title: Prevalence and patterns of anatomical risk factors in patients after patellar dislocation: a case control study using MRI.
abstract: OBJECTIVE
  To assess anatomical risk factors in patients after lateral patellar dislocation (LPD) and controls using MRI.
  
  
  METHODS
  MR images of 186 knees after LPD and of 186 age- and gender-matched controls were analysed. The presence of trochlear dysplasia was assessed by evaluation of trochlear inclination, facet asymmetry, and trochlear depth; patella alta was evaluated by the Insall-Salvati index and Caton-Deschamps index; the lateralised force vector was measured by the tibial tuberosity-trochlear groove (TT-TG) distance.
  
  
  RESULTS
  Compared with controls, dislocators had significantly lower values for all three parameters of trochlear dysplasia (-32 %, -32 %, -44 %) and significantly higher values for patella alta (+14 %,+13 %) and TT-TG (+49 %) (all P < 0.001). Trochlear dysplasia was observed in 112 dislocators (66 %), of whom 61 (36 %) additionally had patella alta and 15 (9 %) an abnormal TT-TG. As isolated risk factors, patella alta (15 %) and abnormal TT-TG (1 %) were rare. Only 25 dislocators (15 %) had no anatomical risk factors. Trochlear dysplasia in conjunction with abnormal TT-TG or patella alta is associated with a 37- and 41-fold higher risk.
  
  
  CONCLUSIONS
  Most dislocators have anatomical risk factors, varying in severity and constellation.
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Charité Campus Mitte, Chariteplatz 1, 10117 Berlin, Germany. toschi.home@gmail.com
authors.forename: Torsten
authors.initials: T
authors.lastname: Köhlitz
authors.forename: Sven
authors.initials: S
authors.lastname: Scheffler
authors.forename: Tobias
authors.initials: T
authors.lastname: Jung
authors.forename: Arndt
authors.initials: A
authors.lastname: Hoburg
authors.forename: Bernd
authors.initials: B
authors.lastname: Vollnberg
authors.forename: Edzard
authors.initials: E
authors.lastname: Wiener
authors.forename: Gerd
authors.initials: G
authors.lastname: Diederichs
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D007719:Knee Joint / Q000002:abnormalities* / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D031222:Patellar Dislocation / Q000453:epidemiology* / Q000473:pathology*; D015995:Prevalence; D015203:Reproducibility of Results; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D055815:Young Adult