Abstract: Objective To analyze mechanical stability of human pelvis and to provide the pelvic surgery with biomechanical data.Methods six cadaveric specimens of the L3 to the proximal 1/3 part of femur were used and fixed on a custom experimental rig.The specimens had no structural abnormality and partial soft tissues were dissected,reserving the hip joint capsules and the ligaments of the pelvic ring.Markers with black dots against white background were used to mark the kinematic key points of the pelvis.Axial loadings from the L3 were applied by material testing machine in the gradient of 0 N to 500 N.Images of the front and lateral views were obtained using two Charge Coupled Device (CCD) cameras.Based on Image J software,relative distance of L5,the abduct degree in coronal plane and rotational degree in vertical plane were calculated by measuring the marker’s movement.Results Under a vertical loading of 500 N,the average relative distance of L5 was 1.157±0.794 mm,the average abduct degree in coronal plane was 0.370±0.260° and the average rotational degree in vertical plane was 1.051±1.728°.Conclusion Human pelvis shows optimal mechanical stability according to the displacement calculation of pelvic specimen,digital marker tracing method and the center-of-mass algorithm method are applied in combination.

Key words: Marker, Tract-Trace, Center of mass, Image J software, Pelvis, Stability