Insufficiency fracture following total hip arthroplasty (THA) frequently occurs in the superior and inferior pubic ramus, the puboischial rami, or the ischium around the obturator foramen, while it rarely occurs in the medial wall of the acetabulum. Here, we report three cases showing insufficiency fracture in the medial wall of the acetabulum following THA. In our three cases, two fractures resulted from the development of bone fragility due to osteolysis at the prosthesis site, and the convergence of mechanical stress on the acetabular load bearing point due to loosening of the cup. We consider it appropriate to describe these fractures as another entity of stress fracture, namely, osteolytic fracture, rather than either pathologic fracture or insufficiency fracture.
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