Abstract
Multiple full-length standing anteroposterior radiographs are common practice to quantify the mechanical axis angle (MAA) in young patients with lower limb malalignment in the frontal plane treated with a temporary hemiepiphysiodesis.Is it possible to predict the MAA measured with gold-standard radiographs from a non-invasive method using the marker-based motion capture technique in a standing position and has an increased body mass index (BMI) a negative effect on this prediction?Forty-six children and adolescents with valgus or varus malalignment of the knee were measured several times during the treatment period. In total 175 data sets were evaluated in this prospective study. BMI was included into the linear mixed effect regression to detect the influence of this variable on the prediction model. Bland and Altman plots were obtained to examine methods’ agreement.The X-ray-based MAA highly correlated (r = 0.808, p < 0.001) with the marker-based MAA. The association between measurements was stronger in patients with a BMI < 25 (r = 0.881, p < 0.001) than in patients with a BMI ≥ 25 (r = 0.747, p < 0.001). The Bland and Altman plots illustrated a better agreement between both methods for patients with a BMI < 25 (bias of 0.7°) than for patients with a BMI ≥ 25 (bias of 3.7°).Determination of frontal plane lower limb alignment using motion capture technique is an alternative method to assess the MAA non-invasively. The approach is therefore relevant for clinical and scientific use when cumulative radiation dosage becomes a problem or when radiation may be prohibited (e.g. healthy control group). A higher BMI overestimates the valgus malalignment in the motion capture method which may result from excess body tissue and the difficulty in palpating bony landmarks on the skin.
Published Version
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