The significance of stem-cement loosening of grit-blasted femoral components

This study analyzed 15 patients who underwent revision for loosening at the stem-cement interface. The femoral components were from the same manufactu rer and had grit-blast roughened surfaces. An apparent radiographic deficie ncy in the cement mantle was present in at least one zone in 13 patients. I n 9 of 12 patients with localized osteolysis; the osteolysis developed in a zone with an apparent radiographic cement mantle defect. Loosening occurre d due to tension failure of the stem-cement interface followed by axial sub sidence and movement into relative retroversion. Motion between the stem an d the cement mantle fueled an abrasive wear mechanism between the roughened metal surface and the cement mantle, generating excessive metal and cement particles that gained access to endosteal bone via defects in the cement m antle and resulting in localized osteolysis. Although the roughened surface played a central role in these failures, it is unlikely the layer ofpolymethyl-methacrylate (precoat) played a role in the mechanism of failure. In some cases, debonding occurred as a result of tension failure of the metal-precoat interface. In others, tension failure occurred within the cement mantle, leaving the precoat and some cement from the mantle on the stems. There was no difference in the mechanism of failu re of stems with precoat proximally compared to stems with precoat proximal ly and distally. One stem had no precoat; findings in this patient were ind istinguishable from the others. The significance of debonding depends on th e surface roughness of the stem. Debonding carries a poorer prognosis with a rougher stem surface because of abrasive wear with the generation of nume rous metal and cement particulates, which lan lead to rapid osteolysis if t here are cement mantle defects. Stems with a higher metal-cement bond stren gth may require a higher quality cement mantle for long-term success.