New concepts - Biomechanical studies of a newly designed femoral prosthesis (cervico-trochanter prosthesis)

Objective. A newly designed stemless (cervico-trochanter) prosthesis was developed for the purpose of reducing the incidence of the stress-shielding effect caused by the traditional stem-type prosthesis. Design. Both mechanical test and three-dimensional finite element analysis were performed for comparing the differences of strain and stress distributions between the intact, C-T and PCA prosthetic femora. Background. The stress-shielding effect and polyethylene (PE) wear debris were thought to be the main factors that resulted in local bone loss after the implantation of stem-type prostheses. In this study, we developed the new C-T prosthesis, which aimed to resolve the above-mentioned problems. Methods. Six pairs of femora taken from human male cadavers were used to compare the strain magnitudes of intact (n = 12), C-T (n = 12) and PCA (n = 4) prosthetic femora in specific positions. Failure load tests of C-T (n = 8) and PCA (n = 12) prosthetic femora were also carried out from the load-displacement curve. The analysis of variance (ANOVA) test was used for statistical analysis. In addition, three-dimensional finite element stress analyses were performed using a commercial package, ANSYS, on a Convex 3810 computer. Results. Both mechanical test and finite element results showed that the C-T prosthetic femora has a lower stress-shielding tendency than the PCA prosthetic femora (P < 0.001). The C-T prosthetic femora also withstood an average bearing load of 6312 N, which is greater than that of the PCA prosthesis at 5358 N (P < 0.01). Conclusions. The C-T prosthetic femur could withstand a higher failure load than the PCA prosthesis, which effectively reduced the incidence of the stress-shielding effect. Moreover, the particular design of the C-T prosthesis also reduced localized osteolysis because of the overall coverage of the neck-trochanteric area.