Modelling skin pelvic landmark coordinates into corresponding internal bone for wheelchair users.

The purpose of this study was to investigate the relationships, by linear regression, between internal and external pelvic landmarks identified by two techniques: manual digitization or skin markers. It was hypothesized that the body mass index or the skinfold thickness are significant variables in these relationships. The internal pelvic landmarks were obtained with a stereoradiographic method. Results showed that the external coordinates are generally statistically different from the internal ones; manual digitization of the landmark reduces the soft tissue artifacts compared to the use of skin markers. Different regression models were obtained according to the external acquisition method. Body mass index or skinfold thickness was generally included as a significant variable in models along the direction of the soft tissue thickness: postero-anterior direction for the anterior-superior iliac spine, medio-lateral direction for the apex of the iliac crests. With the use of skin markers, models obtained for a specific internal landmark coordinate include generally many variables, such as the other two coordinates of the landmark, body mass index, or skinfold measurements. This study presented preliminary results on the relationships between internal and external pelvic landmark coordinates. More research is needed before the full relationships are understood and adequate models are developed.

Development and evaluation of a new body-seat interface shape measurement system.

A new system has been developed to capture the body-seat interface shape. It can repeatedly and accurately measure interface deformation. The shape sensing array system uses optical fiber technology and is noninvasive. The system can cover an interface as large as 400 x 480 mm and the shape is measured over a 10 x 12 array of sensors laminated on ribbon substrates. The accuracy and repeatability of this system were assessed. Measurement errors were evaluated by comparing the shape with a reference shape obtained by a mechanical digitizer. The root-mean-square error in the Z direction for the system was 3.79 mm. The repeatability of the system was within 0.38 mm under controlled conditions. Different interface materials noticeably affected measurements. With the development of this interface shape measurement device, the basic information gathered through its use may prove to be fundamental in the successful design of generic-shape contoured support surfaces. Furthermore, we expect that the new shape measurement device will provide a quick and effective tool for cushion evaluation and clinical guidelines for cushion prescription.

Powered tilt/recline systems: why and how are they used?

Prolonged static sitting can lead to discomfort, pain, pressure sores, spinal curvatures, and loss of functional independence. In order to counteract these harmful effects, adjustable tilt and/or recline systems are often prescribed. Considering the current context of assistive technology service delivery and budget cuts, it is essential to have a better knowledge of the use of these technical aids and user's satisfaction with them. The purpose of this study was to characterize the use of powered tilt and recline systems. A questionnaire was developed for this purpose, and 40 subjects were interviewed at home. They were asked to identify, from a list of 25 objectives, the reasons for which they used their repositioning system and to rank these reasons in order of importance. For each objective, they were also asked to identify the frequency and range of use as well as their satisfaction level with their system. Results revealed that 97.5% of the subjects were using their powered tilt and recline system everyday, and their satisfaction was high. The main objectives for using this type of assistive technology were to increase comfort and to promote rest. Although mainly descriptive, results are of clinical relevance and can be helpful when selecting wheelchairs.

Stability of children with cerebral palsy in their wheelchair seating: perceptions of parents and therapists.

PURPOSE: To draw up a clinical portrait of children with cerebral palsy (CP) in relation to their postural stability in the sitting position, by means of questionnaires addressed to their parents and clinicians and to identify the parameters related to body geometry, activities of daily living (ADL) and the period of the day that are linked with their postural instability. METHOD: Parents and therapists of 31 children with CP (17 boys, 14 girls; mean age, 12.7 years; age range, 8-18 years) took part in the study. As a first step, four questionnaires were developed by the research team. Nine clinicians were then involved in a focus group to validate their content. They were thereafter sent to the parents and therapists of the children. Descriptive analyses (percentage) were performed on the results of the questionnaires. RESULTS: A high percentage of instability was reported by both children's clinicians and parents (81% and 70%, respectively). This instability mainly occurred after less than half an hour in the wheelchair. Sliding and posterior pelvic tilt, pelvic obliquity and pelvic rotation were identified as the main problems of instability encountered by these children. CONCLUSION: The children involved in this study experienced some difficulties in achieving various ADL, because of their instability in the seated position. As the maintenance of postural stability is essential to the performance of most motor acts, it is essential to better understand the parameters associated with postural instability of children with CP in the seated posture.

Assessment of seated postural control in children: comparison of a force platform versus a pressure mapping system.

OBJECTIVE: To establish the validity and reliability of a pressure mapping system to measure seated postural control in children. DESIGN: A concurrent validity and reliability study. SETTING: Gait and posture laboratory of a rehabilitation center. PARTICIPANTS: Thirteen able-bodied children volunteers. INTERVENTION: Measurements were taken on a seating simulator in quiet sitting and while reaching. The localization of the center of pressure (COP) in the anteroposterior and mediolateral directions was measured simultaneously by means of a pressure mapping system and a force platform. MAIN OUTCOME MEASURES: Concurrent validity was first assessed by Pearson and Spearman correlation coefficients and then by Student paired t tests and Wilcoxon signed-rank test (P<.05) on the range and root mean square (RMS) amplitudes of COP. Reliability was evaluated using intraclass correlation coefficients and coefficients of variation. RESULTS: The COP signals were significantly correlated between both instruments for the RMS and range in both tasks and directions (mean r> or =.87) and for the time series while reaching (r> or =.99), as well as during quiet sitting (r> or =65). Both instruments showed generally fair to good reliability in quiet sitting and excellent reliability when reaching. CONCLUSIONS: The pressure mapping system can detect the COP displacement as effectively as the force platform. In a clinical context, it could help in the evaluation of seated stability and also help in evaluating the efficacy of seating components for wheelchair users.

Biomechanics of manual wheelchair propulsion in elderly: system tilt and back recline angles.

OBJECTIVE: To investigate the effects of the system tilt and back recline angles on the biomechanics of wheelchair propulsion for a group of older, disabled patients. It was hypothesized that increasing both the system tilt and backrest recline angles would have a positive effect on the biomechanical efficiency of manual wheelchair propulsion. DESIGN: Three kinetic variables were estimated during a 10-m, steady-state propulsion between 0.96 m/sec and 1.01 m/sec. The fraction of the mechanical effective force is defined by the ratio between the tangential and the total force applied to the pushrim: It expresses the directionality of force application. The mechanical use is defined as the ratio between the total force generated during wheelchair propulsion and that generated during maximal isometric contraction. The biomechanical efficiency is defined as the product of mechanical effective force and the mechanical use. RESULTS: On average, the fraction of the mechanical effective force was found to be low when compared with other studies. Tilting the system by 10 degrees and reclining the back by 10 degrees increase significantly the biomechanical efficiency of the subject by 10%. The biomechanical efficiency variable was more sensitive to the system tilt than to the back recline adjustment. CONCLUSIONS: The results of this study confirm the hypothesis that system tilt angle but not back recline significantly affects biomechanical efficiency. The findings of this study will help in designing and adjusting a wheelchair intended for self-propelled, older people.