Effect of the material’s stiffness on stress-shielding in osseointegrated implants for bone-anchored prostheses: a numerical analysis and initial benchmark data

Purpose: This study attempted to establish the link between design of implants for bone-anchored prostheses and stress-shielding, affecting the stability of the bone-implant coupling using numerical approach. The objectives were to share a numerical model capable to evaluate the long-term stability of implants and to use this model to extract data sets showing how shape and material stiffness of threaded, press-fit and modular press-fit implants affect stress-shielding intensity. Methods: Three designs were considered: threaded, press-fit and modular press-fit. The effect of shape and material stiffness of each design on stress-shielding intensity was assessed using Young’s modulus (10 to 210 GPa). Furthermore, the impact of the diameter of percutaneous part (10 to 18 mm) and thickness of medullar part (5 to 1 mm) was investigated for the modular press-fit implant. Results: The threaded design generated 4% more bone mass loss at the distal femur but an overall loss of bone mass was by 5% lower to press-fit design. The influence of Young’s modulus on bone mass changes was noticeable for modular press-fit implant, depending on diameter of percutaneous or medullary part. A 20 GPa change of stiffness caused a bone mass change from 0.65% up to 2.45% and from 0.07% up to 0.32% for percutaneous parts with 18 mm and 10 mm diameter, respectively. Conclusions: Results suggested that threaded implant provides greater stability despite an increased bone loss at the distal femur. Altogether, this work provided an initial model that could be applied in subsequent studies on the long-term stability of current and upcoming implants.

Download Full-text

Interface biomechanics of the Anca Dual Fit hip stem: An in vitro experimental study

Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine ◽

10.1243/0954411011536163 ◽

2001 ◽

Vol 215 (6) ◽

pp. 555-564 ◽

Cited By ~ 6

Author(s):

L Monti ◽

L Cristofolini ◽

M Viceconti

Keyword(s):

Load Transfer ◽

Bone Ingrowth ◽

Stress Shielding ◽

Primary Stability ◽

Stair Climbing ◽

Term Stability ◽

Long Term Stability ◽

Cemented Stem

The Anca Dual Fit hip stem (Cremascoli Wright, Milan, Italy) is a partially cemented stem developed to overcome the drawbacks of both cemented and uncemented fixations. Its design was based on the hypothesis that partial cementing would ensure the primary stability necessary to allow bone ingrowth on the cement-free stem surfaces. At the same time, the limitation of the cement to the proximal regions would prevent stress-shielding by increasing proximal load transfer. After finite element (FE) simulations and in vitro primary stability assessment, an analysis of the long-term stability of the Anca Dual Fit stem was necessary to conclude the preclinical testing. Three stems were implanted in composite femurs and subjected to testing for 1 × 106 cycles, each cycle reproducing the activity of stair climbing. The simulation was designed so as to replicate the physiological loading in a simplified, yet relevant way for this test. Various measurements were collected before, during and after the test in order to give exhaustive information on the response of the implant to long-term, cyclic loading. The present study confirmed the positive results of previous investigations, and proved that the Anca Dual Fit stem has excellent long-term stability; therefore successful clinical outcomes are predicted.

Download Full-text