title: End-stage extension of the knee and its influence on tibial tuberosity-trochlear groove distance (TTTG) in asymptomatic volunteers.
abstract: OBJECTIVE
  Increased tibial tuberosity-trochlear groove distance (TTTG) is one potential correcting parameter in patients suffering from lateral patellar instability. It was hypothesized that end-stage extension of the knee might influence the TTTG distance on MR images.
  
  
  METHODS
  Transverse T1-weighted MR images of the knee were acquired at full extension, 15° and 30° flexion of the knee in 30 asymptomatic volunteers. MRI parameters: slice thickness: 3 mm, matrix: 256 × 384, FOV: 150 × 150 mm. Two observers independently measured the TTTG at all positions.
  
  
  RESULTS
  Mean TTTG for observer 1 was 15.1 ± 3.2 mm at full extension, 10.0 ± 3.5 mm at 15° flexion and 8.1 ± 3.4 mm at 30° flexion. Mean TTTG for observer 2: 14.8 ± 3.3 mm at full extension, 9.4 ± 3.0 mm at 15° flexion, 8.6 ± 3.4 mm at 30° flexion. Mean values were significantly different (p < 0.001) between full extension and 15° as well as 30° flexion for both observers. Mean values were significantly different (p < 0.001) between 15° and 30° for observer 1, but not for observer 2 (n.s.). Interobserver agreement was very good (intraclass correlation coefficient: 0.87-0.88; p < 0.001).
  
  
  CONCLUSIONS
  The TTTG increases significantly at the end-stage extension of the knee. Therefore, the comparability of published TTTG values measured on radiographs, CT and MRI at various flexion/extension angles of the knee are limited.
authors.affiliation: Department of Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland, tobiasjdietrich@gmail.com.
authors.forename: Tobias J
authors.initials: TJ
authors.lastname: Dietrich
authors.forename: Michael
authors.initials: M
authors.lastname: Betz
authors.forename: Christian W A
authors.initials: CW
authors.lastname: Pfirrmann
authors.forename: Peter P
authors.initials: PP
authors.lastname: Koch
authors.forename: Sandro F
authors.initials: SF
authors.lastname: Fucentese
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000502:physiology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D012016:Reference Values; D013977:Tibia / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed