Meniscal tibial slope: comparison with bony slope

Purpose of the study X-ray measurements of the proximal tibial slope only study bony structures, without considering cartilage and meniscii thickness. It is well known that the posterior horn of the meniscii is thicker than the anterior one, and this could decrease the bony postero-distal slope. The aim of this study was to measure the meniscal slope, including cartilage and meniscii, and to compare it to the usual bony slope. Material and methods 19 knee cadaver specimens without meniscal or chondral lesions were studied. Four metallic clamps were inserted at the most anterior or posterior part of the medial or lateral meniscosynovial border. Lateral plain X-ray was taken for each knee. The bony proximal tibial slope and the medial and lateral meniscal slopes were measured and compared for each knee. Paired Wilcoxon T-test and correlations were calculated with a 5 per cent significant limit. Results The mean paired difference between bony slope and medial or lateral meniscal slope was -6 degrees : the actual meniscal slope was less oblique than the bony slope, and it was almost perpendicular to the proximal tibial axis. There was a very significant correlation between bony and medial meniscal slopes. There was no correlation between bony and lateral meniscal slopes, nor between medial and lateral meniscal slopes. Discussion These results suggest that the proximal tibial meniscal slope, which is the mechanically active one, is less oblique than the usually measured bony slope. Medial meniscal slope and bony slopes are very strongly correlated for one given knee. But medial and lateral meniscal slopes can be very different for one given knee. Conclusion These results could have an influence on the design of total or unicondylar knee replacements : the polyethylene slope of the tibial surface, which should reconstruct the natural articular design, should reproduce the meniscal, and not the bony slope. The medial and lateral slopes, should perhaps be individually reconstructed.