Medial femorotibial osteoarthritis and genu-valgum: Where is the problem?

Frontal malalignment of the lower limbs has been shown to be closely linked to the onset and progression of knee osteoarthritis. Restoration of a satisfactory alignment after total knee arthroplasty has a positive impact on implant durability and functional result. An angle measurement commonly used to assess this alignment is the HKA angle (hipknee-ankle). It is measured on a full length AP radiograph of the lower limbs between the femoral mechanical axis and the tibial mechanical axis. However, various authors have demonstrated that this measurement, although widely used, could be very inaccurate in case of poor patient positioning during radiographic acquisition. This is especially true when flexion is associated with a rotation of the lower limb. In this context, the EOS system (EOS imaging, Paris, France) allows, on the basis of a biplane x-ray acquisition, for the construction of a 3D model of the lower limbs in a weight-bearing position. This 3D model provides various clinical parameters, including the HKA angle which, calculated in the knee frontal plane, remains independent of patient positioning during the x-ray acquisition.