title: 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, evaluate, and monitor patellofemoral function. The objective of this study was to assess a sequential 3D analysis method based on biplanar radiographs, using an in vitro protocol.
  
  
  OBJECTIVE
  Biplanar radiography combined with novel 3D reconstruction methods provides a reliable evaluation of patellofemoral function, without previous imaging.
  
  
  METHODS
  Eight cadaver specimens were studied during knee flexion cycles from 0° to 60° induced by an in vitro simulator. The protocol was validated by investigating sequential and continuous motion using an optoelectronic system, evaluating measurement accuracy and reproducibility using metallic beads embedded in the patella, and comparing the 3D patellar geometry to computed tomography (CT) images.
  
  
  RESULTS
  The differences in position between the sequential and continuous kinematic analyses were less than 1mm 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 translations and less than 3° for rotations, except rotation in the coronal plane. For patellar tilt, uncertainty was 5°. Mean difference in geometry was 0.49 mm.
  
  
  CONCLUSIONS
  Sequential analysis results are consistent with continuous kinematics. This analysis method provides patellar position parameters without requiring previous CT or magnetic resonance imaging. A clinical study may deserve consideration to identify patellofemoral kinematic profiles and position criteria in vivo.
  
  
  METHODS
  IV, experimental study.
authors.affiliation: Institut de biomécanique humaine Georges-Charpak, arts et metiers ParisTech (ENSAM), 151, boulevard de l'Hôpital, 75013 Paris, France; Département de chirurgie orthopédique et traumatologie, unité de chirurgie du membre inférieur, hôpital Lapeyronie, CHRU Montpellier, 371, avenue Gaston-Giraud, 34295 Montpellier cedex 5, France. Electronic address: louisdagneaux@gmail.com.
authors.forename: L
authors.initials: L
authors.lastname: Dagneaux
authors.affiliation: Institut de biomécanique humaine Georges-Charpak, arts et metiers ParisTech (ENSAM), 151, boulevard de l'Hôpital, 75013 Paris, France; Hôpital Avicenne, université Paris 13, Sorbonne Paris Cité, AP-HP, 93017 Bobigny, France.
authors.forename: P
authors.initials: P
authors.lastname: Thoreux
authors.affiliation: Institut de biomécanique humaine Georges-Charpak, arts et metiers ParisTech (ENSAM), 151, boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: B
authors.initials: B
authors.lastname: Eustache
authors.affiliation: Département de chirurgie orthopédique et traumatologie, unité de chirurgie du membre inférieur, hôpital Lapeyronie, CHRU Montpellier, 371, avenue Gaston-Giraud, 34295 Montpellier cedex 5, France.
authors.forename: F
authors.initials: F
authors.lastname: Canovas
authors.affiliation: Institut de biomécanique humaine Georges-Charpak, arts et metiers ParisTech (ENSAM), 151, boulevard de l'Hôpital, 75013 Paris, France.
authors.forename: W
authors.initials: W
authors.lastname: Skalli
mesh_terms: D000368:Aged; D001696:Biomechanical Phenomena / Q000502:physiology; D002102:Cadaver; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000502:physiology*; D011859:Radiography; D015203:Reproducibility of Results
keywords: 3D; Biplanar x-rays; EOS; In vitro; Instability; Kinematics; Patellofemoral