title: Magnetic resonance imaging analysis of rotational alignment in patients with patellar dislocations.
abstract: BACKGROUND
  The role of anatomic risk factors in patellofemoral instability is not yet fully understood, as they have been observed in patients either alone or in combination and in different degrees of severity.
  
  
  OBJECTIVE
  To prospectively analyze rotational limb alignment in patients with patellofemoral instability and in controls using magnetic resonance imaging (MRI).
  
  
  METHODS
  Cross-sectional study; Level of evidence, 3.
  
  
  METHODS
  Thirty patients (mean age, 22.9 y; range, 12-41 y) with a history of patellar dislocation and 30 age- and sex-matched controls (mean age, 25.2 y; range, 16-37 y) were investigated. The patients underwent MRI of the leg at 1.5 T using a peripheral angiography coil and a T2-weighted half-Fourier acquisition single-shot turbo spin echo (HASTE) sequence for measuring femoral antetorsion, tibial torsion, knee rotation, and mechanical axis deviation (MAD). The mean values of these parameters were compared between patients and controls. In addition, the patients underwent an assessment to determine the influence of rotational limb alignment on lateral trochlear inclination, trochlear facet asymmetry, trochlear depth, Insall-Salvati index, and tibial tuberosity-trochlear groove distance.
  
  
  RESULTS
  Patients had 1.56-fold higher mean femoral antetorsion (20.3° ± 10.4° vs 13.0° ± 8.4°; P < .01) and 1.6-fold higher knee rotation (9.4° ± 5.0° vs 5.7° ± 4.3°; P < .01) compared with controls. Moreover, patients had 2.9 times higher MAD (0.81 ± 0.75 mm vs -0.28 ± 0.87 mm; P < .01). Differences in tibial torsion were not significant. Also, there were no significant correlations between parameters of rotational alignment and standard anatomic risk factors.
  
  
  CONCLUSIONS
  Our results suggest that some patients with nontraumatic patellar instability have greater internal femoral rotation, greater knee rotation, and a tendency for genu valgum compared with healthy controls. Rotational malalignment may be a primary risk factor in patellar dislocation that has so far been underestimated.
authors.affiliation: Department of Radiology, Charité-Universitätsmedizin Berlin, Campus Charité Mitte, Germany. gerd.diederichs@charite.de
authors.forename: Gerd
authors.initials: G
authors.lastname: Diederichs
authors.forename: Torsten
authors.initials: T
authors.lastname: Köhlitz
authors.forename: Evgenios
authors.initials: E
authors.lastname: Kornaropoulos
authors.forename: Markus O
authors.initials: MO
authors.lastname: Heller
authors.forename: Bernd
authors.initials: B
authors.lastname: Vollnberg
authors.forename: Sven
authors.initials: S
authors.lastname: Scheffler
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D031222:Patellar Dislocation / Q000473:pathology / Q000503:physiopathology*; D057071:Patellofemoral Joint / Q000473:pathology / Q000503:physiopathology*; D012399:Rotation; D055815:Young Adult