New Insights into Osteointegration and Delamination from a Multidisciplinary Investigation of a Failed Hydroxyapatite-Coated Hip Joint Replacement

Abstract

Hydroxyapatite (HA) coatings have become very popular in uncemented total hip arthroplasty (THA). Analysis of retrievals and tissue samples from an HA-coated femoral stem, which failed within 14 months after THA, provides exceptional insights into the failure mechanism, as well as the process of osteointegration of such an implant. Methods: Retrievals were photo-documented. Samples were examined by micro-computed tomography, X-ray diffraction (XRD) and embedded in polymethylmethacrylate for histology. Results: The coating had partially delaminated. The sandblasted surface of the stem was partially polished by the delaminated HA coating, indicating failure before revision. In the tissue samples, the HA coating was well integrated by newly formed bone trabeculae. No adverse biological reaction was observed. XRD analysis showed that residues of the HA coating were still present and could clearly be differentiated from the surrounding bone. Preferential orientation of the HA crystallites could be identified within the newly formed bone, representing a potential mechanical weakness induced either by physiologic strain or by the coating. Conclusion: current HA coatings, relatively thick and made of high crystallinity HA, may be prone to delamination, as also seen in our study. Recent efforts have aimed towards thinner (<1 μm) coatings with nanocrystalline HA structures that possibly relate to lower delamination risks. However, the question arises if HA coatings are beneficial since sandblasted non-coated stems offer similar results without the risk of delamination. XRD not only permits differentiation between the HA from the coating and the HA of the ongrown bone, it also provides new insights into the microstructure of this newly formed bone.

Effect of femoral stem surface coating on clinical and radiographic outcomes of cementless primary total hip arthroplasty: a patient-matched retrospective study

“…Furthermore, the ProxCoat stem resulted in fewer femoral revisions compared to the Original stem (0% vs 2.2%), with all Original stems revised due to aseptic loosening. Many studies have reported on outcomes of HA-coated stems [1,8,9,28,29], but only a few have reported on outcomes of other coatings. Studies on stems with first plasma-sprayed titanium and then HA coating have reported satisfactory mid-and long-term outcomes [6,[30][31][32], this coating combination may provide stronger biological and mechanical bone fixation compared to only HA coating [6,33,34].…”

Atomically Resolved Interfacial Analysis of Bone‐Like Hydroxyapatite Nanoparticles on Titanium

“…[11] One common cause for failed tissue integration on hydroxyapatite-coated titanium implants is delamination of the HA coating from the titanium implant. [12] The risk of delamination is associated with the thickness of the HA layer and for this reason, thinner coatings (<1 μm) are being pursued. [13] A successful method of improving the osseointegrating property of titanium implants involves the application of hydroxyapatite nanoparticles (nanoHA) to the implant surface.…”

“…[ 11 ] One common cause for failed tissue integration on hydroxyapatite‐coated titanium implants is delamination of the HA coating from the titanium implant. [ 12 ] The risk of delamination is associated with the thickness of the HA layer and for this reason, thinner coatings (<1 μm) are being pursued. [ 13 ]…”

Evaluation of the Cathodic Electrodeposition Effectiveness of the Hydroxyapatite Layer Used in Surface Modification of Ti6Al4V-Based Biomaterials

“…Usually, the interfacial delamination of the HA layer is initially caused by vertical cracking of the coating throughout the thickness, which occurs at the HA–Ti6Al4V and HA–human bone interface [ 34 ]. The delamination of the hydroxyapatite layer can lead to the formation of inflammation in the surrounding organs, and consequently bone loss and even loosening of such an implant [ 22 , 35 ]. The analysis of literature data shows that research on this issue is conducted in various directions.…”