title: Coronal tibiofemoral subluxation: a new measurement method.
abstract: BACKGROUND
  Coronal tibiofemoral (CTF) subluxation is a common finding in knee osteoarthritis (OA) which can be related to poor pain scores and tibial spine impingement. In this study we describe a new method for measuring CTF subluxation and present validation of the method using cadaveric knees.
  
  
  METHODS
  A prototype software code based on the ICP mathematical algorithm was developed to measure CTF subluxation; the code finds the rigid transformation that best aligns the articular surfaces, measures CTF subluxation and the angle between articular surfaces. For validation, three stripped fresh frozen cadaveric knee specimens were transfixed to a specially designed knee fixation device where tibiofemoral angle and CTF subluxation can be measured directly. Fluoroscopic images were obtained with the tibiofemoral joint in neutral alignment and with 5, 10 and 15 (mm) of medial and lateral subluxation. This procedure was repeated with a neutral tibiofemoral angle, 10° of varus and 10° of valgus. All images were analyzed independently by two investigators using the prototype software.
  
  
  RESULTS
  The interclass correlation coefficient between the two investigators for CTF subluxation and tibiofemoral angle was 0.93 and 0.99 respectively. The CTF subluxation and tibiofemoral angle measured by the software correlated to the CTF subluxation and tibiofemoral angle were defined using the knee fixation device, with Pearson product moments of 0.86 and 0.94 respectively.
  
  
  CONCLUSIONS
  Our suggested prototype software is precise, repeatable and reliable at measuring CTF subluxation and tibiofemoral angle. It may prove to be a useful tool to evaluate CTF subluxation in a clinical setting.
authors.affiliation: Computer Assisted Surgery Center, Department of Orthopaedic Surgery, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States. Electronic address: khamaisys@hss.edu.
authors.forename: Saker
authors.initials: S
authors.lastname: Khamaisy
authors.affiliation: Computer Assisted Surgery Center, Department of Orthopaedic Surgery, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States. Electronic address: zuiderbaana@hss.edu.
authors.forename: Hendrik A
authors.initials: HA
authors.lastname: Zuiderbaan
authors.affiliation: Computer Assisted Surgery Center, Department of Orthopaedic Surgery, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States. Electronic address: theinr@hss.edu.
authors.forename: Ran
authors.initials: R
authors.lastname: Thein
authors.affiliation: Computer Assisted Surgery Center, Department of Orthopaedic Surgery, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States. Electronic address: nawabid@hss.edu.
authors.forename: Danyal H
authors.initials: DH
authors.lastname: Nawabi
authors.affiliation: School of Engineering and Computer Science, The Hebrew University of Jerusalem, Jerusalem, Israel. Electronic address: josko@cs.huji.ac.il.
authors.forename: Leo
authors.initials: L
authors.lastname: Joskowicz
authors.affiliation: Computer Assisted Surgery Center, Department of Orthopaedic Surgery, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, NY, United States. Electronic address: pearlea@hss.edu.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pearle
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena; D002102:Cadaver; D005269:Femur / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D031221:Knee Dislocation / Q000150:complications / Q000175:diagnosis*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000150:complications*; D011859:Radiography; D015203:Reproducibility of Results; D013977:Tibia / Q000000981:diagnostic imaging / Q000503:physiopathology*
keywords: Iterative closest point; Knee osteoarthritis; Tibiofemoral joint; Tibiofemoral subluxation