Measurement of the Posterior Femoral Offset: Navigation Is More Precise than Standard X-rays

Appropriate reconstruction of the bone anatomy is necessary to obtain a good functional outcome after total knee replacement (TKR) (1, 2). Restoration of the native posterior femoral offset has been described as a significant prognostic factor, mainly for completion of a good range of motion in flexion (3). The measurement of the posterior offset prior to the TKR on standard X-ray or CT-scan may be inaccurate because the thickness of the remaining cartilage cannot be assessed. The measurement of the posterior offset prior to the TKR on MRI is not routinely performed. The postoperative evaluation of offset restoration may also be inaccurate, as the rotational positioning of the femur may impact the 2D image of the implant and the measure performed. We hypothesized that the measurement of the restoration of the posterior femoral offset by a navigation system during the implantation is more precise than the conventional post-operative measurement on post-operative standard X-rays.