Does preclinical analysis based on static loading underestimate post-surgery stem micromotion in THA as opposed to dynamic gait loading?

The success of cementless hip stems depends on the primary stability of the implant quantified by the amount of micromotion at the bone-stem interface. Most finite element (FE)-based preclinical studies on post-surgery stem stability rely on static analysis. Hence, the effect of dynamic gait loading on bone-stem relative micromotion remains virtually unexplored. Furthermore, there is a paucity of research on the primary stability of grooved stems as opposed to plain stem design. The primary aim of this FE study was to understand whether transient dynamic gait had any incremental effect on the net micromotion results and to further draw insights into the effects of grooved texture vis-a-vis a plain model on micromotion and proximal load transfer in host bone. Two musculoskeletal loading regimes corresponding to normal walking (NW) and stair climbing (SC) were considered. Although marginally improved load transfer was predicted proximally for the grooved construct under static loading, the micromotion values (max: NW similar to 7 mu m; SC similar to 10 mu m) were found to be considerably less in comparison to plain stem (max: NW similar to 50 mu m; SC similar to 20 mu m). For both physiological load cases, a significant surge in micromotion values was predicted in dynamic analyses as opposed to static analyses for the grooved stem (similar to 390% greater). For the plain model, the increase in these values from static to dynamic loading is relatively moderate yet clinically significant (similar to 230% greater). This suggests that the qualitative similarities notwithstanding, there were significant dissimilarities in the quantitative trends of micromotion for different cases under both analyses.

Automated summary

The success of cementless hip stems depends on the primary stability of the implant at the bone-stem interface. Most studies on stem stability focus on static analysis and neglect the effect of dynamic gait loading. This finite element study compared the micromotion and load transfer of a grooved stem versus a plain stem under normal walking and stair climbing conditions. The results showed that dynamic loading significantly increased micromotion values for both stem designs, with the grooved stem exhibiting lower micromotion values overall.