Assessing morse taper function: The relationship between impaction force, disassembly force, and design variables

Increasing experience with modular total hip implants has revealed problems with the Morse taper, including disassembly, corrosion, and wear debris. There are no standards for taper dimensions, manufacturing tolerances, or surface finish, and it is not known how these variables affect the function of the tapered connection. In this study, the relationship between the pull-off strength of a Morse taper and the force of impaction was determined for several commercial hip implants. The purpose of this study is to introduce this method of assessing Morse taper function, and to relate differences in taper performance to different design variables among the manufacturers. The results showed that taper distraction strength varies more than two-fold among the devices tested. Because of the many design differences noted among the different implants, the relative importance of each cannot be determined. Further work is warranted to refine these findings, and to identify the clinical significance of differences in taper distraction strength.