Obesity-specific joint center estimation in gait analysis

Gait analysis aims at gathering quantitative information about the mechanics of the musculo-skeletal system during the execution of a motor task. Typically, in gait analysis, variables such as kinematics, joint moments, and powers are determined. This information is used to evaluate pathological gait patterns. Errors in locating the three-dimensional (3D) position of the hip joint center (HJC) can strongly affect the calculation of typical clinical 3D gait analysis variables. This consequentially leads to incorrect interpretations. The problem of inaccuracy in HJC location increases significantly in patients where bony landmarks are difficult to identify, such as in obese or overweight participants. Nevertheless, gait analysis remains as the state of the art method for clinicians as well as for research purpose. Often medical imaging-based methods are recommended to identify the 3D HJC localization. However, these methods typically expose patients to radiation and are often expensive and time- consuming due to long post-processing times. To estimate the position of the HJC several none- invasive predictive methods, based on experimental data, and functional models were introduced to gait analysis in recent years. Research has attempted to determine which of these methods best determine the HJC most accurately in various populations. Among those, only a few studies recruited children or clinically diagnosed patients. To date, no study aimed at identifying the accuracy of the proposed HJC location methods in a population of overweight or obese children and adolescents. However, all currently available non-invasive methods are strongly affected by the amount of subcutaneous fat present (wobbling mass), thus great inaccuracies are introduced. A study to identify how well existing HJC estimation methods work for this very specific population is strongly recommended. Therefore, the primary aim of this study is to evaluate and to compare current non- invasive HJC estimation methods for clinical 3D gait analysis in a population of overweight children and adolescents. In addition, new approaches will be evaluated and tested. Consequentially this may increase the accuracy and reliability of clinical gait analysis in overweight patients.

Gait analysis aims at gathering quantitative information about the mechanics of the musculo- skeletal system during locomotion. Typically, in gait analysis, variables such as kinematics, joint moments, and powers are determined. This information is used to evaluate pathological gait patterns. Errors in locating the three-dimensional (3D) position of the hip joint center (HJC) can strongly affect the calculation of 3D gait analysis variables. This consequentially leads to incorrect interpretations. The problem of inaccuracy in HJC location increases significantly in patients where bony landmarks are difficult to identify, such as in overweight or obese populations. The primary aim of this project was to evaluate the accuracy of current non- invasive HJC estimation methods for clinical 3D gait analysis in a population of overweight or obese children and adolescents. The project followed a two -fold approach: Firstly, we have evaluated the utility of 3D free-hand ultrasound (3DFUS) to register anatomical landmarks at the pelvis and localize the hip joint center in a cohort of 16 lean and 19 obese individuals. Our data supported the idea that 3DFUS can serve as a tool to inform marker placement and hip joint center location, especially in groups with higher amount of body fat. Secondly, we investigated the most accurate method for estimating the HJC in clinical 3D gait analysis for young individuals with high amounts of soft tissue. We compared the HJC locations identified with five regression-based and two functional methods to the HJC position obtained through 3DFUS in a cohort of 14 overweight or obese individuals. Our results suggest that regression- based methods are preferable to functional methods in this population, as the latter demonstrated the highest variability in accuracy with high errors for some individuals. Based on our findings we recommend using the regression method presented by Hara et al. due to its superior overall accuracy of less than 9 mm on average in all planes compared to 3DFUS and the lowest impact on kinematic and kinetic output variables. We do not recommend using the Harrington equations (single and multiple) as they require pelvic depth as input, which can be massively biased when a lot of soft tissue is present around the pelvis. Based on the results obtained in this project, we provide recommendations for which methods serve best to estimate the HJC position in individuals with overweight or obesity. This information serves as a guide for clinicians and researcher who seek to conduct clinical 3D gait anaylsis in a population where gait anaylsis is generally difficult due to the presence of a lot of soft tissue artifacts.