Computational analysis of the effects of interprosthetic distance on normal and reduced cortical thickness femur models

Abstract

Distal femoral fractures associated with the femoral stem in a well-fixed hip arthroplasty pose a risk of an interprosthetic fracture, the treatment of which is known as difficult. To effectively prevent and treat IP fractures, biomechanical effects must be demonstrated. We defined eight variations of the interprosthetic distance ranging from 48 mm overlap to 128 mm gap. Femoral geometries with normal and reduced cortical thickness were modeled to evaluate the effects of cortical thickness. In addition to the intact model, a total of 16 finite element models were analyzed under physiological boundary conditions. Maximum and minimum principal strains on the lateral and medial cortex surfaces were always found to be greater in models with reduced cortical thickness than in normal femurs. The model with 48 mm overlapping interprosthetic distance produced the least peak strain and the model with 16 mm interprosthetic gap produced the greatest strain with both normal and reduced cortical thickness. The screw holes produced local strain concentrations and increased the peak strains on the cortex surfaces, especially close to the stem tip. Statistically, a significant correlation ( R2 = 0.9483) was found between strain shielding and interprosthetic distance. Axial stiffness, interfragmentary shear motion, and maximum von-Mises stress on the distal plate showed a high correlation with the interprosthetic distance. It was concluded that the overlapping structures are superior to other fixations we analyzed in that they offer better mechanical stability and eliminates the local strain concentrations.

Interprosthetic Femur Fractures

“…The greatest cortical peak strain was found between implants with a gap of 16 mm, and models with reduced cortical thickness were always found to have greater levels of strain. Suggesting that increased strain, and thus higher risk for fracture, is produced when there is gapping between implants, particularly when the implant ends are close together in osteoporotic bone 22 . Given these findings, management of interprosthetic fractures should include not only fracture fixation but also management of osteoporosis to improve bone quality.…”

Multi-Scale Topology Optimization of Femoral Stem Structure Subject to Stress Shielding Reduce

“…By using computed tomography (CT), three-dimensional (3D) models of Dorr Type A femur and five commonly used primary total hip arthroplasty cementless stem designs were developed in [22] and the femoral strain along the implant bone was analyzed with FEA. In addition, the selection of materials [23][24][25], the geometry of the femur stem [26][27][28][29] and the analysis and calculation of stress [30,31] have been proposed. However, maximizing the mechanical properties of humans is a technical problem faced by total hip replacement surgery.…”