A new 3D software for analysis and planning of lower limb and patellofemoral alignment: Reliability and accuracy

Abstract

Background: The new software, mediCAD® 3D Knee Sport (mediCAD Hectec GmbH, Altdorf/Landshut, Germany), promises to combine automated digital 3D bone model generation, 3D analysis of lower limb geometry including analysis of the patellofemoral joint, and osteotomy planning. The aim of this study was to evaluate its reliability and accuracy. Methods: In this retrospective multi-observer study, three post-mortem CTs were analysed by three observers at three points in time. Reliability was evaluated by calculating the intraclass correlation coefficient (ICC) of interobserver agreement. Accuracy was evaluated using the mean deviation D from the mean and the standard deviation SD from D. Results: Ten of 18 alignment parameters showed excellent, two good and three moderate interobserver agreement. Poor agreement was found for the mechanical medial proximal tibial angle, the trochlear sulcus angle and trochlea depth. Mean interobserver ICC of all parameters ranged from 0.32 to 0.99. Fifteen of 18 parameters showed a low mean deviation D from the mean of < 2 mm / 2°. Three parameters related to the patellofemoral joint showed medium or high D (patella tilt, trochlear sulcus angle, patellar ridge angle). These parameters also showed the highest values for the SD of D. The trochlear sulcus angle was found to be the only parameter with high mean deviation (D ≥ 5 mm/5°) with D being 5.67 ± 3.23°. Conclusions: The current version of the software achieves good interobserver reliability and accuracy with the exception of a few measurement parameters.