Fatigue of the cement/bone interface and loosening in total joint arthroplasty: Fid-Bau Portal

Fatigue of the cement/bone interface and loosening in total joint arthroplasty

Yang, D. / Stoffel, K. / Ross, A. / Arola, D.

Loosening of the implant is one of the primary causes of total hip replacement (THR) failure. Although considered a complicated function of both mechanical and biological factors, the process initiates and progresses with cyclic loading. The long term success of THRs and potential need for future revision surgery is often assessed in terms of the short term migration (i.e. over a period of 6 months). In this study the influence of the bone surface texture on the initial migration and steady-state loosening of cemented total joints was studied. Model cemented hip replacements were prepared and subjected to cyclic loads that induced pure shear fatigue of the cement/bone interface. The femoral canals were textured using specific cutting tools to achieve a desired surface topography. Loosening of the implant with cyclic loading was characterized in terms of the initial migration (Region I), steady state loosening (Region II) and unstable loosening (Region III). Results from the experiments showed that the initial migration and rate of steady state loosening were dependent upon the bone surface topography. The apparent fatigue strength ranged from 0.8 to 5.1 MPa and denotes the cyclic shear stress required for loosening of 1 mm within 10 million cycles. Regardless of the bone surface topography the ratio of apparent fatigue strength and ultimate shear strength of the interfaces was approximately 0.24. There was a strong correlation between the normalized initial migration and the apparent fatigue strength (i.e. specimens with the highest initial migration exhibited the lowest fatigue strength).