Introduction <p>Accurate anatomical determination of the knee joint line is critically important for the success of both primary and revision total knee arthroplasty procedures. This study aimed to evaluate the reliability of anatomical landmarks for determining the knee joint line using plain radiography, computed tomography (CT), and magnetic resonance imaging (MRI) in the Turkish population.</p> Materials and methods <p>This retrospective study included 186 patients. Anatomical reference points for the knee joint line were defined as the adductor tubercle, medial and lateral epicondyles, fibular head, tibial tuberosity, and inferior pole of the patella. Measurements obtained from all three imaging modalities were compared, and the relationships between femoral width (FW) and reference points were analyzed using correlation and linear regression analyses.</p> Results <p>No statistically significant differences were found between the measurement results of the reference points across the imaging methods (lowest <i>r</i> = 0.91, <i>p</i> &lt; 0.001). A strong correlation was observed between FW and the adductor tubercle joint line (ATJL) and medial epicondyle joint line (MEJL). Intraclass correlation coefficients (ICC) were greater than 0.90, indicating excellent reliability.</p> Conclusions <p>The adductor tubercle was identified as a reliable anatomical landmark for determining the knee joint line. Additionally, plain radiography, which offers advantages in terms of cost and reduced radiation exposure, may be a sufficient alternative for clinical applications. These findings can provide valuable contributions to surgical planning for accurate joint line determination. However, further studies are needed to validate these results in patients requiring surgical intervention.</p>