Stress analysis of an anatomically adapted femoral prosthesis stem (Lubinus SPII)

Objective: Very good clinical long-term results of the Lu binus SP II hip p rosthesis stem were reported in the literature. We therefore asked whether there is a relationship between these findings with biomechanical data of s train gauge measurements. Method: 14 strain gauges were applied at a femur being measured at 10 diffe rent load cases before and after implantation of the stem. Results: After stem implantation a similar patterns of principal stress dis tributions was observed, however, the magnitude was markedly reduced. A str iking reduction of the hoop stresses at the femoral calcar was seen in the case of a missing collar contact. Even in the case of a perfect collar cont act the hoop stresses were diminished after strem implantation. The S-shape d physiological stem did not correspond with a specific stress pattern meas ured at the femoral surface. Conclusion: These results suggest that the stresses at the femoral calcar m ay be lower than the limits of bone growth while the other parts of the fem ur are more physiologically stressed. However, the prosthesis may tolerate a missing collar contact during a long follow-up period. The large experime ntal data file presented here could be used to validate future finite eleme nt analyses which could evaluate the stress distribution within internal pa rts of the bone and the cement layer.