Influence of the Fixation Length on Micromotion and Migration of Femoral Hip Revision Implants: An Experimental Study

Demographic changes and decreasing primary implantation ages will result in increasing numbers of revision operations in the future. Despite the long clinical experience aseptic loosening is still the main reason for total hip revision. Increased relative motions in the bone-implant interface, preventing the implant ingrowth, or wear particle induced osteolysis are known reasons for aseptic implant loosening.

Aim of this study was to evaluate the influence of bone defects on micromotions in the bone-implant interface of a modular revision hip stem experimentally.

Therefore, a measurement device for calculating implant micromotion and migration was developed and tested using an uncemented femoral hip revision implant system implanted in five composite femora. Seven reproducible bone defects were successively created and both micromotions and migrations were measured for 1500 load cycles.

Recorded micromotions in the composite bone were below the bony integration threshold of 150

μ

m, while the motion fraction associated to implant migration increased with decreasing fixation length. A decreasing stabilisation capability was qualitatively observed for increasing bone defects.

The use of composite femora offered the opportunity of repeatable and reproducible experiments by means of identical geometry and bone material. In further works the data of interfacial micromotion are to be validated using human femur specimens.