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Sagittal patellar flexion angle: a novel clinically validated patellar height measurement reflecting patellofemoral kinematics useful throughout knee flexion

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Knee Surgery, Sports Traumatology, Arthroscopy Aims and scope

Abstract

Purpose

Patellar height measurements on lateral radiographs are dependent on knee flexion which makes standardisation of measurements difficult. This study described a plain radiographic measurement of patellar sagittal height which reflects patellofemoral joint kinematics and can be used at all degrees of flexion.

Methods

The study had two parts. Part one involved 44 normal subjects to define equations for expected patellar position based on the knee flexion angles for three new patellar height measurements. A mixed model regression with random effect for individual was used to define linear and polynomial equations for expected patellar position relating to three novel measurements of patella height: (1) patellar progression angle (trochlea), (2) patellar progression angle (condyle) and (3) sagittal patellar flexion. Part two was retrospective and involved applying these measurements to a surgical cohort to identify differences between expected and measured patellar position pre- and post-operatively.

Results

All three measurements provided insight into patellofemoral kinematics. Sagittal patellar flexion was the most useful with the least residual error, was the most reliable, and demonstrated the greatest detection clinically.

Conclusions

Clinically applied radiographic measurements have been described for patellar height which reflect the sagittal motion of the patella and can be used regardless of the degree of flexion in which the radiograph was taken. The expected sagittal patellar flexion linear equation should be used to calculate expected patellar height.

Level of evidence

IV.

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Acknowledgements

We would like to acknowledge and thank Debby Chambers, Dianna Dunn and Jil Wood for coordinating access to patient data and imaging facilities. To Sonya Fisher who gave up time to perform radiographs for part 1 of the study.

Funding

There was no funding for this project.

Author information

Authors and Affiliations

  1. Surgical and Orthopaedic Research Laboratory, Prince of Wales Hospital, Prince of Wales Clinical School, University of NSW, Barker St, Randwick, 2052, NSW, Australia

    Michael J. Dan, William C. H. Parr, Nancy Briggs & William R. Walsh

  2. Royal Prince Alfred Hospital, Sydney, NSW, Australia

    James McMahon

  3. Sydney Knee Specialists, Kogarah, NSW, Australia

    Samuel MacDessi

  4. Lingard Hospital, Merewether, Australia

    Bruce Caldwell

Authors
  1. Michael J. Dan
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  2. James McMahon
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  3. William C. H. Parr
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  5. Samuel MacDessi
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  6. Bruce Caldwell
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  7. William R. Walsh
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Corresponding author

Correspondence to Michael J. Dan.

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The author(s) declare that they have no competing interests.

Ethical approval

The study was done in agreement with the ethical standards of the University of NSW ethics committee (ID HC180217) and in line with the 1964 Helsinki declaration.

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Dan, M.J., McMahon, J., Parr, W.C.H. et al. Sagittal patellar flexion angle: a novel clinically validated patellar height measurement reflecting patellofemoral kinematics useful throughout knee flexion. Knee Surg Sports Traumatol Arthrosc 28, 975–983 (2020). https://doi.org/10.1007/s00167-019-05611-2

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  • DOI: https://doi.org/10.1007/s00167-019-05611-2

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