Mechanics of femoral head osteonecrosis using three-dimensional finite element method

Abstract

A three-dimensional finite element model of a femoral head was developed using a surface modeling technique. The distribution of the stress index S (S = effective stress / yield strength, sigma/sigmaY) in various sizes of segmental osteonecrosis was assessed. The stress index of the femoral head was within physiological limits when the necrotic angle was less than 110 degrees. Within both the subchondral region and the deep necrotic region adjacent to the necrotic-viable interface, values of the stress index significantly higher than the normal physiological level (>0.1) appeared when the necrotic angle was 110 degrees or more. In the analysis of 28 osteonecrotic femoral head specimens, fracture appeared in two major locations: the deep necrotic region near the underlying necrotic-viable interface (19 femoral heads) and the subchondral region (7 femoral heads). In 2 femoral heads, the fracture involved both regions. Both sites of fracture coincided with the region of stress index greater than 0.1 in the finite element model study. These results may provide baseline information for predicting the collapse of the femoral head and determining the treatment modality of early stage osteonecrosis.

Numerical studies on alternative therapies for femoral head necrosis

“…transtrochanteric rotational osteotomy (Lee et al 2006), bone grafting (Brown et al 1993Penix et al 1983;Lian et al 2008), intertrochanteric osteotomy (Baker et al 1989), prediction of femoral head collapse (Volokh et al 2006) or solely stress analyses of necrotic femoral heads (Yang et al 2002). None of these papers address the risk of subtrochanteric fractures after surgery or even analyze the long-term success.…”

The effect of the necrotic area on the biomechanics of the femoral head - a finite element study

“…Type L3: the necrosis involved the three pillars including the cortical bone and marrow same area, the femoral head would collapse in the end. Yang pointed out that the yield stress of necrotic bone is 5.5 MPa, the stress index is 0.1, and the critical stress of collapse is 0.55 MPa [14]. In this study, the peak von Mises stresses of the necrosis areas in type M, C, and L1 ONFH models were 0.22 MPa, 0.43 MPa, and 0.44 MPa, respectively, which did not exceed the critical stress.…”

“…Some studies have expounded the femoral head collapse from biological factors or mechanical factors. Yang pointed out that biomechanical base of the femoral head collapse was a combined result of poor function condition of internal structure of osteonecrosis, the elastic modulus of the necrotic bone, and the yield strength [14]. However, many studies have reported that type L2 and L3 ONFH patients had poor prognoses and treatment effects in combination with numerous clinical follow-up data, up until now, the causes of collapse have not been completely understood.…”

“…Collapse indices were selected from previous studies, including displacement variation, peak von Mises stress variation, and stress index. Yang set the yield stress of the necrotic tissue as 5.5 MPa and used the stress index (effective stress/yield strength) to judge the collapse of the femoral head [14]. Fang demonstrated that the critical stress of collapse of necrotic tissue was 0.55 MPa as the criterion of stress index was 0.1 [27].…”

“…Previous studies showed that the location and lesion size of ONFH were major factors of femoral head collapse [4,[11][12][13]. However, there are some shortcomings in their research, such as the FE model design is relatively simple, only one of the factors is analyzed, and the classification is not considered [6,14,15].…”