Survivorship comparison of THARIES and conventional hip arthroplasty in patients younger than 40 years old.

Early and high failure rates for conventional hip replacements in young and active patients are well documented. The hypothesis tested in this study is total hip articular replacement by internal eccentric shells (THARIES) resurfacing hip arthroplasty is a sufficiently durable alternative to conventional total hips in patients younger than 40 years old. Survivorship analysis techniques were applied to 106 THARIES and 98 conventional hip replacements. The primary outcome variable investigated was time to failure, as measured by the need for revision of the prosthesis in the absence of sepsis. Other definitions of prosthesis failure were also investigated. Analysis revealed that even within this young, high-risk population there were subpopulations with different risks for failure. The lowest risk patients comprised all rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) patients, regardless of age. The intermediate risk patients comprised all non-RA, non-JRA patients older than 30 years of age and the highest-risk patients were all non-RA, non-JRA patients younger than 30 years of age. A comparison of THARIES and conventional prostheses within each of these three subpopulations revealed similar patterns of failure over time, with the conventional total hip replacement having significantly better hip function than the THARIES group only in the highest-risk population, when using a failure definition of revision surgery for aseptic loosening. A broader and more important conclusion was that all acrylic-fixed implants, THARIES or THRs are predicted to undergo early mechanical loosenings in younger-than-30, non-RA, non-JRA patients. In patients younger than 30 years age acrylic fixation of THA is inadvisable.