Strain shielding in distal femur after patellofemoral arthroplasty under differ...

• Author(s): Meireles, Susana ; Completo, António ; Simões, José A. ; Flores, Paulo
• Date: 2010
• Persistent ID: http://hdl.handle.net/1822/23352
• Origin: RepositóriUM - Universidade do Minho
• Subject(s): Patellofemoral arthroplasty; Strain shielding; Experimental strains
• Document Type: Article
• Language: English

Description

Strain shielding, a mechanical effect occurring in structures combining stiff with more flexible materials, is considered to lead to a reduction in bone density in bone surrounding the implant and be related with weakness of the implant fixation, which leads to implant loosening. Several studies describe a significant decrease in postoperative bone mineral density adjacent to the joint implants, which can compromise their fixation at long term. Therefore the aim of the present study was the quantification of the strain shielding effect on the distal femur after patellofemoral arthroplasty. For this purpose three activities of daily living were considered: level walking, climbing stairs and deep bending at different angles of knee flexion. To determine the strain shielding effect, cortical bone strains were measured experimentally with tri-axial strain gauges in synthetic femurs before and after patellofemoral arthroplasty for the different daily activities. The results showed that the patellofemoral arthroplasty in general reduced the strains in the medial and distal regions of the femur for the deep bending activity occurring, consequently strain shielding effect in these regions, strain decreases of 72.0% and -67.5 % were measured. On the other side, higher values of strain were found in the anterior region after patellofemoral replacement for this activity with an increase of +182.0%. The occurrence of strain shielding looks more important when the angle of knee flexion and applied load increase. The strain shielding and over-loading may have relevant effects on bone remodeling surrounding the patellofemoral implant, suggesting a potential effect of later bone resorption in the medial and distal femur regions in case of a great frequency of the deep bending activity.