Xin Wei Lei MD, PhD, Presenter: Nothing to Disclose

Ji Qi MD, PhD, Abstract Co-Author: Nothing to Disclose

To explore the biomechanics influences of different size necrosis on femoral head and predict the collapse of the articular surface and guide the appropriated microsurgical treatment to preserve the femoral head.

1. A detailed acetabulum-cartilage-femoral head three-dimensional finite element model (FEM) of a health volunteer was established with the aid of two software of Matlab and ANSYS 7.0 which could derive a nonlinear FEM from MRI imagings. 2.Fifty different ratio of necrosis articular surface area (NASA)to whole articular surface area(WASA) of the femoral head(5%、10％、15％、20％、25％、30％、35％、40％、45％、50%) with different depth(5mm、10mm、15mm、20mm、25mm) models were simulated. 3. Put a pressure of 2063N (equal to a normal walking pressure by a person with 75 kilogram weight) on the necrosis femoral head model and analyses the stress distribution while predict the collapse of the femoral head.

1. In normal condition, the cortical shell bore 60% of the total pressure, and the cancellous bore the rest.  2. The stress was redistribution after the development of osteonecrosis of femoral head. The enduring pressure of cortical shell will increase with the rising ratio of NASA. When the ratio of NASA reached 5%, the enduring pressure of cortical shell would occupy the 61% of total pressure, while the ratio of NASA reached 50%, the enduring pressure of cortical shell would occupy the 76% of total pressure.  3.The study demonstrated that the stress was concentrations obviously around the cortical boundary of the necrosis portion especially when the ratio of NASA was 25% or more. The depth of the lesion has no obvious influence on the load-bearing of cortical shell at the same ratio of NASA.  

The necrosis of subchondral bone (cortical shell) easily caused collapse of femoral head. However, that whether focus of cancellous bone would cause collapse or not was related to geometry shape and size of focus itself. And 25% of ratio of NASA was the critical scenario of collapse of the femoral head .It is reasonable to reinforce the cortical shell by a supporting structure.

 It is reasonable to reinforce the cortical shell by a supporting structure.

Lei, X, Qi, J, Prediction of Femoral Head Collapse in Osteonecrosis Using Three-dimensional Finite Element Method.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6016953.html