Tamara Reid Bush

An approach for hip joint center calculation for use in seated postures

In seated postures, such as those in office or automotive seats, locating the hip joint center (HJC) using three markers on the pelvis has been difficult if not impossible. A two-target approach by Bell et al. (J. Biomech. 23 (1990) 617) has been used, however, this method was shown to have inaccuracies when compared to the three-target method developed by Seidel et al. (J. Biomech. 28 (1995) 995). A new two-target method that is specific to the seated environment, has better accuracy than the Bell et al. approach, and is based on the Seidel et al. approach was developed and tested on 13 seated subjects. This new method used three targets and an initial reference file to estimate the HJC location. Once the HJC was located, assumptions were made that the magnitudes between the HJC and the respective anterior superior iliac spine, and the HJC and the respective lateral epicondyle remained constant. The primary concern when evaluating this new method was the affect of seated posture movement, in particular leg splay and spinal flexion on the assumptions. The results obtained with the new approach were compared to Seidel et al. and provided HJC locations with average differences of 3.8, 1.2 and 2.8mm for spinal flexion in the anterior/posterior, medial/lateral and superior/inferior directions, respectively, and 2.3, 1.0 and 1.4mm for knee splay. The proposed method provided better HJC estimation than the Bell et al. approach particularly in the superior/inferior dimensions.

Support Force Measures of Midsized Men in Seated Positions

Two areas not well researched in the field of seating mechanics are the distribution of normal and shear forces, and how those forces change with seat position. The availability of these data would be beneficial for the design and development of office, automotive and medical seats. To increase our knowledge in the area of seating mechanics, this study sought to measure the normal and shear loads applied to segmental supports in 12 seated positions, utilizing three inclination angles and four levels of seat back articulation that were associated with automotive driving positions. Force data from six regions, including the thorax, sacral region, buttocks, thighs, feet, and hand support were gathered using multi-axis load cells. The sample contained 23 midsized subjects with an average weight of 76.7 kg and a standard deviation of 4.2 kg, and an average height of 1745 mm with a standard deviation of 19 mm. Results were examined in terms of seat back inclination and in terms of torso articulation for relationships between seat positions and support forces. Using a repeated measures analysis, significant differences (p<0.05) were identified for normal forces relative to all inclination angles except for forces occurring at the hand support. Other significant differences were observed between normal forces behind the buttocks, pelvis, and feet for torso articulations. Significant differences in the shear forces occurred under the buttocks and posterior pelvis during changes in seat back inclination. Significant differences in shear forces were also identified for torso articulations. These data suggest that as seat back inclination or torso articulation change, significant shifts in force distribution occur.

Quantifying the effects of external shear loads on arterial and venous blood flow: Implications for pressure ulcer development

INTRODUCTION Forces applied to the skin cause a decrease in regional blood flow. This decrease in blood flow can cause tissue necrosis and lead to the formation of deep, penetrating wounds called pressure ulcers. These wounds are detrimental to individuals with compromised health, such as the elderly and spinal-cord injured. Although surface pressure is known to be a primary risk factor for developing a pressure ulcer, a seated individual rarely experiences pressure alone but rather combined loading which includes pressure as well as shear force on the skin. However, little research has been conducted to quantify the effects of shear forces on blood flow. METHODS Fifteen men were tested in a magnetic resonance imaging scanner under no load, a normal load, and a combination of normal and shear loads. Changes in arterial and venous blood flow in the forearm were measured using magnetic resonance angiography phase-contrast imaging. FINDINGS The blood flow in the anterior interosseous artery and basilic vein of the forearm decreased with the application of normal loads, and decreased further with the addition of shear loads. Marginal to significant differences at a 90% confidence level (P=0.08, 0.10) were observed, and medium to high effect sizes (0.3 to 0.5) were obtained. INTERPRETATION Based on these results, shear force is an important factor to consider in relation to pressure ulcer propagation and prevention, and hence, future prevention approaches should also focus on mitigating shear loads.

THE USE OF ELECTROMYOGRAPHY FOR SEAT ASSESSMENT AND COMFORT EVALUATION

A need to develop methodologies to obtain objective measurements of the effects of different seat contours on people is evident. In an effort to monitor muscle activity during static postures, eletromyography (EMG) was employed. In an experimental setting, fatigue was induced in back extensor muscles for different seated postures. The resultant EMG signals were then sampled bilaterally for three different vertebral levels and the effects of the different seating systems on posture were evaluated. In preliminary tests involving 4 subjects of similar size and build, utilizing three differently contoured seats findings support the use of EMG to quantify muscular fatique as a viable means of objectively measuring the effects of different seat contours. (A) For the covering abstract of the conference see IRRD 875189.

Biomechanical Analysis of Opening Glass Jars: Using Kinematics

The research theorizes that there are three styles of hand movement when removing a lug closure from a glass jar; lid hand movement alone, jar hand movement alone, or the movement of both hands. However, it is hypothesized that experimental set up will significantly impact how participants move as they remove jar lids; that an unrestrained subject will move differently from one restrained for ease of experimental set up. Each study participant will open glass jars with lug style closures in two fashions: restrained, so that the test jar remains on the table, and unrestrained.

An Evaluation of Postural Motions, Chair Motions, and Contact in Four Office Seats

The goal of this study was to use biomechanical procedures and models to measure people and office chairs in terms of fit, movement, and support during changes in recline and spinal curvature. Testing was performed with four office chairs in a simulated keyboarding workspace with fourteen subjects ranging from petite, light women to tall, heavy men. Postures, body motions and chair motions were measured with a video-based system. A Lordosimeter measured changes in lumbar spinal curvature. Torso positions relative to the keyboard and desktop were evaluated for changes in recline angle and lumbar curvature. Pressure distributions were measured on the back of the chairs and related to changes in torso posture (back inclination and lumbar curvature). Based on the contact areas between the subjects back and the seat back, the amount of support was evaluated for changes in recline angle and lumbar curvature. Chair D, the LEAP chair had the best overall performance. LEAP was found to move with people as they moved their spine from flexion to extension. During recline motions LEAP demonstrated a reduction in travel of the wrist and head as compared to the other chairs and a reduction in the pressure necessary to recline the seat, specifically in the shoulder region. The LEAP chair also provided a consistent pressure map for all test conditions, confirming that the chair maintained contact with the torso.

Do Canes or Walkers Make Any Difference? NonUse and Fall Injuries

Purpose of the Study Examine patterns of cane and walker use as related to falls and fall injuries. Hypotheses Among people who fall at home, most do not have an assistive device with them when they fall. Nonusers who fall sustain more severe injuries. Design and Methods This was a cross-sectional study using a self-administered written survey completed by 262 people aged 60 and older who were community dwelling, cognitively intact, and current cane/walker users with a history of falls. They were recruited through clinical practice sites, churches, and senior housing in central Michigan. Outcomes of interest included patterns of device use, reasons for nonuse, device use at time of fall, and fall-related injuries. Results Seventy-five percent of respondents who fell were not using their device at the time of fall despite stating that canes help prevent falls. Reasons for nonuse included believing it was not needed, forgetfulness, the device made them feel old, and inaccessibility. Perceived risk was not high enough to engage in self-protective behavior. However, nonuse led to a significantly higher proportion of falls resulting in surgery than among device users. Among respondents requiring surgery, 100% were nonusers. Most respondents never received a home safety evaluation (68%) and only 50% received training on proper device use. Implications Providers must place increased emphasis on the importance of cane/walker use for injury prevention through patient education to promote personal relevance, proper fitting, and training. New strategies are needed to improve device acceptability and accessibility.

Comparison Between Healthy and Reduced Hand Function Using Ranges of Motion and a Weighted Fingertip Space Model

Detection and quantification of changes in hand function are important for patients with loss of function and clinicians who are treating them. A recently developed model, the weighted fingertip space (WFS) quantifies the hand function of individuals in three-dimensional space and applies kinematic weighting parameters to identify regions of reachable space with high and low hand function. The goal of this research was to use the WFS model to compare and contrast the functional abilities of healthy individuals with the abilities of individuals with reduced functionality due to arthritis (RFA). Twenty two individuals with no reported issues with hand function and 21 individuals with arthritis affecting the hand were included in the research. Functional models were calculated from the ranges of motion and hand dimension data for each individual. Each model showed the volume of reachable space for each fingertip of each hand, the number of ways to reach a point in space, the range of fingertip orientations possible at each point, and the range of possible force application directions (FADs) at each point. In addition, two group models were developed that showed how many individuals in both the healthy and RFA groups were able to reach the same points in space. The results showed differences between the two groups for the range of motion (ROM) measurements, the individual model calculations, and the group models. The ROM measurements showed significant differences for the joints of the thumb, extension of the nonthumb metacarpophalangeal (MCP) joints, and flexion of the distal interphalangeal (DIP) joints. Comparing the models, the two groups qualitatively showed similar patterns of functional measures in space, but with the RFA group able to reach a smaller volume of space. Quantitatively, the RFA group showed trends of smaller values for all of the calculated functional weighting parameters and significantly smaller reachable volume for all of the fingers. The group models showed that all healthy individuals were able to reach an overlapping space, while 18 of 21 RFA individuals were able to reach similar spaces. Combined, the results showed that the WFS model presents the abilities of the hand in ways that can be quantitatively and qualitatively compared. Thus, the potential of this hand model is that it could be used to assess and document the changes that occur in hand function due to rehabilitation or surgery, or as a guide to determine areas most accessible by various populations.

Kinematic Measures during a Clinical Diagnostic Technique for Human Neck Disorder: Inter- and Intraexaminer Comparisons

Diagnoses of human musculoskeletal dysfunction of the cervical spine are indicated by palpable clues of a patients structural compliance/noncompliance as this body segment responds to diagnostic motion demands applied by a clinician. This process includes assessments of motion range, motion performance, and changes in tissue responses. However, biomechanical quantification of these diagnostic actions and their reproducible components is lacking. As a result, this study sought to use objective kinematic measures to capture aspects of the diagnostic process to compare inter- and intraexaminer motion behaviors when performing a specific clinical diagnostic protocol. Pain-free volunteers and a group determined to be symptomatic based on a psychometric pain score were examined by two clinicians while three-dimensional kinematic data were collected. Intraexaminer diagnostic motion ranges of cervical lateral flexion and secondary rotations were consistent for each examiner and for each subject group. However, interexaminer comparisons for motion range, secondary rotations, and average velocities yielded consistently larger measures for one examiner for both subject groups (P < 0.05). This research demonstrates that fundamental aspects of the clinical diagnostic process for human neck disorders can be identified and measured using kinematic parameters. Further, these objective data have the potential to be linked to clinical decision making.

A Comparison of Pressure Mapping between Two Pressure-Reducing Methods for the Sacral Region

PURPOSE: The objective of this study was to quantify tissue interface pressures that occurred in the sacrum, shoulder, and buttock/thigh regions while using (1) pillows or (2) a wedge system for off-loading of sacral pressures. SUBJECTS AND SETTING: Twenty-one volunteers (11 females and 10 males) residing near a Midwestern, university community consented to participate in the study. Testing was conducted in a hospital bed with pillows and a commercially available wedge system. METHODS: Pressures were measured under 3 test conditions: (1) bed alone, (2) pillows positioned above and below the sacral region, and (3) wedges positioned above and below the sacral region. Each condition was tested with the elevation of the head of the bed at 3 different angles with respect to the foot of the bed (0°, 20°, and 30°). Two pressure mats were used to capture data; one was located in the shoulder region and the other in the sacral/buttocks/thigh region. RESULTS: Between the pillows and the wedge, the wedge system was the most effective in reducing pressures on the sacral area. In comparison to the bed condition, both the pillow and wedge conditions produced significantly lower mean sacral pressures than the bed alone (P < .05). Because the pillow and wedge systems tilted the body onto one side, higher pressures were identified on the buttock/thigh when compared to the bed alone (P < .05). CONCLUSIONS: Pressure reduction occurred in the sacral region with the pillow and wedge systems; however, this reduction resulted in increased pressures in the posterior-lateral regions of the buttocks and thighs. When using off-loading devices, consideration should be given to all factors, including tissue interface pressures on the sacrum, increased pressures on other body locations, and the likelihood that these increased pressures will result in tissue damage.