Background Measured bone density correlates well with the mechanical properties of the bone. Our objective was to evaluate optical densitometry as a method of measuring the periprosthetic bone density of the tibial platform in total knee replacement using serial dual-energy X-ray absorptiometry (DXA) as the reference test.Methods 30 patients who underwent a cemented total knee replacement were followed up for over 2 years. Standard radiographs of the knee were obtained at 12 and 24 months. These were photographed with a digital camera and enhanced with image processing software. A DXA scan was performed at the same time as the reference method. 3 regions of interest were defined under the tibial plateau (medial, lateral and stem positions).Results After 24 months of follow-up there was a significant decrease in density in the 3 regions, both with the optical and DXA methods. The concordance between methods was studied using Bland and Altman plots, Cronbach's alpha and intraclass correlation coefficients resulted in values from 0.72 to 0.87, depending on the region and the follow-up time.Interpretation Quantification of optical density values with a standardized measurement system on conventional radiographs is a reliable and efficient method of determining the bone mineral density.

We prospectively measured the changes in bone mineral density (BMD) in the proximal tibia of 20 total knee arthroplasties, ten with cruciform stems and ten with cylindrical stems. The measurements were made one, four and seven years after surgery. We observed a uniform density decrease in three regions of interest from one to seven years of follow-up. Cylindrical stems showed an asymmetrical density decrease between the three regions of interest, with no change in the central region, a slight decrease in the lateral region, and large decrease in the medial region. Multivariate analysis with general linear model showed the stem type factor as statistically significant for medial region of interest (p=0.006). The cylindrical stem produces heterogeneous BMD changes under the tibial platform in knee arthroplasties, and this could be a potential risk factor for asymmetrical subsidence of this component. Résumé Nous avons de façon prospective mesuré les modifications de la densité minérale osseuse (BMD) au niveau de la partie proximale du tibia chez 20 patients ayant bénéficié d'une prothèse totale du genou, 10 avec une quille cruciforme et 10 avec une quille cylindrique. Les mesures ont été réalisées de 1.4 à 7 ans après l'intervention chirurgicale. Nous avons observé une diminution uniforme de la densité minérale osseuse dans trois zones, durant cette période de 1 à 7 ans de suivi. La quille cylindrique montre que la densité minérale osseuse diminue de façon asymé-trique dans ces 3 régions sans modification au niveau de la région centrale, avec une légère diminution de la région externe (latérale) et une diminution plus importante de la région interne (médiale). Une analyse de régression multi variable montre que le type de quille est l'élément le plus significatif au niveau de la région interne (p=0.006). La quille cylindrique étant un facteur statistiquement significatif et entraînant des modifications hétérogènes de la BMD, sous le plateau tibial. Ces modifications peuvent être un risque potentiel de migration du composant tibial.

We studied 47 reverse oblique intertrochanteric femoral fractures that were treated with gamma nails between 1992 and 2000. Fracture reduction was satisfactory in 38 patients (81%), the hip screw position was correct in 42 (89%) and there were no peri-operative complications. However, in three patients the nail displaced, resulting in non-union in one and protrusion into the acetabulum in another. A logistical regression analysis of our series showed that an incorrect position of the hip screw in the femoral head was the only predictor for complications. Thus, we consider that the gamma nail is a good option for the treatment of these complex fractures.

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