Analysis of Shoulder and Knee Joint Muscles using Developed CPM Machine and Finite Element Method

Abstract

Shoulder and knee joints pain, injury and discomfort are public health and economic issues world-wide. As per the Indian orthopedic association survey, there are about 50% of the patient visits to doctors' offices because of common shoulder and knee injuries such as fractures, dislocations, sprains, and ligament tears. Shoulder and knee are the most complex, maximum used and critical joints in the human body. The shoulder and knee joint muscle behaviour during different exercises is one of the major concerns to the orthopedic surgeon for analysing the exact healing and duration of the injury. Quantification of mechanical stresses and strains in the human joints and the musco-skeletal system is still a big concern for the researchers. The injury mechanisms and analysis of the post-operative progress is one of the most critical studies for orthopedic surgeons, biomechanical engineers and researchers. In the present work a classical 3D Finite Element Method (FEM) modelling technique has been used to investigate the stresses induced in the shoulder joint muscles during abduction arm movement and knee joint muscles during flexion leg movement for different range of motion. 3D model provides valuable information for analysing complex bio-mechanical systems and characterization of the joint mechanics. Reverse modelling method was used for generating fast, accurate and detailed contours of the shoulder and knee model. Scanning of the complicated shoulder and knee joint bones were made by 3D scanner (ATOS III) to generate ‘.stl’ file. Accurate and detailed 3D bone geometry of the shoulder and knee joint models was done using CATIA V5 software from the scanned ‘.stl’ file. The higher order geometrical features (curve and surfaces) were designed by filtering and aligning number of cloud points, tessellation of polygonal model, recognition and defining the referential geometrical entities. According to quadratic dependency, a non-homogeneous bone constitutive law was implemented. Different muscles were then added on the shoulder and knee joint models in CATIA V5. 3D models were then imported in ‘.igs’ format into ANSYS workbench for the stress analysis. A 3D FEM model was developed for the five important shoulder joint muscles, namely deltoid, supraspinatus, subscapularies, teres minor and infraspinatus. Thekinematics for shoulder abduction arm movement was prescribed as an input to finite element simulations and the Von Mises stresses and equivalent elastic strain in the shoulder muscles were plotted. Individual and group muscle analysis was done to evaluate the Von Mises stresses and equivalent elastic strain of the shoulder muscles during the abduction arm movement. During the individual muscle analysis, the Von Mises stresses induced in deltoid muscle was maximum (4.2175 MPa) and in group muscle analysis it was (2.4127MPa) compared to other individual four rotor cuff muscles. During the individual muscle analysis, the equivalent elastic strain induced in deltoid muscle was maximum (3.5146 mm/mm) and in group muscle analysis it was (2.0106 mm/mm) compared to other individual four rotor cuff muscles. The percentage analysis of individual muscles contribution for abduction arm movement predicted by FEM analysis was maximum (46.85%) in the deltoid muscle. The results showed that deltoid muscle was the most stressed muscle in both individual and group muscle analysis. The Surface Electromyography (SEMG) test was conducted on the shoulder prone subjects using the developed low cost shoulder Continuous Passive Motion (CPM) machine. The percentage analysis of individual muscles contribution for abduction arm movement predicted by SEMG analysis was maximum (48.15%; 46.15% and 47.05%) in the deltoid muscle. Deltoid was the most contracted (stressed) muscle observed during the SEMG analysis amongst the five shoulder muscles. The results showed by both FEM and SEMG methods that deltoid muscle was the most sensitive amongst the five shoulder joint muscles during abduction arm movement. FEM analysis was done to investigate the Von Mises stresses in two important knee joint muscles such as the rectus femoris and biceps femoris muscle during the flexion leg movement. During the muscle analysis, the Von Mises stresses induced in rectus femoris muscle was the maximum (1.5579 MPa). The results showed that rectus femoris muscle was the most stressed muscle than the biceps femoris muscle during flexion leg movement. The SEMG test was conducted on the knee prone subjects using the developed low cost knee CPM machine. The average percentage contraction (stress distribution) exhibited by SEMG analysis on the rectus femoris muscle was 70% of the totalmuscles contraction. The results by both FEM and SEMG methods showed that rectus femoris was the most stressed muscle during the flexion leg movement. The present work provides in depth information to the researchers and orthopedicians for the better understanding of the shoulder and knee joint mechanism in human anatomy. It predicts the most stressed muscle in the shoulder joint during the abduction arm movement and in the knee joint during the flexion leg movement at different range of motion.