Mathematical models in the evaluation of weight distribution asymmetry in lower limbs: Implication for practice
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School of Rehabilitation, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia
Department of Orthopedic and Traumatology, Faculty of Medicine, University Kebangsaan Malaysia Medical Centre, Kuala Lumpur, Malaysia
Baharudin Omar   

Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia. Tel.: +60 176996429.
Submission date: 2016-04-27
Acceptance date: 2016-08-16
Online publication date: 2016-11-10
Publication date: 2019-12-19
Pol. Ann. Med. 2017;24(2):148–152
Mathematical models quantify asymmetry in weight distribution on bilateral lower limbs using indexes or ratios.

This study investigates the efficacy of mathematical models to evaluate weight distribution asymmetry in healthy and different clinical populations.

Material and methods:
This cross-sectional study recruited 188 participants (149 healthy, 27 stroke and 12 unilateral total knee replacement) through convenience sampling for this study. Two digital weighing scales were used to capture the loading on bilateral lower limbs. The data is further computed with different mathematical models.

Results and discussion:
The symmetry index model has problems of inflation with increasing asymmetry values. Symmetry ratio model exhibits low sensitivity to differences in weight distribution, and did not provide the magnitude and direction of absolute weight distribution asymmetry. The direction of the asymmetry is not meaningful from the symmetry angle model, and it fails to predict factual asymmetry values.

Modified symmetry index has better sensitivity to differences in bilateral lower limb weight distribution and is able to quantify the extent of asymmetries and identifies the side of asymmetry. Based on the study results, we suggest the application of the mathematical models to quantify limb loading in the following order: modified symmetry index, symmetry index, symmetry angle, and symmetry ratio for clinical or research practice.

We thank Dr. Leonard Henry Joseph for his guidance and assistance with study administration. Ministry of higher education fund supported this study – ERGS grant (ERGS/1/ 2013/SKK10/UKM/02/2[70TD$DIF]). The grant funding had no role in the study design, data collection, analysis, or writing of this manuscript.
None of the authors have a potential conflict of interest related to the manuscript or the work it describes.
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