Novel method for evaluation of frontal plane knee alignment using bony prominences in patients with osteoarthritis

[Purpose] Angle measurement using images of bony prominences (AMI) determines frontal plane knee alignment from the skin surface without using radiation. The purpose of this study was to assess the validity and reliability of images obtained with the AMI method. [Participants and Methods] The study included 21 patients with osteoarthritis. We measured the functional axis of the lower limb, obtained via full-leg radiography and correlated the findings with the angle of dissection and the angle measured with the AMI method. Additionally, we assessed the reliability of the AMI method. [Results] The angle obtained using the AMI method and the radiographic anatomic axis (the full-leg radiograph)/the mechanical axis were well correlated. The AMI method also showed high reliability. [Conclusion] The AMI method is a valid and reliable alternative to full-leg radiography for imaging of functional and anatomical knee axes. As AMI does not use special equipment or involve radiation exposure, the method can be used in outside medical facilities and can be repeated over time without increased risk to patients.