BackgroundThe 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.MethodsIn 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.ResultsTen 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°.ConclusionsThe current version of the software achieves good interobserver reliability and accuracy with the exception of a few measurement parameters.

Background: Three-dimensional (3D) imaging and analysis offer new possibilities in preoperative diagnostics and surgical planning. Simultaneous 3D analysis of the joint angles and the patellofemoral anatomy allow for a realistic assessment of bony pathologies in patients with patellofemoral complaints. This study aims to develop a standardized and validated assessment of the 3D patellofemoral morphology and to establish reference ranges. Methods: Thirteen patellofemoral anatomic landmarks were defined on 3D bone models of the lower limbs based on computer tomography data and evaluated regarding inter-and intra-observer variability. Further, 60 3D models of the lower limbs of young subjects without any previous knee operation/injury were assessed and rescaled reference values for relevant patellofemoral indices were obtained. Results: The mean inter-and intra-observer deviation of all landmarks was below 2.3 mm. The interobserver intraclass correlation coefficient (ICC) was between 0.8 and 1.0 and the intra-observer ICC between 0.68 and 0.99 for all patellofemoral parameters. The calculated reference ranges are: Insall-Salvati index 1.0-1.4; patella tilt 6-18 degrees; patella shift-4 to 3 mm; patella facet angle 118-131 degrees; sulcus angle 141-156 degrees; trochlear depth 3-6 mm; tibial-tuberosity to trochlear groove distance (TT-TG) 2D 14-21 mm; TT-TG 3D 11-18 mm; lateral trochlear inclination 13-23 degrees; trochlear facet angle 43-65 degrees. Conclusion: The demonstrated 3D analysis of the patellofemoral anatomy can be performed with high inter-and intra-observer correlation. Applying the obtained reference ranges and using existing 3D assessment tools for lower limb alignment, a preoperative 3D analysis and planning for complex knee procedures now is possible. (c) 2021 Elsevier B.V. All rights reserved.

Fragestellung Die 3D-Darstellung und Analyse bietet neue Möglichkeiten bei der präoperativen Diagnostik und operativen Planung. Durch simultane Analyse der Gelenkwinkel/Beinachsen und der patellofemoralen Anatomie kann die knöcherne Pathologie bei patellofemoralen Beschwerden oder Achsdeformitäten erfasst werden. Zudem werden in der präoperativen Planung bei endoprothetischen Versorgungen oder Umstellungsosteotomien Veränderungen im patellofemoralen Gelenk mit dargestellt.