The Effect of a Longitudinal Defect in a Long Bone on ItsTorsional Stiffness and Stress Distribution

摘要

A mechanical model of a femur mid-diaphysis with a rectangular defect in the exterior cortexwas developed with computer technique and finite element method to calculate and analyze the influenceof a longitudinal defect in a long bone on its torsional stiffness and the stress distribution. The defectwidths range from one-tenth of the femur outer diameter(0.1OD) to 0.3 OD, and defect lengths range from1 to 5OD. The result shows that defects with a length of 1OD had little influence on the femur torsionalstiffness or stress distribution. The torsional stiffness decreased most dramatically as the defect lengthincreased from 2 to 4OD. Shear stress peaked at the center of the defect. This conclusion provides animportant theoretical gist to the operative methods and the dimension control of the defect size in clinicalorthopaedics as follows: 1) If the treatment effect will not be influenced the length of the bone defectshould be made shorter than 1OD as can as possible; 2) Orthopaedic surgeons should try their best to makethe length of bone defect shorter than 2-3OD. A long defect had better be made into two shorter defects andthere is a 0.5cm-long normal cortex in the middle of them if patient’s condition is not allowed. 3) If thewidth of the defect exceeds 0.3OD, the length of defect should be controlled within 2 OD. 4) In order to getrid of the stress concentration, the shape of defect should be made curved instead of rectangular. 5) Thisconclusion prompt that a longitudinal defect in a long bone influences its torsional stiffness dramatically,so the affected limb should not bear torsional stress after operation for fear bone fracture.