title: An Anatomic Study on Whether the Patella is Centered in an Ideal Anteroposterior Radiograph of the Knee.
abstract: BACKGROUND
  Currently, an anteroposterior radiograph of the knee is judged based on a centered position of the patella between the femoral condyles. We are not aware of any anatomic literature supporting this recommendation.
  
  
  OBJECTIVE
  Orthogonal images are required for accurate assessment of knee deformity. Although an image with the patella centered at the distal femur is generally accepted as a true anteroposterior (AP) radiograph of the knee, there is minimal anatomic data to support that this view is orthogonal to a true lateral view of the knee where the condyles are overlapped. We designed an anatomical study to test the relationship between these two radiographic views.
  
  
  METHODS
  We studied 428 well-preserved cadaveric skeletons ranging from 40 to 79 years of age at death. Centering of the patella was calculated based on distal femoral and patellar widths. Multiple regression analysis was then performed to determine the relationship between patellar centering and age, gender, ethnicity, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), femoral anteversion, and contralateral centering.
  
  
  RESULTS
  Average patellar centering was 0.13 ± 0.04, indicating that the average patella was laterally positioned in the distal femur. Only mLDFA and contralateral centering showed statistically significant independent correlations with patellar centering with modest standardized beta coefficients of 0.10 and 0.23, respectively.
  
  
  CONCLUSIONS
  In the average specimen, the patella is laterally deviated by 13% of the condylar width. Clinicians should be aware that a lateral view with the femoral condyles overlapped is not always orthogonal to a patella-centered AP view when planning and implementing deformity correction.
authors.affiliation: School of Medicine, Case Western Reserve University, Cleveland, OH USA.
authors.forename: Ademola A
authors.initials: AA
authors.lastname: Ajuwon
authors.affiliation: Case Western Reserve University, Cleveland, OH USA.
authors.forename: Ronak
authors.initials: R
authors.lastname: Desai
authors.affiliation: School of Medicine, Case Western Reserve University, Cleveland, OH USA.
authors.forename: Kathleen
authors.initials: K
authors.lastname: Farhang
authors.affiliation: School of Biomedical Engineering, Case Western Reserve University, Cleveland, OH USA.
authors.forename: Colin E
authors.initials: CE
authors.lastname: Lasko
authors.affiliation: Orthopaedic Surgery, Rainbow Babies and Children's Hospital at Case Western Reserve University, 11100 Euclid Avenue, RBC 6081, Cleveland, OH 44106 USA.
authors.forename: Raymond W
authors.initials: RW
authors.lastname: Liu
keywords: knee alignment; knee anatomy; knee deformity analysis; knee radiographs