Debonding of Porous Coating: A Late Failure Mode of Uncemented, Partially Threaded Acetabular Components—Retrieval Analysis

Abstract

Titanium plasma-sprayed (TPS) porous coatings have been used in total hip arthroplasty for decades. They are considered reliable, and very few failure cases have been described so far. This retrieval study described a series of 20 acetabular components—where total or partial debonding occurred during in vivo use and aimed to explain the underlying failure mechanisms. Implants were examined using optical and electron microscopy (SEM), metallographic sections of retrievals were prepared while pathologic samples of periprosthetic tissues were examined for presence of wear debris. Data from metallographic slides indicated that debonding was initiated at free borders of the coating and tended to progress at the interface between the TPS layer and the shell. In some cases, total debonding occurred leading material wear of both the TPS layer and acetabular shell leading to massive release of metallic debris and accelerated polyethylene wear in third body mechanism. SEM examination demonstrated that splats forming the TPS layer exhibited features suggesting a high temperature gradient between the plasma sprayed layer and the substrate material existed, leading to porosity of splats and suboptimal bonding strength. This study demonstrated that coating application parameters and certain design features (screw holes, fins) may promote long-term failure due to debonding. Surgeons should be aware of this complication as it is most likely underreported, while manufacturers should consider more rigorous pre-clinical testing as suboptimal coating bonding may result in failures during long-term clinical use.