Three-dimensional Finite Element Analysis On Fixation Of The Femoral Shaft Fractures With Self-locking Nails And Interlocking Nails

Objectives: Two intramedullary nails were used to fix fracture of femoral shaft, which were compared on the distribution of stress and strain by means of Three Dimensional Finite Element Analysis(3-DFEA).We aim to : (1)predict the optimal indication of the self-locking nail;(2)estimate the risk of nails and/or screws broken following fixation, and the management of the complication;(3)discuss if self-locking nail could replace the interlocking nail. Materials & Methods: Three-dimensional finite-element models of femoral shaft fracture which fixed with locked interlocking nail ( C2) and self-locking nail (CD were developed using CT-scan and computer aided design(CAD) methods, and the material properties adapted to simulate nail and bone. The stress and strains of models were detected under vertical loads (350N, 700N,1400N,2100N), walking and torsion loads(0-50Nm), and then were compared each other. Results: There are areas of stress concentration in bone, nail, and screws under all kinds of loads. (1) Under vertical loads and walking loads, the maximum stress in bone of C1 is lower than that of C2, the maximum stress in screws of Cl is lower than that of C2, and the strains(migration) of the femoral head of Cl is lower than that of C2. (2) The maximum stress in nail of Cl is lower than that of C2 when under vertical loads while it is larger under walking loads. (3) The bones and nails of Cl and C2 can keep elasticity when give 0-30Nm torsional moment at the proximal portion of the femur, but they all yield when the moment over 30Nm ; The strains of Clare larger than those of C2 in the whole procedure. ? Fatigue times test: Under 0-1.2 units of body weight axial stress, the times of self-locking nail are 2.2*1013 while the times of the latter are 9.9* 1012. ?Under vertical impacted loads, the failure loads of the self-locking nail is 1660.2N while the interlocking nail's loads is 1467.2N. Conclusion: 1. The most suitable cases of fixation with the self-locking nail are those with femoral fracture near the middle of the shaft. 2. The self-locking nail is one instrument with rational construction and good biomechanical characteristics, which implies that it can be applied to fix femoral shaft fractures safely. The risk of nails and/or screws broken is relatively low when a patient whose body weight is 700N stand or slow walk after fixed with the self-locking nail. 3. To fix femoral shaft fracture, the self-locking nail may be used partly instead of domestic interlocking nail. For the weakness in anti-torsion strength, we suggest that immediate fully weight-bearing or walking after the fixation of the fracture should be avoided. All above-mentioned conclusions need to confirm in clinic practice, especially by randomized control trial(RCT) to provide more detail data.