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

Abstract

We investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem. 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%; mean bone attachment 37.287 +/- 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 +/- 2.068%; mean bone attachment 18.9411 +/- 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating 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 attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.

Bone Remodeling and Hydroxyapatite Resorption in Coated Primary Hip Prostheses

“…However, bone ongrowth in the porous HA-coated regions was distributed more evenly without large differences. As they also noted more ingrowth and ongrowth of bone to the porous HA-coated surface, it is thought the HA counteracts the bone resorptive action of the local stress shielding, at least during the early postoperative years [5].…”

“…However, these opposing processes of bone gain and loss do not work at the same time, but whether they persist and to what degree are unknown. Although short-term retrieval studies report the HA coating after 2 to 4 years implantation is partly broken down through osteoclastic resorption [2,3,5,10,11,18,19,27,28], none of these studies reported whether patient demographics might influence residual HA coating or bone ongrowth. Therefore, we asked three questions: (1) Is the resorption of HA coating and bone ongrowth mainly correlated with time in vivo or with demographics, and when time in vivo is predominant, at which point can we expect all the HA to have completely resorbed?…”

“…Bauer et al [2] also reported a general increase of bone apposition from proximal to distal (in the coated portion of the stem). Coathup et al [5] compared bone remodeling around one femoral stem design with three different proximal coatings in 21 postmortem cases and observed a larger amount of bone ingrowth into the surface of the plain porous implants at the most distal metaphyseal level compared with the two proximal levels. However, bone ongrowth in the porous HA-coated regions was distributed more evenly without large differences.…”

“…Although age certainly is related to bone stock quality, a direct correlation between age and bone ongrowth onto implants such as uncemented HA-coated hip stems has not yet been proven. In longer-term human histomorphometric retrieval studies [1,5,11,27,28], the influence of demographics on bone ongrowth and HA resorption could not be studied because of the low number of retrievals or heterogeneity of the described implant designs.…”

Tapered uncemented HA-coated femoral stems: a radiological study

“…4,12 Osteointegration may be confirmed by the presence of bridging bone formation between the endosteum and the prosthesis. 4,7,9,13 Long-term remodelling of this peri-prosthetic bone is vital for component survival. 4,13 The surface finish of the implant plays a vital role in the host bone/component reaction, and different surface finishes have been employed with varying success.…”