title: A simple method of measuring tibial tubercle to trochlear groove distance on MRI: description of a novel and reliable technique.
abstract: OBJECTIVE
  Tibial tubercle-trochlear groove (TT-TG) distance is a variable that helps guide surgical decision-making in patients with patellar instability. The purpose of this study was to compare the accuracy and reliability of an MRI TT-TG measuring technique using a simple external alignment method to a previously validated gold standard technique that requires advanced software read by radiologists.
  
  
  METHODS
  TT-TG was calculated by MRI on 59 knees with a clinical diagnosis of patellar instability in a blinded and randomized fashion by two musculoskeletal radiologists using advanced software and by two orthopaedists using the study technique which utilizes measurements taken on a simple electronic imaging platform. Interrater reliability between the two radiologists and the two orthopaedists and intermethods reliability between the two techniques were calculated using interclass correlation coefficients (ICC) and concordance correlation coefficients (CCC). ICC and CCC values greater than 0.75 were considered to represent excellent agreement.
  
  
  RESULTS
  The mean TT-TG distance was 14.7 mm (Standard Deviation (SD) 4.87 mm) and 15.4 mm (SD 5.41) as measured by the radiologists and orthopaedists, respectively. Excellent interobserver agreement was noted between the radiologists (ICC 0.941; CCC 0.941), the orthopaedists (ICC 0.978; CCC 0.976), and the two techniques (ICC 0.941; CCC 0.933).
  
  
  CONCLUSIONS
  The simple TT-TG distance measurement technique analysed in this study resulted in excellent agreement and reliability as compared to the gold standard technique. This method can predictably be performed by orthopaedic surgeons without advanced radiologic software.
  
  
  METHODS
  II.
authors.affiliation: Department of Orthopedic Surgery and the Sports Medicine Center, Mayo Clinic and Mayo Foundation, Mayo Clinic 200 First St., SW, Rochester, MN, 55905, USA.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Camp
authors.affiliation: Mayo Medical School, Mayo Clinic and Mayo Foundation, Rochester, MN, USA.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Heidenreich
authors.affiliation: Department of Orthopedic Surgery and the Sports Medicine Center, Mayo Clinic and Mayo Foundation, Mayo Clinic 200 First St., SW, Rochester, MN, 55905, USA.
authors.forename: Diane L
authors.initials: DL
authors.lastname: Dahm
authors.affiliation: Musculoskeletal Division, Department of Radiology, Mayo Clinic and Mayo Foundation, Rochester, MN, USA.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Bond
authors.affiliation: Musculoskeletal Division, Department of Radiology, Mayo Clinic and Mayo Foundation, Rochester, MN, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Collins
authors.affiliation: Department of Orthopedic Surgery and the Sports Medicine Center, Mayo Clinic and Mayo Foundation, Mayo Clinic 200 First St., SW, Rochester, MN, 55905, USA. krych.aaron@mayo.edu.
authors.forename: Aaron J
authors.initials: AJ
authors.lastname: Krych
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D031222:Patellar Dislocation / Q000175:diagnosis*; D015203:Reproducibility of Results; D013977:Tibia / Q000033:anatomy & histology*; D055815:Young Adult
keywords: Magnetic resonance imaging (MRI); Patellar instability; Tibial tubercle to trochlear groove (TT–TG) distance