A comparison of bone remodelling around hydroxyapatite-coated, porous-coated and grit-blasted hip replacements retrieved at post-mortem

We investigated the implant-bone interface around one design of femoral ste m, proximally coated with either a plasma-sprayed porous coating (plain por ous) or a hydroxyapatite porous coating (porous HA), or which had been grit -blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarth roplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mo rtem, We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified. There was significantly more ingrowth (p = 0.012) and attachment of bone (p < 0.05) to the porous HA surface (mean bone ingrowth 29.093 +/- 2.019%; me an bone attachment 37.287 +/- 2.489%) than to the plain porous surface (mea n bone ingrowth 21.762 +/- 2.068%; mean bone attachment 18.9411 +/- 1.971%) . There was no significant difference in attachment between the plain porou s and Interlok surfaces. Bone grew more evenly over the surface of the HA c oating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time. This study shows that HA coating increases the amount of ingrowth and attac hment of bone and leads to a more even distribution of bone over the surfac e of the implant. This may have implications in reducing stress shielding a nd limiting osteolysis induced by wear particles.