A model femur for in vitro testing of femoral components

A total hip replacement femoral component was embedded using acrylic bone cement into a full length model femur consisting of a thin-walled cylindrical fixture and was loaded anatomically. The strains in the prosthesis, the fixture and the cement were determined as was the effect of prosthesis misorientation. This method of fixation, unlike others tested, gave prosthesis stresses of magnitude and distribution similar to those which occurred in similar prostheses implanted in human femora. A metal fixture was found to be suitable for in vitro testing of femoral components, since the fixture stresses were adequately low. High stresses occurred in the cement, and in spite of acrylic precompression due to polymerization in situ, could result in acrylic fatigue fracture and interface failure, both possible causes of the loosening which occurs clinically. The load transmission from prosthesis to model femur was discussed.