Introduction:: Various reference axes are used in total knee arthroplasty to determine the femoral rotation including transepicondylar axis, posterior condylar axis and Whiteside’s line. However, there are currently no golden standards as to the ideal axes to determine the true femoral rotation.

Materials and Methods: A prospective observational study was performed to analyse the various axes used to determine femoral rotation during total knee replacement. All consecutive patients who underwent MRI of the knee between December 2006 and May 2007 were considered to be included in the study. Patients below the age of 20 years, above the age of 40 years and mass lesions obscuring the bony landmarks were excluded. The transepicondylar, posterior condylar, posterior femoral cortical, anterior femoral cortical and tibial anteroposterior axes were measured on the PACS system.

Results: Of the 100 patients, there were 75 males and 25 females with a mean age of 31(20–39) years. The mean relation between the posterior condylar axes and transepicondylar axes was 3.9 (SD−1.71, 95% CI 3.58–4.26), posterior condylar axes and posterior femoral cortical axes was 5.85 (SD−2.76, CI 5.3–6.4), posterior condylar axis and anterior cortical axis was 6.21 (SD−3.09, CI 5.6–6.8) and posterior condylar axes and tibial anteroposterior axes was 89.6 (SD−5.18, CI 88.5–90.6).

Conclusion: The transepicondylar axis appears to be the most consistent amongst the landmarks used to determine femoral rotation. However even the transepicondylar axis shows a significant variation. If transepicondylar axis is not available we suggest the use of femoral anterior cortical axes as a reference landmark