Can interepicondylar distance predict joint line position in primary and revision knee arthroplasty?

Restoration of the position of the prosthetic joint line (JL) to the same level as the original JL is a challenging problem in primary adn revision knee arthroplasty, and there is no reliable method for achieving this objective. We hypothesized that there is a constant ratio between the interepicondylar distance (IED) and the perpendicular distance from this interepicondylar line to the JL and analyzed 100 computed tomography scans of the knee to study this relationship. The IED and the perpendicular distance from this interepicondylar line to the JL was measured using both the clinical epicondylar axis (CEA) and the surgical epicondylar axis (SEA). Results showed that the ration between the IED adn the perpendicular distance from the interepicondylar line to the JL was 3.0 using the CEA and 3.3 using the SEA. The ratio was found to be constant, irrespective of the patient's sex or height. We suggest using the CEA because of the ease in localizing epicondyle peaks and conclude that the position of the JL from the interepicondylar line is one-third the IED using the CEA. This will prove to be a valuable aid in restoring the JL position during knee arthroplasty.