The initial instability of cemented and non-cemented femoral stems fixated with a bone grafting technique

To reconstruct intramedullary bone stock in revision surgery of failed total hip arthroplasties, a method was developed using impacted trabecular bone grafts. In an in vitro model with femora of the goat, the initial stabilities of both cemented and non-cemented hydroxylapatite-coated stems in this graft construction were determined in a loading experiment immediately after insertion. Displacements of stems relative to bone were determined with roentgen-stereophotogrammetric analysis. The most important movements were axial rotations (cemented stems up to 2·1°, non-cemented stems up to 6·8°) and subsidence (cemented stems up to 0·5 mm, non-cemented stems up to 2·9 mm). These motions were caused predominantly by slippage and compaction of grafts. It is concluded that the cemented stems reach a better initial stability, probably by cement penetrating in the graft layer. For non-cemented stems used in combination with the grafting technique developed, additional means to guarantee initial stability are needed.