Editorial Commentary: Posterior Tibial Slope: The "Unknown Size" of the Knee Joint.

The posterior tibial slope (PTS) plays an immensely important role in almost every orthopaedic operation on the knee joint. The PTS is a decisive factor in the reconstruction of a torn anterior or posterior cruciate ligament, in high tibial osteotomy and, of course, in total knee arthroplasty. It is therefore all the more surprising that in current clinical practice relatively little emphasis is placed on the exact measurement of PTS. If the true value is not known, the influence of the same is pure coincidence. In the coronal plane, it is clinically valid practice to determine the hip-knee-ankle angle and thus to be able to determine the mechanical and anatomical axes at the tibia and femur. In the sagittal plane, however, an in-depth analysis is often dispensed with and only a short lateral knee radiograph is used. Different axes are described to determine the PTS. In addition, it is often overlooked that a determination of the PTS on lateral radiographs can only represent an average, since the medial and lateral tibial plateau shows considerable differences purely anatomically. In the future, we should place more emphasis on an analysis of the sagittal plane in the knee joint including PTS at least as profound as the analysis of the frontal plane. Here, radiographs of the entire lateral tibia must be requested to determine the true axis and thus the true PTS.