Dimitrios Lyras - Sky Ridge Medical Center, Joint and Spine Department, Lone Tree, Colorado, USA
Craig Loucks - Sky Ridge Medical Center, Joint and Spine Department, Lone Tree, Colorado, USA
Robert Greenhow - Sky Ridge Medical Center, Joint and Spine Department, Lone Tree, Colorado, USA

    Background: The aim of this study is to evaluate the geometry of the distal femur and the proximal tibia in the osteoarthritic knee using ۳D reconstructive CT scan imaging. Methods: ۴۴۹ patients with knee osteoarthritis were treated surgically in our center with patient-specific technology total knee arthroplasty. Preoperatively, all the patients underwent a CT scan according to a standard protocol. Using this database, the Hip-Knee-Angle (HKA), the Femur Valgus Angle (FVA), the Tibia Varus Angle (TVA), the Posterior Tibia Slope (PTS), and the angle between the posterior condylar axis and the anatomical transepicondylar axis (PCA) for each patient were recorded and statistically evaluated. Results: In overall, the mean HKA angle was ۱۷۷.۳±۵.۵۵, the mean FVA angle was ۳.۱۹±۲.۰۸, the mean TVA was ۳.۲۸±۲.۳۵, the PTS angle was ۹.۰۲±۳.۴۶, and the PCA angle was ۲.۸۶±۰.۷۸. Evaluation of the correlations between HKA and PCA (r=۰.۰۳۵), HKA and PTS (r=-۰.۰۴۷), and PCA and PTS (r=۰.۰۵) showed non-significant relationships (P=۰.۴۶, P=۰.۳۲, and P=۰.۲۹ respectively). No significant differences were revealed from the comparison of male patients with female patients, regarding the mean HKA, FVA, TVA, PTS, and PCA. Conclusion: The posterior condylar axis is a well-defined but not a reliable axis, while the transepicondylar and the anteroposterior are reliable, but not easily defined axes. Given the large ranges and standard deviations of the location of posterior condylar axis, and the important inter- and intraobserver variability in the intraoperative location of the transepicondylar and the anteroposterior axes, the use of a preoperative ۳D CT scan is recommended.      

۳D CT scan, Knee Geometry, Patient specific instruments, Posterior Condylar Axis, Total knee arthroplasty