FABRICATION AND ANALYSIS OF AN ARTICIAL HUMAN HIP JOINT FOR SQUAT POSTURE

Abstract

The bone is highly adaptive to habitual loading, regulating its structure according to components of its loading regime and mechanical environment, inclusive of strain magnitude - strain rate - strain frequency - strain distribution and deformation. Certainly, the greatest forces usually applied to bone, arise from muscular contractions. Indeed, in the past three decades have seen substantial advances in our understanding of “how these forces shape bone throughout life”. It is essential to estimate the strength of the bone to realize the fact that, the capacity/capability of bone and its joints under different configurations of human body viz., different activities, dissimilar weights, altered postures, etc., is limited. The human bones possess different strengths like mechanical elements and linkages, under different configurations i.e., the shoulder joint, hip joint, femur bone, knee joint, tibia, etc., would have different load carrying capacities. The load carrying capacities are described by the bone strength. In addition to the bone strength, it is also essential to understand the mechanical failures of human bones. This background helps the implant designer to have better understanding of types of failure and causes of failure, in context to human subjects. The compatibility and feasibility of fixing the implant is always being challenge to the implant designer in context to the human subjects, whether it can retain to its original mobility and strength with specified geometry. The strength of a bone is described the stresses induced under different load. Therefore, the present study is focused to evaluate the stresses induced in the femur bone with different combination of body weight, length of bone, and body postures. The numerical analysis has been done on the femur bone to investigate the stress distribution along the length of the femur bone. The femur bone is numerically investigated under the five familiar configurations obtained while performing successful deep squat. The bone properties are taken close to the human bone properties in the numerical analysis. The maximum deformation is observed at the superior femur and greater trochanter for all the postures. The maximum deformation is observed for the chair posture followed by knee bend and pre-squat postures. It could be due to the change of nature of axial and translating force components at contact surface of femur head inside the acetabulum cup. The location of maximum stress in the femur bone vary based on the body posture. This non-uniform distribution of the stress along the femur bone is due to irregular geometry, the change of bone properties and the physical configuration of the femur bone viz., one end fixed and other is loaded. The maximum stress is observed at the “medial epicondyle” under the ii standing posture. The knee-bend posture exhibits the maximum stress at the “patellar surface - close to lateral epicondyle”. The maximum stress is observed at the “patellar surface – close to medial epicondyle” under the chair posture. The maximum stress is observed at the “patellar surface - close to lateral epicondyle” under the chair posture. The maximum stress is observed at the “intercondylar fossa - just above the lateral condyle” under the chair posture. The dry bone has been investigated experimentally to reveal the stress distribution along the femur bone as well as to estimate the stresses in critical locations of pelvis bone. The variation of stress with respect to body mass is noted to be independent. The higher body mass results high stress. The stress behavior with respect to the strain gauge location for critical body postures would be as follows. 𝜎𝑆𝐺4 < 𝜎𝑆𝐺2 < 𝜎𝑆𝐺3 < 𝜎𝑆𝐺1; #𝑠𝑡𝑎𝑛𝑑𝑖𝑛𝑔 𝑝𝑜𝑠𝑡𝑢𝑟𝑒; 𝜎𝑆𝐺3 < 𝜎𝑆𝐺2 < 𝜎𝑆𝐺4 < 𝜎𝑆𝐺1; #𝑘𝑛𝑒𝑒 𝑏𝑒𝑛𝑑 𝑝𝑜𝑠𝑡𝑢𝑟𝑒; 𝜎𝑆𝐺3 < 𝜎𝑆𝐺2 < 𝜎𝑆𝐺4 < 𝜎𝑆𝐺1; #𝑐ℎ𝑎𝑖𝑟 𝑝𝑜𝑠𝑡𝑢𝑟𝑒; 𝜎𝑆𝐺3 < 𝜎𝑆𝐺2 < 𝜎𝑆𝐺4 < 𝜎𝑆𝐺1; #𝑝𝑟𝑒 − 𝑠𝑞𝑢𝑎𝑡 𝑝𝑜𝑠𝑡𝑢𝑟𝑒; 𝜎𝑆𝐺3 < 𝜎𝑆𝐺2 < 𝜎𝑆𝐺4 < 𝜎𝑆𝐺1; #𝑑𝑒𝑒𝑝 − 𝑠𝑞𝑢𝑎𝑡 𝑝𝑜𝑠𝑡𝑢𝑟𝑒; A mathematical model has been developed to predict the stress variation in the femur bone while performing the successful deep squat. The magnitude of stress is relatively high in pre-squat posture while performing successful squat as well as standing activity. It is evident that, the stresses in femur head are insignificant as compared to the shank and neck portions of the femur bone. The neck portion experiences high stress as compared to femur shaft and femur head portions. In all three zones of the femur bone the compressive or tensile stress is noticed to be increased with the knee flexion till presquat posture. Further, the extension of the knee i.e., the standing-up activity exhibits more compressive or tensile stress than the sitting-down activity. The deep squat posture exhibits less stress as compared to pre-squat posture. On the other hand, the nature of the stress was also evaluated for complete duty cycle. When the knee flexion varies from 0 to 90°, the femur bone experiences compression stress. While the remaining portion from 90° to 155°, the femur bone experiences tensile stress.