Shear stress and von Mises stress distributions in the periphery of an embedded acetabular cup implant during impingement.

As literature implies, daily activities of total hip arthroplasty (THA) patients may include movements prone to implant-implant impingement. Thus, high shear stresses may be induced at the acetabular implant-bone interface, increasing the risk of implant loosening. The aim of the current study is to determine whether or not impingement events may pose an actual risk to acetabular periprosthetic bone. An existing experimental workflow was augmented to cover complete three-dimensional strain gage measurement. von Mises and shear stresses were calculated from 1620 measured strain values, collected around a hemispherical cup implant at 2.5 mm interface distance during worst-case impingement loading. A shear stress criterion for acetabular periprosthetic bone was derived from the literature. At the impingement site, magnitudes of von Mises stress amount to 0.57 MPa and tilting shear stress amount to -0.3 MPa at 2.5 mm interface distance. Conclusion can be drawn that worst-case impingement events are unlikely to pose a risk of bone material failure in the periphery around fully integrated cementless acetabular hip implants in otherwise healthy THA patients. As numerical predictions in the literature suggested, it can now be confirmed that impingement moments are unlikely to cause acetabular implant-bone interface fixation failures.