A Critical Review of Two Bioceramics for Total Hip Arthroplasty

Ceramic materials have played an important role in the development of modern total hip replacements. Following the introduction of the modular low-friction total hip (THA) in the 1960s, subsequent improvements have addressed the various failure modes for this prosthetic implant. Over the past two decades, clinical practitioners have generally moved away from hard-on-hard articulation couples (i.e., metal-on-metal or ceramic-on-ceramic (CoC)) to hard-on-soft bearing pairs (i.e., ceramic or metal on advanced polyethylene). Zirconia-toughened alumina (ZTA) femoral heads have emerged as a preferred choice due to their demonstrably improved strength, toughness, and polyethylene wear resistance, as supported by significant clinical data. Yet, despite these advancements, the longevity of modern THA has not improved significantly over that of the earliest cemented hip systems. This review chapter compares the performance of two biomaterials, ZTA and silicon nitride, for use in total hip arthroplasty. While silicon nitride currently lacks clinical data in THA due to its FDA approval for spinal fusion devices only, in vitro studies suggest potential advantages. These include the possible development of future THA designs that exceed the lifespan of young, active patients, and potentially reduce the need for revision surgeries due to polyethylene wear, deep infections, and other complications typically encountered after 15–20 years of service. The mechanical properties of silicon nitride femoral heads are at least as favorable as ZTA, with greater resistance to hydrothermally induced degradation. Silicon nitride also has a bioactive surface chemistry that makes the material highly biocompatible, and resistant to bacterial infection. In articulation against the most advanced polyethylene liner, silicon nitride exhibits wear properties comparable to, if not superior to ZTA. Additionally, it possesses the potential to mitigate long-term polyethylene oxidation and embrittlement, a contributing factor to THA failure. While ZTA femoral heads boast established clinical success, advancements in bearing materials are crucial for extending THA longevity to match the lifespans of the most demanding patients. In this context, silicon nitride emerges as a promising candidate, supported by its favorable in vitro performance.