Should the presence of menisci be considered when measuring the posterior tibial slope in total knee arthroplasty ?

Objectives: In planning a total knee arthroplasty, the sagittal tibial slope is commonly measured on a lateral view radiograph. Such a measurement does not include cartilage and menisci, although these structures have a relevant role in loading distribution on the tibial plateau. Aims of this investigation were to assess whether the posterior tibial slope is affected by the presence of cartilage and menisci and whether any correlation exists between the degree of tibial bone slope and cartilage and meniscal thickness. Methods: Magnetic resonance studies of the knees of 80 subjects, 45 males and 35 females, with an average age of 38.9 years, were analysed.Using an imaging visualization software, the sagittal anatomical axis of the tibia was identified. The angle between the latter and a line tangent to the bone profile of the tibial plateau (bone slope) and a line tangent to the superior border of the anterior and posterior portion of the menisci (meniscal slope) were calculated. Results: The tibial bone slope averaged 8 on the medial side and 7.7 on the lateral side. The meniscal slope averaged 4.1 on the medial side and 3.2 on the lateral side. The meniscal slope was significantly reduced compared to the bone slope, on both the medial and lateral sides. A significant correlation was found, on the lateral side, between the severity of the posterior bone slope and the difference between the bone and meniscal slope. Conclusions: The presence of cartilage and menisci leads to a significant reduction in the posterior tibial slope measured on the bone profile. On the lateral side, the greater the posterior bone slope, the larger the difference between the bone and meniscal slope.