Background: Modular acetabular components have become increasingly popular due to the intra-operative flexibility they afford for primary and revision arthroplasty. There are however concerns regarding acetabular modularity which can result in significant complications (failure of the polyethylene liner locking mechanism, dissociation of the liner from the acetabular shell, accelerated polyethylene wear, acetabular osteolysis, recurrent dislocation of the prosthesis). The Harris-Galante modular cementless acetabular component has been associated with reports of frequent failure of the acetabular locking mechanism.
Case Report: We report a unique case of a per-acetabular dislocation in a Harris-Galante total hip arthroplasty occurring secondary to failure of the polyethylene liner locking mechanism, resulting in liner dislocation and subsequent femoral head erosion through the acetabular shell. The patient underwent a failed reduction of his dislocated hip arthroplasty by the emergency physicians. Radiographs revealed evidence of the acetabular shell failure with fragmentation, an eccentric position of the femoral head and an abnormal articulation between the femoral head and the ilium with an associated cavitary defect.
Conclusions: We advocate revision of the hip arthroplasty without any attempt at closed reduction, to deal with the acetabular failure and associated osteolysis. We advise vigilance in assessing radiographs to avoid potential complications associated with forceful reduction in this situation.

Keywords: per-acetabular dislocation, total hip arthroplasty, harris-galante