center of mass displacement

The movement of the center of mass (COM) during human walking has been hypothesized to follow a sinusoidal pattern in the vertical and mediolateral directions. The vertical COM displacement has been shown to increase with velocity, but little is known about the mediolateral movement of the COM. In our evaluation of the mediolateral COM displacement at several walking speeds, 10 normal subjects walked at their self-selected speed and then at 0.7, 1.0, 1.2, and 1.6 m/s in random order. We calculated COM location from a 15-segment, full-body kinematic model using segmental analysis. Mediolateral COM displacement was 6.99 +/- 1.34 cm at the slowest walking speed and decreased to 3.85 +/- 1.41 cm at the fastest speed (p < 0.05). Vertical COM excursion increased from 2.74 +/- 0.52 at the slowest speed to 4.83 +/- 0.92 at the fastest speed (p < 0.05). The data suggest that the relationship between the vertical and mediolateral COM excursions changes substantially with walking speed. Clinicians who use observational gait analysis to assess walking problems should be aware that even normal individuals show significant mediolateral COM displacement at slow speeds. Excessive vertical COM displacement that is obvious at moderate walking speeds may be masked at slow walking speeds.

How humans walk: bout duration, steps per bout, and rest duration.

Much is known about human walking, but it is not known how walking is used during typical activities. Since improving walking ability is a key goal in many surgical, pharmacological, and physiotherapeutic interventions, understanding typical community mobility demands regarding the length of walking bouts, the number of sequential steps frequently performed, and the duration of common nonwalking (rest) behavior seems prudent. This study documents the gait of daily living in 10 nondisabled employed adults to define walking bout duration, sequential step counts, and length of rest periods over a 2-week period. Subjects wore a StepWatch Activity Monitor (OrthoCare Innovations; Mountlake Terrace, Washington) that counted steps in each 10-second time window. Custom code summed sequential steps, periods of walking behavior (bouts), and periods without steps (rest). Sixty percent of all walking bouts lasted just 30 seconds or less; a 2-minute walking bout was just 1 percent of total walking bouts. Forty percent of all walking bouts were less than 12 steps in a row, and 75 percent of all walking bouts were less than 40 steps in a row. Rest periods were predominantly very short, with half of all rests periods lasting 20 seconds or less. The community mobility demand for nondisabled employed adults appears to involve frequent short-duration walking behavior with low numbers of sequential steps strung together and many short-duration nonwalking (rest) behaviors.

Gait efficiency using the C-Leg

Microprocessor-controlled prosthetic knees are claimed to improve gait efficiency in transfemoral (TF) amputees. This hypothesis was tested in a prospective randomized crossover trial that compared the Mauch SNS knee and the C-Leg microprocessor-controlled knee in eight TF amputees. The subjects were given a 3-month acclimation period in each knee. Then, their net oxygen cost (mL/kg/m) was measured while they walked overground at four speeds in random order: 0.8 m/s, 1.0 m/s, 1.3 m/s, and self-selected walking speed (SSWS). The C-Leg caused small reductions in net oxygen cost that were not statistically significant compared with the Mauch SNS at any of the walking speeds (p > 0.190). Subjects chose higher SSWSs with the C-Leg compared with the Mauch SNS (mean +/- standard deviation = 1.31 +/- 0.12 m/s vs 1.21 +/- 0.10 m/s, respectively, p = 0.046) but did not incur higher oxygen costs (p = 0.270), which suggests greater efficiency only at their SSWS.

The effect of prosthetic foot push-off on mechanical loading associated with knee osteoarthritis in lower extremity amputees.

Lower extremity amputation not only limits mobility, but also increases the risk of knee osteoarthritis of the intact limb. Dynamic walking models of non-amputees suggest that pushing-off from the trailing limb can reduce collision forces on the leading limb. These collision forces may determine the peak knee external adduction moment (EAM), which has been linked to the development of knee OA in the general population. We therefore hypothesized that greater prosthetic push-off would lead to reduced loading and knee EAM of the intact limb in unilateral transtibial amputees. Seven unilateral transtibial amputees were studied during gait under three prosthetic foot conditions that were intended to vary push-off. Prosthetic foot-ankle push-off work, intact limb knee EAM and ground reaction impulses for both limbs during step-to-step transition were measured. Overall, trailing limb prosthetic push-off work was negatively correlated with leading intact limb 1st peak knee EAM (slope=-.72±.22; p=.011). Prosthetic push-off work and 1st peak intact knee EAM varied significantly with foot type. The prosthetic foot condition with the least push-off demonstrated the largest knee EAM, which was reduced by 26% with the prosthetic foot producing the most push-off. Trailing prosthetic limb push-off impulse was negatively correlated with leading intact limb loading impulse (slope=-.34±.14; p=.001), which may help explain how prosthetic limb push-off can affect intact limb loading. Prosthetic feet that perform more prosthetic push-off appear to be associated with a reduction in 1st peak intact knee EAM, and their use could potentially reduce the risk and burden of knee osteoarthritis in this population.

Regional Foot Pressure During Running, Cutting, Jumping, and Landing

Background Evaluating shoes during sport-related movements may provide a better assessment of plantar loads associated with repetitive injury and provide more specific data for comparing shoe cushioning characteristics. Hypothesis Accelerating, cutting, and jumping pressures will be higher than in straight running, differentiating regional shoe cushioning performance in sport-specific movements. Study Design Controlled laboratory study. Materials and Methods Peak pressures on seven anatomic regions of the foot were assessed in 10 male college athletes during running straight ahead, accelerating, cutting left, cutting right, jump take-off, and jump landing wearing Speed TD and Air Pro Turf Low shoes (Nike, Beaverton, Ore). Pedar insoles (Novel, Munich, Germany) were sampled at 99 Hz during the 6 movements. Results Cutting and jumping movements demonstrated more than double the pressure at the heel compared with running straight, regardless of shoe type. The Air Pro Turf showed overall lower pressure for all movement types (P < .0377). Cutting to the left, the Air Pro Turf shoe had lower heel pressures (36.6 ± 12.5 N/cm2) than the Speed TD (50.3 ± 11.2 N/cm2) (P < .0001), and the Air Pro Turf had lower great toe pressures than the Speed TD (44.8 ± 8.1 N/cm2 vs 54.4 ± 8.4 N/cm2; P = .0002). The Air Pro Turf also had significantly lower pressures than the Speed TD at the central forefoot during acceleration (38.2 ± 8.3 N/cm2 vs 50.8 ± 7.4 N/cm2; P <.0001). Conclusion Sport-related movements load the plantar surface of the foot more than running straight. Shoe cushioning characteristics were more robustly assessed during sport-related movements (4 significant results detected) compared with running straight (1 significant result detected). Clinical Relevance There is an interaction between shoe cushioning characteristics and sport-related movements that may influence plantar pressure and repetitive stress injuries.

Comparative gait analysis of ankle arthrodesis and arthroplasty: initial findings of a prospective study.

Background: Little is known about functional outcomes of ankle arthroplasty compared with arthrodesis. This study compared pre-surgical and post-surgical gait measures in both patient groups. Methods Eighteen patients with end-stage ankle arthritis participated in an ongoing longitudinal study (pre-surgery, 12 months post-surgery) involving gait analysis, assessment of pain and physical function. Outcome measures included temporal-distance, kinematic and kinetic data, the Short Form 36 (SF-36) body pain score, and average daily step count. A mixed effects linear model was used to detect effects of surgical group (arthrodesis and arthroplasty, n = 9 each) with walking speed as a covariate (α = 0.05). Results Both groups were similar in demographics and anthropometrics. Followup time was the same for each group. There were no complications in either group. Pain decreased (p < 0.001) and gait function improved (gait velocity, p = 0.02; stride length, p = 0.035) in both groups. Neither group increased average daily step count. Joint range of motion (ROM) differences were observed between groups after surgery (increased hip ROM in arthrodesis, p = 0.001; increased ankle ROM in arthroplasty, p = 0.036). Peak plantar flexor moment increased in arthrodesis patients and decreased in arthroplasty patients (p = 0.042). Conclusion Initial findings of this ongoing clinical study indicate pain reduction and improved gait function 12 months after surgery for both treatments. Arthroplasty appears to regain more natural ankle joint function, with increased ROM. Long-term follow up should may reveal more clinically meaningful differences. Level of Evidence: II, Prospective Observational Study

Systematic Variation of Prosthetic Foot Spring Affects Center-of-Mass Mechanics and Metabolic Cost During Walking

Lower-limb amputees expend more energy to walk than non-amputees and have an elevated risk of secondary disabilities. Insufficient push-off by the prosthetic foot may be a contributing factor. We aimed to systematically study the effect of prosthetic foot mechanics on gait, to gain insight into fundamental prosthetic design principles. We varied a single parameter in isolation, the energy-storing spring in a prototype prosthetic foot, the controlled energy storage and return (CESR) foot, and observed the effect on gait. Subjects walked on the CESR foot with three different springs. We performed parallel studies on amputees and on non-amputees wearing prosthetic simulators. In both groups, spring characteristics similarly affected ankle and body center-of-mass (COM) mechanics and metabolic cost. Softer springs led to greater energy storage, energy return, and prosthetic limb COM push-off work. But metabolic energy expenditure was lowest with a spring of intermediate stiffness, suggesting biomechanical disadvantages to the softest spring despite its greater push-off. Disadvantages of the softest spring may include excessive heel displacements and COM collision losses. We also observed some differences in joint kinetics between amputees and non-amputees walking on the prototype foot. During prosthetic push-off, amputees exhibited reduced energy transfer from the prosthesis to the COM along with increased hip work, perhaps due to greater energy dissipation at the knee. Nevertheless, the results indicate that spring compliance can contribute to push-off, but with biomechanical trade-offs that limit the degree to which greater push-off might improve walking economy.

The effects of a controlled energy storage and return prototype prosthetic foot on transtibial amputee ambulation

The lack of functional ankle musculature in lower limb amputees contributes to the reduced prosthetic ankle push-off, compensations at other joints and more energetically costly gait commonly observed in comparison to non-amputees. A variety of energy storing and return prosthetic feet have been developed to address these issues but have not been shown to sufficiently improve amputee biomechanics and energetic cost, perhaps because the timing and magnitude of energy return is not controlled. The goal of this study was to examine how a prototype microprocessor-controlled prosthetic foot designed to store some of the energy during loading and return it during push-off affects amputee gait. Unilateral transtibial amputees wore the Controlled Energy Storage and Return prosthetic foot (CESR), a conventional foot (CONV), and their previously prescribed foot (PRES) in random order. Three-dimensional gait analysis and net oxygen consumption were collected as participants walked at constant speed. The CESR foot demonstrated increased energy storage during early stance, increased prosthetic foot peak push-off power and work, increased prosthetic limb center of mass (COM) push-off work and decreased intact limb COM collision work compared to CONV and PRES. The biological contribution of the positive COM work for CESR was reduced compared to CONV and PRES. However, the net metabolic cost for CESR did not change compared to CONV and increased compared to PRES, which may partially reflect the greater weight, lack of individualized size and stiffness and relatively less familiarity for CESR and CONV. Controlled energy storage and return enhanced prosthetic push-off, but requires further design modifications to improve amputee walking economy.

The relationship between lumbar spine kinematics during gait and low-back pain in transfemoral amputees.

Morgenroth DC, Orendurff MS, Shakir A, Segal A, Shofer J, Czerniecki JM: The relationship between lumbar spine kinematics during gait and low-back pain in transfemoral amputees. Objective:Low-back pain is an important cause of secondary disability in transfemoral amputees. The primary aim of our study is to assess the differences in lumbar spine kinematics during gait between transfemoral amputees with and without low-back pain. Design:Lumbar spine kinematics in three planes were measured when the subjects walked in a motion analysis laboratory. Nine transfemoral amputees with low-back pain, eight transfemoral amputees without low-back pain, and six healthy, nonamputee subjects participated. Results:The Amputee Pain and Amputee No Pain groups were essentially the same in terms of all demographic and potentially confounding variable measures. Transfemoral amputees with low-back pain showed greater transverse plane rotational excursion in their lumbar spine during walking when compared with transfemoral amputees without low-back pain (P = 0.029; effect size = 1.03). There were no significant differences in sagittal or coronal plane lumbar spine excursions during walking between these two groups. Conclusions:Although our study design does not allow for proving causation, increased transverse plane rotation has been associated with intervertebral disc degeneration, suggesting that increased transverse plane rotation secondary to walking with a prosthetic limb may be a causative factor in the etiology of low-back pain in transfemoral amputees. Identifying differences in lumbar motion can lead to potential preventative and therapeutic intervention strategies.

Comparison of transtibial amputee and non-amputee biomechanics during a common turning task

The biomechanics of amputee turning gait has been minimally studied, in spite of its integral relationship with the more complex gait required for household or community ambulation. This study compares the biomechanics of unilateral transtibial amputees and non-amputees completing a common turning task. Full body gait analysis was completed for subjects walking at comparable self-selected speeds around a 1m radius circular path. Peak internal and external rotation moments of the hip, knee and ankle, mediolateral ground reaction impulse (ML GRI), peak effective limb length, and stride length were compared across conditions (non-amputee, amputee prosthetic limb, amputee sound limb). Amputees showed decreased internal rotation moments at the prosthetic limb hip and knee compared to non-amputees, perhaps as a protective mechanism to minimize stress on the residual limb. There was also an increase in amputee sound limb hip external rotation moment in early stance compared to non-amputees, which may be a compensation for the decrease in prosthetic limb internal rotation moment during late stance of the prior step. ML GRI was decreased for the amputee inside limb compared to non-amputee, possibly to minimize the bodys acceleration in the direction of the turn. Amputees also exhibited a shorter inside limb stride length compared to non-amputees. Both decreased ML GRI and stride length indicate a COM that is more centered over the base of support, which may minimize the risk of falling. Finally, a longer effective limb length was found for the amputee inside limb turning, possibly due to excessive trunk shift.