title: The tibial-tubercle trochlear groove distance in patients with trochlear dysplasia: the influence of the proximally flat trochlea.
abstract: OBJECTIVE
  Increased tibial tubercle trochlear groove distance (TT-TG) is frequently associated with trochlear dysplasia (TD). Since the trochlear groove appears more distally in patients with TD compared to controls, it is unknown whether TT-TG might be comparable and meaningful.
  
  
  METHODS
  Fifty patients with TD were retrospectively analysed and compared to 52 age- and gender-matched patients (CG). TT-TG was measured on transverse MR images, as the distance between the trochlear groove of minimal 2 mm depth proximally and the centre of the patellar tendon at its distal insertion. The height of the femoral reference point above joint line was recorded for both groups. TT-TG measurement was repeated in CG using the first (P25), second (P50) and third quartile (P75) above joint line of TD.
  
  
  RESULTS
  Patients with TD had a significantly smaller vertical distance between the most proximal trochlear deepening and the femorotibial joint line (20.6 mm, range 10.3-30.9) compared to CG (33.8 mm, range 25.4-41.1; p < 0.001). TT-TG values measured at 20 mm (P50) and 15 mm (P25) proximal to the femorotibial joint line were significantly smaller compared when measured with the most proximal reference point [1.8 mm (95 % CI 1.3-2.3, p < 0.001) and 2.4 mm (95 % CI 1.9-3.0, p < 0.001)] in CG. The inter-rater reliability was excellent (ICC 0.99).
  
  
  CONCLUSIONS
  TT-TG distance depends significantly on the femoral reference point. Since the trochlear groove is seen more distally in patients with TD compared to controls, TT-TG of the patients with highest risk of recurrent patellar instability might be underestimated.
  
  
  METHODS
  Diagnostic study, Level I.
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Zurich, Switzerland. ph.tscholl@sunrise.ch.
authors.forename: Philippe M
authors.initials: PM
authors.lastname: Tscholl
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Zurich, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Antoniadis
authors.affiliation: Radiology, Orthopedic University Hospital Balgrist, University of Zurich, Zurich, Switzerland.
authors.forename: Tobias J
authors.initials: TJ
authors.lastname: Dietrich
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Zurich, Switzerland.
authors.forename: Peter P
authors.initials: PP
authors.lastname: Koch
authors.affiliation: Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, University of Zurich, Zurich, Switzerland.
authors.forename: Sandro F
authors.initials: SF
authors.lastname: Fucentese
mesh_terms: D000328:Adult; D000818:Animals; D005260:Female; D005269:Femur / Q000002:abnormalities* / Q000000981:diagnostic imaging*; D006801:Humans; D007593:Joint Instability / Q000209:etiology*; D007719:Knee Joint / Q000002:abnormalities / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D031222:Patellar Dislocation / Q000209:etiology; D057071:Patellofemoral Joint / Q000002:abnormalities* / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013977:Tibia / Q000000981:diagnostic imaging*
keywords: MRI; Osteotomy; Patellar dislocation; TT–TG; Trochlear dysplasia