Femoral bone defect classifications in revision total hip arthroplasty: a comprehensive review and proposal of a new algorithm of management.

The number of primary total hip arthroplasties (THAs) and revisions is expected to steadily grow in the future. The femoral revision surgery can be technically demanding whether severe bone defects need to be addressed. The femoral revision aims to obtain a proper primary stability of the stem with a more proximal fixation as possible. Several authors previously proposed classification systems to describe the morphology of the bony femoral defect and to drive accordingly the surgeon in the revision procedure. The previous classifications mainly considered cortical and medullary bone at the level of the defect of poor quality by definition. Therefore, the surgical strategies aimed to achieve a distal fixation bypassing the defect or to fill the defect with bone impaction grafting or structured bone grafts up to the replacement of the proximal femur with megaprosthesis. The consensus on a comprehensive and reliable classification system and management algorithm is still lacking. A new classification system should be developed taking into account the bone quality. The rationale of a new classification is that 'functional' residual bone stock could be present at the level of the defect. Therefore, it can be used to achieve a primary (mechanical) and secondary (biological) stability of the implants with a femoral fixation more proximal as possible.