The femoral stem/cement interface in total hip replacement.

A study of the cement prosthesis interface has been carried out on the femoral component of 5 total hip relacements which had been in place between 7 weeks and 5 years. In every case a thin layer of connective tissue at varying stages of organization was present between the prosthesis and the cement. This suggests that the prosthesis is not rigidly fixed to the cement and is capable of micromovement. The gap presumably comes about by a combination of factors which include thermal expansion of the femoral stem, shrinkage of the cement and organization of the film of blood or tissue fluid present on the stem at the time of implantation. This information must be used when construction mathematical models of joint replacements, but its clinical significance is not yet fully clear.