title: Is tibial tuberosity-trochlear groove distance an appropriate measure for the identification of knees with patellar instability?
abstract: OBJECTIVE
  Tibial tuberosity-trochlear groove distance (TT-TG) has been regarded as a useful tool for establishing therapeutic choices for patellar instability. Recently, it has been shown that TT-TG negatively correlated with the quadriceps angle, suggesting that if used individually, neither provide a valid measure of instability. This study aimed to compare TT-TG distance between both knees in patients with unilateral instability to assess whether this measurement is a decisive element in the management decisions for patellar instability.
  
  
  METHODS
  Sixty-two patients (18 male and 44 female), reporting to a specialist patella clinic for recurrent unilateral patellar instability, were included in the study. Patients underwent bilateral long leg computed tomography scan to determine TT-TG distance in both knees. Tibial TT-TG in symptomatic and asymptomatic knees in the same individual was compared statistically.
  
  
  RESULTS
  Mean TT-TG distance in the symptomatic knee was 16.9 (±4.9) mm, compared to 15.6 (±5.6) mm in the asymptomatic knee. Tibial TT-TG was not significantly different between stable and unstable knees (n.s.).
  
  
  CONCLUSIONS
  The lack of difference in TT-TG distance between stable and unstable knees suggests that TT-TG distance alone may not be a decisive element in establishing therapeutic choices for patellar instability. It should, therefore, be interpreted with caution during clinical evaluations.
  
  
  METHODS
  II.
authors.affiliation: Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, NE1 8ST, UK, nick.caplan@northumbria.ac.uk.
authors.forename: N
authors.initials: N
authors.lastname: Caplan
authors.forename: D
authors.initials: D
authors.lastname: Lees
authors.forename: M
authors.initials: M
authors.lastname: Newby
authors.forename: A
authors.initials: A
authors.lastname: Ewen
authors.forename: R
authors.initials: R
authors.lastname: Jackson
authors.forename: A
authors.initials: A
authors.lastname: St Clair Gibson
authors.forename: D
authors.initials: D
authors.lastname: Kader
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging*; D007719:Knee Joint / Q000000981:diagnostic imaging*; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D013977:Tibia / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed; D055815:Young Adult