PurposeTo assess a quantitative and reproducible association between the position of the knee joint line and recognizable anatomical landmarks around it in order to help in restoring joint line in arthroplasty cases.MethodsMagnetic resonance imaging (MRI) of 130 normal knees were investigated. Anatomical measurements of the knee joint distances on the obtained planes were performed manually by distance measurements using a ruler tool, followed by 6 anatomical bony landmarks determination about the knee to identify the joint line which included the joint line, medial epicondyle, lateral epicondyle, medial flare, lateral flare, and proximal tibiofibular joint. The entire process was examined twice by two independent fellowship trained musculoskeletal radiologists, with a 2-week interval between the first and second sets of readings.ResultsThe lateral epicondyle to the joint line of the knee (LEJL) could be a reliable landmark for accurate distance measurements for the knee joint line level, with an absolute distance of 24.4 ± 2.8 mm. The analysis showed that the femorotibial ratio between the LEJL and proximal tibiofibular joint (PTFJ) was 1.0 (LEJL/PTFJJL = 1.0 ± 0.1), confirming the location of the knee joint at the midpoint between the lateral epicondyle and PTFJ, revealing two identifiable landmarks.ConclusionsLEJL is the most precise landmark for determination of an accurate knee joint line because the knee is located at the midline between the lateral epicondyle and PTFJ. These reproducible quantitative relationships can be widely employed in various imaging modalities to help restore the knee JL in arthroplasty surgeries.