title: Variability of Measurement of Patellofemoral Indices with Knee Flexion and Quadriceps Contraction: An MRI-Based Anatomical Study.
abstract: OBJECTIVE
  The purpose of this study was to investigate the impact of varying knee flexion and quadriceps activity on patellofemoral indices measured on magnetic resonance imaging (MRI).
  
  
  METHODS
  MRI of the knee was performed in 20 patients for indications other than patellar or patellofemoral pathology. Axial and sagittal sequences were performed in full extension of the knee with the quadriceps relaxed, full extension of the knee with the quadriceps contracted, 30° flexion of the knee with the quadriceps relaxed, and 30° flexion with the quadriceps contracted. Bisect offset, patella tilt angle, Insall-Salvati ratio and Caton-Deschamps index were measured.
  
  
  RESULTS
  With the knee flexed to 30° and quadriceps relaxed, the mean values of patellar tilt angle, bisect offset, Insall-Salvati ratio and Caton-Deschamps index were all within normal limits. With the knee extended and quadriceps contracted, the mean patellar tilt angle (normal value, <15°) was 14.6° and the bisect offset (normal value, <65%) was 65%, while the Caton-Deschamps index was 1.34 (normal range, 0.6 to 1.3). With the knee extended and quadriceps relaxed, the mean Caton-Deschamps index was 1.31.
  
  
  CONCLUSIONS
  MRI scanning of the knee in extension with the quadriceps contracted leads to elevated patellofemoral indices. MRI taken with the knee in 30° of flexion allows more reliable assessment of the patellofemoral joint and minimises the confounding effect of quadriceps contraction.
authors.affiliation: Department of Orthopaedics, Royal Orthopaedic Hospital, Birmingham, UK.
authors.forename: Edward
authors.initials: E
authors.lastname: Laugharne
authors.affiliation: Department of Orthopaedics, Royal Orthopaedic Hospital, Birmingham, UK.
authors.forename: Navi
authors.initials: N
authors.lastname: Bali
authors.affiliation: Department of Orthopaedics, Walsall Manor Hospital, Walsall, UK.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Purushothamdas
authors.affiliation: Department of Orthopaedics, Walsall Manor Hospital, Walsall, UK.
authors.forename: Faris
authors.initials: F
authors.lastname: Almallah
authors.affiliation: Department of Orthopaedics, Walsall Manor Hospital, Walsall, UK.
authors.forename: Rik
authors.initials: R
authors.lastname: Kundra
keywords: Instability; Magnetic resonance imaging; Malalignment; Patellofemoral