[Finite element analysis on fracture relevance as bone defect of proximal femur]

Based on establishment three-dimensional finite element models with the different defects of proximal femur, analysis of the local stress and strain changes under normal walking condition, speculate the probable rang of fracture and provide a theoretical basis for clinical work.

By CT scanning the whole femur, establish Three-dimensional finite element models were established with analogous to the loaded lower extremity under normal walking condition. The stress distribution of the zone of lesser trochanter, intertrochanter and femur neck were analyzed.

(1) To the defects of lateral cortex of proximal femur at lesser trochanter level, defect of 5%-25%, the local maximum stress were up to 96.74-179.10 MPa. When the defect was greater than 10%, the local maximum was greater than the ultimate stress 141 MPa. While, the stresses of medial femur were 46.15-62.13 MPa, which was much lower than that of yielding stress. (2) At the level of intertrochanter with 5%-25% defect, the stresses were 45.70-127.11 MPa, all of them were lower than that of the ultimate stress. Whereas the changes of stress of medial femur were as the same as the stress at lesser trochanter level. (3) When the intramedullary defect of femur neck not involving inner cortex was less 40%, the local stress was lower than yielding stress 93 MPa. When the defects were 45% and 50%, the local maximum stress were up to 100.20 MPa and 119.40 MPa. (4) While intramedullary defects of femur neck involving half of medial cortex were 15%-50%, the stress were 87.79-1207.40 MPa. When the defects were above the level of 45%, the local maximum is greater than 141 MPa.

The defects in lateral cortex of proximal femur has little influence on the medial cortex at the same level. And have little influence on the strength of femur; If defects located in the lateral cortex of lesser trochanter, 5% was relative safe, 5%-10% was at the risk of fracture, and defects larger than 10% would result in fracture. When defects located in the lateral femur at the level of intertrochanter area, 20% was relative safe, but defects larger than 25% would have the risk of fracture. If intramedullary defects in femur neck was smaller than 45% and not involved inner cortex, it was believed safe. When intramedullary defects in femur neck involved half of cortex, it was relatively safe below 20%, 20%-40% was at the risk of fracture, and larger than 40% resulted in fracture.