Migration, particles, and fluid pressure. A discussion of causes of prosthetic loosening.

Distal migration of the femoral component of a total hip replacement by as little as 0.33 mm during the first 6 postoperative months is predictive of the need for revision many years later. Because the fate of the prostheses is defined so early, it is unlikely that wear particles initiate loosening. However, the progression from the stage of early migration to clinical loosening has unknown causes, of which particles may be one. Slight instability associated with migration will lead to locally high fluid pressures surrounding the migrating prosthesis. Recent experiments applied a moderate fluid pressure to an implant to bone interface. This induced osteocyte death near the implant and subsequent bone resorption. Thus, there is evidence that fluid pressure and ensuing flow could be a main cause of not only pain, but also osteolysis necessitating revision.