title: Evaluation of a modified knee rotation angle in MRI scans with and without trochlear dysplasia: a parameter independent of knee size and trochlear morphology.
abstract: OBJECTIVE
  Regarding TT-TG in knee realignment surgery, two aspects have to be considered: first, there might be flaws in using absolute values for TT-TG, ignoring the knee size of the individual. Second, in high-grade trochlear dysplasia with a dome-shaped trochlea, measurement of TT-TG has proven to lack precision and reliability. The purpose of this examination was to establish a knee rotation angle, independent of the size of the individual knee and unaffected by a dysplastic trochlea.
  
  
  METHODS
  A total of 114 consecutive MRI scans of knee joints were analysed by two observers, retrospectively. Of these, 59 were obtained from patients with trochlear dysplasia, and another 55 were obtained from patients presenting with a different pathology of the knee joint. Trochlear dysplasia was classified into low grade and high grade. TT-TG was measured according to the method described by Schoettle et al. In addition, a modified knee rotation angle was assessed. Interobserver reliability of the knee rotation angle and its correlation with TT-TG was calculated.
  
  
  RESULTS
  The knee rotation angle showed good correlation with TT-TG in the readings of observer 1 and observer 2. Interobserver correlation of the parameter showed excellent values for the scans with normal trochlea, low-grade and high-grade trochlear dysplasia, respectively. All calculations were statistically significant (p < 0.05).
  
  
  CONCLUSIONS
  The knee rotation angle might meet the requirements for precise diagnostics in knee realignment surgery. Unlike TT-TG, this parameter seems not to be affected by a dysplastic trochlea. In addition, the dimensionless parameter is independent of the knee size of the individual.
  
  
  METHODS
  II.
authors.affiliation: Department of Orthopedics, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany. daniel.dornacher@uni-ulm.de.
authors.forename: Daniel
authors.identifier: http://orcid.org/0000-0001-5275-2894
authors.initials: D
authors.lastname: Dornacher
authors.affiliation: Department of Orthopedics, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: Angela
authors.initials: A
authors.lastname: Trubrich
authors.affiliation: Department of Traumatology, Hand and Reconstructive Surgery, University of Ulm, Albert-Einstein-Allee 23, 89081, Ulm, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Guelke
authors.affiliation: Department of Orthopedics, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Reichel
authors.affiliation: Department of Orthopedics, University of Ulm, Oberer Eselsberg 45, 89081, Ulm, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kappe
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D005269:Femur / Q000002:abnormalities / Q000000981:diagnostic imaging*; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology; D007719:Knee Joint / Q000002:abnormalities / Q000000981:diagnostic imaging*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D031222:Patellar Dislocation / Q000000981:diagnostic imaging* / Q000503:physiopathology; D057071:Patellofemoral Joint / Q000000981:diagnostic imaging*; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Correlation; Knee realignment surgery; Knee rotation angle; TT–TG; Trochlear dysplasia