title: Upright weight-bearing CT of the knee during flexion: changes of the patellofemoral and tibiofemoral articulations between 0° and 120°.
abstract: OBJECTIVE
  To prospectively compare patellofemoral and tibiofemoral articulations in the upright weight-bearing position with different degrees of flexion using CT in order to gain a more thorough understanding of the development of diseases of the knee joint in a physiological position.
  
  
  METHODS
  CT scans of the knee in 0°, 30°, 60° flexion in the upright weight-bearing position and in 120° flexion upright without weight-bearing were obtained of 10 volunteers (mean age 33.7 ± 6.1 years; range 24-41) using a cone-beam extremity-CT. Two independent readers quantified tibiofemoral and patellofemoral rotation, tibial tuberosity-trochlear groove distance (TTTG) and patellofemoral distance. Tibiofemoral contact points were assessed in relation to the anteroposterior distance of the tibial plateau. Significant differences between degrees of flexion were sought using Wilcoxon signed-rank test (P < 0.05).
  
  
  RESULTS
  With higher degrees of flexion, internal tibiofemoral rotation increased (0°/120° flexion; mean, 0.5° ± 4.5/22.4° ± 7.6); external patellofemoral rotation decreased (10.6° ± 7.6/1.6° ± 4.2); TTTG decreased (11.1 mm ±3.7/-2.4 mm ±6.4) and patellofemoral distance decreased (38.7 mm ±3.0/21.0 mm ±7.0). The CP shifted posterior, more pronounced laterally. Significant differences were found for all measurements at all degrees of flexion (P = 0.005-0.037), except between 30° and 60°. ICC was almost perfect (0.80-0.99), except for the assessment of the CP (0.20-0.96).
  
  
  CONCLUSIONS
  Knee joint articulations change significantly during flexion using upright weight-bearing CT. Progressive internal tibiofemoral rotation leads to a decrease in the TTTG and a posterior shift of the contact points in higher degrees of flexion. This elucidates patellar malalignment predominantly close to extension and meniscal tears commonly affecting the posterior horns.
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland. anna.hirschmann@usb.ch.|Clinic of Radiology and Nuclear Medicine, University of Basel Hospital, Petersgraben 4, 4031, Basel, Switzerland. anna.hirschmann@usb.ch.
authors.forename: Anna
authors.initials: A
authors.lastname: Hirschmann
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
authors.forename: Florian M
authors.initials: FM
authors.lastname: Buck
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
authors.forename: Ramin
authors.initials: R
authors.lastname: Herschel
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
authors.forename: Christian W A
authors.initials: CWA
authors.lastname: Pfirrmann
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
authors.forename: Sandro F
authors.initials: SF
authors.lastname: Fucentese
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007717:Knee; D007718:Knee Injuries; D007719:Knee Joint / Q000502:physiology; D008297:Male; D010329:Patella / Q000502:physiology*; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology*; D012399:Rotation; D013977:Tibia / Q000502:physiology; D014057:Tomography, X-Ray Computed / Q000295:instrumentation; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult
keywords: Contact point; Patellofemoral; Tibiofemoral; Upright weight-bearing CT; Weight-bearing knee joint alignment