# System for Evaluation and Compensation of Leg Length Discrepancy for Human Body Balancing
###### Abstract  
Leg Length Discrepancy (LLD) causes a shift of the Center of Mass (CoM) of the human body, as well as an asymmetry in load distribution on the lower extremities. Existing LLD evaluation methods do not take into account this shift in the human body's CoM. In this paper, a methodology and mechatronic system for the Evaluation and Compensation of LLD for Human Body Balancing are described. The human body's CoM is measured with two force plates located on two parallel manipulators. Since persons with LLD experience a shift in their CoM, by raising the force plate that is under the shorter leg, the human body can be balanced. For this purpose, the Human Body Balancing Algorithm (HBBA) was proposed and developed. By running the HBBA, the height difference between the force plates under the left and right leg can be measured, which then represents the LLD evaluation. Based on this evaluation, it is possible to design and make a shoe insole which compensates the influence of LLD with the goal of equalizing the load on the legs. A virtual mathematical model of the system was created and the simulation results of the HBBA are presented. The mechatronic system, developed and used to conduct experiments and measurements, is described in detail. leg length discrepancy; human body balancing algorithm; 3-RPS parallel manipulator; force plate; center of mass; leg load distribution +
Footnote †: journal: Applied Soft  
and methods for changing roll and pitch of moving platforms, thus allowing practitioners to determine status of functional LLD. Moreover, the mechanical design of the proposed system is based on parallel manipulators that provide a firm ground for trajectory planning and analysis of walk dynamics. Individuals with LLD have a displaced Center of Mass (CoM), which results in inefficient and energy-consuming muscle operation that causes muscle fatigue. LLD causes painful conditions due to irregular ligament stretching, inadequate joint surface loading and abnormally high loading of joint and bone structures due to the deviation of the body's CoM from the expected values. The aforementioned painful conditions frequently remain clinically unnoticed or not enough attention is paid to them, as initially they do not create significant clinical symptoms. At the moment when symptoms occur, it is necessary to take extensive measures for the purpose of improving the condition of LLD patients. Improved quality of life and alleviation of orthopedic conditions caused by LLD may be achieved by clinical and non-clinical treatments that result in equalization of leg lengths. Clinical treatments involve: slowing down or stopping the growth of the longer leg, shortening the longer leg and lengthening the shorter leg. Non-clinical methods include the application of shoe lifts and shoe insoles [6]. LLD measuring is essential for determining the required treatment for the purpose of leg length equalization. LLD measuring methods are divided into imaging methods and clinical methods. A review and comparison of LLD measuring methods may be found in [8]. Imaging methods refer to scanning the pelvis and legs, as well as computer image processing for the purpose of measuring the distance between the ankle joint and pelvis joint with very high precision. The most frequently used imaging methods for LLD measuring are: radiography, computerized tomography (CT), ultrasonography and magnetic resonance imaging (MRI) [8]. The most frequent clinical methods used for LLD measuring are tape measure and standing on blocks. Tape measure is a direct method for LLD measuring. It is used for measuring the distance between the protruding pelvis bone (anterior inferior iliac spine (ASIS)) and ankle joint (medial malleolus) (true leg length) or for measuring the distance between the belly button (umbilicus) and ankle joint (apparent leg length). Standing on blocks is an indirect method for LLD measuring. It is based on placing blocks below the shorter leg in order to level the pelvis.