title: Patellar Tendon-Trochlear Groove Angle Measurement: A New Method for Patellofemoral Rotational Analyses.
abstract: BACKGROUND
  The tibial tubercle-trochlear groove (TT-TG) is used as the gold standard for patellofemoral malalignment.
  
  
  OBJECTIVE
  To assess 3 patellar tendon-trochlear groove (PT-TG) angle measurement techniques and the PT-TG distance measurement (tendinous cartilaginous TT-TG) as predictors of patellar instability.
  
  
  METHODS
  Cohort study (diagnosis); Level of evidence, 3.
  
  
  METHODS
  Three PT-TG angle measurements and the PT-TG distance were measured in 82 participants with patellar instability and 100 controls using magnetic resonance imaging (MRI). Measurement landmarks were the line tangent to the posterior femoral condyles, the deepest point of the trochlea, the transepicondylar line, and the patellar tendon center. All measurements were recorded once by 1 examiner, and the measurements were recorded twice by 2 examiners in a random group of 100 knees. Mean values and standard deviations (SDs) were obtained. Normality cutoff values were defined as 2 and 3 SDs above the mean in the control group. The sensitivity, specificity, and positive likelihood ratio (LR+) were calculated. Inter- and intrarater reliability were assessed based on the intraclass correlation coefficient (ICC).
  
  
  RESULTS
  The measurements from the patellar instability and control groups, respectively, for angle 1 (16.4° and 8.4°), angle 2 (31° and 15.6°), angle 3 (30.8° and 15.7°), PT-TG distance (14.5 and 8.4 mm), and patellar tilt (21.1° and 7.5°) were significantly different (P < .05). The angle measurements showed greater sensitivity, specificity, and LR+ than the PT-TG distance. Inter- and intrarater ICC values were >0.95 for all measurements.
  
  
  CONCLUSIONS
  The PT-TG angle and the PT-TG distance are reliable and are different between the patellar instability and control groups. PT-TG angles are more closely associated with patellar instability than PT-TG distance.
  
  
  CONCLUSIONS
  PT-TG angle measurements show high reliability and association with patellar instability and can aid in the assessment of extensor mechanism malalignment. A more sensitive and specific evaluation of extensor mechanism malalignment can improve patient care by preventing both redislocation and abnormal tracking of overlooked malalignment and complications of unnecessary tibial tuberosity medialization.
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Betina B
authors.initials: BB
authors.lastname: Hinckel
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Riccardo G
authors.initials: RG
authors.lastname: Gobbi
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Eduardo N
authors.initials: EN
authors.lastname: Kihara Filho
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Marco K
authors.initials: MK
authors.lastname: Demange
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: José Ricardo
authors.initials: JR
authors.lastname: Pécora
authors.affiliation: Institute of Orthopedics and Traumatology of the Clinical Hospital, Medical School, University of São Paulo, São Paulo, Brazil.
authors.forename: Gilberto Luis
authors.initials: GL
authors.lastname: Camanho
keywords: MRI; TT-TG; patellar dislocation; patellar instability; patellofemoral; risk factor; tibial tubercle–trochlear groove