title: The Relationship Between Tibial Tuberosity-Trochlear Groove Distance and Abnormal Patellar Tracking in Patients With Unilateral Patellar Instability.
abstract: OBJECTIVE
  To evaluate the role of tibial tuberosity-trochlear groove (TT-TG) distance in patellofemoral kinematics by retrospectively reviewing the dynamic computed tomography scans of patients with unilateral patellofemoral instability and comparing unstable and contralateral asymptomatic knees.
  
  
  METHODS
  We reviewed all dynamic computed tomography scans obtained at one tertiary care hospital from 2008 through 2013 and identified 25 patients with a history of recurrent unilateral patellofemoral instability. During the scans, subjects performed active knee extension against gravity. Both knees were imaged simultaneously. Lateral patellar tilt (LPT) and bisect offset (BO) were measured to assess tracking. TT-TG distance was measured to assess alignment. Measurements were made in full extension, maximum flexion, and approximately 10° increments in between. The significance level was set at P < .05.
  
  
  RESULTS
  LPT, BO, and TT-TG distance were highest in extension and decreased with flexion. Measurements were higher in symptomatic than in asymptomatic knees, with significant differences identified for LPT, BO, and TT-TG distance at 5° and 15° and for TT-TG distance at 25° and 35° (P < .05). TT-TG distance was associated with LPT and BO, with r(2) values in symptomatic knees of 0.55 for TT-TG distance and LPT and of 0.45 for TT-TG distance and BO.
  
  
  CONCLUSIONS
  In patients with unilateral patellar instability, LPT, BO, and TT-TG distance are higher on the unstable side. An association exists between TT-TG distance and the tracking parameters studied, suggesting that TT-TG distance relates to patellar tracking, and a laterally positioned tibial tuberosity may predispose to instability episodes.
  
  
  METHODS
  Level IV, diagnostic study.
authors.affiliation: Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
authors.forename: Ariel A
authors.initials: AA
authors.lastname: Williams
authors.affiliation: Department of Orthopaedic Surgery, Akron General Medical Center, Akron, Ohio, U.S.A.
authors.forename: John J
authors.initials: JJ
authors.lastname: Elias
authors.affiliation: Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.; Regeneration Orthopedics, Chesterfield, Missouri, U.S.A.
authors.forename: Miho J
authors.initials: MJ
authors.lastname: Tanaka
authors.affiliation: Department of Radiology, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
authors.forename: Gaurav K
authors.initials: GK
authors.lastname: Thawait
authors.affiliation: Department of Radiology, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
authors.forename: Shadpour
authors.initials: S
authors.lastname: Demehri
authors.affiliation: Department of Radiology, The Johns Hopkins University, Baltimore, Maryland, U.S.A.
authors.forename: John A
authors.initials: JA
authors.lastname: Carrino
authors.affiliation: Department of Orthopaedic Surgery, The Johns Hopkins University, Baltimore, Maryland, U.S.A.. Electronic address: editorialservices@jhmi.edu.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Cosgarea
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D061330:Multidetector Computed Tomography; D010329:Patella / Q000000981:diagnostic imaging* / Q000503:physiopathology; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology; D012189:Retrospective Studies; D013977:Tibia / Q000000981:diagnostic imaging*; D055815:Young Adult