Cementless total hip femoral components rely on press-fit for initial stability and bone healing and remodeling for secondary fixation. However, the determinants of satisfactory press-fit are not well understood. In previous studies, human cortical bone loaded circumferentially to simulate press-fit exhibited viscoelastic, or time dependent, behavior. The effect of bone viscoelastic behavior on the initial stability of press-fit stems is not known. Therefore, in the current study, push-out loads of cylindrical stems press-fit into reamed cadaver diaphyseal femoral specimens were measured immediately after assembly and with stem-bone diametral interference and stem surface treatment as independent variables. It was hypothesized that stem-bone interference would result in a viscoelastic response of bone that would decrease push-out load thereby impairing initial press-fit stability. Results showed that push-out load significantly decreased over a period due to bone viscoelasticity. It was also found that high and low push-out loads occurred at relatively small amounts of stem-bone interference, but a relationship between stem-bone interference and push-out load could not be determined due to variability among specimens. On the basis of this model, it was concluded that press-fit fixation can occur at relatively low levels of diametral interference and that stem-bone interference elicits viscoelastic response that reduces stem stability over time. From a clinical perspective, these results suggest that there could be large variations in initial press-fit fixation among patients.
Cortical Bone Viscoelasticity and Fixation Strength of Press-Fit Femoral Stems: An In-Vitro Model
Norman, T. L., Ackerman, E. S., Smith, T. S., Gruen, T. A., Yates, A. J., Blaha, J. D., and Kish, V. L. (May 6, 2005). "Cortical Bone Viscoelasticity and Fixation Strength of Press-Fit Femoral Stems: An In-Vitro Model." ASME. J Biomech Eng. February 2006; 128(1): 13–17. https://doi.org/10.1115/1.2133766
Download citation file: