Biomedical subjects

Steven J Stanhope

Publications and source records attributed to Steven J Stanhope.

11 recordsLinked to original sources

PubMed2006

Biomechanic modeling of sit-to-stand to upright posture for mobility assessment of persons with chronic stroke.

OBJECTIVE: To test the suitability of using biomechanic measures associated with a minimum measured input model (MMIM) approach to assess mobility of people with chronic stroke during the execution of a sit-to-stand (STS) to upright posture motor task. DESIGN: Single group, observational. SETTING: Institutional settings in the United States and Italy. PARTICIPANTS: Twenty-nine subjects with chronic unilateral lower-limb impairments and resultant mobility limitations secondary to stroke. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Manual measurement of lower-limb strength; performance-based tests including repeated chair standing, walking speed, and standing balance; and ground reactions measured with a force platform during STS and upright posture. The ground reactions were fed to a telescopic inverted pendulum model of the musculoskeletal system. Parameters representing the model outputs were compared with performance-based and strength measures to assess, respectively, motor ability and impairment-related changes in subjects' motor strategies. RESULTS: The parameters derived from the model effectively differentiated between motor strategies associated with different performance-based scores, and allowed the identification of relevant difficulties encountered in STS execution. These difficulties could be associated with different strength scores. This was also true for subjects scoring the maximum in both performance-based and strength tests. CONCLUSIONS: The MMIM is a relatively inexpensive and noninvasive approach that enhances mobility assessment of hemiparetic subjects with different motor ability levels. It provides information that correlates well with performance-based and strength scores and, in addition, it allows for subject-specific motor strategy identification.

Aged↗

PubMed2005

Using induced accelerations to understand knee stability during gait of individuals with muscle weakness.

The purpose of this case series was to quantify the effectiveness of different compensatory strategies used by individuals with muscle weakness to produce knee extension during the stance phase gait. Subjects were three males with less than anti-gravity strength in the quadriceps femoris and a variable pattern of weakness elsewhere in the lower extremity. They walked independently at a self-selected speed without assistive devices. Gait analysis of the pelvis and bilateral lower extremity segments was performed with a six-camera, two force platform motion capture system. Joint angles and net internal moments were computed from the motion data. Induced acceleration analysis was performed to quantify the relative ability of each lower extremity joint moment and gravity to produce knee angular acceleration. Results showed that a variety of adaptive strategies both within and across limbs can control knee position during gait. One subject generated knee extension almost exclusively via the hip extensor moment. Another relied less on the hip extensor moment (39%) and more on the ankle plantar flexor moment (61%) to create knee extension. The third subject used the ipsilateral hip extensor moment (24%) and the contralateral ankle plantar flexor moment (67%) to assist knee extension. The strategy selected by each subject likely was influenced by both their total pattern of impairments and the effectiveness of the available compensations. This case series demonstrates how an induced acceleration analysis can augment a traditional gait analysis to expand and enhance our understanding of compensatory movement control strategies.

Acceleration↗

PubMed2005

Limb positioning is critical for defining patellofemoral alignment and femoral shape.

The source of patellofemoral pain is a common orthopaedic complaint that often is difficult to determine because of the lack of correlation between symptoms and specific clinical measurements. Excessive joint contact stresses resulting from patellofemoral malalignment and pathologic femoral shape often are associated with this pain. These measures are likely sensitive to the limb position (orientation and position relative to the imaging system with which they are quantified). Because of this sensitivity, the measures have large variations and do not show correlations with subjective symptoms. The purpose of this study was to determine if varying limb position resulted in significant changes in standard clinical measures of patellofemoral alignment and femoral shape. This dependence was investigated by simulating alterations in limb position through resectioning of three-dimensional magnetic resonance image sets (20 healthy knees) to create axial images with altered orientation (eight images) or location (four images) relative to a fixed reference. By quantifying the variability of the clinical measures across all images, it was determined that simulated alterations in limb position produced greater variability in femoral shape and patellofemoral alignment measures than the variability seen across control subjects. This indicated that a standardized method for establishing limb position relative to the imager is warranted.

Adult↗

PubMed2004

A three-dimensional data visualization technique for reporting movement pattern deviations.

Relative motion plots are the most prevalent method for displaying interjoint coupling. The method, however, is limited when amplitude and timing comparisons of like data are of interest. Another limitation of relative motion plots is that the second parameter (e.g., angle) is included at the expense of a continuous time reference. In this paper, we present a novel method for displaying three-dimensional movement pattern deviations. Parameter-parameter-time data (e.g., knee and hip angle as a function of time) are color-coded based on the magnitude and direction of the deviation. The color-coded deviations are mapped to an individual's three-dimensional parameter-parameter-time trajectory, resulting in a multi-color, three-dimensional curve depicting how an individual's parameter-parameter-time pattern differs relative to a reference pattern. The algorithmic development of the color-coded parameter-parameter-time display is presented and comparative patient and normative data are reported.

Algorithms↗

PubMed2004

Sensitivity of femoral orientation estimates to condylar surface and MR image plane location.

PURPOSE: To define the femoral anatomic region that provides the most reliable reference for measuring femoral orientation, from which patellofemoral and tibiofemoral orientation can be measured. MATERIALS AND METHODS: After a three-dimensional image-based osteo-alignment procedure, two independent estimates of distal femoral orientation, the anterior (AFA) and posterior femoral angles (PFA), were acquired. These sets were comprised of 31 axial femoral orientation estimates each (obtained across a region 10 mm above to 20 mm below the patellar center) from 42 normal axial magnetic resonance (MR) image sets. An analysis of variance was conducted to determine the influence of image plane location, sex, and side on femoral orientation measures. RESULTS: The AFA presented greater variability across subjects (average SD = 3.13 degrees) as compared to the PFA (average SD = 1.78 degrees ). There were significant differences in the AFA based on image plane location and sex. In contrast, no differences were found between sides, sexes, or image plane locations for the PFA. CONCLUSION: In total, the posterior femoral condylar surface is more reliable than the anterior condylar surface for measuring femoral orientation and is best measured at least 8 mm below the patellar center.

Adult↗

PubMed2004

A novel method for displaying gait and clinical movement analysis data.

Plotting kinematic and kinetic data of a patient's movement patterns relative to normative values (i.e., mean and +/-1 S.D.) is a common method used by clinicians to visually assess deviations and interpret the patient's gait analysis data. This method of data interpretation is often time consuming and complex, especially when the process requires the inspection of a plethora of line graphs for numerous variables that are displayed across several report pages. In this paper we propose an alternate method for displaying movement pattern deviations relative to normative data by color-coding the magnitude and the direction of the deviation. An advantage of this approach is that a single page summary of all the deviation magnitudes can be displayed simultaneously, in a manner that is concise, visually effective and reduces complexity. The purpose of this paper is to describe the algorithmic development of the color-coding method.

Algorithms↗

PubMed2004

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.

Adult↗

PubMed2004

Association between subject functional status, seat height, and movement strategy in sit-to-stand performance.

OBJECTIVES: To explore the association between an individual's functional status, movement task difficulty, and effectiveness of compensatory movement strategies within a sit-to-stand (STS) paradigm. DESIGN: Cross-sectional study. SETTINGS: Rehabilitation unit of the Istituto Nazionale Riposo e Cura Anziani Geriatric Hospital of Florence, Italy. PARTICIPANTS: A convenience sample (131 subjects) of the outpatient clinic and day-hospital population. MEASUREMENTS: A performance-based test (repeated chair standing) was used to divide the subjects into five functional groups. Subjects performed a series of single STS tasks across a range of five descending seat heights. They were instructed to stand without using arms or compensatory strategies. If unable, swinging the arms was allowed, and if the inability persisted, subjects could push with their arms during subsequent attempts. The strategy or inability to stand formed the dependent measures. RESULTS: Subjects within the two highest functional groups could complete the single STS task at all seat heights, with a slight increased use of compensatory strategies at the lowest seat height. The effectiveness of the compensatory strategies decreased rapidly as a function of seat height and functional status. One-third (35.5%) of the subjects in the middle functional group swung their arms at the lower seat heights. Across the three least functional groups, 11.8%, 30.6%, and 83.3% of the subjects, respectively, were unable to stand at the lowest seat height. CONCLUSION: The individual's functional status and difficulty of the task influenced the effectiveness of a compensatory strategy to maintain the ability to stand, supporting the idea that disability depends on the interplay between environmental demands and physical ability.

Aged↗

PubMed2003

A proposed test to support the clinical movement analysis laboratory accreditation process.

This paper describes a testing methodology and resultant set of four variables that can be used to quickly and easily document the correct installation, configuration, and combined working status of force platform (FP) and three-dimensional (3D) motion capture components of a clinical movement analysis (CMA) laboratory. Using a rigid, rod-shaped testing device, CMA laboratory data are collected simultaneously from the FP and motion capture components (typically, video-based kinematic measurements) as the device is manually loaded while being pivoted broadly about a point on the FP. Using a computational method based on static equilibrium, it is possible to independently measure the rod's orientation and tip position during the moving trial, using FP derived data exclusively, and to compare these estimates to rod orientation and tip position estimates derived exclusively from the motion capture component. The motion laboratory accreditation test (MLAT) variables include: the difference (angle) between the orientation of the long axis of the testing device as independently determined from kinematic measures (motion capture component) and the FP derived data; and the difference (x, y, z) between the center of pressure position (FP derived) and the position of the testing device tip (motion capture derived) that loads the FP. A numerical dynamics model was explored to evaluate the appropriateness of the static equilibrium-based FP data model and to determine guidelines for testing device movement frequency and FP loading. The MLAT technique provides a simple means of detecting the combined presence of errors from many sources, several of which are explored in this paper. The MLAT has been developed to help meet one criteria of the CMA laboratory accreditation process, and to serve as a routine quality assessment tool.

Accreditation↗

PubMed2003

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. DESIGN: Cross-sectional study. SETTING: Geriatric rehabilitation research hospital. PARTICIPANTS: Sixty elderly women (aged 70-93) with FP referred to a geriatric rehabilitation department for chronic back pain without apparent comorbid conditions. MEASUREMENTS: Multidimensional clinical assessment included the severity of FP (standing occiput-to-wall distance) demographic (age) and anthropometric (height, weight) data, clinical profile (number of falls, pain assessment, Mini-Mental State Examination, Comorbidity Severity Index, Geriatric Depression Scale, Multidimensional Fatigue Inventory), measures of skeletal fragility (number of vertebral fractures by spine radiograph, bone mineral density (BMD), and T-score of lumbar spine and proximal femur), muscular impairment assessment (muscle strength and length), motor performance (Short Physical Performance Battery, Performance Oriented Mobility Assessment, instrumented gait analysis), and evaluation of disability (Barthel Index, Nottingham Extended Activities of Daily Living Index). RESULTS: The severity of FP was classified as mild in 11, moderate in 28, and severe in 21 patients. Although there were no differences between FP groups on the skeletal fragility measurements, the moderate and severe FP groups were significantly different from the mild FP group for greater pain at the level of the cervical and lumbar spine. The severe FP group was also significantly different from the mild but not the moderate FP group in the following categories: clinical profile (greater depression, reduced motivation), muscle impairment (weaker spine extensor, ankle plantarflexor, and dorsiflexor muscles; shorter pectoralis and hip flexor muscles), the motor function performance-based tests (lower scores in the balance and gait subsets of the Performance Oriented Mobility Assessment), the instrumented gait analysis (slower and wider base of support), and disability (lower score on the Nottingham Extended Activities of Daily Living Index). The total number of vertebral fractures was not associated with differences in severity of FP, demographic and anthropometric characteristics, clinical profile, muscular function, performance-based and instrumental measures of motor function, and disability, but it was associated with reduced proximal femur and lumbar spine BMD. CONCLUSION: The severity of FP in elderly female patients (without apparent comorbid conditions) is related to the severity of vertebral pain, emotional status, muscular impairments, and motor function but not to osteoporosis, and FP has a measurable effect on disability. In contrast, the presence of vertebral fractures in patients with FP is associated with lower BMD but not patients' clinical and functional status. Therefore, FP, back pain, and mobility problems can occur without osteoporosis. Older women with FP and vertebral pain may be candidates for rehabilitation interventions that address muscular impairments, posture, and behavior modification. Randomized controlled trials are needed to support these conclusions.

Aged↗

PubMed1997

Changes in knee joint function over a wide range of walking speeds.

OBJECTIVE: Changes in patterns of knee joint flexion-extension rotations, moments and powers were investigated during the stance phase across a wide range of walking speeds that includes the very slow speeds used by many patients referred for gait analysis. DESIGN: Each subject walked at 25, 50, 75, 100, and 125% of a scaled natural speed of 0.785 statures.s(-1). BACKGROUND: The results of earlier studies suggest that control subjects, as they walk at progressively slower speeds, increasingly use a large internal knee flexor moment in the early stance phase. METHODS: Eighteen healthy adult subjects (nine male and nine female) were tested. RESULTS: The shapes of the mean patterns were similar for the three fastest, most natural walking speeds. At the two slowest speeds, however, subjects used little knee flexion and small knee moments through mid-stance, resulting in negligible joint power through the first 80% of the stance phase. At these speeds, most subjects had moment patterns that could not be classified with confidence as 'normal' or as predominantly flexor or extensor. Only four subjects had knee flexor moment patterns at the slowest speeds, and these included much smaller flexor moments in the early stance phase than in some previous reports. RELEVANCE: Many patients walk at very slow speeds for which 'normal' joint kinetic patterns have not been described. The knee joint kinetic data provided here from healthy subjects is useful in helping to distinguish 'abnormal' patterns caused by neuromuscular pathologies or adaptations from patterns reflecting the effects of slow walking speed alone.

Journal Article↗