Radiographic reliability of anatomical knee landmarks for joint line determination in healthy adults

The correct identification of the knee joint line is essential for successful primary and revision total knee arthroplasty (TKA). Small misalignments can cause restricted range of motion, patellofemoral maltracking, and extensor mechanism imbalance leading to pain and functional impairment. This study aimed to evaluate the reliability of five radiographic anatomical landmarks - the fibular head, inferior patellar pole, tibial tubercle, and both femoral epicondyles - for estimating the joint line level in healthy Turkish adults.

A retrospective radiographic analysis was conducted on 100 healthy adults (61 male, 39 female; 18-50 years). Perpendicular distances from these five bony landmarks to the joint line were measured digitally by two independent observers using a PACS system under standardized calibration to minimize projection errors. Inter-observer reliability was assessed by the intraclass correlation coefficient (ICC). Power analysis was based on the fibular-head-joint-line (FH-JL) distance as the primary outcome measure.

The FH-JL distance measured 11.4 ± 1.8 mm with a coefficient of variation of 15.8%, showing the highest reliability. Sex-based differences were significant (11.8 mm in men vs. 10.7 mm in women, p = 0.002). ICC values for all measurements ranged from 0.91 to 0.96, indicating excellent agreement between observers. No age-related differences were found (p = 0.835). The fibular head showed strong correlations with both epicondyles (r = 0.724 and r = 0.689).

In healthy adults, the fibular head serves as a reliable radiologic landmark that may assist in joint line restoration during revision TKA, pending validation in clinical settings. The study also acknowledges its limitations of using plain radiographs and excluding the adductor tubercle as a reference point.