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A novel method for determining sagittal pediatric patellar height with the Blumensaat-Epiphyseal Containment of the Knee Angle

Beck, Jennifer J.a,b; Boguszewski, Daniel V.a; Joshi, Nirav B.a; Cheung, Edward C.a; Bowen, Richard E.a,b; Oppenheim, William L.a,b

Journal of Pediatric Orthopaedics B: November 2018 - Volume 27 - Issue 6 - p 510–515
doi: 10.1097/BPB.0000000000000527

Defining normal pediatric patellar height is complicated. Current methods use ratios calculated from lateral radiographs, but often provide inconsistent results and are time-consuming. It has been observed that the angle formed by Blumensaat’s line and the distal femoral physis, when extended, form an area of patellar containment throughout a range of knee flexion. Deemed the Blumensaat-Epiphyseal Containment of the Knee (BECK) Angle, the objective of this study was to investigate this as a simple alternative to identify normal pediatric patellar height. Lateral radiographs were taken every 15° from 0° to 90° flexion on 10 fresh-frozen cadaveric knees. Patellar height was measured as the percentage of pole-to-pole patellar length contained within the BECK angle. The method was then applied to normal lateral radiographs of 105 pediatric knees, divided into age groups of 7–9, 10–12, and 13–16 years old. BECK angle patellar containment was compared with previously described methods. For cadaveric specimens, at least 50% patellar containment occurred between 0° and 71° flexion without quadriceps tension and between 21° and 81° flexion with 30 N of quadriceps tension. For pediatric radiographs, flexion ranged from 9° to 81°. At least 50% patellar containment occurred in 96% of knees in all three age groups. Knee flexion fell within a range of 15°–60° in 92 of the 105 pediatric knees. Limiting the analysis to this range, at least 50% patellar containment occurred in 99% of knees in all three age groups. On the basis of this study, normal pediatric knee lateral radiographs between 15° and 60° flexion should show at least 50% patellar containment within the BECK angle. Level of Evidence: Diagnostic Level II study.

aDepartment of Orthopedic Surgery, University of California Los Angeles

bOrthopaedic Institute for Children, Los Angeles, California, USA

Correspondence to Jennifer J. Beck, MD, Orthopedic Institute for Children, 403 W Adams Blvd, Los Angeles, CA 90007, USA Tel: +1 213 741 1122; fax: +1 213 741 8324; e-mail:

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