Posterior single-stepping thresholds are prospectively related to falls in older women

BACKGROUND

Falls are a leading cause of injury in older women. Stepping thresholds quantify balance-reaction capabilities. It is unclear how such evaluations predict falls in comparison to, or as a complement to, other objective measures of gait, standing postural control, strength, and balance confidence.

AIMS

The objective of this study was to determine if stepping thresholds are prospectively related to falls in older women.

METHODS

For this prospective cohort study, 125 ambulatory, community-dwelling women, age ≥ 65 years were recruited. Using a treadmill to deliver perturbations to standing participants, we determined anteroposterior single- and multiple-stepping thresholds. Here, thresholds represent the minimum perturbation magnitudes that consistently evoke one step or multiple steps. In addition, gait kinematics, obstacle-crossing kinematics, standing sway measures, unipedal stance time, the functional reach, lower extremity isometric strength, grip strength, balance confidence, and fall history were evaluated. Falls were prospectively recorded for one year.

RESULTS

Seventy-four participants (59%) fell at least once. Posterior single-stepping thresholds were the only outcome that predicted future fall status (OR = 1.50, 95% CI 1.01-2.28; AUC = .62). A multivariate approach added postural sway with eyes closed as a second predictive variable, although predictive abilities were not meaningfully improved.

DISCUSSION

These results align with the previous evidence that reactive balance is a prospective indicator of fall risk. Unlike previous studies, strength scaled to body size did not contribute to fall prediction.

CONCLUSION

Posterior single-stepping thresholds held a significant relationship with future fall status. This relationship was independent of, and superior to that of, other measures of standing balance, gait, strength, and balance confidence.

The accuracy of rapid treadmill-belt movements as a means to deliver standing postural perturbations

Treadmill-induced postural perturbations are a promising tool in assessing and reducing the risk of falls. We evaluated the accuracy with which two treadmills (Simbex ActiveStep^® and an AMTI instrumented treadmill) achieved commanded displacements, peak velocities, and average initial accelerations. To do so, we included a range of perturbation magnitudes (20, 30, and 40 cm displacements) applied in unweighted and weighted (body mass = 46-84 kg) conditions. Across treadmills and perturbation magnitudes, absolute errors in displacement (< 0.5 cm) and peak velocity (< 4 cm/s) were small (relative error < 5%). Between-treadmill differences in displacement and peak velocity were marginal (< 3%), regardless of the perturbation magnitude and participant body mass. Observed accelerations were more than 5% smaller than commanded values. The front, but not back, AMTI belt demonstrated less acceleration accuracy than the ActiveStep^® (≈ 5% difference). In summary, both treadmills demonstrated a reasonable, consistent level of accuracy in delivering postural perturbations.

The relationships between compensatory stepping thresholds and measures of gait, standing postural control, strength, and balance confidence in older women

BACKGROUND

Compensatory stepping thresholds evaluate the response to postural disturbances. Although such fall-recovery measures are a promising indicator of fall risk, the relationships between stepping thresholds and other measures used to predict falls are not well established.

RESEARCH QUESTION

We sought to quantify the relationships between stepping thresholds and other measurements used to assess fall risk in older women, a population at high risk for falls and related injuries, including fractures.

METHODS

We studied 112 ambulatory, community-dwelling women, age 65 years or older. Using a treadmill to deliver standing postural disturbances, we determined anterior and posterior single-stepping and multiple-stepping thresholds. These thresholds represented the magnitude of the disturbance that elicited one step or more than one step, respectively. We also assessed balance confidence, functional reach, unipedal stance time, isometric strength, obstacle crossing, postural sway, and gait kinematics. Outcomes were normalized to body size.

RESULTS

After accounting for age, stepping thresholds were, at most, moderately correlated (Pearson partial correlation coefficients r = 0.20 to 0.40 and r = -0.21 to -0.31) to several assessments of gait, postural control, and strength. Approximately 24-52% of the variance in stepping thresholds was explained by a combination of age and other fall risk assessments, which frequently consisted of balance confidence, unipedal stance time, obstacle crossing, the Romberg ratio of postural sway, and/or strength.

SIGNIFICANCE

Our results suggest that anteroposterior fall-recovery ability, as assessed by stepping thresholds, can only be partially inferred from age and a combination of assessments of sway, strength, unipedal tasks, and balance confidence. Compensatory stepping thresholds may provide information on stability maintenance unique from other assessments of fall risk. Further investigation would be necessary to determine whether stepping thresholds are better predictors of falls in older women.

Net ankle quasi-stiffness is influenced by walking speed but not age for older adult women

BACKGROUND

Insufficient plantar flexor resistance due to plantar flexor weakness, an impairment common in patient populations, causes substantial gait deficits. The bending stiffness of passive-dynamic ankle-foot orthoses (PD-AFOs) has the capacity to replace lost plantar flexor resistance. Many patients who are prescribed PD-AFOs are older adults. While PD-AFO bending stiffness should be customized for patients, a method to objectively prescribe this stiffness does not exist. Quantifying natural plantar flexor resistance during non-pathological gait could provide a reference value for objectively prescribing PD-AFO bending stiffness.

RESEARCH QUESTION

This study investigated the effect of age on plantar flexor resistance in 113 participants above the age of 65 years. We did so while also considering the confounding influence of gait speed, an aspect known to be reduced with old age.

METHODS

Ambulatory, community-dwelling older adult women (ages 65-91 years) with no current or recent lower-extremity injuries or surgeries underwent an instrumented gait analysis at a self-selected speed. Plantar flexor resistance was quantified via net ankle quasi-stiffness (NAS) defined as the slope of ankle joint moment-angle curve during late stance.

RESULTS

showed that NAS was not significantly influenced by age (r = -0.11, p = 0.12), and that the confounding factor of walking speed had a significant, positive relationship with NAS (r = 0.59, p < 0.001).

SIGNIFICANCE

By determining that gait speed, not age, is related to NAS in older adults, this study represents the initial step towards objectively prescribing PD-AFO bending stiffness to achieve a targeted gait speed for older adults with plantar flexor weakness.

The circumstances, orientations, and impact locations of falls in community-dwelling older women

OBJECTIVE

We sought to characterize the circumstances, orientations, and impact locations of falls in community-dwelling, ambulatory, older women.

METHODS

For this longitudinal, observational study, 125 community-dwelling women age≥65years were recruited. Over 12-months of follow-up, fall details were recorded using twice-monthly questionnaires.

RESULTS

More than half (59%) of participants fell, with 30% of participants falling more than once (fall rate=1.3 falls per person-year). Slips (22%) and trips (33%) accounted for the majority of falls. Approximately 44% of falls were forward in direction, while backward falls accounted for 41% of falls. About a third of all falls were reported to have lateral (sideways) motion. Subjects reported taking a protective step in response to 82% of forward falls and 37% of backward falls. Of falls reporting lateral motion, a protective step was attempted in 70% of accounts. Common impact locations included the hip/pelvis (47% of falls) and the hand/wrist (27%). Backwards falls were most commonly reported with slips and when changing direction, and increased the risk of hip/pelvis impact (OR=12.6; 95% CI: 4.7-33.8). Forward falls were most commonly reported with trips and while hurrying, and increased the risk of impact to the hand/wrist (OR=2.6; 95% CI: 1.2-5.9).

CONCLUSION

Falls in older ambulatory women occur more frequently than previously reported, with the fall circumstance and direction dictating impact to common fracture locations. Stepping was a common protective recovery strategy and that may serve as an appropriate focus of interventions to reduce falls in this high risk population.

Gait patterns of patients with inclusion body myositis

Inclusion body myositis (IBM) is a progressive, inflammatory muscle disease that is known to cause quadriceps weakness and knee buckling during gait. This is the first known report of gait characteristics in patients with IBM. Nine subjects with IBM and quadriceps weakness underwent gait analysis and quantitative strength testing. A wide range of strength and gait abilities were present in the subject group. Subjects with stronger knee extensors exhibited nearly normal sagittal knee kinematics and kinetics. As quadriceps strength decreased, kinematic and kinetic patterns were increasingly abnormal. Exceptions to this pattern could be explained by examining strength at adjacent joints. Gait analysis and strength testing is a helpful tool in evaluating the functional status of this population and aiding in determination of the needs for interventions such as assistive devices.

Loads on the uprights of a knee-ankle-foot orthosis

BACKGROUND

Objective design criteria for orthotic components is lacking. This paucity of data results in prescription guidelines based on assumptions or practitioners' past experience, and the potential for incorrectly designed components. The purpose of this study was to directly measure loads on the knee joint of a knee-ankle-foot orthosis.

STUDY DESIGN

Case series.

CASE DESCRIPTION AND METHODS

Three subjects who had been prescribed a knee-ankle-foot orthosis for quadriceps weakness underwent gait analysis and orthotic upright load data collection. A load sensor to measure the three force and three moment components was used in place of the lateral knee joint while the subjects walked in three knee flexion positions.

FINDINGS AND OUTCOMES

Forces were highest in compression and moments were greatest in the sagittal plane. The kinetics did not increase solely with patient weight. There was substantial variability between subjects.

CONCLUSIONS

This data will help guide orthotic component design and prescription guidelines. Knowledge of loading conditions will lead to more optimal orthotic intervention for patients and increased patient satisfaction.

CLINICAL RELEVANCE

This study is one of the first to directly measure loads on the upright of a KAFO. These data provide objective targets for engineering design. The data from this small case series can also be used to establish guidelines for patient device selection.

Effect of local alignment on compartmental patterns of knee osteoarthritis

BACKGROUND

Previous studies have shown that lower-extremity malalignment increases the risk and rate of progression of knee osteoarthritis. The authors of such studies have used full-length lower-extremity radiographs to quantify alignment. However, a radiograph that includes only the knee is commonly ordered for a patient with early symptoms of knee osteoarthritis. The purpose of this study was to investigate whether local malalignment, as determined with use of a standing short knee radiograph, is associated with an increased risk of having osteoarthritis and having more severe compartmental disease.

METHODS

Short fluoroscopically guided standing anteroposterior knee radiographs of 306 patients (608 knees) with radiographic evidence of knee osteoarthritis were used to determine the compartment-specific Kellgren-Lawrence grade of osteoarthritis and the local (distal femoral to proximal tibial) knee alignment. The relationship between local alignment and compartmental patterns of osteoarthritis was assessed.

RESULTS

Each degree of increase in the local varus angle was associated with a significantly increased risk of having predominantly medial compartment osteoarthritis, even when we adjusted for age, sex, and body mass index (odds ratio, 1.39; 95% confidence interval, 1.29 to 1.49; p < 0.001). A similar association was found between valgus angulation and lateral compartment osteoarthritis (odds ratio, 1.55; 95% confidence interval, 1.36 to 1.75; p < 0.001). Analysis of the 362 knees with predominantly medial compartment osteoarthritis showed that each degree of increase in the varus angle was associated with a significantly increased adjusted risk of having severe medial disease (odds ratio, 1.52, p < 0.001). In the forty-seven knees with predominantly lateral compartment osteoarthritis, a similar trend was found between an increase in the valgus angle and the severity of the lateral disease, with the results approaching but not reaching significance.

CONCLUSIONS

In patients with early symptomatic knee osteoarthritis, there is a clear relationship between local knee alignment, as determined from short standing knee radiographs, and the compartmental pattern and severity of the knee osteoarthritis. This study provides data with which physicians can assess how knee alignment contributes to the observed patterns and severity of osteoarthritis in an individual patient.

Gait changes over time in stance control orthosis users

This report presents objective motion analysis measurements of 14 stance control orthoses (SCO) users during a prospective open-enrollment 6-month clinical field trial. Participants were fitted with a Dynamic Knee Brace System (DKBS) which is a novel electromechanical SCO developed by the authors. Seven of the 14 subjects that had been prescribed but did not use a KAFO at the time of enrollment were defined as novice users. Those subjects who at the time of enrollment were using a locked KAFO for ambulation were defined as experienced users. Results showed that all subjects significantly increased peak knee flexion from 49.0 +/- 15.5 degrees to 55.9 +/- 11.4 degrees between the initial and six month tests (p = 0.02). They also tended to increase peak hip flexion from 39.6 +/- 13.4 degrees to 46.0 +/- 14.5 degrees between the 3 month and 6 month tests (p = 0.09). Novice users significantly increased velocity from 74.7 +/- 19.4 cm/s to 81.2 +/- 19.0 cm/sec between the initial and 3-month tests (p = 0.005). These same users increased stride length from 109 +/- 15.3 cm to 112 +/- 16.6 cm over the same time period (p = 0.008). Experienced KAFO users, however, tended to increase velocity from 68.8 +/- 20.5 cm/s to 83.2 +/- 16.8 cm/s at 3 months (p = 0.06). This was combined with a significant increase in cadence from 76.2 +/- 14.1 steps/min to 83.9 +/- 8.3 steps/min between the initial and 3 month tests (p = 0.05). Joint kinetics showed no changes for users over the duration of the testing period. These results indicate that KAFO users make significant gains in temporodistance measures, while changes in joint kinematics take longer to develop.

Muscle activation patterns in snapping triceps syndrome

OBJECTIVE

To compare the muscle activation pattern in subjects with and without "snapping triceps syndrome" (dislocation of the medial head of the triceps and ulnar nerve over the medial epicondyle).

DESIGN

Controlled study.

SETTING

Biomechanics laboratory.

PARTICIPANTS

Eight male subjects (9 elbows), with symptomatic snapping triceps and 9 male controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Activation pattern of the 3 triceps heads during active elbow extension at 0 degrees , 45 degrees , 70 degrees , 90 degrees , and 115 degrees of flexion, recorded by fine-wire electromyography.

RESULTS

There were no significant differences between subjects and controls in the firing pattern of the triceps heads. The medial head fired first in 6 of 9 symptomatic elbows and in 7 of 9 controls at 90 degrees of flexion, and in 6 of 9 elbows of both subjects and controls at 115 degrees of flexion, positions where snapping typically occurs. There was no significant difference between the groups as to how often the medial head fired maximally.

CONCLUSIONS

This study suggests the firing pattern of the triceps heads may not contribute to the pathogenesis of this syndrome. Rather, the authors believe the anatomic position of the medial head causes it to dislocate over the medial epicondyle, often resulting in ulnar neuritis.

Consumer opinions of a stance control knee orthosis

Stance control knee orthoses (SCOs) have become very popular recently. However, there is little information regarding opinions of actual orthosis users. The purpose of this study was to quantify the users' opinions of a SCO, and see whether factors found important for knee orthoses in past studies hold true for a stance control orthosis as well. A standardized survey was employed as part of a larger field trial study of the Dynamic Knee Brace System, a SCO developed by the authors. The Dynamic Knee Brace System scored well in areas of effectiveness, operability, and dependability, but areas in need of improvement included weight, cosmesis, and donning and doffing. These findings match well with previous knee orthosis studies. This study shows that wearing a stance control knee orthosis can be a positive experience for an orthosis user.

Gait of stance control orthosis users: the dynamic knee brace system

Individuals with weak or absent quadriceps who wish to walk independently are prescribed knee-ankle-foot orthoses (KAFOs). New stance control orthosis (SCO) designs automatically release the knee to allow swing phase flexion and extension while still locking the joint during stance. Twenty-one participants were fitted unilaterally with the Dynamic Knee Brace System (DKBS), a non-commercial SCO. Thirteen subjects were experienced KAFO users (average 28 +/- 18 years of experience) while eight were novice users. Novice users demonstrated increased velocity (55 vs. 71 cm/sec, p = 0.048) and cadence (77 vs. 85 steps/min, p < 0.05) when using the DKBS over the traditional locked KAFO. Experienced KAFO users tended to have reduced velocity and cadence measures when using the SCO (p < 0.10). Knee range of motion was significantly greater for the novice group than for the experienced group (55.2 +/- 4.8 vs. 42.6 +/- 3.8 degrees, p = 0.05). Peak knee extension moments tended to be greater for the experienced group (0.29 +/- 0.21 vs. 0.087 +/- 0.047 Nm/kg, p = 0.09). This report describes gait changes during the introductory phase of DKBS adoption. Experienced KAFO users undoubtedly had ingrained gait patterns designed to compensate for walking with a standard locked KAFO. These patterns may have limited the ability of those users from taking full and immediate advantage of the SCO capabilities. Also, alternate SCO systems may engender different results. Comparison studies and longer term field studies are needed to clarify benefits of the various bracing options.

Effect of environmental temperature on shock absorption properties of running shoes

OBJECTIVE

To determine the effect of temperature changes on the shock attenuation of 4 running shoe shock absorption systems.

DESIGN

Prospective.

SETTING

Motion analysis laboratory.

INTERVENTIONS

The shock attenuation of 4 different running shoes representing common shock absorption systems (Nike Air Triax, Asics Gel Nimbus IV, Adidas a3 cushioning, Adidas Supernova cushion) was measured at ambient temperatures of -20 degrees C, -10 degrees C, 0 degrees C, +10 degrees C, +20 degrees C, +30 degrees C, +40 degrees C, and +50 degrees C. Repeated-measures analysis of variance was used to determine differences between shoes.

OUTCOME MEASURES

Shock attenuation as indicated by peak deceleration (g) measured by a mechanical impactor following ASTM Standard F1614-99.

RESULTS

Shock attenuation decreased significantly with reduced temperature for each shoe tested. The Adidas a3 shoe exhibited significantly higher peak decelerations (lower shock attenuation) at cold temperatures compared with the other shoes.

CONCLUSIONS

Cold ambient temperatures significantly reduce the shock attenuation of commonly used running shoes. These findings have important clinical implications for individuals training in extreme weather environments, particularly those with a history of lower limb overuse injuries.