THE NATURAL-HISTORY OF DEBONDING OF THE FEMORAL COMPONENT FROM THE CEMENT AND ITS EFFECT ON LONG-TERM SURVIVAL OF CHARNLEY TOTAL HIP REPLACEMENTS

Two hundred and ninety-seven consecutive Charnley total hip replacemen ts that had been followed for at least twenty years or until revision or death were analyzed to determine the effect of early debonding of t he smooth-surfaced femoral component on its subsequent survival. Radio graphically evident debonding was not found to have a significant effe ct, with the numbers available, on the long-term survival of the femor al component when the maximum thickness of the radiolucent line betwee n the superolateral border of the prosthesis and the cement had been l ess than 2.0 millimeters during the first one to five years after the operation. The radiographic finding of debonding also was not found to be associated with pain in the hip. These data show that most compone nts with early debonding functioned well during a long period of follo w-up and suggest that debonding of a smooth femoral component of a Cha rnley total hip replacement should not be considered to be analogous t o loosening. In contrast, when the maximum thickness of the radiolucen t line between the superolateral border of the prosthesis and the ceme nt was 2.0 millimeters or more, an early appearance of debonding was a ssociated,vith a significantly poorer (p < 0.0001) probability of surv ival of the Charnley femoral component without revision because of ase ptic loosening. Thus, pronounced early subsidence of the component wit hin the cement mantle had a strong negative impact on the long-term pe rformance of the implant, The results of the present study should not be extrapolated to prostheses,vith substantially different design char acteristics, as it appears that different types of femoral components behave differently when debonding occurs.