An Anatomic Study on Whether the Patella is Centered in an Ideal Anteroposterior Radiograph of the Knee

HSS Journal Online First Article

Ademola A. Ajuwon, MD

School of Medicine, Case Western Reserve University, Cleveland, OH

Ronak Desai, MD

Case Western Reserve University, Cleveland, OH

Kathleen Farhang, BS

School of Medicine, Case Western Reserve University, Cleveland, OH

Colin E. Lasko

School of Biomedical Engineering, Case Western Reserve University, Cleveland, OH

Raymond W. Liu, MD

Orthopaedic Surgery, Rainbow Babies and Children's Hospital at Case Western Reserve University, Cleveland, OH



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.


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.


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.


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.


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.

This Online First article was published online in December 2014.
View the full HSS Journal article at

About the HSS Journal

HSS Journal, an academic peer-reviewed journal published three times a year, February, July and October. The Journal accepts and publishes peer reviewed articles from around the world that contribute to the advancement of the knowledge of musculoskeletal diseases and disorders.


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