Abstract:

BACKGROUND: Finite element technology is a digital simulation of the real stress situation; however, photoelastic technology can truly display the overall stress distribution of the test model.
OBJECTIVE: To make the pelvis photoelastic model by laser rapid prototyping technology, and then to investigate the stress distributions of the pelvis under normal gait loading conditions by three-dimensional photoelastic analysis and to compare the result with that gained by the finite element method.
METHODS: The pelvic potoelastic model was made by laser rapid prototyping technology, including the fifth lumbar vertebrae and bilateral proximal femur. Mass loading was imposed on the femur. Four groups of muscles forces were imposed through steel wire fixed on iliac wing, anterior superior iliac spine, posterior superior iliac spine and inferior ramus of pubis. The femur was assumed to adduct for 15° and moved from flexed 22° to extend 12° during four gait phases. After stress froze, slices were cut along the arcuate line. Isochromatic lines and isoclinic lines were observed in the field of polarized light.
RESULTS AND CONCLUSION: ①Stress was concentrated on the center of ilium posterior superior roof of acetabulum, iliopubic eminence and cacroiliac joint, and the maximum stress was on the posterior superior roof of acetabulum. ② The main stress was transferred from posterior superior roof of acetabular to the cacroiliac joint and superior ramus of pubis partly. The area from roof to tubercle of the iliac crest loaded more stress with the femur extending. ③The stress on the acetabular area was mainly from the acetabular contact forces produced by mass loading, and the role of the muscle contraction force was limited. The three-dimensional photoelastic analysis could reflect distribution of stress on acetabulum. The result was in accordance with the data of finite element method.