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Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment

  • Lukas JudEmail author
  • Tudor Trache
  • Timo Tondelli
  • Philipp Fürnstahl
  • Sandro F. Fucentese
  • Lazaros Vlachopoulos
KNEE
  • 4 Downloads

Abstract

Purpose

Flexion and rotation of the knee joint are supposed to alter the measurement of the mechanical leg axis on long leg radiographs. However, in patients with varus or valgus alignment it has not been systematically analyzed so far. The hypothesis is that measurement of the mechanical leg axis is more influenced by flexion and rotation in presence of varus or valgus alignment compared to patients with a straight coronal alignment.

Methods

3D surface models of the lower extremities of seven individuals with varying degrees of coronal alignment were created based on CT data. The coronal alignment of the seven individuals captured the range between 9° varus and 9° valgus with equal steps of 3°. Combinations of internal and external rotations of 10°, 20°, and 30° with flexion of 5°, 10°, 15°, 20°, and 30° were simulated. The mechanical leg axis was measured for each combination as the antero-posterior (ap)-projected hip–knee–ankle (HKA-) angle.

Results

294 simulations with all combinations of rotation and flexion were performed. Ranges of deviation of HKA never showed a critical deviation of more than 3° from median values. Deviations from baseline appeared normally distributed for all flexion and rotation combinations (p < 0.05) and the probability for a deviation from the mean mechanical leg axis of more than 3° was less than 0.03 for all combinations. Comparability of the models, therefore, could be assumed.

Conclusion

Deviations in HKA-angle measurements, caused by rotation or flexion, does not vary relevantly through the range of coronal alignment of 9° varus to 9° valgus. As a clinical relevance, deviations in HKA-angle measurements can be considered as comparable in patients with different coronal alignment.

Level of evidence

III.

Keywords

Mechanical leg axis Hip–knee–ankle-angle Coronal malalignment Realignment surgeries Knee osteotomy Knee arthroplasty Total knee replacement 

Notes

Funding

There is no funding source.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

The local ethical committee approved this study (Zurich Cantonal Ethics Commission, 2018-02242).

Informed consent

All patients gave their informed consent for their participation in and the publication of this study.

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Copyright information

© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2019

Authors and Affiliations

  1. 1.Department of Orthopedics, Balgrist University HospitalUniversity of ZurichZurichSwitzerland
  2. 2.Computer Assisted Research and Development Group (CARD), Balgrist University HospitalUniversity of ZurichZurichSwitzerland

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