Background One of the important factors affecting the biomechanics of the knee joint is the posterior tibial slope which is the tibial plateau's anatomical inclination toward the posterior of the sagittal plane. This inclination, which affects anterior-posterior stability, is important for the kinematics of the knee joint. Changes in the tibial slope may cause a deficit in the stability and function of the knee joint. We aimed to examine the inclination of the posterior horn of the meniscus and posterior tibial slope in healthy individuals and investigate the effect of body mass index on these measurements. Methodology A total of 34 magnetic resonance images and lateral knee radiographs were evaluated in this study. The study included individuals aged 15 to 78 without a history of previous injury or surgery of their knee. Results In the measurements made on magnetic resonance images, a statistically significant difference was found between 25% lateral meniscus slope (mean ± SD = 28.08 ± 1.88) and 25% medial meniscus slope (mean ± SD = 27.31 ± 1.41) (p = 0.05). At the same time, a statistically significant difference (p = 0.011) was found between 25% medial combined slope (mean ± SD = 29.05 ± 3.80) and 25% lateral combined slope (mean ± SD = 30.62 ± 2.99). There was no statistically significant difference between tibial and meniscus slopes, body mass index, gender, and age. Conclusions Our study results have shown that the 25% lateral meniscus and combined slopes are greater than the 25% medial meniscus slope.