"STUDY OF THE MAKING OF AN ORTHESIS OF THE TRUNK BY TRADITIONAL"
COMPARATIVE STUDY BETWEEN THE MANUFACTURING OF A TRUNK ORTHOSIS BY TRADITIONAL PLASTER MOULD AND COMPUTER AIDED DESIGN CONCERNING 25 ADOLESCENTS TREATED FOR SPINAL DEFORMITIES (KYPHOSIS AND SCOLIOSIS) INTRODUCTION Spinal deformities sometimes require orthopedic treatment using a body jacket. This is particularly true in cases of idiopathic scoliosis and kyphosis on spinal growth dystrophy, when a significant progression of the spinal curve is observed. Orthopedic correction by trunk orthosis should restore a balance in both the frontal and saggital planes. The objective of the treatment is to reduce initial angulation and above all to prevent spontaneous aggravation. To achieve this aim, an orthosis preceded or not by a plaster corrector can be used. Numerous publications have shown the efficiency of this treatment (2,7). Body jackets have evolved considerably in recent years. They are now more comfortable and better tolerated. The present trend is to treat children earlier, and, whenever possible, part time. Medical imaging increasingly uses 3D representation. We have been using this technology to reproduce the external shape of the trunk for several years (1,3,4). This has enabled us to do away with the traditional plaster mould (used previous to the manufacture of a made-to- measure orthosis of the trunk), replaced by an optical print. In order to evaluate the therapeutic efficiency of these new corsets, we carried out a prospective comparative study between the traditionally and 'optically' produced orthoses. MATERIAL AND METHOD We compared two methods for making ortheses of the trunk by studying the cases of 25 adolescents. For each patient requiring orthopedic treatment we made two ortheses : one using the traditional method and one using the optical method. A) TRADITIONAL METHOD : To make a trunk orthosis, a print of the patient's trunk is needed. This is obtained by using a plaster mould of the trunk, called the 'negative'. From this mould, the 'positive' is made in plaster that the orthotist can correct until he obtains the required shape, which can then be manufactured by heat moulding. His know-how is obviously essential. This stage is often an ordeal for the patient when the mould is made on a corrected posture (either by suspension, or traction on a COTREL frame). B) CAD (Computer Aided Design) METHOD Optical mould : to obtain this, an optical scanning unit is used equipped with eight electro- optical light band projectors and four CCD (charge coupled devices) cameras for recording the images, distributed at four symmetrical points (The camera is placed between the higher and lower projectors). This system is precise to the millimetre. The patient, wearing a skin- tight white diposable stockinet which serves to make the optical response uniform, takes up a position in the middle of the scanning unit, arms raised, in a neutral position. Colored markers are placed on the important anatomical reference points to enable the construction of the spine and the rib cage. The rib cage, spine, rib humps, scoliotic curves, anterior superior iliac spine and sternal V are vertically delimited.The taking of the print involves the projection of light bands whose deformation is analysed by the CCD cameras. The software uses the video images obtained to produce a digitized 3D image. Then this 3D image of the trunk is refined by the acquisition of anatomical reference points placed on the patient, and by the superimposition of a theoretical model of the spine and rib cage. Largely automated corrective software enables rectification of the external shape of the trunk and rib hump, and readjustment of the occipital axis both in the frontal and saggital planes by correcting a hyperlordosis or reintroducing a thoracic kyphosis. The software enables vertical and horizontal sections to be visualized, localizing adjustments to be added by superimposition of images before and after correction. It appreciates their accuracy. When the correction is completed, a digitally controlled machine-tool will mill the corrected 'positive' out of a block of injected expanded polyurethane foam. On this external shape, the orthotist will make the prescribed orthosis by the usual heat moulding process. C) PROTOCOL We compared these two methods by making a study of 25 adolescents. Each body jacket was successively put into place following the same protocol : after a progressive tightening over 3 weeks, a frontal and lateral radiological assessment was carried out with the patient in an upright position and wearing the body jacket. Neither the prescriber nor the patient knew the origin of the orthosis used. The x-rays were compared in terms of angulation, frontal and saggital equilibrium. The patient's impression of comfort in the body jacket was taken into account. Then, after the final choice of one of the body jackets, the orthopedic treatment followed its usual course. It is only from this stage on that the sealed envelope was opened in order to discover the origin of the body jacket. The final choice of the orthosis was made using three criteria : reduction of the scoliotic curves on the frontal radiological assessment, modification of the thoracic kyphosis in profile and comfort of the body jacket. Twenty-five adolescents accepted the protocol after parental agreement in writing. 23 suffered from evolutive idiopathic scoliosis and 2 from thoracic kyphosis through spinal growth dystrophy. There were 20 girls and 5 boys whose average age was 13 years and 5 months (11 yrs 4 mths to 16 yrs 9 mths). 1) Concerning the cases of scoliosis, there were 7 thoracic curves, 8 thoraco-lumbar curves and 8 double major curves. The body jackets were put into place without plaster correction. We used TLSO-type monovalve body jackets fastening at the back. The average thoracic angle was 25.1° (between extremes of 17° and 32°) and the average lumbar angle 22.8° (16°/30°). The evolution of the curve was appreciated by two radiological assessments at 6-month intervals associated with a Risser-test. 2) For the treatment of the kyphoses, we used a Plexidur bivalve body jacket with a manubrial support between two periods with plaster casts (see table 1). RESULTS Concerning the two cases of thoracic and thoraco-lumbar kyphosis (developed after Scheuermann's disease), the CAD orthosis was chosen in both cases. In the first case the corrections were similar but the comfort was much greater. In the second case (thoraco-lumbar kyphosis) the comfort was greater with the CAD orthosis but above all the thoraco-lumbar kyphosis presented a better correction 11° against 17° with the traditional body jacket and the thoracic kyphosis was improved with the CAD body jacket whereas it was worsened by the traditional body jacket (table 1). Concerning the scolioses (23 cases) : 11 traditional body jackets and 12 CAD body jackets were chosen. a) If we compare the radiological results of the two body jackets for each patient : for the frontal radiological correction, the better result was obtained 5 times with the CAD body jacket, 5 times with the traditional one and in 13 cases the result was considered as equivalent. for the lateral radiological correction, the better result was obtained 16 times with the CAD body jacket, once with the traditional one, and in 6 cases was considered as equivalent. b) If we take as a basis for analysis the body jacket initially chosen : For the traditional body jackets (chosen 11 times), the frontal radiological analysis shows that the result is better 5 times, identical 6 times and in profile the result is better once only, identical 5 times and worse 5 times. For the CAD body jackets (chosen 12 times), the frontal result was better 5 times, identical 7 times. But in profile the result was better 10 times and identical twice. In terms of average correction of the curves, table 2 shows that the traditional and CAD body jackets are equivalent relative to the correction of thoracic curves, and that the lumbar correction is a little better with the traditional body jacket. In the saggital plane, the CAD body jacket enables the thoracic and lumbar curves to be maintained in a more natural posture. DISCUSSION Concerning the quality of the frontal and lateral radiological results, we chose a priori the frontal reduction as more important, but very quickly, the lateral analysis seemed significant to us. This study thus showed us that optical acquisition made possible the manufacture of trunk orthoses which were as efficient in terms of reduction and control of frontal radiological curves. In profile, CAD orthoses obtain better results. This is probably due to the fact that the traditional orthosis is made in suspension, which corrects frontal scoliotic curves but makes thoracic hypo-kyphosis worse and diminishes lumbar lordosis. Our study compared orthoses whose conditions of manufacture are different since with the traditional method the orthosis is made on a mould in suspension, whereas the CAD orthosis is made on a patient without suspension. Of course, other types of body jacket exist whose manufacture does not require suspension of the patient and with which the correction is carried out by the progressive addition of support inside the body jacket. (CTM body jacket biblio. Ref.). There is no equivalent study in the literature allowing us to compare results as this manufacturing process remains very innovative. There do exist other systems for taking optical prints either by laser imaging processes (5) or by optical processes using the deformation of bands of light but analysing only the posterior face of the trunk (6-7). So far, the study by laser imaging carried out by Poncet (5) and colleagues, remains an experimental study of reconstruction of the trunk authorizing the comparison of the internal 3D geometry of the spine and external 3D geometry of the trunk. The 3D imaging of the trunk is obtained using a laser-imaging system, while the digitizing of two posterior anterior x-rays enables a 3D image of the spine and the rib cage to be generated for each patient. In the future this will enable spinal deformities to be related to the external shape of the trunk. The work of STOKES (6) and THEOLOGIS (7) analyses the posterior face of the trunk only and enables spinal deformity and back surface asymmetry in idiopathic scoliosis to be compared.This, of course, helps in the early detection of progression in adolescent idiopathic scoliosis, but unfortunately these studies only concern the posterior face of the trunk; there is thus notably no analysis of thoracic deformity. These studies, however, encourage us to continue our work in two directions : the first being to find a link between progressive scoliosis and 3D global deformity of the trunk following THEOLOGIS's example.The second axis of research being the pre and post-operative follow- up of scoliotic patients who have been operated on. The superimposition of pre and post- operative images will enable us to appreciate corrections from a morphological point of view, notably in terms of reduction of rib humps and readjustment of the trunk. Indeed, this optical process is a wonderful tool for measuring the trunk, even if the measurements are static. CONCLUSION We compared two ways of making orthoses of the trunk for adolescent scoliosis and hyper- kyphosis. As the traditional method serves as a reference, we showed that the optical process was equally efficient, or even more so, in maintaining and correcting saggital curves. This process is not only reliable but also comfortable for the patients, as it is rapid and free of constraints. Today we have abandoned the traditional method in favor of exclusive use of the CAD process. The relevant literature has confirmed the idea that the optical system used in the manufacture of trunk orthoses can also be used for research and clinical follow-up of our scoliotic patients. Besides, the projection of alternating bands of light is a simple process of 3D representation of surfaces. 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