Poor bone quality or hip structure as risk factors affecting survival of total-hip arthroplasty.

BACKGROUND: The principal long-term complication after total hip arthroplasty (THA) has been aseptic fixation failure. Many hip prostheses and operative techniques have been developed to improve outcomes, but few measures have been taken to cope with poor bone quality or hip structure. We assessed risk factors for aseptic fixation failure after THA.
METHODS: We assessed, by multivariate analysis, survival of 405 primary Charnley THAs to identify risk factors for aseptic fixation failures. We also investigated risk factors for development of rapid polyethylene wear (penetration depth of the femoral head into the socket polyethylene > or = 2 mm/year)
FINDINGS: In the entire series of 405 THAs, with use of radiographic fixation failure or revision for a loose socket as the endpoint, development of rapid polyethylene wear and the preoperative diagnosis of atrophic osteoarthrosis (defined by scarce osteophyte formation) were identified as risk factors for socket loosening (p < or = 0.02). A medullary canal with an unfavourable geometry (a stovepipe canal, Noble's canal-flare index < 3.0) was the only risk factor for femoral fixation failure (p < or = 6.7x10(3)). The only variable related to development of rapid polyethylene wear was the type of steel used in the femoral prosthesis--Ortron 90 prostheses significantly lowered the rate of development of rapid wear from 12.7% to 0.4%. In the 248 THAs in which these femoral prostheses were used, socket survival was affected only by the preoperative diagnosis of atrophic osteoarthrosis (for radiographic fixation failure and revision, p=4.0x10(-5) and p=0.042, respectively).
INTERPRETATION: In THA, the critical risk factors are poor bone quality, which manifests as atrophic osteoarthrosis, for socket survival and poor bone structure for femoral-prosthesis survival. To ensure longer durability of THAs, these factors should be assessed further and efforts, especially biological initiatives, should be made to resolve them.