Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment
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Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment Lukas Jud1 · Tudor Trache1 · Timo Tondelli1 · Philipp Fürnstahl2 · Sandro F. Fucentese1 · Lazaros Vlachopoulos1 Received: 8 August 2019 / Accepted: 28 October 2019 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2019
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
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