Three-dimensional analysis of the sitting posture

Background. An evaluation of the sitting posture is particularly important in subjects who, for pathological reasons, are unable to stand upright; the data obtained allow the most suitable aids to be chosen and their ideal adaptation. The aim of this study was to define a quantitative method of measuring sitting posture in both static (position relating to pelvis - shoulders - head) and dynamic conditions (possibility of moving trunk and head both in rotation and lateral flexion). Methods. The materials used include an optoelectronic system for movement analysis (with appropriate adaptations and dedicated software) and a specially built chair that meets the requirements of the test and also allows for the possible difficulties of the subjects to be tested. A total of 15 healthy male subjects aged between 14 and 16 years old were enrolled in the study. The pelvis, shoulders and head segments were identified using 8 markers so that their reciprocal relations could be defined on the frontal and horizontal planes; the possibilities of rotation, lateral flexion and (for the head alone) flexion-extension were then measured. Results. In addition to the remarkable symmetry of the data obtained (healthy subjects), the statistical analysis of the results show minimum degrees of rotation-inclination of the segments studied, both in relation to the external space and between one another. The dynamic test confirms the symmetry of data and shows that cervical mobility is approximately double in rotations compared to lateral flexion; the cervical contribution to rotation is considerably greater than the thoracic and lumbar vertebrae together; the cervical contribution to lateral flexion is almost the same as the sum of the thoracic and lumbar components. Lastly, in cervical movements on a sagittal plane, flexion corresponds to approximately 40% whereas the extension occupies the remaining 60%. Conclusions. In conclusion, a three-dimensional analysis of the sitting posture and the relative possibility of trunk and head movement appears to be a feasible test that is repeatable, reliable and useful for the functional evaluation of wheelchair subjects and to define the aids that are often suggested in their rehabilitation programme.