Assessment of geometric and mechanical parameters in wheelchair seating: a variability study

Randomised clinical trial comparing pressure characteristics of pelvic circumferential compression devices in healthy volunteers

INTRODUCTION

The role of pelvic circumferential compression devices (PCCDs) is to temporarily stabilise a pelvic fracture, reduce the volume and tamponade the bleeding. Tissue damage may occur when PCCDs are left in place longer than a few hours. The aim of this randomised clinical trial was to quantify the pressure at the region of the greater trochanters (GTs) and the sacrum, induced by PCCDs in healthy volunteers.

MATERIALS AND METHODS

In a crossover study, the Pelvic Binder(®), SAM-Sling(®) and T-POD(®) were applied successively onto 80 healthy participants in random order. The pressure was measured using a pressure mapping system, with the volunteers in supine position on a spine board and on a hospital bed. Data were analysed using Mixed Linear Modelling.

RESULTS

On a spine board, the pressure exceeded the tissue damaging threshold at the GTs and the sacrum. Pressure at the GTs was highest with the Pelvic Binder(®), and lowest with the SAM-Sling(®). Pressure at the sacrum was highest with the Pelvic Binder(®). The pressure at the GTs and sacrum was reduced significantly for all three PCCDs upon transfer to a hospital bed.

CONCLUSION

The results of this randomised clinical trial in healthy volunteers showed that patients with pelvic fractures, temporarily stabilised with a PCCD, are at risk for developing pressure sores. The pressure on the skin exceeded the tissue damaging threshold and is, besides PCCD type, influenced by BMI, waist size and age. Regardless with which PCCD trauma patients are stabilised, early transfer from the spine board is of key importance to reduce the pressure to a level below the tissue damaging threshold. Clinicians should be aware of the potential deleterious effects associated with the application of a PCCD, and every effort must be made to remove the PCCD once haemodynamic resuscitation has been established.

Adaptation of a seated postural control measure for adult wheelchair users

PURPOSE

Clinical measures of seated postural control in adults are not standardized and most are derived from in-house tools. The purpose of this study is to adapt a pediatric instrument to evaluate seated postural control in adult wheelchair users.

METHOD

The new instrument is called the Seated Postural Control Measure for Adults (SPCMA) 1.0. Five preliminary versions were pretested with some 20 adults by two raters and a group of experts.

RESULTS

This instrument comprises three sections: Section 1, level of sitting scale for adults (1 item, 7-point ordinal scale); Section 2, static postural alignment (22 items, 7-point ordinal scale); and Section 3, postural alignment after a dynamic activity, propulsion of the wheelchair on flat terrain and an incline (22 items, 7-point ordinal scale).

CONCLUSIONS

The SPCMA for Adults 1.0 improves the quality and uniformity of evaluations done by different raters, which facilitates more rigorous follow-up of clients over time, communication between professionals, and objective verification of the attainment of intervention objectives.

Variation in sitting pressure distribution and location of the points of maximum pressure with rotation of the pelvis, gender and body characteristics

The pressure distribution and the locations of the points of maximum pressure, usually below the ischial tuberosities, were measured for subjects sitting on a flat, hard and horizontal support, and at various angles of the rotation of the pelvis. The pressure data were analysed for force- and pressure-related quantities. Multiple regression was applied to explore relationships between these quantities and (i) a set of body characteristics and (ii) the pelvis rotation. The maximum pressure and the pressure gradient were mainly found to be explained by the ectomorphic index and the distance between the maximum pressure points by gender and the angle of rotation of the pelvis.

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.

Accessing the influence of repositioning on the pelvis' 3-D orientation in wheelchair users

This study aimed at evaluating the effects of mechanical repositioning, obtained by the increase in seat-to-back (STB) and system tilt angles, on the position of the pelvis with spinal-cord injured subjects seated in a wheelchair. The noninvasive method used combined magnetic resonance imaging (MRI) images of the whole pelvis obtained in a supine posture and ultrasound images of the pelvic iliac crests obtained in four seating positions. The matching of the two image data sets enabled the location of fourteen pelvic landmarks in the seated positions. From these landmarks, the pelvic tilt, obliquity, and transverse rotation, and the three-dimensional (3-D) motion of the pelvis were calculated. Results showed that the increase in STB angle is not equal to the calculated increase in pelvic tilt and that the pelvis rotated posteriorly, moved forward and downwards. An increase in the system tilt moved the pelvis rearwards and downwards, which counter-balanced the movement seen with the increase in STB. At the return to the first position, no significant changes were observed in the pelvis' position and orientation compared to the initial posture. Results also demonstrated the importance in calculating the total 3-D rotations and translations to characterize adequately the pelvic movement.

Differences between pelvic skin and bone landmark identification in different seated positions on spinal-cord injured subjects

The purpose of this paper was to determine the differences between internal and external pelvic landmark locations in different seating positions. A computer tool developed for the registration of two series of images was used to obtain the internal geometry. First, images of the pelvis were acquired by magnetic resonance imaging (MRI) for each subject, in a supine position; internal landmarks were then identified on the images. Second, ultrasound images of the iliac crests were acquired in four seated positions. A registration algorithm was applied to obtain the transformation matrix between the two image reference systems. The MRI anatomical landmarks were, therefore, transferred into the ultrasound referential, to obtain their three-dimensional (3-D) location in the different seating positions. The external landmarks in those seated positions were identified with a 3-D digitizer. The results revealed that generally the internal and external coordinates of corresponding landmarks are statistically different. The differences are not only due to soft tissue thickness but also to different interpretations of the landmarks' locations between the supine and the seated postures. However, these differences generally did not affect significantly the accuracy with which orientation indexes can be estimated (pelvic tilt, obliquity, transverse rotation). Correlations were found between the internal and external coordinates, implying that linear regressions can be established.

Analysis of pressure distribution at the body-seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm

In this paper, a semi-automatic method for segmenting pressure distribution image-based data at the body-seat interface is presented. The purpose of this work was to estimate the surface and the load supported by the ischial tuberosity (IT) region. The proposed method involves three steps: (1) detecting the IT region using a pressure-distribution image gradient; (2) estimating the contour of the IT region by an iterative active contour algorithm and finally (3) estimating the percentage of the surface and the weight-bearing of the IT region in a group of able-bodied (AB) and spinal-cord injury (SCI) subjects. It was found in this study that the weight bearing on the IT for the spinal-cord injured group is distributed on half the surface in comparison with the AB group or the powered wheelchair users groups. The findings of this study provide insights concerning pressure distribution in sitting for the paraplegic and able-bodied.

Analysis of sliding and pressure distribution during a repositioning of persons in a simulator chair

This study was undertaken to investigate the effect of system tilt and back recline angles on sliding and pressure distribution of seated subjects. Ten able-bodied subjects adopted successively 12 postures on a multiadjustable simulator chair. The system tilt angle was varied from 0 degrees to 45 degrees posterior tilt, while the seat to back angle varied from 90 degrees to 120 degrees. A maximum of 40.2% of weight shift was found when combining a system tilt angle of 45 degrees to a seat to back angle of 120 degrees. Maximum value of 74 mm of sliding was observed for the acromion marker during repositioning. Significant weight shift at the level of the seat is obtained only when the system tilt angle exceeds 15 degrees in a posterior direction. We can put forward here that a small tilt < or =15 degrees can be used to adjust back pressure distribution, whereas large posterior tilts are used for an effective weight shift at the seat level. The peak pressure gradient remains in general in the interval of +/-30% from the neutral posture for the able-bodied subjects and is fairly constant at 15 degrees of tilt. A significant amount of displacement along the back and seat reference plane were found for the shoulder and hip markers, but this displacement does not necessarily correspond to a pure translation motion of the pelvic segment.