Can hip abduction reduce the risk of femoral head necrosis deteriorated into osteoarthritis? A 3D finite element analysis

Objective: The purpose of this study was to investigate biomechanical behavior changes of femoral head necrosis (FHN) by increasing lower extremity abduction (LEA) angle, offering scientific basis on choosing the LEA procedure for the exact classifications. Methods: Thirty computational models were constructed and used to simulate six different abducent angles with five different progresses of FHN. The initial model was validated by the bony density distribution in Xrays images and the photograph of the cadaver bone in crosssection. The stress transfer path (STP) of each model was analyzed and the contact stresses were assessed. Results: During the midstance phase, STP of type A showed strong similarities with the healthy level; STP distribution was from the top of the femoral head to the calcar; the damage area of STP of type B was approximately 25% of the healthy. While STPs in both type C1 and C2 were broken off. As the increase of the abduction angle, STP of type B transformed into type A, STP of type C1 transformed into type B. STP of type C2 transformed into type C1. There was no significant difference in contact stress between the four settings of FHN and normal femoral head. Conclusions: We found computational biomechanical technique to be a sensitive and useful method for distinguishing the biomechanical difference of FHN during abduction gait. These results showed that LEA motion could effectively reduce collapse risk and interrupt the disease pathway of FHN deteriorated into osteoarthritis. Furthermore, our findings indicated that the LEA procedure was suitable for type A, B and C1, while type C2 of FHN involved surgical intervention might get a better clinical outcome.