The contribution of trabeculae and the failure initiation in the proximal femur: a finite element analysis.

backgroundThis study employed finite element analysis to simulate the process of hip fractures, aiming to: (1) quantify the contribution of trabeculae to proximal femoral strength, (2) compare fracture patterns before and after the removal of trabecular bone, and (3) identify the fracture initiation site.

methodsBilateral hip CT scans from 10 healthy volunteers were included in this study. Two types of geometric models of the ipsilateral proximal femur were constructed using Mimics: an intact model (cortical-cancellous composite model) and a cancellous-excised model. In total, 20 geometric models were generated (two per volunteer). Material properties were assigned based on Hounsfield Unit (HU) values. A lateral fall condition was simulated, and the element deletion technique in Abaqus was employed to simulate crack initiation and propagation, with the complete formation of a fracture line defined as the endpoint of the finite element simulation.

resultsThe cohort consisted of 10 volunteers (6 males and 4 females), with a mean age of 71.7 years. Among the intact models, 6 exhibited femoral neck fractures, 3 showed intertrochanteric fractures, and 1 presented with a femoral head fracture. The mean failure load was approximately 4255 N for the intact models and 1387 N for the cancellous-excised models, representing an average reduction in bone strength of 67.2%. Regions of relatively high von Mises stress in the intact models were predominantly localized to the medial and lateral cortex of the femoral neck, regardless of fracture types. Tissue failure consistently initiated at the endosteal-trabecular junction of the proximal femur and progressively propagated until complete structural fracture occurred. Although three different fracture types were observed in the intact models, all cancellous-excised models resulted in femoral neck fractures.

conclusionsTrabecular bone in the proximal femur plays a critical role in load transfer and contributes significantly to its mechanical strength. Hip fractures initiate at the junction between the endosteum and trabecular bone. Effective prevention of trabecular bone loss or targeted reinforcement of the bone tissue at the interface between trabecular and cortical bone may potentially reduce the incidence of hip fractures in the elderly.