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Abstract
The specific objectives are: (1) the conception of a prototype of the dynamic positioning system for spinal surgeries (called MFPF for Multi-Functional Positioning Frame), that includes a lower limb positioning system, a sternum lifting system and numerous adjustments in order to adapt to various patient physiologies and spinal pathologies. (2) The evaluation of the MFPF for both healthy volunteers and patients afflicted with a spinal pathology who are candidates for operative treatment. (3) The verification of the following hypothesis: (1) The variation of lower limb position and/or sternum position can significantly modify the sagittal curves of the spine. (2) The MFPF allows an improved positioning relative to currently used surgical frames. (3) The MFPF respects natural human body kinematic. (4) The MFPF is safe with regards to interface pressures on the body.
In this project, a paediatric prototype was designed using CAD software (CATIA V5R15). Following this, the parts and assemblies were machined at various workshops. Finally, the prototype was built and used for the evaluation phase.
For the second objective, evaluation of the MFPF, the experimental protocol was the following: First, subject morphological and flexibility parameters were measured: height, weight, length and circumference of corporal segments. Then, optical captors were placed on the subject's lower limb articulations so that their positions could be recorded by a camera system during experimental displacement and a force sensing array (FSA) was installed on the MFPF cushions. Next, the subjects were installed on the MFPF, and interface pressure measurements were made for the thoracic, pelvic and thigh cushions. For the healthy volunteers and spondylolisthesis patients, radiographs were taken in two different positions while for AIS patients a lateral and a postero-anterior (PA) radiographs were taken in a single position. The subjects were removed from the MFPF and placed on the Relton-Hall frame. Interface pressure measurements were made for the thoracic and pelvic cushions. Finally, the subjects answered a questionnaire about MFPF comfort and ergonomics.
Several results arose from these experimentations: (1) The interface pressures measured on the MFPF (peak and average) were lower than on the Relton-Hall frame, both globally and also specifically for the thoracic and pelvic cushions. The interface contact area for the thoracic cushion was the same for both frames while for the pelvic cushion it was lower on the MFPF. A preliminary study has shown good repeatability of the pressure measurements. (2) The patient body kinematics observed followed the motion of the surgical frame, however, the lower limbs had less of a range of motion (from 45° in flexion to 8° in extension) relative to the mechanical system (from 55° in flexion to 20° in extension). A similar situation was found for the sternum vertical displacer with a patient thoracic translation of 6 cm relative to that of the mechanical system reaching 15 cm. (3) Different clinical indices were analysed including: lordosis, kyphosis, scoliotic Cobb angles, and several Spondylolisthesis indices. The conclusions that were drawn were: lower limb positioning has a significant impact on lumbar lordosis, sternum vertical displacement has a significant impact on thoracic kyphosis; a reduction of AIS Cobb angles arises when a patient is placed in the prone position on the MFPF and however, this correction is less important than under anaesthesia on Relton-Hall frame. Finally, a 25° change in both PT and SS was observed for spondylolisthesis patients when going from the extended to flexed lower limb position. (4) Ergonomics, evaluated with patient installation and removal times (always less than 5 minutes), was judged to be good. Comfort, evaluated by each patient via questionnaire, was also judged to be good for awaked periods of 20 minutes.
The MFPF allows for different movements of the body which have a significantly impact on the sagittal spinal curves of the spine while maintaining safe interface pressure levels. The MFPF will allow surgeons to position their patients in a variety of ways in order to obtain their preferred intra-operative spinal geometry. The MFPF is adjustable and will allow additional movements which will be tested in the future such as: raising or lowering the thoracic cushions, raising or lowering the pelvic cushions, moving the head, moving the arms, as well as combinations of these movements that could be tested in the continuation of the project.
In parallel to this project an adult prototype was designed and built. (Abstract shortened by UMI.)
