Contexte et but. L'arthrose primitive est generalement selectionnee ou stratifiee dans les etudes epidemiologiques ou therapeutiques. Ceci implique des exclusions, notamment celles des arthroses secondaires a des vices architecturaux, dont pronostic et traitement different. Les parametres des dysmorphies doivent etre mesures, et ceci, aujourd'hui, sur radiographies numerisees reduites aussi bien que standard. Methodes. Nous avons cree un arthrometre dessine sur film transparent pour etre place sur les radiographies ; il comporte des rapporteurs adaptes et des reglettes millimetrees, celles-ci dans les proportions de 100 %, 75 % et 66 % de la taille standard. L'instrument a ete teste sur 112 cliches (60 hanches, 35 genoux, 17 pieds) de tailles (reductions) variees et comportant tous les types de dysmorphies courantes. Resultats. Les mesures voulues ont ete faites aisement sur la gamme des cliches depuis la taille standard jusqu'a la reduction de 50 %. L'arthrometre a permis de connaitre et de mesurer, notamment dans leur forme moderee, non evidente, les dysmorphies congenitales ou acquises suivantes : dysplasie et subluxation congenitales de la hanche, coxa valga, protrusion acetabulaire, caput varum ; pour le genou : genu varum ou valgum, anomalies de niveau et desequilibres de la rotule, angle trochleen insuffisant, enfin pied creux ou plat. Angles et quotients (index ratio) ne changent pas sur film reduit alors que les segments doivent evidemment etre convertis selon l'echelle utilisee. Les valeurs normales et limites sont mentionnees. Conclusion. L'arthrometre a pour but de mesurer directement tous les parametres des dysmorphies classiques sans tracer de lignes sur les cliches. Il est applicable aux radiographies reduites courantes actuelles aussi bien qu'aux films standards. Cependant, il s'agit ici d'une presentation de l'instrument et de son emploi. L'etude de la reproductibilite des mesures reste a faire, notamment concernant les interlignes.
Background. Primary osteoarthritis is usually selected in either epidemiological or therapeutic studies.This implies exclusions. Among secondary osteoarthritis considered for either stratification or exclusion - or for prognosis and treatment in daily practice - are those due to architectural defects. Parameters of the latter should be measured to ascertain diagnosis. At present, measurements have to be performed either on digitized reduced films or standard radiographs. Objective. To finalize an instrument liable to measure the main angles and segments characteristic of the hip, knee and foot main dysmorphies on different sizes of films. Methods. An arthrometer drawn on transparent material to be placed on radiographs was designed, involving several appropriate protractors and millimetric scales; it was tested on 60 hip, 35 knee and 17 foot radiographs with various architectural defects. Angles and segments most often used according to literature were measured. Reduction rates of films were various, reflecting the range of radiograph sizes currently used in everyday practice. Results. Measurements were easily performed on radiographs from standard (''100%'') up to 50% of reduction rate. So the arthrometer allows to recognize, especially in moderate, not obvious forms, the following developmental or acquired dysmorphies: hip congenital dysplasia and subluxation, including coxa valga and neck excess of anteversion; acetabular protrusion and coxa vara; tilt deformity; knee: patellar height abnormalities, patellar maltracking, trochlear depth insufficiency; foot: pes cavus, flat foot. Angles and segments ratios do not change in reduced film, whereas segments (absolute lengths) obviously should be converted according to the reduction rate for retrieving the classical values established for decades(table shown). Conclusion. The arthrometer allows to measure the relevant parameters of various dysmorphies without drawing lines over the films themselves. It is suitable to reduce as well to standard radiographs. However, only the instrument and its ability to be used in various films sizes are here presented. Study of reproducibility of measurements - especially concerning the joint space width - remain to be performed.