The adductor tubercle: a reliable landmark for analysing the level of the femorotibial joint line.

Purpose: The ratio of femoral width and distance from medial epicondyle to joint line helps estimate the femoral joint line position from femoral width. The approximately radial position of the medial epicondyle on femoral condyle spheres is probably responsible for this relationship, The adductor tubercle approximately lies diametrically opposite to the joint line on condylar sphere. Then, a linear correlation could also exist between the femoral width and distance of adductor tubercle to joint line and is the purpose of the current study.

Methods: Femoral width, along with the distance to joint line from the medial epicondyle, the adductor tubercle and fibular pole, was measured on 110 standard antero-posterior knee radiographs. Correlation between femoral width and these measurements was evaluated. The individual ratio of FW with adductor tubercle joint line, medial epicondyle joint line and fibula joint line was calculated using linear regression analysis. Intra-observer and inter-observer reliability was assessed.

Results: Linear correlation was found between femoral width and distance of adductor tubercle to joint line (r = 0.83). It was more reliable than the correlation between femoral width and distance from medial epicondyle to joint line (r = 0.52). Inter-observer repeatability was better for distance from adductor tubercle to joint line than for distance from medial epicondyle to joint line.

Conclusions: We conclude that adductor tubercle can be used as a morphologic landmark to determine the knee joint line position, because a linear correlation between femoral width and distance from the adductor tubercle to the joint line was found.