title: Imaging characteristics of contralateral asymptomatic patellofemoral joints in patients with unilateral instability.
abstract: OBJECTIVE
  To test the hypothesis that in patients with unilateral patellofemoral instability ( PI patellofemoral instability ), the contralateral asymptomatic joints have abnormal morphology and imaging features of osteoarthritis ( OA osteoarthritis ) at four-dimensional ( 4D four-dimensional ) computed tomography (CT).
  
  
  METHODS
  The institutional review board approved this HIPAA-compliant retrospective study. Informed consent was waived. Radiology records were reviewed to identify 25 patients (male-female ratio, 0.56; median age, 20 years; range, 13-43 years) with unilateral PI patellofemoral instability undergoing 4D four-dimensional CT and 25 age- and sex-matched control patients undergoing multidetector CT. Trochlear groove depth ( TGD trochlear groove depth ), tibial tuberosity-trochlear groove ( TT-TG tibial tuberosity-trochlear groove ) distance, and patellar height ratio ( PHR patellar height ratio ) were determined to compare morphology, and bisect offset ( BO bisect offset ) measurements were obtained to compare lateral displacement of the patella between the two groups by using the Wilcoxon rank-sum test. All images were interpreted by trained observers. Tracking patterns of the patellae were determined by obtaining BO bisect offset measurements at various flexion angles with 4D four-dimensional CT.
  
  
  RESULTS
  In the contralateral asymptomatic joints, TGD trochlear groove depth (median, 3.0 mm; 95% confidence interval [ CI confidence interval ]: 2.5, 4.6; P < .0001), TT-TG tibial tuberosity-trochlear groove (median, 15 mm; 95% CI confidence interval : 12.7, 18; P = .008), PHR patellar height ratio (median, 1.17; 95% CI confidence interval : 1.09, 1.2; P = .002), and patellar lateral displacement ( BO bisect offset , 85%; 95% CI confidence interval : 76.2%, 98.2%; P < .0001) were different from measurements obtained in the control group: TGD trochlear groove depth median, 5.0 mm (95% CI confidence interval : 2.2, 7.6); TT-TG tibial tuberosity-trochlear groove median, 10.9 mm (95% CI confidence interval : 3.4, 20.7); PHR patellar height ratio median, 0.92 (95% CI confidence interval : 0.67, 1.36); and BO bisect offset median, 63% (95% CI confidence interval : 59%, 68.4%). OA osteoarthritis was detected in 40% of asymmetrical contralateral joints (10 of 25). By using 4D four-dimensional CT data, multiple regression analysis demonstrated that TGD trochlear groove depth (P = .026) and BO bisect offset measurements obtained at 30° of knee flexion (P = .047) had an association with the presence of OA osteoarthritis .
  
  
  CONCLUSIONS
  Abnormal morphology and imaging features of OA osteoarthritis are relatively common in contralateral asymptomatic joints of young patients with unilateral PI patellofemoral instability .
authors.affiliation: From the Russell H. Morgan Department of Radiology and Radiological Science (S.D., G.K.T., J.A.C.) and Department of Orthopaedic Surgery (A.A.W., A.J.C.), Johns Hopkins University School of Medicine, 601 N Caroline St, JHOC 5165, Baltimore, MD 21287; Department of Radiology, Boston University School of Medicine, Boston, Mass (A.K.); and Department of Biomedical Engineering, Akron General Medical Center, Akron, Ohio (J.J.E.).
authors.forename: Shadpour
authors.initials: S
authors.lastname: Demehri
authors.forename: Gaurav K
authors.initials: GK
authors.lastname: Thawait
authors.forename: Ariel A
authors.initials: AA
authors.lastname: Williams
authors.forename: Andrew
authors.initials: A
authors.lastname: Kompel
authors.forename: John J
authors.initials: JJ
authors.lastname: Elias
authors.forename: John A
authors.initials: JA
authors.lastname: Carrino
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Cosgarea
mesh_terms: D000293:Adolescent; D000328:Adult; D003430:Cross-Sectional Studies; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D008297:Male; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D011857:Radiographic Image Interpretation, Computer-Assisted; D012008:Recurrence; D012189:Retrospective Studies