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

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HSS Journal ®

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.

Questions/Purposes

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.

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Disclosures

Conflict of Interest

Ademola A. Ajuwon, MD, Ronak Desai, MD and Kathleen Farhang, BS have declared that they have no conflict of interest. Colin E. Lasko reports other from ArthroCare Corp and Zimmer Inc., outside the work. Raymond W. Liu, MD reports other from Orthopediatrics LLC, outside the work.

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This article does not contain any studies with human or animal subjects performed by the any of the authors.

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Correspondence to Raymond W. Liu MD.

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Ajuwon, A.A., Desai, R., Farhang, K. et al. An Anatomic Study on Whether the Patella is Centered in an Ideal Anteroposterior Radiograph of the Knee. HSS Jrnl 11, 117–122 (2015). https://doi.org/10.1007/s11420-014-9419-3

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  • DOI: https://doi.org/10.1007/s11420-014-9419-3

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