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


Jud, Lukas; Trache, Tudor; Tondelli, Timo; Fürnstahl, Philipp; Fucentese, Sandro F; Vlachopoulos, Lazaros (2020). Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment. Knee surgery, sports traumatology, arthroscopy: official journal of the ESSKA, 28(10):3128-3134.

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.

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.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Balgrist University Hospital, Swiss Spinal Cord Injury Center
Dewey Decimal Classification:610 Medicine & health
Scopus Subject Areas:Health Sciences > Surgery
Health Sciences > Orthopedics and Sports Medicine
Language:English
Date:1 October 2020
Deposited On:09 Jan 2020 09:40
Last Modified:24 Sep 2020 01:02
Publisher:Springer
ISSN:0942-2056
OA Status:Closed
Publisher DOI:https://doi.org/10.1007/s00167-019-05779-7
PubMed ID:31705148

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