Sequential 3D analysis of patellofemoral kinematics from biplanar x-rays: In vitro validation protocol.

Abstract

Background: Developing criteria for assessing patellofemoral kinematics is crucial to understand, eval-uate, and monitor patellofemoral function. The objective of this study was to assess a sequential 3Danalysis method based on biplanar radiographs, using an in vitro protocol.Hypothesis: Biplanar radiography combined with novel 3D reconstruction methods provides a reliableevaluation of patellofemoral function, without previous imaging.Material and methods: Eight cadaver specimens were studied during knee flexion cycles from 0◦to60◦induced by an in vitro simulator. The protocol was validated by investigating sequential and con-tinuous motion using an optoelectronic system, evaluating measurement accuracy and reproducibilityusing metallic beads embedded in the patella, and comparing the 3D patellar geometry to computedtomography (CT) images.Results: The differences in position between the sequential and continuous kinematic analyses were lessthan 1 mm and 1◦. The protocol proved reliable for tracking several components of knee movements,including patellar translations, flexion, and tilt. In this analysis, uncertainty was less than 2 mm for trans-lations and less than 3◦for rotations, except rotation in the coronal plane. For patellar tilt, uncertaintywas 5◦. Mean difference in geometry was 0.49 mm.Discussion: Sequential analysis results are consistent with continuous kinematics. This analysis methodprovides patellar position parameters without requiring previous CT or magnetic resonance imaging.A clinical study may deserve consideration to identify patellofemoral kinematic profiles and positioncriteria in vivo.Level of evidence: IV, experimental study.